LTC4126-10 [ADI]
Wireless Li-Ion Charger with 1.2V Step-Down DC/DC Converter;
| 型号： | LTC4126-10 |
| 厂家： | 
ADI |
| 描述： | Wireless Li-Ion Charger with 1.2V Step-Down DC/DC Converter 无线 |
| 文件： | 总24页 (文件大小：1648K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC4126-ADJ
Wireless Li-Ion Charger with
1.2V Step-Down DC/DC Converter
FEATURES
DESCRIPTION
The LTC®4126-ADJ is a low-power wireless single-cell
Li-Ion battery charger with an integrated step-down DC/
DCregulator.Thestep-downregulatorisalow-noisemulti-
mode charge pump which is powered from the battery and
provides a regulated 1.2V at the output. The switching
frequency is set to either 50kHz or 75kHz depending on the
mode to keep any switching noise out of the audible range.
n
Wireless Li-Ion Battery Charger Plus High
Efficiency Multi-Mode Charge Pump DC/DC
Programmable Charge Current from 1mA to 50mA
Via an External Resistor
n
n
n
n
n
n
n
n
n
n
n
Wideband Rx Frequency: DC to >10MHz
Integrated Rectifier with Overvoltage Limit
Charge Voltage: 4.2V
Low Battery Disconnect: 3.0V
The constant-current constant-voltage Li-Ion battery
charger has automatic recharge, automatic termination
by safety timer, and battery temperature monitoring via
an NTC pin. Charge current is programmable from 1mA
to 50mA via an external resistor. Undervoltage protection
disconnects the battery from all loads when the battery
voltage is below 3.0V.
NTC Pin for Temperature Qualified Charging
DC/DC Regulated Output: 1.2V
DC/DC Output Current: Up to 60mA
50kHz/75kHz Switching, No Audible Noise
Pushbutton and/or Digital on/off Control for DC/DC
Thermally Enhanced 12-Lead 2mm × 2mm LQFN
Package
Thesmallpackageandminimalexternalcomponentcount
make the LTC4126-ADJ and its variants suitable for hear-
ing aid applications and other low power portable devices.
See the chart below.
APPLICATIONS
n
Hearing Aids
n
Low Power Li-Ion Powered Devices
Wireless Headsets
PARAMETER
LTC4126-ADJ
Programmable
6 Hours
LTC4126-10
10mA
3 Hours
4.1V/4.2V
Active Low
1MΩ
LTC4126
7.5mA
6 Hours
4.2V/4.35V
Active High
N/A
n
Charge Current
Charge Timer
Charge Voltage
EN Pin Polarity
EN Pin Pull-Up
n
IoT Wearables
4.2V
Active High
N/A
NTC Upper Threshold 76.5% of V
62% of V
3.5V
1.05V
1.7s
76.5% of V
3.2V
CC
CC
CC
V
3.2V
1.1V
LOBAT3
Threshold
Timing
1.1V
110ms
DC/DC
Mode 3
110ms
All registered trademarks and trademarks are the property of their respective owners.
Top and Bottom View of the IC with
Complete Application Circuit
TYPICAL APPLICATION
ꢗꢂ
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ꢕꢄꢔꢄꢑ
ꢔꢉꢍR
ꢔꢉꢁꢂ
ꢉ
Rꢅ
ꢊꢆꢋꢌ
ꢙꢁꢏꢁꢄꢔꢃ ꢁꢡꢎ
ꢢ ꢣ.ꢤꢥꢔ
ꢔꢁR ꢏꢔꢍ
ꢀ
ꢉꢉ
ꢁ
ꢃꢄꢉꢒꢐꢑꢊꢛꢔꢙꢝ
ꢉꢈꢏ
ꢞꢔꢄ
CHRG
ꢟ
ꢃꢚꢛꢁꢜꢋ
ꢒ.ꢑꢀ
ꢃ
Rꢅ
ꢆꢇꢈ
ꢃ
ꢄRꢔꢂꢕꢖꢁꢄꢄꢗR
ꢄꢅ
ꢂꢄꢉ
ꢍRꢎꢏ
ꢟ
ꢀ
ꢐ.ꢑꢀ
TO BAT
ꢑ.ꢑꢇꢌ
ꢎꢘꢄ
ꢁꢂ
ꢠ
R
ꢍRꢎꢏ
ꢐꢑ.ꢒꢓ
ꢏꢂꢙ
ꢒꢐꢑꢊꢛꢔꢙꢝ ꢄꢔ0ꢐ
Rev. 0
1
Document Feedback
For more information www.analog.com
LTC4126-ADJ
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Notes 1, 2)
ꢓꢟꢄ ꢥꢡꢉꢞ
Input Supply Voltages
V ........................................................... –0.3V to 6V
CC
ACIN ..........................................................–10V to 6V
ꢊꢋ
ꢊꢊ
ꢃꢓꢆ
ꢉꢃ
ꢊ
ꢋ
ꢢ
ꢑ
ꢊ0 ꢠꢓꢅꢓꢊ
ACIN – V Differential ...........................–16V to 0.3V
CC
ꢜ
ꢘ
ꢐ
ꢠꢓꢅꢓꢋ
ꢤꢅꢓ
Input/Output Currents
ꢊꢢ
ꢈꢃꢍ
I
I
................................................................ 200mA
ACIN
PBEN
ꢄRꢟꢈ
................................................................. –60mA
OUT
BAT .............................................................. –0.3V to 6V
ꢅꢆꢡꢃ
ꢙ
ꢦ
PBEN, NTC, EN,
PROG.........................–0.3V to [Max (V , BAT) + 0.3V]
CC
CHRG........................................................... –0.3V to 6V
Operating Junction Temperature Range... –20°C to 85°C
Storage Temperature Range .................. –40°C to 125°C
Maximum Reflow (Package Body)
ꢀꢁꢂꢃ ꢄꢅꢆꢇꢅꢈꢉ
ꢊꢋꢌꢀꢉꢅꢍ ꢎꢋꢏꢏ × ꢋꢏꢏ × 0.ꢐꢑꢏꢏꢒ
ꢗ ꢘꢙꢚꢆꢛ θ ꢗ ꢜꢋꢚꢆꢝꢞ
ꢓ
ꢔꢕꢅꢖ
ꢔꢅ
ꢉꢖꢄꢟꢠꢉꢍ ꢄꢅꢍ ꢎꢄꢡꢃ ꢊꢢꢒ ꢡꢠ ꢈꢃꢍꢛ ꢕꢣꢠꢓ ꢤꢉ ꢠꢟꢀꢍꢉRꢉꢍ ꢓꢟ ꢄꢆꢤ
Temperature..........................................................260°C
ORDER INFORMATION
TAPE AND REEL
PACKAGE**
TYPE
MSL
PART NUMBER
PART MARKING* FINISH CODE
LHNJ e4
PAD FINISH
RATING
TEMPERATURE RANGE
LQFN (Laminate Package
with QFN Footprint)
LTC4126EV-ADJ#TRPBF
Au (RoHS)
3
–20°C to 85°C
Consult Marketing for parts specified with wider operating temperature ranges. *Device temperature grade is identified by a label on the shipping container.
Parts ending with PBF are RoHS and WEEE compliant. **The LTC4126-ADJ package dimension is 2mm × 2mm × 0.74mm compared to a standard QFN
package dimension of 2mm × 2mm × 0.75mm.
This product is only available in tape and reel or in mini-reel.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating
temperature range, otherwise specifications are at TA = 25°C (Notes 2, 3). VACIN = VCC = 5V, VBAT = 3.8V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
2.7
2.7
3.1
TYP
MAX
5.5
4.25
4.25
80
UNITS
V
l
V
V
Input Voltage Range
Battery Voltage Range
CC
Charging
V
BAT
Not Charging, DC/DC On
Charging Done, DC/DC Off, V
Charging Done, DC/DC Off, V
V
I
I
V
CC
Quiescent Current
> V
< V
50
42
4
µA
µA
µA
µA
µA
µA
VCC
NTC
NTC
DIS
DIS
70
BAT Quiescent Current
Charging Done, DC/DC Off, V = 4.25V
8
BATQ
BAT
V
V
V
= V = 0, DC/DC On, I = 0
OUT
37
5
75
ACIN
ACIN
ACIN
CC
= V = 0, DC/DC Off
10
CC
= V = 0, Battery Disconnected
0
0.1
CC
(V < V
)
DISCONNECT
BAT
Rev. 0
2
For more information www.analog.com
LTC4126-ADJ
ELECTRICAL CHARACTERISTICS The ldenotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Notes 2, 3). VACIN = VCC = 5V, VBAT = 3.8V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
AC Rectification
V
V
V
V
High Voltage Limit
Low Voltage Limit
V
V
Rising
Falling
5.25
4.75
5.5
5
5.75
5.25
V
V
V
CC(HIGH)
CC(LOW)
CC
CC
CC
CC
ACIN to V Voltage Drop
7.5mA from ACIN to V
0.6
CC
CC
Battery Charger
l
V
Battery Charge Voltage
Battery Charge Current
4.158
4.200
4.242
V
CHG
CHG
I
R
= 0Ω
47
40
50
50
53
60
mA
mA
PROG
l
l
l
R
R
= 107kΩ
0.76
75
1.01
100
1.26
125
mA
%
PROG
PROG
= 0Ω to 107kΩ, As a Percentage
of Typical Value
ΔV
ΔV
V
-to-V Differential Undervoltage Lockout
V
V
Falling
Rising
9
55
27
80
45
105
mV
mV
UVLO
UVCL
CC
BAT
CC
CC
Threshold (Indicated at ACPR Pin)
V
-to-V Differential Undervoltage Current
CC
I
I
= 0.9 • I
= 0.1 • I
200
120
mV
mV
BAT
BAT
BAT
CHG
CHG
Limit Threshold Voltage
I
Charge Current Threshold for DUVCL Fault
Indication
(V – V ) Falling
40
60
%
%
DUVCL
CC
BAT
(V – V ) Rising
CC
BAT
V
Recharge Battery Threshold Voltage
Safety Timer Termination Period
As a Percentage of V
96.5
5.1
97.5
6
98.5
6.9
%
RECHRG
CHG
t
Timer Starts at the Beginning of the
Charge Cycle, V > (V + 100mV)
hours
TERMINATE
CC
BAT
f
f
Slow Blink Frequency
1.14
4.58
76.5
1.5
Hz
Hz
SLOW
FAST
Fast Blink Frequency
V
V
V
Cold Temperature Fault Threshold Voltage
Rising Threshold Voltage
Hysteresis
75.0
33.4
78
%V
%V
%V
%V
COLD
CC
CC
CC
CC
Hot Temperature Fault Threshold Voltage
Falling Threshold Voltage
Hysteresis
34.9
1.5
36.4
HOT
NTC Disable Threshold Voltage
NTC Leakage Current
150
250
100
mV
nA
nA
DIS
I
V
V
= 2.5V
= 0V
–100
1.16
NTC
NTC
NTC
–150
1.2
Step-Down DC/DC Regulator
l
V
DC/DC Regulator Output Voltage
V
V
> V
LOBAT2 OUT
or V
< V
= 0
<
BAT
1.24
V
OUT
BAT
LOBAT1
DISCONNECT
, I
= 0
V
V
< V < V
, I
V /3
BAT
V
V
LOBAT2
BAT
LOBAT1 OUT
l
l
l
l
V
V
V
V
Low Battery Alert 1 Threshold
Low Battery Alert 2 Threshold
Low Battery Alert 3 Threshold
Falling
BAT
3.52
3.22
3.12
2.93
3.6
100
3.3
100
3.2
100
3
3.68
3.38
3.28
3.07
LOBAT1
LOBAT2
LOBAT3
Hysteresis
Falling
mV
V
V
BAT
Hysteresis
Falling
mV
V
V
BAT
Hysteresis
V Falling
BAT
mV
V
Low Battery Disconnect Threshold Voltage
DC/DC Switching Frequency
DISCONNECT
SW
l
l
f
3:1 Mode (V > V
)
)
40
60
50
75
60
90
kHz
kHz
BAT
LOBAT2
LOBAT2
2:1 Mode (V < V
BAT
R
Effective Open-Loop Output Resistance (Note 4)
V
= 3.5V, I = 3mA
OUT
4.6
6.5
Ω
OL
BAT
Rev. 0
3
For more information www.analog.com
LTC4126-ADJ
ELECTRICAL CHARACTERISTICS The ldenotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C (Notes 2, 3). VACIN = VCC = 5V, VBAT = 3.8V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
OUT Current Limit
V
= 0V
80
mA
LIM
OUT
Pushbutton Pin (PBEN)
l
l
V
V
Logic Low Input Voltage
Logic High Input Voltage
Pull-up Resistance to BAT
Logic High Input Leakage
Debounce Time Low
0.4
V
V
IL
1.1
IH
R
V
V
< V
= V
4
0
MΩ
μA
PU
PBEN
PBEN
IL
I
t
t
0.1
503
63
IH
BAT
348
23
425
43
ms
ms
DBL
DBH
Debounce Time High
EN Pin
l
l
V
V
Logic Low Input Voltage
Logic High Input Voltage
Logic Low Input Leakage
Logic High Input Leakage
0.4
V
V
IL
1.1
IH
I
I
0
0
1
1
μA
μA
IL
IH
Logic Output Pins (STAT1, STAT2, ACPR)
V
V
Logic Low Output Voltage
Logic High Output Voltage
100μA into Pin
25μA out of Pin
0.2
V
V
OL
OH
V
OUT
– 0.2
Open-Drain Output (CHRG)
Pin Leakage Current
Pin Pull-Down Current
V
V
= 5V
0
0.5
μA
μA
CHRG
CHRG
= 400mV
200
300
450
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
characterization and correlation with statistical process controls. The
junction temperature (T in °C) is calculated from the ambient temperature
J
(T , in °C) and power dissipation (P , in watts) according to the formula:
A
D
T = T + (P • θ ),
J
A
D
JA
where the package thermal impedance θ = 92°C/W).
JA
Note 2: All currents into pins are positive; all voltages are referenced to
Note that the maximum ambient temperature consistent with these
specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal resistance, and
other environmental factors.
GND unless otherwise noted.
Note 3: The LTC4126EV-ADJ is tested under conditions such that T ≈ T .
The LTC4126EV-ADJ is guaranteed to meet performance specifications
from 0°C to 85°C junction temperature. Specifications over the –20°C
to 85°C operating junction temperature range are assured by design,
J
A
Note 4: See DC/DC Converter in Operation section.
Rev. 0
4
For more information www.analog.com
LTC4126-ADJ
TA = 25°C, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
Charge Current vs Battery Voltage
Charge Voltage vs Temperature
Li-Ion Battery Charge Profile
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ꢀ.ꢁꢁ
ꢀ.ꢁꢂ
ꢀ.ꢁ0
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.0
ꢀ.0
ꢀ.0
ꢀ.0
ꢀ.0
ꢀ.0
ꢀ.0
ꢀ.0
0
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.0
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ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0
ꢀ
ꢀ ꢁꢂ
ꢀꢀ
ꢀ
R
ꢂ ꢃꢀ
ꢀ
ꢂ ꢃꢀ
ꢁꢁ
ꢁꢁ
ꢂ ꢇꢈ.ꢉꢊ
R
ꢀRꢁꢂ
ꢃ ꢄꢅ.ꢆꢇ
ꢄRꢅꢆ
ꢀꢁꢂRꢃꢄ ꢀꢅRRꢄꢆꢇ
ꢀꢁꢂꢂꢃRꢄ ꢅꢆꢇꢂꢁꢈꢃ
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
0
ꢀ0 ꢀ00 ꢀꢁ0 ꢀ00 ꢀꢁ0 ꢀ00 ꢀꢁ0 ꢀ00
ꢀ.ꢁ
ꢀ
ꢀ.ꢀ
ꢀ.ꢁ
ꢀꢁꢂ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
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ꢀꢁꢂꢃ ꢄꢂꢁꢅꢆ
ꢀ
ꢀꢁꢂ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢂ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢁ
Charge Current vs VCC-to-VBAT
Differential Voltage
Charge Current vs Temperature
CHRG Pin Current vs Temperature
ꢀꢁ0
ꢀ0ꢁ
ꢀ00
ꢀꢁꢂ
ꢀꢁ0
ꢀꢁꢂ
ꢀꢁ0
ꢀꢁꢂ
ꢀꢁ0
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0
ꢀ.0
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢀ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.0
ꢀ
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ꢀ
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ꢀꢁꢂ
ꢀꢀ
R
.
R
ꢀ
R
ꢀ ꢁ.ꢂꢃ
ꢀꢁꢂ
R
.
ꢀ
ꢀ ꢁꢂ
ꢀꢀ
ꢀꢁꢂRꢃꢄꢅꢃ ꢆꢇꢅꢈ
CHRG ꢀꢁꢂ ꢀꢃꢄꢄꢅꢆ ꢃꢀ ꢇꢈ ꢉꢊ
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
0
ꢀ0
ꢀ00
ꢀ ꢁ
ꢀꢁ0
ꢀꢁꢂꢃ
ꢀꢁꢂ
ꢀ00
ꢀꢁ0
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢀ
ꢀꢀ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢃ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢀ
VCC Quiescent Current
vs Temperature
ACIN and VCC Waveforms when
Shunt Active
DC/DC Output Voltage
vs Battery Voltage
ꢀꢁ
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀꢁ
ꢀꢀ
ꢀ.ꢁ0
ꢀ0
ꢀ
ꢀ
ꢀ ꢁꢂ
ꢀ ꢁ.ꢂꢃ
ꢀꢀ
ꢀ
ꢁꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀ0
ꢀ.0ꢁ
ꢀ.0ꢁ
ꢀ.0ꢁ
ꢀ.0ꢁ
ꢀ.00
ꢀ
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ꢀꢁꢂꢃ
ꢀꢁꢂ ꢃꢀꢄꢅꢆꢃꢇ
Rꢀꢁꢂꢃꢄꢅꢀꢆ ꢇꢈꢉ ꢊꢋꢆꢀ
ꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ0
ꢀꢁꢂꢃ
ꢀꢁꢁꢂ
ꢀꢁꢂ
Rꢀꢁ.
ꢀꢁꢂ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀ
ꢀ.ꢀ
ꢀ.ꢁ
ꢀꢁꢂ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀꢁꢂꢃ ꢄꢅ00ꢆꢇꢈꢉꢁꢊꢋ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢀ
ꢀꢁꢂ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢉ
Rev. 0
5
For more information www.analog.com
LTC4126-ADJ
TA = 25°C, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
DC/DC Output Voltage vs
Temperature
DC/DC Output Voltage
vs Load Current
ꢀ.ꢁ0
DC/DC Efficiency vs Battery
Voltage
ꢀ.ꢁ0ꢂ
ꢀ.ꢁ0ꢂ
ꢀ.ꢁ0ꢁ
ꢀ.ꢁ00
ꢀ.ꢀꢁꢂ
ꢀ.ꢀꢁꢂ
ꢀ.ꢀꢁꢂ
ꢀ.ꢀꢁꢂ
ꢀ.ꢀꢁ0
ꢀ00
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
0
ꢀ
ꢀ ꢁ.ꢂꢃ
ꢀ
R
ꢀ ꢁ.ꢂꢃ
ꢀ ꢁ.ꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
Rꢀꢁꢂꢃꢄꢅꢀꢆ ꢇꢈꢉ ꢊꢋꢆꢀ
ꢀꢁꢂ ꢃꢄꢅꢆ
ꢀꢁꢂꢃ
ꢀꢁꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂꢃ
Rꢀꢁ.
ꢀꢁꢂ
ꢀꢁꢂꢃ
ꢀꢁꢂ ꢃꢄꢅꢆ
ꢀ.ꢀꢁ
ꢀ.ꢀꢀ
ꢀ.ꢀ0
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀ
ꢀ.ꢀ
ꢀ.ꢁ
ꢄꢀꢅ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ
ꢄꢅꢆꢇ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢀ
ꢁꢂꢃ
ꢁꢂꢃ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢂ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢁ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁ0
DC/DC Switching Frequency
vs Battery Voltage
Maximum DC/DC Output Current
vs Battery Voltage
DC/DC Effective Open-Loop Output
Resistance vs Temperature
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢁ
0
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0
ꢀ
ꢀ ꢁ.ꢁꢂ
ꢀꢁꢂ
ꢀ
ꢀ ꢁ.ꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂ ꢃꢄꢅꢆ
ꢀꢁꢂ ꢃꢄꢅꢆꢇꢈꢉꢊꢋ ꢌꢉꢈꢅ
ꢀ
ꢀ
ꢀ
ꢂ ꢃꢄ0ꢅꢆ
ꢂ ꢃꢄꢅꢆ
ꢂ ꢃꢄꢅꢆ
ꢁ
ꢁ
ꢁ
ꢀ
ꢀ.ꢀ
ꢀ.ꢁ
ꢄꢀꢅ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.0
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀꢁꢂ
ꢀ.ꢁ
ꢀ.0
ꢀ.ꢁ
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀ
ꢀ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢀ
DC/DC Switching Frequency in
3:1 Mode vs Temperature
DC/DC Switching Frequency in
2:1 Mode vs Temperature
BAT No-Load Quiescent Current
(DC/DC On) vs Battery Voltage
ꢀꢁ
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀ
ꢀꢁꢂ ꢃꢄꢅꢆꢇꢈꢉꢊꢋ ꢌꢉꢈꢅ
ꢀRꢁꢂꢃꢄꢅꢆꢁꢇꢈ
ꢀꢁꢂ ꢃꢄꢅꢆ
ꢀꢁꢂꢃꢄ
ꢀꢁꢁꢂꢃ
ꢀꢁꢂ ꢃꢄꢅꢆ
ꢀ
ꢀ
ꢀ ꢁ.ꢂꢃ
ꢀ ꢁ.ꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀ
ꢀ ꢁ.ꢂꢃ
ꢀ
ꢀ 0
ꢀꢁꢂ
ꢀꢁꢂ
0
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀ
ꢀ.ꢀ
ꢀ.ꢁ
ꢄꢀꢅ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢀ
ꢁꢂꢃ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢃ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢉ
Rev. 0
6
For more information www.analog.com
LTC4126-ADJ
TA = 25°C, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
BAT Quiescent Current
DC/DC Output Transient Response
to Load Step
(DC/DC Off) vs Temperature
ꢀ.0
ꢀ.ꢀ
ꢀ.0
ꢀ.ꢁ
ꢀ.0
ꢀ.ꢁ
ꢀ.0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
ꢀ0
0
ꢀ
ꢀ 0ꢁ
ꢀꢀ
0
ꢀꢁ0
ꢀꢁ0
ꢀꢁ0
ꢀꢁ0
ꢀ
ꢀ ꢁ.ꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀ
ꢁꢂꢃ
ꢀ
ꢀ ꢁ.ꢂꢃ
ꢀ
ꢀ ꢁ.ꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂꢃ ꢄꢅRRꢆꢇꢈ
ꢀꢁ0
ꢀꢁ0 ꢀꢁ
ꢀ0
ꢀꢁ
ꢀ0
ꢀꢀ
ꢀ0
ꢀꢁ
ꢀꢁꢂꢃ ꢄꢅ00ꢆꢇꢈꢉꢁꢊꢋ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢂ0
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇꢈꢉ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢉ
PIN FUNCTIONS
NTC (Pin 1): Thermistor Input. Connect a thermistor from
NTC to GND, and a bias resistor from V to NTC. The volt-
age level on this pin determines if the battery temperature
is safe for charging. The charge current and charge timer
are suspended if the thermistor indicates a temperature
that is unsafe for charging. Once the temperature returns
to the safe region, charging resumes. Ground the NTC pin
if temperature qualified charging is not needed.
from PBEN to GND to force a low state on this pin when
the button is pushed. However, the pushbutton is ignored
if the EN input is high. If the pushbutton function is not
needed, leave this pin unconnected.
CC
PROG (Pin 4): Charge Current Program Pin. A 1% resis-
tor, R
, connected from PROG to GND programs the
PROG
charge current as such:
100•1.1V
RPROG
=
– 2.2kΩ
EN (Pin 2): Digital Logic Input Pin to Enable the DC/DC
Converter.Aminimumvoltageof1.1Venablestheregulator
providedthattheLTC4126-ADJisnotinbatterydisconnect
mode(seeBatteryDisconnect/ShipMode underOperation
section). A low voltage (0.4V max) disables the regulator
and allows the pushbutton to control it. If only pushbutton
control is desired, tie this pin to GND. Tie this pin to BAT
if the DC/DC needs to remain enabled all the time. Do not
leave this pin unconnected.
ICHG
with I
being the desired battery charge current. The
CHG
minimum and maximum resistances allowed for R
PROG
are 0Ω and 107kΩ, respectively. Do not leave this pin
unconnected.
ACPR (Pin 5): Digital CMOS Logic Output Pin to indicate
if there is enough input power available to charge the bat-
tery. This pin goes high when the V -to-BAT differential
CC
PBEN (Pin 3): Pushbutton Toggle Input Pin to enable/
disable the DC/DC converter. Enabling of the regulator can
onlyoccuriftheLTC4126-ADJisnotinbatterydisconnect
mode(seeBatteryDisconnect/ShipMode underOperation
section). A weak internal pull-up forces PBEN high when
not driven. A normally open pushbutton is connected
voltage rises above 80mV (typical) and goes low when the
differential voltage drops below 27mV (typical). The low
level of this pin is referenced to GND and the high level
is referenced to the OUT pin voltage. Consequently, this
indicator is not available if the DC/DC is disabled.
Rev. 0
7
For more information www.analog.com
LTC4126-ADJ
PIN FUNCTIONS
CHRG (Pin 6): Open-Drain Charge Status Output Pin. This
pin can be pulled up through a resistor and/or an LED to
indicate the status of the battery charger. This pin has
four possible states: slow blink to indicate charging, fast
blink to indicate a fault, pulled down to indicate charging
done, and high impedance to indicate no input power. To
conservepower,thepull-downcurrentislimitedto300µA.
these indicators are not available if the DC/DC is disabled.
These two pins together with ACPR indicate the various
charging states and fault conditions. However, when no
inputpowerisavailableandtheDC/DCconverterisenabled,
these pins instead indicate the voltage level of the battery.
V
(Pin 11): DC Input Voltage Pin. An internal diode is
CC
connectedfromtheACINpin(anode)tothispin(cathode).
When an AC voltage is present at the ACIN pin, the voltage
on this pin is the rectified AC voltage. When the ACIN pin
is not used (or shorted to GND), connect this pin to a DC
voltage source to provide power to the LTC4126-ADJ and
charge the battery.
ACIN (Pin 7): AC Input Voltage Pin. Connect the external
LC tank, which includes the receive coil, to this pin. Con-
nect this pin to GND when not used.
BAT (Pin 8): Battery Connection Pin. Connect a single-cell
Li-Ion battery to this pin. Whenever enough input power
(AC or DC) is available, the battery will be charged via this
pin. Additionally, the DC/DC Converter is powered from
the battery via this pin. To minimize the effect of switching
noise from the DC/DC converter on charger performance,
this pin should be decoupled with a 1µF capacitor to GND
if the DC/DC converter is enabled while charging.
OUT (Pin 12): DC/DC Converter Output Pin. This pin pro-
vides 1.2V to power hearing aid ASICs. A low ESR ceramic
capacitor of at least 2.2μF should be placed close to this
pin to stabilize the converter.
GND (Exposed Pad Pin 13): Ground Pin. The exposed pad
on the backside of the package must be soldered to the
PCB ground for a low-resistance electrical connection as
well as for optimum thermal performance.
STAT2 (Pin 9), STAT1 (Pin 10): Digital CMOS Logic Status
Output Pins. The low level of these pins is referenced to
GNDandthehighlevelisreferencedtoV .Consequently,
OUT
Rev. 0
8
For more information www.analog.com
LTC4126-ADJ
BLOCK DIAGRAM
ꢛꢛ
ꢁ
ꢀ
ꢂ
ꢃꢃ
ꢀ
ꢦ0ꢧꢂꢕ
ꢝꢤꢧꢂ
ꢁ
ꢌꢖꢂꢍꢎ
ꢌꢖꢂꢃꢍ
ꢆꢃꢊꢋ
Rꢄꢃꢈꢊꢢꢊꢃꢆꢈꢊꢎꢋ ꢆꢋꢌ ꢊꢋꢟꢖꢈ
ꢟꢎꢏꢄR ꢃꢎꢋꢈRꢎꢍ
ꢤ
ꢁ
ꢀ
ꢀ
ꢛꢥꢜꢧꢂ
ꢁ
ꢊ
ꢃꢅꢇ
ꢑꢆꢈ
ꢦ
ꢁ
ꢜ.ꢝꢂ
ꢀ
ꢈꢎꢎ ꢃꢎꢍꢌ
ꢍꢗꢘꢊꢙꢚ
ꢂ
ꢃꢃ
ꢀ
ꢁ
ꢀ
ꢊ
ꢛ00
ꢃꢅꢇꢕ
R
ꢑꢊꢆꢒ
ꢋꢈꢃ
ꢛ
R
ꢋꢈꢃ
ꢈꢎꢎ ꢅꢎꢈ
ꢝ.ꢝꢞ
ꢟRꢎꢇ
ꢍꢎꢇꢊꢃ
ꢜ
R
ꢟRꢎꢇ
ꢀ
ꢁ
ꢋꢈꢃ ꢄꢋꢆꢑꢍꢄ
ꢛꢥ0ꢧꢂ
ꢎꢖꢈ
ꢈꢄRꢉꢊꢋꢆꢈꢄꢌ
RꢄꢃꢅꢆRꢇꢄ
ꢆꢃꢟR
ꢒꢈꢆꢈꢛ
ꢒꢈꢆꢈꢝ
ꢥ
ꢛ0
ꢣ
ꢀ
ꢁ
0.ꢣꢤꢥꢂ
ꢃꢅꢇ
ꢎꢖꢈ
ꢎꢖꢈ
ꢃ. ꢃ.ꢕꢃ. ꢂ.
ꢃꢅꢆRꢇꢄR
ꢃꢎꢋꢈRꢎꢍ
ꢆꢋꢌ
ꢒꢈꢆꢈꢖꢒ
ꢍꢎꢇꢊꢃ
ꢓ.ꢠꢂ
ꢓ.ꢓꢂ
ꢓ.ꢝꢂ
ꢀ
ꢁ
ꢀ
ꢁ
ꢍꢎꢏꢐꢑꢆꢈꢐꢆꢍꢄRꢈꢒ
ꢑꢆꢈꢐꢌꢊꢒꢃꢎꢋꢋꢄꢃꢈ
ꢃꢍꢨ
CHRG
ꢠ
ꢓ.0ꢂ
ꢓ00ꢔꢆ
ꢄꢋ
ꢝ
ꢓ
ꢑꢆꢈ
ꢜꢉ
ꢑꢆꢈ
ꢌꢃꢕꢌꢃ
ꢄꢋꢆꢑꢍꢄ ꢍꢎꢇꢊꢃ
ꢟꢖꢒꢅꢑꢖꢈꢈꢎꢋ
ꢈꢊꢉꢄR ꢆꢋꢌ
ꢌꢄꢑꢎꢖꢋꢃꢄR
ꢄꢋ
PBEN
ꢉꢖꢍꢈꢊꢘꢉꢎꢌꢄ
ꢃꢅꢆRꢇꢄ ꢟꢖꢉꢟ
ꢌꢃꢕꢌꢃ
ꢟꢖꢒꢅꢘ
ꢑꢖꢈꢈꢎꢋ
RꢄꢇꢖꢍꢆꢈꢎR
ꢎꢖꢈ
ꢛ.ꢝꢂ
ꢛꢥ0ꢞꢅꢩ
ꢎꢒꢃꢊꢍꢍꢆꢈꢎR
ꢛꢝ
ꢃꢍꢨ
ꢃꢍꢨ
ꢇꢋꢌ
ꢛꢓ
ꢜꢛꢝꢠꢘꢆꢌꢡ ꢑꢌ
Figure 1. LTC4126-ADJ Block Diagram
Rev. 0
9
For more information www.analog.com
LTC4126-ADJ
OPERATION
The LTC4126-ADJ is a low power battery charger with
an integrated step-down DC/DC converter designed to
wirelessly charge single-cell Li-Ion batteries and provide
a 1.2V output suitable for powering a hearing-aid ASIC.
The part has three principal circuit components: an AC
power controller, a full-featured linear battery charger, and
a step-down DC/DC converter.
are 0Ω and 107kΩ, respectively. Examples of R
CHG
and
PROG
I
are listed in Table 1.
Table 1. ICHG vs RPROG
R (kΩ)
PROG
I (mA)
CHG
0
50
8.87
10
2
52.3
107
1
AC POWER CONTROLLER
As soon as the voltage at the V pin rises 80mV (typi-
CC
A complete wireless power transfer system consists of
transmit circuitry with a transmit coil and receive circuitry
with a receive coil. The LTC4126-ADJ resides on the re-
ceiver side, where an external parallel resonant LC tank
connected to the ACIN pin allows the part to receive power
wirelessly from an alternating magnetic field generated
by the transmit coil. The Rectification and Input Power
Control circuitry (Figure 1) rectifies the AC voltage at the
cal) above the BAT pin voltage, the charger attempts to
charge the battery and a new charge cycle is initiated. A
6-hour charge termination timer starts at the beginning of
this new charge cycle. When the V -to-BAT differential
CC
voltage rises above 154mV (typical), the charger enters
constant-current(CC)modeandchargesthebatteryatthe
full programmed current. When the BAT pin approaches
the final charge voltage, the charger enters constant-
voltage (CV) mode and the charge current begins to drop.
The charge current continues to drop while the BAT pin
voltage is maintained at the proper charge voltage. This
state of CC/CV charging is indicated by a slow blinking
LED (typically 1.14Hz) at the CHRG pin.
ACIN pin and regulates that rectified voltage at the V
CC
pin to less than V
(typically 5.5V).
CC(HIGH)
Operation without Wireless Power
TheLTC4126-ADJcanbealternatelypoweredbyconnect-
ing a DC voltage source to the V pin directly instead of
CC
After the 6-hour charge termination timer expires, charg-
ing stops completely. Once the charge cycle terminates,
the LED at the CHRG pin stops blinking and assumes a
pull-down state. To start a new charge cycle, remove the
receiving power wirelessly through the ACIN pin. Ground
the ACIN pin if a voltage supply is connected to V .
CC
BATTERY CHARGER
power source at ACIN or V and reapply it.
CC
The LTC4126-ADJ includes a full-featured constant-
current (CC)/constant-voltage (CV) linear battery charger
with automatic recharge, automatic termination by safety
timer,badbatterydetection,andout-of-temperature-range
charge pausing. Charge current is programmable from
1mA to 50mA via an external resistor at the PROG pin,
and the final charge voltage is 4.2V.
Automatic Recharge
Aftercharginghasterminated,thechargerdrawsonly3.7µA
(typical) from the battery. If it remains in this state long
enough, the battery will eventually discharge. To ensure
that the battery is always topped off, a new charge cycle
automatically begins when the battery voltage falls below
V
(typically 97.5% of the charge voltage). In the
RECHRG
The value of the resistor at the PROG pin can be calculated
as such:
event that the battery voltage falls below V
while
RECHRG
the safety timer is still running, the timer will not reset.
This prevents the timer from restarting every time the bat-
tery voltage dips below V
100•1.1V
RPROG
=
– 2.2kΩ
ICHG
during a charging cycle.
RECHRG
with I
being the desired battery charge current. The
CHG
minimum and maximum resistances allowed for R
PROG
Rev. 0
10
For more information www.analog.com
LTC4126-ADJ
OPERATION
Bad Battery Fault
DUVCL circuitry prevents this undesirable behavior by
gradually increasing or decreasing the charge current as
input power becomes more or less available.
If the battery fails to reach a voltage above V
by the
RECHRG
end of a full charge cycle of 6 hours, the battery is deemed
faulty and the LED at the CHRG pin indicates this bad
battery fault condition by blinking fast (typically 4.58Hz).
Temperature Qualified Charging
The LTC4126-ADJ monitors the battery temperature dur-
ing the charging cycle by using a negative temperature
coefficient (NTC) thermistor, placed close and thermally
coupled to the battery pack. If the battery temperature
moves outside a safe charging range, the IC suspends
charging and signals a fault condition via CHRG (blinks
fast at 4.58Hz) and the STAT pins until the temperature
returns to the safe charging range. The safe charging
range is determined by two comparators (Too Hot and Too
Cold) that monitor the voltage at the NTC pin as shown in
the Block Diagram. The rising threshold of the Too Cold
Differential Undervoltage Lockout (DUVLO)
A differential undervoltage lockout circuit monitors the
differential voltage between V and BAT and disables
CC
the charger if the V voltage falls to within 27mV (typical
CC
ΔV
) of the BAT voltage. This condition is indicated by
UVLO
a low on the ACPR pin. Charging does not resume until
this difference increases to 80mV at which time the ACPR
pin transitions back high. The DC/DC must be enabled for
proper ACPR indication.
comparator is set to 76.5% of V (V
) and the falling
CC COLD
Differential Undervoltage Current Limit (DUVCL)
threshold of the Too Hot comparator is set to 34.9% of
(V ), each with a hysteresis of 1.5% of V around
The LTC4126-ADJ charger also includes differential
undervoltage current limiting (DUVCL) which gradually
reduces the charge current from the full programmed
V
CC HOT
CC
the trip point to prevent oscillation. If the battery charger
pauses due to a temperature fault, the 6-hour termination
timer also pauses until the thermistor indicates a return
to a safe temperature. Grounding the NTC pin disables
all NTC functionality. Most Li-Ion battery manufacturers
recommend a temperature range of 0°C to 40°C as a safe
charging range.
current towards zero as the V -to-BAT differential volt-
CC
age drops from approximately 154mV to 116mV. See the
curve in the Typical Performance Characteristics section.
When the charge current drops below 40% of the full
programmed value, the LED at the CHRG pin blinks fast
(typically4.58Hz)toindicatetheDUVCLfault.Inthereverse
direction, when the charge current rises above 60% of the
full programmed value, the LED at the CHRG pin resumes
slow blinking to indicate normal operation. Due to the
finite hysteresis of the DUVCL comparator, it is possible
under a very narrow region of coupling conditions for the
LTC4126-ADJ to alternate between slow blinking and fast
blinking. This behavior should be construed as operation
at near (but not 100%) full charge current.
Charge Status Indication via CHRG, ACPR, and
STAT pins
The status of the battery charger is indicated via the
open-drain CHRG pin as well as by the logic pins STAT1,
STAT2, and ACPR according to Table 2. Indication by the
logic pins is available only when the DC/DC is enabled.
Table 2. Charger Status Indication
CHRG
ACPR STAT1 STAT2 STATUS
TheDUVCLfeatureisparticularlyusefulinsituationswhere
the wireless power available is limited. Without DUVCL,
if the magnetic coupling between the receive coil and the
transmit coil is low, DUVLO could be tripped if the charger
tried to provide the full charge current. DUVLO forces the
chargecurrenttodroptozeroinstantly,allowingthesupply
voltage to rise above the DUVLO threshold and switch on
the charger again. In the absence of DUVCL, this oscilla-
tory behavior would result in intermittent charging. The
Hi-Impedance
0
X
X
Not Charging, No Power,
STAT pins indicate Battery
Level (see Table 3)
Pulled LOW
1
1
1
0
0
1
0
1
0
Done Charging
Charging
Blink Slow (1.14Hz)
Blink Fast (4.58Hz)
Temperature Fault/Bad
Battery
Blink Fast (4.58Hz)
1
1
1
Differential Undervoltage
Current Limit (DUVCL)
Rev. 0
11
For more information www.analog.com
LTC4126-ADJ
OPERATION
The open-drain CHRG pin has an internal 300µA (typical) This is referred to as Mode 2. The Thevenin equivalent
pull-down. An LED can be connected between this pin and circuit of the converter in Mode 2 is shown in Figure 2,
V
to indicate the charging status and any fault condition where R is the effective open-loop output resistance of
CC
OL
as indicated in the table above. The ACPR, STAT1, and the converter. R is typically 4.6Ω at room temperature
OL
STAT2 pins are digital CMOS logic outputs that can be for V = 3.5V and f = 50kHz. It varies with the battery
BAT
SW
interpreted by a microprocessor. The low level of these voltage, the switching frequency of the converter, and the
three pins is referenced to GND and the high level is temperature of the die. Figure 2 can be used to determine
referenced to the OUT pin voltage (typically 1.2V). Hence the output voltage (V ) for a specific load current (I
)
OUT
OUT
the status indication via these three pins is only available using the following equation:
if the DC/DC converter is turned on via the EN pin or the
VBAT
pushbutton. Status indication via the CHRG pin is always
available during charging.
VOUT
=
–IOUT •ROL
3
When the battery voltage falls below 3.3V, the charge
pump switches to 2:1 step-down mode (Mode 3) and
again provides a regulated 1.2V output. In Mode 3, the
maximum output current that the DC/DC converter can
provide decreases with battery voltage but does not fall
below approximately 35mA. See the curve in the Typical
Performance Characteristics. The variation of the output
voltage versus the battery voltage for the various modes
of operation is shown in Figure 3.
DC/DC CONVERTER
To supply the system load from the battery to the OUT
pin, the LTC4126-ADJ contains a proprietary low-noise
multi-mode charge pump DC/DC converter which can be
switched on by applying a minimum voltage of 1.1V to the
EN pin or by pressing the pushbutton. The converter can
be active simultaneously with the charger. The switching
frequency of the charge pump is set to either 50kHz or
75kHzdependingonthemodeofoperation.Thisfrequency
ischosentokeepanyswitchingnoiseoutoftheaudioband.
ꢌ.ꢍ
ꢌ.ꢎ
ꢌ.0
Modes of Operation
ꢗꢆꢔꢃ ꢌ
0.ꢏ
0.ꢐ
0.ꢍ
0.ꢎ
0
The charge pump DC/DC converter has 3 modes of opera-
tion depending on the battery voltage. For V > 3.6V, the
BAT
ꢗꢆꢔꢃ ꢎ
charge pump operates in 3:1 step-down mode (Mode 1)
and provides a regulated 1.2V output. In Mode 1, the
maximum output current that the DC/DC converter can
provide is limited by internal current limit circuitry to ap-
proximately 65mA.
ꢗꢆꢔꢃ ꢑ
ꢑ.0
ꢑ.ꢑ
ꢑ.ꢐ
ꢑ.ꢒ
ꢍ.ꢎ
ꢀꢁꢂꢂꢃRꢄ ꢅꢆꢇꢂꢁꢈꢃ ꢉꢅꢊ
ꢍꢌꢎꢐꢓꢁꢔꢕ ꢖ0ꢑ
ꢉ
ꢃꢊꢇ
R
ꢃꢈ
ꢓ
ꢃꢊꢇ
ꢔ
Figure 3. VOUT vs Battery Voltage at IOUT = 0
ꢅ
ꢗꢆꢐRꢉꢄꢘ
ꢐꢉꢀ ꢐꢙꢉꢁ
ꢕꢐꢇ
ꢖ
ꢓ
ꢅ
ꢔ
Handling Large Loads
ꢀꢁꢂꢀꢁ ꢁꢃꢄꢅꢆRꢇꢆR
ꢋꢌꢍꢎꢏꢐꢀꢑ ꢒ0ꢍ
WhileoperatinginMode1orMode2(3:1step-downmode),
if a large load at the output causes the output voltage to
drop below 1.1V, the converter automatically switches
over to Mode 3 (2:1 step-down mode) and attempts to
regulate the output at 1.2V. The converter stays in Mode 3
for110ms(typical)andthenreturnstothepreviousmode.
Figure 2. DC/DC Converter Thevenin Equivalent Circuit
in Mode 2: 3-to-1 Step-Down
When the battery voltage is between 3.6V and 3.3V, the
charge pump still operates in 3:1 step-down mode, but it
can no longer maintain 1.2V regulation and provides one-
third of the battery voltage at its output (only at no load).
If the large load condition persists and V
drops below
OUT
1.1V again, the converter switches back into Mode 3 for
Rev. 0
12
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LTC4126-ADJ
OPERATION
ꢐ00
ꢑ0
ꢗ0
ꢒ0
ꢘ0
ꢓ0
ꢔ0
ꢕ0
ꢖ0
another 110ms and the cycle continues. The duration of
110msischosentopreventmodeswitchingatafrequency
which could fall into the audible range. The switch over to
Mode 3 provides more current drive capability at the cost
of efficiency and this is why the converter tries to stay in
Mode 1 or Mode 2 as much as possible.
ꢜꢆꢚꢃ ꢐ
ꢜꢆꢚꢃ ꢖ
Converter Efficiency
The LTC4126-ADJ DC/DC converter efficiency varies
throughout the battery voltage range and is very much
dependent on the mode it is operating in. The theoretical
maximumefficiencyinMode1canbeexpressedasfollows:
ꢐ0 ꢜꢆꢚꢃ ꢕ
0
ꢕ.0
ꢕ.ꢕ
ꢕ.ꢘ
ꢕ.ꢑ
ꢔ.ꢖ
ꢀꢁꢂꢂꢃRꢄ ꢅꢆꢇꢂꢁꢈꢃ ꢉꢅꢊ
ꢔꢐꢖꢘꢙꢁꢚꢛ ꢋ0ꢔ
Figure 4. Theoretical Maximum Converter
Efficiency vs Battery Voltage
VOUT
Efficiency, ηMode1
=
V
⎛
⎞
BAT
⎜
⎝
⎟
⎠
3
Battery Level Indicator
If regulation is maintained at the OUT pin at 1.2V, the
The LTC4126-ADJ is equipped with a battery voltage
monitor which reports various battery voltage levels via
the STAT pins when not charging and the converter is
enabled. See Table 3. Since the STAT pins indicate either
the charger status or the battery levels based on the state
of ACPR, there may be a delay of up to 1µs before the STAT
pins are valid whenever ACPR changes state.
theoretical maximum efficiency is 85.7% when V
=
BAT
4.2V and 100% when V = 3.6V as calculated from the
BAT
above equation.
When the battery voltage is between 3.6V and 3.3V, the
converter can no longer maintain a 1.2V regulation at OUT
at all loads and is operating in Mode 2. However, the upper
limitonthe efficiencythattheconvertercanachieve in this
mode is determined by switching losses, ohmic losses,
and quiescent current loss.
Table 3. Battery Level Indication
ACPR STAT1 STAT2 STATUS
0
0
0
0
1
0
0
1
1
X
0
1
0
1
X
V
< 3.2V, Low Battery Alert 3
BAT
3.2V < V < 3.3V
BAT
Whenthebatteryvoltagefallsto3.3V,theconverterenters
Mode 3 where the theoretical maximum efficiency can be
expressed as follows:
3.3V < V < 3.6V
BAT
V
> 3.6V
BAT
Power Available, STAT Pins Indicate Charger Status
VOUT
Efficiency, ηMode3
=
V
Battery Disconnect/Ship Mode
⎛
⎞
BAT
⎜
⎝
⎟
⎠
2
When no input power is available and the battery voltage
falls to 3.0V (typical), the LTC4126-ADJ shuts down most
of its functions to prevent the battery from discharging too
deeply, consuming less than 100nA from the battery. Once
in battery disconnect mode, normal functioning can only
In Mode 3, the theoretical maximum efficiency is 72.7%
whenV =3.3Vand80%whenV =3.0Vascalculated
BAT
BAT
from the above equation.
Figure 4 shows graphically the variation of the theoretical
maximum efficiency of the converter over the range of
battery voltages in the three different modes of operation.
resume when power is applied to the ACIN or V pin and
CC
the V pin voltage rises 80mV (typical) above the BAT pin
CC
voltage.
TheLTC4126-ADJisalsoinbatterydisconnectmodeafter
initial installation of the battery regardless of its voltage
level. This implements the ship mode functionality.
Rev. 0
13
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LTC4126-ADJ
OPERATION
Pushbutton Control
ꢆꢁꢇꢈ ꢉꢇꢁꢂꢈꢅ
ꢊꢏꢍꢎ
ꢆꢁꢇꢈ ꢉꢇꢁꢂꢈꢅ
ꢊꢋꢌꢍꢎ
ꢆꢁꢇꢈ ꢉꢇꢁꢂꢈꢅ
ꢊꢋꢌꢍꢎ
PBEN
The LTC4126-ADJ is equipped with a pushbutton control-
ler to turn the DC/DC converter on and off if the EN pin is
not used (held low). A logic high on the EN pin overrides
the pushbutton function and keeps the regulator on. On
the falling edge of the EN signal, the DC/DC shuts off and
1µs later, the pushbutton can control the output as long
as EN remains low. A push on the pushbutton is consid-
ered valid if the PBEN pin is held low for at least 425ms
(typical). Additionally, the PBEN pin needs to return to the
high state for at least 43ms (typical) in between succes-
sive pushes for a push to be considered valid. An invalid
push will not change the state of the converter. A 4MΩ
internal resistor pulls up the PBEN pin to the BAT voltage.
A few different scenarios of valid and invalid pushes are
illustrated in Figure 5.
ꢀ
ꢁꢂꢃ
(a) VALID SUCCESSIVE PUSH, DC/DC TURNS ON AND OFF
ꢃꢁꢁ ꢄꢅꢁRꢃ
ꢆꢁꢇꢈ ꢉꢇꢁꢂꢈꢅ
ꢊꢋꢌꢍꢎ
ꢆꢁꢇꢈ ꢉꢇꢁꢂꢈꢅ
PBEN
ꢊꢏꢍꢎ
ꢀ
ꢁꢂꢃ
(b) HIGH PULSE TOO SHORT, 2ND PUSH IGNORED, DC/DC STAYS ON
ꢆꢁꢇꢈ ꢉꢇꢁꢂꢈꢅ
ꢃꢁꢁ ꢄꢅꢁRꢃ
ꢆꢁꢇꢈ ꢉꢇꢁꢂꢈꢅ
ꢊꢋꢌꢍꢎ
PBEN
ꢊꢏꢍꢎ
ꢀ
ꢁꢂꢃ
ꢊꢐꢋꢑꢒꢓꢔꢕ ꢖ0ꢌ
(c) 1ST PUSH TOO SHORT, DC/DC STAYS OFF, 2ND PUSH VALID, DC/DC TURNS ON
Figure 5. Various Pushbutton Scenarios
Rev. 0
14
For more information www.analog.com
LTC4126-ADJ
APPLICATIONS INFORMATION
WIRELESS POWER TRANSFER
of the cycle, M1 is switched on and the current through
TX
L
rises linearly. During the second half of the cycle, M1
In a wireless power transfer system, power is transmitted
using an alternating magnetic field. An AC current in the
transmit coil generates a magnetic field. When the receive
coil is placed in this field, an AC current is induced in the
receive coil. The AC current induced in the receive coil is
a function of the applied AC current at the transmitter and
the magnetic coupling between the transmit and receive
coils. The LTC4126-ADJ internal diode rectifies the AC
voltage at the ACIN pin.
is switched off and the current through L circulates
TX
through the LC tank formed by C (= C
+ C ) and
TX
TX1
TX2
L . The current through L is shown in Figure 8.
TX
TX
If the transmit LC tank frequency is set to 1.29 times the
driving frequency, switching losses in M1 are significantly
reduced due to zero voltage switching (ZVS). Figure 9 and
Figure 10 illustrate the ZVS condition at different f
frequencies.
TX-TANK
ꢅꢌR ꢎꢅꢏ
ꢌ
ꢌ
ꢅꢍꢄRꢋ
ꢅꢍꢄꢊꢋ
f
= 1.29 • f
DRIVE
TX-TANK
f
f
is set by resistor R connected to the LTC6990.
SET
TX-TANK
DRIVE
ꢉ
ꢉ
Rꢋ
ꢊꢋ
is set by:
ꢁꢐꢑ
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈ0ꢃ
1
fTX−TANK
=
Figure 6. Wireless Power Transfer System
2 • π LTX •CTX
Thepowertransmissionrangeacrosstheairgapasshown
inFigure6canbeimprovedusingresonancebyconnecting
an LC tank to the ACIN pin tuned to the same frequency
as the transmit coil AC current frequency.
The peak voltage of the transmit coil, L , that appears at
TX
the drain of M1 is:
V
= 1.038 • π • V
IN
TX-PEAK
And the peak current through L is:
TX
RECEIVER AND SINGLE TRANSISTOR TRANSMITTER
0.36 • V
fTX−TANK •LTX
IN
ITX−PEAK
=
The single transistor transmitter shown in Figure 7 is an
example of a DC/AC converter that can be used to drive
AC current into a transmit coil, L .
TX
The RMS current through L is:
TX
TheNMOS, M1, isdrivenbya50%dutycyclesquarewave
generated by the LTC6990 oscillator. During the first half
I
= 0.66 • I
TX-RMS
TX-PEAK
ꢐꢑR ꢇꢐꢅ
ꢩꢉꢪꢪ ꢍꢆ ꢊꢪꢪꢫ
ꢐꢀꢑꢒ
ꢅRꢆꢇ
ꢝꢍꢐꢍꢈ
ꢝꢍꢐꢍꢉ
ꢐꢀꢅR
ꢏ
ꢢꢏ
ꢑꢒ
ꢀꢉ
ꢈ00ꢎꢄ
ꢓꢑꢇꢑꢍꢐꢔ ꢑꢞꢆ
ꢤ ꢟ.ꢢꢪꢐ
ꢀ
ꢂꢂꢃꢄ
Rꢁ
ꢀꢈ
ꢊ.ꢟꢎꢄ
ꢏ
ꢀꢀ
ꢑ
ꢀꢡꢇ
R
ꢈꢉ.ꢊꢋ
ꢅRꢆꢇ
ꢣ
ꢤ ꢂꢈꢢꢋꢡꢥ
ꢚꢐꢍ
ꢔꢀꢦꢍꢐꢒꢧ
ꢜ
ꢔꢕꢖꢑꢗꢃ
ꢊ.ꢉꢏ
ꢔꢍꢀꢊꢈꢉꢘꢖꢐꢓꢙ
ꢀ
ꢂꢂꢃꢄ
ꢍꢁꢈ
ꢌꢈ
ꢓꢈ
CHRG
ꢒꢍꢀ
ꢛꢒ
ꢔ
ꢔ
ꢍꢁ
Rꢁ
ꢜ
ꢏ
ꢀ
ꢟ.ꢢꢎꢡ
ꢈꢂꢎꢡ
ꢍꢁꢉ
ꢈꢃꢄ
ꢈ.ꢉꢏ
ꢆꢌꢍ
ꢆꢛ
ꢀ
ꢉ.ꢉꢎꢄ
ꢣ
ꢤ ꢉꢊꢊꢋꢡꢥ
ꢆꢌꢍ
ꢔꢍꢀꢘꢨꢨ0
ꢓRꢑꢏꢛ
ꢇꢒꢓ
PBEN
ꢓꢑꢏ
ꢠꢈ
ꢝꢕꢉꢂꢈꢉꢀꢓꢝ
ꢝꢛꢍ
ꢆꢌꢍ
ꢇꢒꢓ
R
ꢉ0ꢢꢋ
ꢝꢛꢍ
ꢅꢌꢝꢡꢚꢌꢍꢍꢆꢒ
ꢊꢈꢉꢘꢖꢐꢓꢙ ꢄ0ꢟ
ꢍRꢐꢒꢝꢠꢑꢍꢍꢛR
RꢛꢀꢛꢑꢏꢛR
Figure 7. DC/AC Converter, Transmit/Receive Coil, Tuned Resonant LTC4126-ADJ Receiver
(See Table 4 and Table 5 for Recommended Components)
Rev. 0
15
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LTC4126-ADJ
APPLICATIONS INFORMATION
Note that since f
can be easily adjusted, it is best
DRIVE
practicetochoosef
usingtheminimumcomponent
RX-TANK
count (i.e. C ) and then adjust f
to match.
RX
DRIVE
ꢏ00ꢐꢇꢃꢄꢅꢆ
0ꢇ
The amount of AC current in the transmit coil can be
increased by increasing the supply voltage (V ). Since
IN
the amount of power transmitted is proportional to the AC
current in the transmit coil, V can be varied to adjust the
IN
ꢈꢉꢀꢊꢋꢇꢄꢌ ꢍ0ꢎ
power delivery to the receive coil.
ꢀꢁꢂꢃꢄꢅꢆ
The overall power transfer efficiency is also dependent
on the quality factor (Q) of the components used in the
transmitterandreceivercircuitry. Selectcomponentswith
low resistance for transmit/receive coils and capacitors.
Figure 8. Current Through Transmit Coil
ꢄRꢈꢅꢔ
ꢆꢋꢌꢉꢈꢇꢊ
ꢕꢆꢃꢄꢅꢆ
CHOOSING TRANSMIT POWER LEVEL
0ꢆ
As discussed in the previous section, the supply voltage
ꢇꢈꢉꢊ
ꢆꢋꢌꢉꢈꢇꢊ
ꢀꢆꢃꢄꢅꢆ
(V )canbeusedtoadjustthetransmitpowerofthetrans-
IN
mitter shown in Figure 7. Transmit power should be set as
low as possible to receive the desired output power under
worst-case coupling conditions (e.g. maximum transmit
distance with the worst-case misalignment). Although the
LTC4126-ADJ is able to shunt excess received power to
0ꢆ
ꢍꢎꢀꢏꢐꢈꢄꢑ ꢒ0ꢓ
ꢀꢁꢂꢃꢄꢅꢆ
Figure 9. Voltage on the Drain and Gate of NMOS
M1 when fTX_TANK = fDRIVE
maintain the V voltage in the desired range, it has the
CC
adverse effect of raising the die temperature and possibly
the battery temperature, and if the battery temperature
exceeds the Too Hot temperature threshold set by the
thermistor, the charger pauses charging the battery.
ꢄRꢇꢅꢈ
ꢆꢉꢊꢋꢇꢌꢍ
ꢎꢆꢃꢄꢅꢆ
0ꢆ
Using the rated current of the transmit inductor to set an
upper limit, transmit power should be adjusted downward
until charge current is negatively impacted under worst-
case coupling conditions. Once the transmit power level
is determined, the transmit and receive coils should be
arranged under best-case coupling conditions with a
fully-charged battery or a battery simulator to make sure
that the shunting of excess power does not raise the die
temperature too much.
ꢌꢇꢋꢍ
ꢆꢉꢊꢋꢇꢌꢍ
ꢀꢆꢃꢄꢅꢆ
0ꢆ
ꢏꢐꢀꢑꢒꢇꢄꢓ ꢔꢐ0
ꢀꢁꢂꢃꢄꢅꢆ
Figure 10. Voltage on the Drain and Gate of NMOS
M1 when fTX_TANK = 1.29 • fDRIVE
The LC tank at the receiver, L and C , is tuned to the
same frequency as the driving frequency of the transmit
LC tank:
RX
RX
Inadditiontotemperature,anotherparameterthatneedsto
be checked is the maximum negative voltage on the ACIN
pin. Following the procedure above, when evaluating the
rise in temperature of the LTC4126-ADJ under the best-
f
= f
DRIVE
RX-TANK
where f
is given by,
RX-TANK
1
case coupling conditions, ensure that V – V
does
CC
ACIN
fRX−TANK
=
not exceed 16V. Figure 11 shows a typical waveform on
2 • π LRX •CRX
ACIN showing V – V < 16V.
CC
ACIN
Rev. 0
16
For more information www.analog.com
LTC4126-ADJ
APPLICATIONS INFORMATION
ꢀ0
resonant capacitance and R
resistance.
is the equivalent AC load
L-AC
ꢀ
ꢁꢁ
ꢀꢁꢂꢃ
ꢀ
ꢀ
One simplification is as follows:
RL–DC
RL–AC
≈
2
ꢀꢁ
ꢀꢁ
ꢀꢁ0
which assumes that the drop across the Schottky diode is
muchsmallerthantheamplitude|V |.Additionally,R
RX
L-DC
can be approximated as the ratio of the output voltage
(V ) to the output current (I ):
ꢀꢁꢂꢃ ꢄꢅ00ꢆꢇꢈꢉꢁꢊꢋ
OUT
OUT
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢁ
VOUT
IOUT
RL–DC
=
Figure 11. Typical Acceptable Voltage Waveform
on the ACIN Pin with VCC – VACIN < 16V.
The amplitude of the current in the transmit coil |I | can
TX
be either measured directly or its initial (no receiver) value
can be calculated based on the transmitter circuit. This
initial value is a conservative estimate since the amplitude
of the transmitter coil current will drop as soon as the
receiver, with a load, is coupled to it.
Asanalternativetousingtheempiricalmethodtodetermine
themaximumnegativevoltageontheACINpin,thefollowing
formula can be used in conjunction with Figure 12, which
shows a parallel resonant configuration on the receiver:
ωk LTXLRX
VRX
=
ITX
The coupling factor (k) between the two coils could be
obtained by running a finite element simulation inputting
thecoildimensionsandphysicalconfigurations. Aneasier
methodtoobtainthiscouplingnumber,istousetheseries-
aidingandseries-cancellingmeasurementmethodfortwo
loosely coupled coils as shown in Figure 13.
2
⎛
⎞
LRX
RL–AC
1– ω2L C
+ ω
(
)
RX RX
⎜
⎝
⎟
⎠
ꢏ
ꢑꢒꢍ
ꢎ
ꢎ
ꢉ
ꢉ
ꢉ
ꢋ
ꢋ
ꢎ
R
ꢉꢌꢆꢋ
ꢍꢊ
ꢍꢊ
Rꢊ
Rꢊ
Rꢐꢋꢍ ꢑꢒꢍ
And:
LAIDING = LAB
L
CANCELLING = LCD
ꢏ
Rꢊ
L
AIDING –LCANCELLING
k =
ꢉ
ꢋ
R
ꢉꢌꢅꢋ
ꢍꢊ
ꢍꢊ
Rꢊ
Rꢊ
4 LTXLRX
ꢀꢁꢂꢃꢄꢅꢆꢇ ꢈꢁꢂ
Figure 12. Modeling Parallel Resonant Configuration
and Half Wave Rectifier on the Receiver
ꢆ
ꢀ
ꢀ
ꢀ
ꢀ
ꢋ
ꢋ
Rꢍ
ꢋ
ꢋ
Rꢍ
ꢌꢍ
ꢌꢍ
|V | is the amplitude of the voltage on the receiver coil,
RX
TX
ꢎ
ꢇ
ꢏ
ꢁꢂꢃꢄꢅꢆꢇꢈ ꢉꢂꢊ
|I | is the amplitude of the current in the transmit coil,
k is the coupling factor between the transmit and receive
Figure 13. Series-Aiding and Series-Cancelling Method
Configurations Used for Measuring the Coupling Factor k
coils, is the operating frequency in radians per second,
L
is the self-inductance of the transmit coil, L is the
RX
TX
self-inductance of the receive coil, C is the receiver
RX
Rev. 0
17
For more information www.analog.com
LTC4126-ADJ
APPLICATIONS INFORMATION
SINGLE TRANSISTOR TRANSMITTER AND LTC4126-ADJ
RECEIVER-DESIGN EXAMPLE
The transmit coil (L ) used in the example is 7.5µH.
TX
The value of transmit tank capacitance (C ) can be
TX
calculated:
TheexampleinFigure7illustratesthedesignoftheresonant
coupled single transistor transmitter and LTC4126-ADJ
charger. The steps needed to complete the design are
reviewed as follows.
1
CTX
=
= 34nF
4 • π2 • f2TX−TANK •LTX
Since 34nF is not a standard capacitor value, use
a 33nF capacitor in parallel with a 1nF capacitor to
1. Determine the receiver resonant frequency and set
component values for the receiver LC tank:
obtain a value within 1% of the calculated C . The
TX
It is best practice to select a resonant frequency that
yieldsalowcomponentcount.Inthisexample,244kHz
is selected as the receiver resonant frequency. At
recommended rating for C capacitors is 50V with
TX
5% (or better) tolerance.
4. Verify that the AC current through the transmit coil
is well within its rating. In this example, the supply
voltage to the single transistor transmitter is 5V. The
244kHz, the tank capacitance (C ) required with the
RX
selected receive coil (13µH) is 33nF. Since 33nF is a
standard value for capacitors, the tank capacitance
requires only one component. The tank capacitance
calculation is shown below.
peak AC current through the transmit (L ) coil can
TX
be calculated as:
0.36 • V
0.36 • 5V
IN
1
ITX–PEAK
=
=
= 0.76A
CRX
=
= 32.7nF ! 33nF
fTX–TANK •LTX 315kHz • 7.5µH
4 • π2 • f2RX−TANK •LRX
and the RMS current as:
= 0.66 • 0.76A = 0.5A
Selecta33nFcapacitorwithaminimumvoltagerating
I
of 25V and 5% (or better) tolerance for C . A higher
TX-RMS
RX
voltage rating usually corresponds to a higher quality
factor which is preferable. However, the higher the
voltage rating, the larger the package size usually is.
The rated current for the transmit coil is 1.55A (see
the Wurth 760308103206 data sheet for more infor-
mation). So the I
rated current.
calculated is well below the
TX–RMS
2. Set the driving frequency (f ) for the single tran-
DRIVE
sistor transmitter:
5. Also verify that the transmit power level chosen does
not result in excessive heating of the LTC4126-ADJ.
f
is set to the same value as the receiver resonant
DRIVE
frequency:
COMPONENT SELECTION FOR TRANSMITTER AND
RECEIVER
1MHz 50kΩ
NDIV 244kHz
RSET
=
•
= 205kΩ
To ensure optimum performance from the LTC4126-ADJ,
use the components listed in Table 4 and Table 5 for the
receiverandtransmitter,respectively,asshowninFigure7.
Select receive and transmit coils with good quality factors
to improve the overall power transmission efficiency. Use
a ferrite core to improve the magnetic coupling between
the transmit and receive coils and to shield the rest of the
transmit and receive circuitry from the AC magnetic field.
Capacitors with low ESR and low thermal coefficients
such as C0G ceramics should be used in the transmit and
receive LC tanks.
where N = 1 as the DIV pin of the LTC6990 is
DIV
grounded. Select a 205kΩ (standard value) resistor
with 1% tolerance. For more information regarding
the oscillator, consult the LTC6990 data sheet.
3. Set the LC tank component values for the single tran-
sistor transmitter: If f
is 244kHz, the transmit LC
DRIVE
tank frequency (f
) is:
TX-TANK
f
= 1.29 • 244kHz = 315kHz
TX-TANK
Rev. 0
18
For more information www.analog.com
LTC4126-ADJ
APPLICATIONS INFORMATION
Table 4. Recommended Components for the Receiver Shown in Figure 7
ITEM
PART DESCRIPTION
MANUFACTURER/PART NUMBER
L
Receive Coil, 13µH, 10mm
Wurth 760308101208
RX
C
Capacitor, C0G, 33nF, 5%, 50V, 0805 or
Capacitor, C0G, 33nF, 5%, 50V, 1206
Capacitor, X5R, 2.2uF, 10%, 6.3V, 0402
LED, 620nm, Red, 0603, SMD
TDK C2012C0G1H333J125AA
Murata GCM3195C1H333JA16D
Murata GRM155R60J225KE95D
Rohm Semiconductor SML-311UTT86
RX
C
OUT
D1
Table 5. Recommended Components for the Transmitter Shown in Figure 7
ITEM
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Wurth 760308103206
L
Transmit Coil, 7.5µH, 28mm × 15mm
Capacitor, C0G, 33nF, 5%, 50V, 0805
Capacitor, C0G, 1nF, 5%, 50V, 0603
MOSFET, N-CH 20V, 6A, SOT-23-3
TX
C
C
TDK C2012C0G1H333J125AA
TDK C1608C0G1H102J080AA
Vishay Si2312CDS-T1-GE3
Vishay CRCW0402205KFKED
Analog Devices LTC6990IDCB
TDK C1005X5R0J475M
TX1
TX2
M1
R
Resistor, 205kΩ, 1%, 1/16W, 0402
IC, Voltage Controlled Silicon Oscillator, 2mm × 3mm DFN
Capacitor, X5R, 4.7μF, 20%, 6.3V, 0402
Capacitor, X5R, 100μF, 20%, 6.3V, 1206
SET
U1
C1
C2
Murata GRM31CR60J107ME39L
COMPONENT SELECTION FOR CHRG STATUS
ꢗ
ꢂꢂ
INDICATOR
ꢀꢁꢂꢃꢄꢅꢆꢇꢈꢉꢊ
ꢋꢁꢂ
R
ꢌꢏꢈꢎ
TheLEDconnectedattheCHRGpinispoweredbya300µA
(typical)pull-downcurrentsource.Selectahighefficiency
LEDwithalowforwardvoltagedrop.Somerecommended
LEDs are shown in Table 6.
ꢌꢈꢁ
ꢙ
ꢋꢁꢂ RꢍꢎꢏꢎꢁꢐR
ꢁꢑꢍRꢒꢈꢀꢀꢓ ꢂꢐꢔꢕꢀꢍꢉ
ꢖꢏꢁꢑ ꢌꢈꢁꢁꢍRꢓ
R
ꢋꢁꢂ
ꢀꢚꢇꢏꢛꢜ
ꢃꢄꢅꢆꢇꢈꢉꢊ ꢘꢄꢃ
Table 6. Recommended LEDs
MANUFACTURER/
PART NUMBER
Rohm Semiconductor, SML-311UTT86 LED, 620nm, RED, 0603, SMD
Lite-On Inc., LTST-C193KRKT-5A LED, RED, 0603, SMT
Figure 14. NTC Thermistor Connection
PART DESCRIPTION
This can be simplified as:
RHOT
RBIAS
= 0.536
Temperature Qualified Charging
If R
is chosen to have a value equal to the value of
BIAS
To use the battery temperature qualified charging feature,
the chosen NTC thermistor at 25°C (R ), then R /R
25
HOT 25
connect an NTC thermistor, R , between the NTC pin
NTC
= 0.536. Thermistor manufacturers usually publish resis-
and GND, and a bias resistor, R
, from the V pin to
BIAS
CC
tance/temperature conversion tables for their thermistors
the NTC pin (Figure 14). Since the Too Hot comparator
and list the ratio of the resistance, R , of the thermistor at
T
threshold in the LTC4126-ADJ is internally set to 34.9% of
any given temperature, T, to its resistance, R , at 25°C.
25
V , the resistance of the thermistor at the hot threshold,
CC
For the Vishay thermistor NTCS0402E3104*HT with
R
, can be computed using the following equation:
HOT
β25/85 = 3950k, the ratio R /R = 0.536 corresponds to
T
25
RHOT
HOT +RBIAS
approximately 40°C.
= 0.349
R
Rev. 0
19
For more information www.analog.com
LTC4126-ADJ
APPLICATIONS INFORMATION
Similarly, since the Too Cold comparator threshold in
From the conversion table, this ratio corresponds to
about 8°C. Note that changing the value of R to be
the LTC4126-ADJ is internally set to 76.5% of V , the
CC
BIAS
resistance of the thermistor at the cold threshold, R
,
smaller than R moves both the hot and cold thresholds
COLD
25
can be computed using the following equation:
higher. Similarly, R
with a value greater than R will
25
BIAS
move both the hot and cold thresholds lower. Also note
RCOLD
COLD +RBIAS
= 0.765
that with only one degree of freedom (i.e. adjusting the
R
value of R
), the user can only set either the cold or
BIAS
hot threshold but not both.
This can be simplified as:
It is possible to adjust the hot and cold threshold indepen-
dently by introducing another resistor as a second degree
RCOLD
= 3.25
RBIAS
of freedom (Figure 15). The resistor R in effect reduces
D
the sensitivity of the resistance between the NTC pin and
ground.Therefore,intuitivelythisresistorwillmovethehot
threshold to a hotter temperature and the cold threshold
Again, if R
is chosen to have a value equal to the
BIAS
value of the chosen NTC thermistor at 25°C (R ), then
25
R
/R = 3.25. For the same Vishay thermistor with
COLD 25
to a colder temperature. The value of R
and R can
BIAS
D
β25/85 = 3950k, the ratio R /R = 3.25 corresponds to
T
25
now be set according to the following formula:
approximately 0°C.
The hot/cold temperature thresholds can be increased or
ꢗ
ꢂꢂ
decreased by choosing an R
value which is not the
ꢀꢁꢂꢃꢄꢅꢆꢇꢈꢉꢊ
ꢋꢁꢂ
R
R
ꢌꢏꢈꢎ
ꢉ
BIAS
same as R . For example, if a hot temperature threshold
25
of 50°C is desired, consult the resistance/temperature
ꢌꢈꢁ
conversion table of the thermistor to find the ratio R /
50
ꢚ
ꢀꢛꢇꢏꢜꢝ
ꢋꢁꢂ RꢍꢎꢏꢎꢁꢐR
ꢁꢑꢍRꢒꢈꢀꢀꢓ ꢂꢐꢔꢕꢀꢍꢉ
ꢖꢏꢁꢑ ꢌꢈꢁꢁꢍRꢓ
R
ꢋꢁꢂ
R . For the same Vishay thermistor used above, this
25
ratio is 0.3631. Since R /R
calculated as follows:
= 0.536, R
can be
HOT BIAS
BIAS
ꢃꢄꢅꢆꢇꢈꢉꢊ ꢘꢄꢙ
RHOT 0.3631•R25
Figure 15. NTC Thermistor Connection with
Desensitizing Resistor RD
RBIAS
=
=
= 0.677 •R25
0.536
0.536
This means: choose an R
value which is 67.7% of the
BIAS
R
COLD –RHOT
(
)
value of the thermistor at 25°C to set the hot temperature
threshold to 50°C. However, this will automatically shift
the cold temperature threshold upward too. The cold
temperature threshold can be recalculated by computing
RBIAS
=
2.714
RD = 0.197 •RCOLD – 1.197 •RHOT
Notethatthismethodcanonlybeusedtopushthehotand
cold temperature thresholds apart from each other. When
using the formulas above, if the user finds that a negative
the R
/R ratio as follows:
COLD 25
RCOLD RCOLD RBIAS
=
•
= 3.25 • 0.677 = 2.202
R25
RBIAS R25
value is needed for R , the two temperature thresholds
D
selected are too close to each other and a higher sensitiv-
ity thermistor is needed. For example, this method can be
Rev. 0
20
For more information www.analog.com
LTC4126-ADJ
APPLICATIONS INFORMATION
used to set the hot and cold thresholds independently to
60°C and –5°C. Using the same Vishay thermistor with
β25/85 = 3950k whose nominal value at 25°C is 100k, the
circuitry in the AC power control block can cause a fair
amount of on-chip power dissipation if the available AC
power is excessive. If the heat is not dissipated properly
on the PC board, the temperature of the die and subse-
quently, the temperature of the battery may rise above
the hot temperature threshold set by the NTC thermistor
causing the charger to pause charging. For optimum ther-
mal performance, there should be a group of vias directly
under the exposed pad on the backside leading directly
down to an internal ground plane. To minimize parasitic
inductance, the ground plane should be as close as pos-
sible to the top plane of the PC board (Layer 2).
formula results in R
= 147k and R = 52.3k for the
BIAS
D
closest 1% resistor values.
PC BOARD LAYOUT CONSIDERATIONS
Since the exposed pad of the LTC4126-ADJ package is
the only ground pin and serves as the return path for both
the charger and the DC/DC converter, it must be soldered
to the PC board ground for a good electrical connection.
Although the LTC4126-ADJ is a low power IC, the shunt
Rev. 0
21
For more information www.analog.com
LTC4126-ADJ
TYPICAL APPLICATIONS
Full-Featured Application Circuit
V
IN
17.8k
4.75V TO
5.25V
R
BIAS
100k
NTC
BAT
47µF
22mΩ 0.01µF
I
= 7.5mA
+
CHG
V
CC
NTC RESISTOR
THERMALLY
COUPLED
D1
LTC4126-ADJ
AIR GAP
(2mm TO 4mm)
Li-Ion
4.2V
47µF
R
NTC
100k
100k
CHRG
IN2 IN1
LTC4125
WITH BATTERY
IN
ACIN
+
C
RX
68nF
STAT
SW1
IS
IS
1.2V
OUT
–
2.2µF
+
DTH
FTH
PTH1
PTH2
IMON
V
C
L
RX
8µH
L
TX
100nF
TX
6.8µH
20.5k
1.05k
STAT1
STAT2
ACPR
EN
PROG
µP
GPIO
GND
SW2
EN
PTHM
CTS
GND PBEN
1.5M
R
PROG
12.4k
FB
PUSHBUTTON
4126-ADJ TA02
CTD
NTC
GND
C
: TDK C3216C0G1H104J160AA
TX
L
TX
: WURTH 760308101104
R
: VISHAY NTCS0402E3104JHT
NTC
D1: ROHM SEMICONDUCTOR SML-311UTT86
: AVX 0603YC683JAT2A
C
RX
: SUNLORD MQQRC060630S8R0
L
RX
Minimum Component Count Application Circuit
ꢎꢂ
ꢋꢁR ꢏꢋꢐ
ꢁ
ꢟ ꢠ0ꢡꢋ
ꢋꢆꢁꢂ
ꢃꢄꢆꢘꢊꢇꢙꢕꢋꢓꢚ
ꢆꢞꢏ
ꢛꢋꢄ
ꢆ
Rꢅ
ꢜ
ꢃꢔꢕꢁꢖꢗ
ꢘ.ꢇꢀ
ꢃ
ꢃ
Rꢅ
ꢄRꢋꢂꢌꢍꢁꢄꢄꢎR
ꢄꢅ
ꢂꢄꢆ
ꢐRꢑꢏ
ꢜ
ꢀ
ꢁꢂ
ꢊ.ꢇꢀ
ꢇ.ꢇꢈꢉ
ꢑꢒꢄ
ꢝ
ꢏꢂꢓ
ꢘꢊꢇꢙꢕꢋꢓꢚ ꢄꢋ0ꢘ
Rev. 0
22
For more information www.analog.com
LTC4126-ADJ
PACKAGE DESCRIPTION
ꢛ
ꢜ
ꢞ
ꢡ ꢄ ꢄ ꢄ
ꢬ ꢬ ꢬ
ꢞ
ꢞ
× ꢏ ꢟ
ꢞ
ꢦ ꢦ ꢠ ꢠ ꢠ
ꢞ
0 . ꢟ ꢌ 0 0
0 . 0 0 0 0
0 . ꢟ ꢌ 0 0
ꢝ ꢝ ꢝ
ꢞ
× ꢟ
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
23
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
For more information www.analog.com
LTC4126-ADJ
TYPICAL APPLICATION
Wireless 10mA Li-Ion Battery Charger (4.2V) Tuned at 204kHz with Pushbutton Enabling and C/10 Trickle Charging Function
I
= 10mA
CHG
BAT
NTC
R
100k
BIAS
LTC4126-ADJ
+
V
IN
5V
R
NTC
V
CC
C2
100µF
AIR GAP
(4mm TO 6mm)
D
CHRG
NTC RESISTOR
THERMALLY
COUPLED
Li-Ion
4.2V
C1
4.7µF
1.2V
2.2µF
OUT
f
= 255.6kHz
LC_TANK
ACIN
WITH BATTERY
C
47nF
TX1
L
L
RX
TX
6.8µH
PROG
C
13µH
TX2
10nF
STAT1
STAT2
ACPR
+
V
DIGITAL I/O
f
= 205.8kHz
C
RX
47nF
DRIVE
OE
LTC6990
M1
Si2312CDS
SET
OUT
EN GND PBEN
R
VCC
1k
R1
243k
DIV
PUSHBUTTON
GND
C
VCC
2.2μF
C
C
: TDK CGA5H2C0G1H473J115AA
: AVX 06033A103JAT2A
: WURTH 760308101104
: KEMET C0805C473J3GACAUTO
: WURTH 760308101208
TX1
TX2
R
V
CC
TRKL1
30.1k
L
C
TX
RX
ꢀꢁꢂ
L
R
RX
: VISHAY NTCS0402E3104JHT
NTC
V
IN
+
–
M1: VISHAY Si2312CDS-T1-GE3
D1: ROHM SEMICONDUCTOR SML-311UTT86
V
TH
TRICKLE CHARGE
WHEN BATTERY
IS BELOW 2.8V
4126-ADJ TA03
R
TRKL2
6.34k
R
PROG
8.87k
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LTC4120
400mA Wireless Power Receiver Buck Battery Wireless 1 to 2 Cell Li-Ion Charger, 400mA Charge Current, Dynamic Harmonization
Charger Control, Wide Input Range: 12.5V to 40V, 16-Lead 3mm × 3mm QFN Package
LTC4123
Low Power Wireless Charger for Hearing Aids Wireless Single NiMH Charger, Integrated Rectifier with Overvoltage Limit, 25mA Charge
Current, Zn-Air Detect, Temperature Compensated Charge Voltage, 6-Lead 2mm × 2mm
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LTC4125
100mA Wireless Li-Ion Charger with Low
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Wireless Single Li-Ion Charger with PowerPath , Pin-Selectable Charge Current:
10mA/25mA/50mA/100mA, Pin-Selectable Charge Voltage: 4.0V/4.1V/4.2V/4.35V, 12-
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Receiver Load, Foreign Object Detection, Wide Operating Switching Frequency Range:
50kHz to 250kHz, Input Voltage Range 3V to 5.5V, 20-Lead 4mm × 5mm QFN Package
LTC4126/
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7.5mA/10mA Wireless Li-Ion Charger with
1.2V Step-Down DC/DC Converter
Wireless Single Li-Ion Charger, Integrated Rectifier with Overvoltage Limit, 7.5mA/10mA
Charge Current, Pin Selectable Float Voltages (LTC4126: 4.2V, 4.35V/LTC4126-10: 4.1V,
4.2V), 12-Lead 2mm × 2mm QFN Package
LTC6990
LTC6992
TimerBlox: Voltage Controlled Silicon Oscillator Fixed-Frequency or Voltage-Controlled Operation, Frequency Range of 488Hz to 2MHz,
Low-Profile SOT-23 and 2mm × 3mm DFN Packages
TimerBlox: Voltage Controlled Pulse-Width
Modulator (PWM)
Pulse Width Modulation by 0V to 1V Analog Input, Frequency Range of 3.81Hz to 1MHz,
Low-Profile SOT-23 and 2mm × 3mm DFN Packages
Rev. 0
09/20
www.analog.com
ANALOG DEVICES, INC. 2020
24
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