LTC3355_15 [Linear]
20V 1A Buck DC/DC with Integrated SCAP Charger and Backup Regulator;
| 型号： | LTC3355_15 |
| 厂家： | 
Linear |
| 描述： | 20V 1A Buck DC/DC with Integrated SCAP Charger and Backup Regulator |
| 文件： | 总20页 (文件大小：490K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3355
20V 1A Buck DC/DC with
Integrated SCAP Charger
and Backup Regulator
FEATURES
DESCRIPTION
The LTC®3355 is a complete input power interrupt ride-
throughDC/DCsystem.Thepartchargesasupercapacitor
n
V Voltage Range: 3V to 20V
OUT
1A Current Mode Buck Main Regulator
5A Boost Backup Regulator Powered from Single
Supercapacitor
IN
n
V
Voltage Range: 2.7V to 5V
n
n
whiledeliveringloadcurrenttoV ,andusesenergyfrom
OUT
the supercapacitor to provide continuous V
backup
OUT
power when V power is lost. The LTC3355 contains a
IN
n
n
Boost Regulator Operates Down to 0.5V for
Maximum Utilization of Supercapacitor Energy
Programmable Supercapacitor Charge Current to
1A with Overvoltage Protection
nonsynchronousconstantfrequencycurrentmodemono-
lithic 1A buck switching regulator to provide a 2.7V to 5V
regulatedoutputvoltagefromaninputsupplyofupto20V.
A 1A programmable CC/CV linear charger charges the
n
n
n
n
n
n
n
Charger Supports Single Cell CC/CV Battery Charging
supercapacitor from V . When the V supply drops
OUT
IN
Programmable V Current Limit
IN
below the PFI threshold, the devices’s constant frequency
Programmable Boost Current Limit
nonsynchronous current mode 5A boost switching
V Power Fail Indicator
IN
CAP
OUT
regulator delivers power from the supercapacitor to V
.
OUT
V
V
Power Good Indicator
Power On Reset Output
A thermal regulation loop maximizes charge current while
limiting the die temperature to 110°C. The IC has boost,
Compact 20-Lead 4mm × 4mm QFN Package
chargerandV programmablecurrentlimits.TheLTC3355
IN
is available in a 20-lead 4mm × 4mm QFN surface mount
APPLICATIONS
package.
n
Ride-Through “Dying Gasp” Supplies
Power Meters/Industrial Alarms/Solid State Drives
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
n
TYPICAL APPLICATION
Supercapacitor Charger and Ride-Through Power Supply
Backup Operation
6.8µH
0.091Ω
10µF
V
IN
SW1
V
IN
12V
14
12
10
5
6
4
7
CAPACITOR = 3F
= 0.125A
10µF
1µF
I
VOUT
V
INM5
V
PFO
BUCK
1A
OUT
4V
V
OUT
FB
V
INS
15
2
47µF 1A (MAX)
4.7pF
402k
100k
2.49M
200k
V
IN
8
6
4
2
0
PFI
1
LTC3355
BOOST
V
CAP
10 PFOB
13 RSTB
14
16
17
11
19
V
OUT
3.3µH
SW2
2.4V
V
CAP
SCAP
9
8
3
CPGOOD
1F TO 50F
665k
332k
EN_CHG
MODE
CFB
0
5
10
TIME (SECONDS)
15
20
V
CBST
INTV
I
I
CC
CHG
BSTPK
154k
3355 TA01b
18
12
20
220pF
1µF
60.4k
200k
3355 TA01a
3355fb
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For more information www.linear.com/LTC3355
LTC3355
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V , V , V
........................................................22V
IN INS INM5
V
V
V
V
V
.................................................................. 0.1V
IN
SW1
SW2
OUT
INS
.......................................................... –0.4V to 22V
............................................................ –0.4V to 6V
, INTV , PFOB, RSTB,
20 19 18 17 16
PFI
FB
V
V
1
2
3
4
5
15
14
13
12
11
OUT
CAP
CC
CPGOOD, V ............................................. –0.3V to 6V
CAP
21
GND
MODE
RSTB
PFI, EN_CHG, MODE, FB.............................. –0.3V to 6V
V
I
INS
CHG
CFB ............................................–0.3V to INTV + 0.3V
CC
V
IN
CFB
I
, I
, I
................................................1mA
CPGOOD PFOB RSTB
6
7
8
9 10
Operating Junction Temperature Range
(Notes 2, 3)............................................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
UF PACKAGE
20-LEAD (4mm × 4mm) PLASTIC QFN
T
JMAX
= 125°C, θ = 47°C/W
JA
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3355EUF#PBF
LTC3355IUF#PBF
TAPE AND REEL
PART MARKING
3355
PACKAGE DESCRIPTION
20-Lead (4mm × 4mm) Plastic QFN
20-Lead (4mm × 4mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
LTC3355EUF#TRPBF
LTC3355IUF#TRPBF
3355
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on nonstandard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
3355fb
2
For more information www.linear.com/LTC3355
LTC3355
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted. (Note 2)
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
V
V
Operating Voltage Range
3
20
V
IN
IN
l
l
I
V
V
Quiescent Current
OUT
Charger Off, Not Switching, V = 3.3V, No
OUT
Load, In Regulation, Supercapacitor Charged
60
110
120
265
215
420
µA
µA
Q
IN
Quiescent Current
l
l
V
FB Reference Voltage
FB Line Regulation
FB Input Bias Current
0.775
0.825
V
%/V
nA
V
FB
V
= 2.7V to 5V
0.1
OUT
I
FB
–20
2.7
5.4
1.8
20
5
V
V
OUT
V
OUT
V
OUT
Voltage Range
VOUT
Overvoltage Limit
Buck or Boost Enabled
Boost Enabled
5.65
2
5.95
2.2
V
Undervoltage Lockout Threshold
V
V
V
V
V -V
V
> 7V
IN
4.65
V
INM5
INTVCC
VCAP
IN INM5
INTV Internal Voltage Power Supply
2
0
5
5
V
CC
V
V
Voltage Range
V
CAP
CAP
I
Current Accuracy
V
= 2V, V
= 3.3V, I = 1A
VCAP
–10
10
%
VCAP
CAP
OUT
EN_CHG = High
EN_CHG = High
EN_CHG = High
V
Programmable Current Range
Reference Voltage
0.1
0.78
60.4
–20
1
A
V
CAP
CHG
CHG
V
I
I
0.82
604
20
ICHG
R
Set Resistor Range
kΩ
nA
V
ICHG
I
CFB Input Bias Current
CFB Reference Voltage
CFB Hysteresis
CFB
V
EN_CHG = High
EN_CHG = High
0.78
0.8
30
0.82
CFB
mV
CFB Overvoltage Hysteretic Comparator CFB Rising
Switch Point CFB Falling
V
CFB
V
+0.035
CFB
V
V
I
V
Input Current Limit
V
-V to Disable Charger
INS IN
37
42
43
50
mV
mV
ICL
IN
V
-V to Disable Buck
INS IN
V
V
Common Mode Range
3.0
20
V
MHz
kHz
V
INS(CMI)
INS
f
Switching Frequency
Foldback Frequency (Buck Only)
PFI Falling Threshold
PFI Hysteresis
FB ≥ 0.5V
FB ≤ 0.3V
0.75
1
1.25
SW
100
0.8
17
l
V
0.775
–20
0.825
20
PFI
mV
nA
I
PFI
PFI Leakage Current
1A Buck Regulator
I
SW1 Peak Current
PWM Mode (Note 5)
Burst Mode® (Note 5)
1.3
1.65
0.5
2
A
A
SW1
t
Soft-Start Time
1000
µs
%
SS
DC Max
Maximum Duty Cycle
PMOS On-Resistance
PMOS Leakage Current
FB = 0V
100
–2
R
0.5
1
2
Ω
PMOS
LEAKP
I
Buck Disabled
µA
3355fb
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For more information www.linear.com/LTC3355
LTC3355
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted. (Note 2)
SYMBOL PARAMETER
5A Boost Regulator
CONDITIONS
MIN
TYP
MAX
UNITS
l
I
V
Quiescent Current
V = 3.3V, No Load, In Regulation, No
OUT
80
160
280
5.5
µA
VOUT
OUT
Switching, Burst Mode
I
SW2 Peak Current
R
R
= 200k, PWM Mode
= 200k, Burst Mode
4.5
5
1.5
A
A
SW2
IBSTPK
IBSTPK
R
NMOS On-Resistance
70
mΩ
µA
%
NMOS
I
NMOS Leakage Current
Boost Disabled
–5
88
5
98
5
LEAKN
DC Max
Boost Maximum Duty Cycle
Boost Input Supply Voltage Range
Boost Minimum Input Supply
Boost Error Amplifier Voltage Gain
Boost Error Amplifier Transconductance
92
V
0.75
0.5
V
SBOOST
V
= 4V
V
OUT(MAX)
A
(Note 5)
850
27
V/V
μS
V
V
g
m
V
I
I
Reference Voltage
Set Resistor Range
0.775
200
0.825
1000
IBSTPK
BSTPK
BSTPK
R
kΩ
IBSTPK
Logic (MODE, EN_CHG, CPGOOD, RSTB, PFOB)
V
V
Input Low Logic Voltage
Input High Logic Voltage
Input Low/High Current
Output Logic Low Voltage
Logic High Leakage Current
CPGOOD Rising Threshold
CPGOOD Hysteresis
MODE, EN_CHG
0.4
V
V
IL
MODE, EN_CHG
1.2
-1
IH
I , I
IL IH
MODE, EN_CHG
1
50
1
µA
mV
µA
%
V
PFOB, CPGOOD, RSTB; Sink 100µA
PFOB, CPGOOD, RSTB; 5V
OL
OH
I
V
as a % of Final Target
90
90
92.5
2.5
95
CAP
∆V
CAP
as a % of Final Value
%
RSTB Falling Threshold
RSTB Hysteresis
V
OUT
as a % of Final Target
92.5
2.5
95
%
∆V
OUT
as a % of Final Value
%
RSTB Delay
250
ms
Note 3: The LTC3355 has a thermal regulation loop that limits the
maximum junction temperature to 110°C by limiting the charger current.
Note 4: The current limit features of this part are intended to protect the
IC from short-term or intermittent fault conditions. Continuous operation
above the maximum specified pin current may result in device degradation
or failure.
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.
Note 2: The LTC3355 is tested under pulsed load conditions such that
T ≈ T . The LTC3355E is guaranteed to meet specifications from
J
A
0°C to 85°C junction temperature. Specifications over the –40°C to
125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3355I is guaranteed over the –40°C to 125°C operating junction
temperature range. 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
impedance and other environmental factors. The junction temperature
Note 5: Guaranteed by design and/or correlation to static test.
Note 6: The LTC3355 has a thermal shutdown that will shut down the part
when the die temperature reaches 155°C.
(T , in °C) is calculated from the ambient temperature (T , in °C) and
J
A
power dissipation (P , in Watts) according to the formula:
D
T = T + (P • θ )
JA
J
A
D
where θ = 47°C/W for the UF package.
JA
3355fb
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For more information www.linear.com/LTC3355
LTC3355
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C unless otherwise noted
Buck Efficiency
Boost Efficiency
Maximum Buck Load Current
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
1.20
1.00
0.80
0.60
0.40
0.20
0
V
= 4V
V
= 2.4V
OUT
CAP
MODE = HIGH
MODE = HIGH
V
V
V
= 18V
V
V
V
= 3.3V
V
= 4V
IN
IN
IN
OUT
OUT
OUT
OUT
= 12V
= 6V
= 4V
= 5V
L = 6.8µH
INPUT CURRENT SET RESISTOR = 0Ω
14 16
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
4
6
8
10 12
(V)
18 20
V
LOAD CURRENT (A)
LOAD CURRENT (A)
IN
3355 G01
3355 G02
3355 G03
Oscillator Frequency
vs Temperature
Maximum Boost Load Current
Buck Switch Voltage Drop
1200
1.2
1.0
700
600
V
= 4V
OUT
1150
1100
500
0.8
0.6
0.4
0.2
0
1050
1000
950
400
300
200
100
900
850
800
0
2.25 2.75 3.25
(V)
–25
0
50
75 100 125
0.75 1.25 1.75
3.75
–50
25
100 200
400
500 600 700 800 9001000
0
300
V
SWITCH CURRENT (mA)
TEMPERATURE (°C)
CAP
3355 G04
3355 G06
3355 G05
Buck Frequency
vs Feedback Voltage
Typical Minimum Buck Input
Voltage (VOUT = 3.3V)
Typical Minimum Buck Input
Voltage (VOUT = 5V)
1000
900
800
700
600
500
400
300
200
100
0
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
6.3
6.1
5.9
5.7
5.5
5.3
5.1
4.9
4.7
4.5
V
= 3.3V
V
= 5V
OUT
OUT
L = 6.8µH
INPUT CURRENT SET RESISTOR = 0.05Ω
L = 6.8µH
INPUT CURRENT SET RESISTOR = 0.05Ω
0
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
1
10
100
1000
1
10
100
1000
FB (V)
V
LOAD CURRENT (mA)
V
OUT
LOAD CURRENT (mA)
OUT
3355 G08
3355 G09
3355 G07
3355fb
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For more information www.linear.com/LTC3355
LTC3355
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C unless otherwise noted
Boost Switch Current Limit vs
Temperature
Buck Switch Current Limit vs
Temperature
VOUT vs VINS-VIN
5.2
1.8
1.7
1.6
1.5
1.4
4.0
V
= 12V
IN
3.5
3.0
2.5
2.0
1.5
1.0
5.1
5.0
V
= 3.3V
OUT
V
= 5V
OUT
V
= 4V
OUT
4.9
4.8
4.7
4.6
4.5
V
= 3.3V
OUT
V
= 4V
OUT
V
= 5V
OUT
V
V
VOUT
= 7V
IN
0.5
0
= 3.3V
OUT
I
= 200mA
4.4
44 45
40 41 42 43
46 47 48 49 50
–25
0
50
75 100 125
–50
25
–50 –25
0
25
50
75 100 125
V
-V (mV)
INS IN
TEMPERATURE (°C)
TEMPERATURE (°C)
3355 G12
3355 G10
3355 G11
Charge Current
vs Junction Temperature
Charge Current vs VINS-VIN
Charge Current vs VOUT-VCAP
1200
1000
300
250
200
150
1200
1000
800
600
400
200
0
V
V
= 7V
= 3.3V
V
V
= 7V
IN
OUT
IN
OUT
= 3.3V
800
600
R
= 60.4k
ICHG
400
200
0
100
50
0
R
ICHG
= 604k
500 600
(mV)
50
TEMPERATURE (°C)
100 125
30 32 34 36 38 40 42 44 46 48 50
-V (mV)
0
100 200 300 400
-V
700 800
–50 –25
0
25
75
V
V
OUT CAP
INS IN
3355 G13
3355 G14
3355 G15
Boost Load Regulation
Buck Load Regulation
Buck Line Regulation
4.050
4.045
4.040
4.035
4.030
4.025
4.020
4.015
4.010
4.005
4.000
4.050
4.045
4.040
4.035
4.030
4.025
4.020
4.015
4.010
4.005
4.000
4.050
4.045
4.040
4.035
PWM MODE
I
= 50mA
OUT
I
= 500mA
OUT
4.030
4.025
4.020
4.015
4.010
4.005
4.000
PWM MODE
PWM MODE
V
V
V
= 18V
= 12V
= 6V
IN
IN
IN
V
CAP
V
CAP
V
CAP
= 3.6V
= 2.4V
= 1.5V
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
(V)
0.001
0.01
0.1
1
LOAD CURRENT (A)
V
LOAD CURRENT (A)
IN
3355 G18
3355 G16
3355 G17
3355fb
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For more information www.linear.com/LTC3355
LTC3355
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C unless otherwise noted
Logic Input Threshold vs
Temperature (EN_CHG, MODE)
PFI Threshold vs Temperature
Boost Line Regulation
4.050
4.045
4.040
4.035
4.030
4.025
4.020
4.015
4.010
4.005
4.000
1000
810
805
800
795
PWM MODE
950
900
50mA
850
800
750
700
650
500mA
790
600
0.75 1.25 1.75 2.25 2.75 3.25 3.75
(V)
–50 –25
0
25
50
75 100 125
–25
0
50
75 100 125
–50
25
TEMPERATURE (°C)
V
TEMPERATURE (°C)
CAP
3355 G19
3355 G21
3355 G20
Buck Load Step Burst Mode
Operation
Buck Load Step PWM
Boost Load Step PWM
V
V
V
OUT
OUT
OUT
100mV/DIV
100mV/DIV
100mV/DIV
AC-COUPLED
AC-COUPLED
AC-COUPLED
LOAD
CURRENT
500mA/DIV
LOAD
CURRENT
500mA/DIV
LOAD
CURRENT
500mA/DIV
3355 G22
3355 G23
3355 G24
50µs/DIV
50µs/DIV
50µs/DIV
LOAD STEP = 100mA to 600mA
LOAD STEP = 100mA to 600mA
LOAD STEP = 100mA to 600mA
V
V
= 12V
= 4V
V
V
= 12V
= 4V
V
V
= 2.4V
= 4V
IN
OUT
IN
OUT
CAP
OUT
Boost Load Step Burst Mode
Operation
Boost Error Amplifier Voltage
Gain vs Temperature
Boost Error Amplifier
Transconductance vs Temperature
30
29
28
27
26
25
24
23
22
21
20
750
700
650
600
V
OUT
100mV/DIV
AC-COUPLED
LOAD
STEP
500mA/DIV
3355 G25
50µs/DIV
LOAD STEP = 100mA to 600mA
V
V
= 2.4V
= 4V
CAP
OUT
550
–50
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
3355 G27
3355 G30
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LTC3355
PIN FUNCTIONS
PFI (Pin 1): Input to the Power-Fail Comparator. The input
voltage below which the PFOB pin indicates a power-fail
condition can be programmed by connecting this pin to
CFB (Pin 11): This pin is used to program the V
age via an external resistor divider. The reference voltage
is 0.8V.
volt-
CAP
an external resistor divider between V and ground.
IN
I
(Pin 12): This pin programs the V
charge current
CHG
CAP
FB (Pin 2): Sets the V
voltage for both the buck and
by connecting a resistor to ground.
RSTB (Pin 13): Open-drain reset output is high imped-
ance when the V voltage is higher than 92.5% of the
OUT
boostvoltagecontrolloopsviaanexternalresistordivider.
The reference voltage is 0.8V.
OUT
MODE (Pin 3): This pin sets the buck and boost switch-
ing modes. A low is PWM mode, a high is Burst Mode
operation.
programmed regulation voltage.
V
(Pin 14): This pin is the constant current, constant
CAP
voltage linear charger output and connects to the super-
V
(Pin 4): Input Current Limit Sense Voltage Pin. Con-
capacitor.
INS
nect a sense resistor from V to V . Must be locally
INS
IN
V
(Pin15):TheOutputVoltageSupply.Thebuckpowers
OUT
bypassed with a low ESR ceramic capacitor. Connect to
V if input current limit is not needed.
this supply from V when the input voltage is present and
IN
IN
the boost powers this supply from V
voltage has dropped out.
when the input
CAP
V (Pin 5): Input Power Pin Supplies Current to the In-
IN
ternal Regulator and Buck Power Switch. Must be locally
SW2 (Pin 16, 17): Boost Output of the Internal Power
Switch. Connect these pins to the rectifier diode and
inductor. Minimize trace area at these pins to reduce EMI.
bypassed with a low ESR ceramic capacitor.
V
(Pin 6): This pin is used to filter an internal supply
INM5
regulator which generates a voltage of V – 4.65V. Con-
IN
to V .
INTV (Pin18):Thispinisusedtofilteraninternalsupply.
CC
nect a 1µF ceramic capacitor from V
INM5
IN
Connect a 1µF ceramic capacitor from this pin to ground.
SW1 (Pin 7): Buck Output of the Internal Power Switch.
Connect this pin to the catch diode and inductor. Minimize
trace area at this pin to reduce EMI.
INTV is 2.5V during start-up until V
exceeds 2.5V
CC
OUT
then INTV follows V
.
CC
OUT
V
CBST
(Pin 19): This pin is the output of the boost internal
EN_CHG (Pin 8): A high on this pin enables the superca-
pacitor charger.
error amplifier. The voltage on this pin controls the peak
switch current for the boost regulator. Connect an RC
series network from this pin to ground to compensate
the boost control loop.
CPGOOD (Pin 9): Open-drain output is high impedance
when the V
voltage is higher than 92.5% of the pro-
CAP
grammed voltage.
I
(Pin 20): This pin programs the boost peak current
BSTPK
limit by connecting a resistor to ground.
PFOB (Pin 10): Open Drain of the Power-Fail Comparator.
Pulled low and enables the boost converter when the PFI
inputhasdeterminedthattheinputsupplyhasdroppedout.
GND(ExposedPadPin21):Ground.Theexposedpadmust
be connected to a continuous ground plane on the second
layer of the printed circuit board by several vias directly
under the part to achieve optimum thermal conduction.
3355fb
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LTC3355
SIMPLIFIED BLOCK DIAGRAM
V
OUT
R1
R2
C
OUT
C
VINM5
15
6
2
3
5
V
V
INM5
FB
MODE
V
IN
OUT
L1
V
V
IN
IN
ENB
START-UP
INTV
CC
CAP REG
OVP
+
–
CLK
OVP
EN
LOGIC
1A
UVLO
0.8V
SW1
7
VC
0.8V
+
–
D1
D2
SS
C
VIN
R7
R8
FB
PFI
1
R
SENSE
BUCK
–
+
PFOB
I
V
IN
LIM
V
10
LOGIC
MAIN
INPUT
SUPPLY
V
INS
–
+
4
CLK UVLO
C
IN
ENB
0.8V
OVP
ENB
MODE
FB
SW2
SW2
EN
CPGOOD
RSTB
16
17
–
+
9
LOGIC
BILIM
0.74V
+
–
5A
0.8V
–
+
CC/CV CHARGER
CLK
D
13
–
+
FB
0.8V
CFB
V
REF
V TO I
0.8V
V
0.74V
BOOST
EN
I
I
250ms
DELAY
OUT
REF
I
L2
INTV
CC
EN_CHG
V
I
CAP
CHG
CBST
BSTPK
R6
18
11
8
14
12
19
20
R3
C1
R5
R
C
R4
SCAP
C
C
3355 F01
Figure 1. LTC3355 Block Diagram
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LTC3355
OPERATION
The LTC3355 is a 1A buck regulator with a built-in
will be reduced. If the charge current has been reduced to
zero and the input current continues to increase the buck
regulator current drive capability will be reduced. The
maximum sense voltage is 50mV. The input current limit
includes the LTC3355 quiescent current for high accuracy
over a wide current range.
backup boost converter to allow temporary backup, or
ride-through, of V
during a sudden loss of V power.
IN
OUT
The device contains all functions necessary to provide
seamless charging of a supercapacitor (or other storage
element),monitoringofV ,V andV ,andautomatic
IN OUT
CAP
switch-over to backup power. When the buck is disabled
Boost Switching Regulator
an internal circuit blocks reverse current between V
OUT
and V .
IN
When V is not available, a monolithic 1MHz constant
IN
frequencypeakcurrentmodeboostregulatorwithinternal
slope compensation is enabled and the buck regulator
is disabled via the PFI pin. The boost regulator uses the
Start-Up
When the part first starts up the only voltage available
is V since V and V are at zero volts. An internal
voltage stored at V as an input supply and regulates
IN
OUT
CAP
CAP
2.5V regulator powers INTV from V during start-up.
the V
voltage. An error amplifier compares the divided
OUT
CC
IN
INTV powers all of the low voltage circuits. The buck
output voltage at FB with a reference voltage of 0.8V and
adjusts the peak inductor current accordingly. The I
CC
regulator is enabled and will drive V
positive through
OUT
BSTPK
an inductor until the feedback voltage at FB equals 0.8V.
When V exceeds 2.5V INTV will exactly track V
OUT
pin sets the peak boost current over a range of 1A to 5A
allowing for lower current backup applications. The boost
switching regulator is compensated by adding a series RC
OUT
CC
and the current for the internal low voltage circuits will
now be supplied from V
instead of V . A 1µF external
networkfromtheV
pintoground.Theboostregulator
OUT
IN
CBST
ceramic capacitor is required for INTV to filter internal
can operate over an input voltage range (V ) of 0.5V
CC
CAP
switching noise.
to 5V. The boost regulator uses the same feedback pin
and error amplifier as the buck and regulates to the same
Buck Switching Regulator
V
voltage. The MODE pin is used to control the boost
OUT
switching regulator mode. The boost is in PWM mode
when the MODE pin is low and in Burst Mode operation
when the MODE pin is high. In PWM mode as the load
current is decreased, the switch turns on for a shorter
period each cycle. If the load current is further decreased,
the boost converter will skip cycles to maintain output
voltage regulation.
The LTC3355 uses a 1MHz constant frequency peak cur-
rent mode nonsynchronous monolithic buck regulator
with internal slope compensation to control the voltage at
V
when V is available. An error amplifier compares
OUT
IN
the divided output voltage at FB with a reference voltage
of 0.8V and adjusts the peak inductor current accordingly.
Burst Mode operation can also be selected to optimize ef-
ficiency at low load currents via the MODE pin. The buck
is in PWM mode when the MODE pin is low and in Burst
Mode operation when the MODE pin is high. The buck
is internally compensated and can operate over an input
voltage range of 3V to 20V. An internal soft-start ramp
limits inrush current during start-up. Frequency foldback
protection helps to prevent inductor current runaway
during start-up or short-circuit conditions.
Charger
The supercapacitor is charged by an internal 1A constant
current/constant voltage linear charger that supplies
current from V
to V . The charger will be enabled
OUT
CAP
when V is above a programmable voltage via the PFI
IN
pin, when the EN_CHG pin is high and when V
is in
OUT
pin de-
regulation. The value of the resistor on the I
CHG
termines the charger current. An internal amplifier servos
the I voltage to 0.8V to create the reference current
Input Current Limit
CHG
for the charge. The V
voltage is divided down by an
CAP
The (optional) input current limit is programmed via an
external resistor divider that is connected to the CFB pin.
A hysteretic comparator compares the CFB voltage to a
3355fb
external sense resistor connected between V and V .
INS
IN
As the input current limit is reached the charge current
10
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LTC3355
OPERATION
V
Status Monitor
0.8V reference voltage and turns the charger off when
CAP
these voltages are the same. The V
voltage represents
CAP
The CPGOOD pin is a 5V open-drain output. An internal
comparator determines when V has reached 92.5% of
the fully charged supercapacitor voltage available to sup-
CAP
ply the boost regulator when V has dropped out. When
IN
the programmed regulation voltage which then switches
CFB decays to 30mV below the CFB reference voltage the
charger will be turned on. The LTC3355 includes a soft-
start circuit to minimize the inrush current at the start of
charge. When the charger is enabled, the charge current
rampsfromzerotofull-scaleoveraperiodofapproximately
1ms. This has the effect of minimizing the transient load
theCPGOODpinhigh.CPGOODisnormallyconnectedtoa
low voltage supply (V ) via an external pull-up resistor.
OUT
Thermal Regulation
As the die temperature increases due to internal power
dissipation, a thermal regulator will limit the die tem-
perature to 110°C by reducing the charger current. The
thermal regulation protects the LTC3355 from excessive
temperature and allows the user to push the limits of the
power handling capability of a given circuit board without
the risk of damaging the LTC3355. Another feature is that
the charge current can be set according to typical, rather
thanworst-caseambienttemperaturesforagivenapplica-
tion with the assurance that the charger will automatically
reduce the charge current in worst-case conditions.
current on V
.
OUT
The V
output also has an overvoltage protection cir-
CAP
cuit which monitors the CFB voltage. If the CFB voltage
increases above the CFB reference voltage by 35mV a
hysteretic comparator switches in an 8k resistor from
V
to ground. This will bleed any excess charge from
CAP
the supercapacitor. When the CFB voltage decays to the
CFB reference voltage the comparator will remove the
8k bleed resistor. Excess charge can come from leakage
currents associated with the boost rectifier diode.
Thermal Shutdown
V Status Monitor
IN
The LTC3355 includes a thermal shutdown circuit in ad-
dition to the thermal regulator. If for any reason, the die
temperature exceeds 155°C, the entire part shuts down.
Thepartwillresumenormaloperationoncethetemperature
drops about 15°C, to approximately 140°C.
The PFI input always monitors the V voltage and de-
IN
termines when V is in dropout. V is divided down
IN
IN
by an external resistor divider and this voltage is then
compared to a reference voltage of 0.8V. If the PFI volt-
age is below the reference voltage the buck regulator and
the charger will be disabled and the boost regulator will
be enabled. The PFOB pin is a 5V open-drain output. This
pin is driven internally by the PFI comparator. When the
V
Overvoltage, Undervoltage Lockout
OUT
The LTC3355 includes an overvoltage protection circuit
to ensure that V does not exceed 5.65V (nominal).
OUT
PFI comparator determines that V has dropped out the
IN
An internal resistor divider from V
amplifier that will regulate V
is connected to an
OUT
PFOB output switches low. PFOB is normally connected
to a low voltage supply, via an external pull-up resistor.
The pull-up resistor for this output can be connected to
as the overvoltage limit
OUT
is reached. The LTC3355 includes undervoltage lockout
which disables the boost when V is < 2V typical.
OUT
V
if another supply is not available.
OUT
V
Status Monitor
OUT
The RSTB pin is a 5V open-drain output. An internal
comparator determines when V has reached 92.5% of
OUT
the programmed regulation voltage which then switches
the RSTB pin high. RSTB is normally connected to a low
voltage supply (V ) via an external pull-up resistor.
OUT
3355fb
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LTC3355
APPLICATIONS INFORMATION
FB Resistor Network
I
Set Resistor
BSTPK
The V
voltage is programmed with a resistor divider
The boost peak current limit is set by connecting a re-
OUT
between the V
pin and the FB pin. Choose the resistor
sistor from I
to ground. Choose the resistor value
OUT
BSTPK
according to:
values according to:
1E6
R6
V
0.8V
⎛
⎜
⎝
⎞
⎠
OUT
Boost Peak Current Limit (Amps)=
R1=R2
–1
⎟
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain boost peak cur-
rent accuracy.
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain output voltage
accuracy.
PFI Resistor Network
CFB Resistor Network
The V dropout voltage is programmed with a resistor
IN
The V
voltage is programmed with a resistor divider
CAP
divider between the V pin and PFI pin. Choose the resis-
IN
between the V pin and the CFB pin. Choose the resistor
CAP
tor values according to:
values according to:
V
0.8V
⎛
⎞
⎠
V
0.8V
IN
⎛
⎝
⎞
⎠
R3=R4 CAP –1
R7=R8
–1
⎟
⎜
⎝
⎜
⎟
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain the PFI threshold
voltage accuracy.
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain the capacitor float
voltage accuracy.
The V voltage must be greater than the buck dropout
IN
I
Set Resistor
CHG
voltage (100% duty cycle) when the PFI level is reached
to ensure that V
stays in regulation.
The charge current at V
fromI
is set by connecting a resistor
OUT
CAP
toground.Choosetheresistorvalueaccordingto:
CHG
Input Voltage Range
60400
R5
Charger Current (Amps)=
The minimum input voltage is determined by the dropout
of the buck regulator. The dropout is dependent on the
maximum load current and the buck internal switch resis-
tance. The minimum input voltage due to buck dropout is:
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain charge current
accuracy.
V
= V
+ (I
• 1Ω)
IN(MIN)
OUT
SW(PEAK)
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LTC3355
APPLICATIONS INFORMATION
Buck Inductor L1 Selection and
Maximum Output Current
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
A good starting point for the inductor value is:
VOUT + VD
1.8
fSW
ΔI = 1–DC •
(
)
L
L = V + V •
(
)
L•fSW
D
OUT
where f is the switching frequency of the buck, DC is
SW
where f is the switching frequency in MHz, V
is the
OUT
SW
the duty cycle and L is the value of the inductor.
buck output voltage, V is the catch diode drop (~0.5V)
D
To maintain output regulation, the inductor peak current
must be less than the buck switch current limit. The
maximum output current is:
and L is the inductor value in µH.
The inductor’s RMS current rating must be greater than
the maximum load current and its saturation current
should be 30% higher. To keep the efficiency high, the
series resistance (DCR) should be less than 0.1Ω, and
the core material should be intended for high frequency
applications. Table 1 lists several inductor vendors.
ΔIL
2
IOUT(MAX) =ILIM
–
Choosing an inductor value so that the ripple current is
smallwillallowamaximumoutputcurrentneartheswitch
current limit.
For robust operation and fault conditions (start-up or
short-circuit)andhighinputvoltage(>15V),thesaturation
current should be chosen high enough to ensure that the
inductor peak current does not exceed 2.2A.
Table 1. Inductor Vendors
VENDOR
Murata
TDK
URL
PART SERIES
LQH5BPB
LTF5022T
FDS50xx
TYPE
www.murata.com
www.tdk.com
www.toko.com
www.coilcraft.com
www.sumida.com
www.vishay.com
Shielded
Shielded
Shielded
The current in the inductor is a triangle wave with an av-
erage value equal to the load current. The peak inductor
and switch current is:
Toko
Coilcraft
Sumida
Viashay
XAL40xx, LPS40xx Shielded
DCRH5D, CDRH6D Shielded
ΔIL
2
ISW(PEAK) =IL(PEAK) =IOUT(MAX)
whereI
+
IHLP2020
Shielded
isthepeakinductorcurrent,I
isthe
One approach to choosing the inductor is to start with
the simple rule above, look at the available inductors, and
choose one to meet cost or space goals. Then use the
equations to check that the buck will be able to deliver the
required output current. These equations assume that the
inductor current is continuous. Discontinuous operation
L(PEAK)
OUT(MAX)
maximumoutputloadcurrentand∆I istheinductorripple
L
current. The LTC3355 limits the switch current in order to
protect the part. Therefore, the maximum output current
that the buck will deliver depends on the switch current
limit, the inductor value, the input and output voltages.
occurs when I
is less than ∆I /2.
OUT
L
3355fb
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LTC3355
APPLICATIONS INFORMATION
Buck Input Capacitor
operating conditions (applied voltage and temperature).
A physically larger capacitor, or one with a higher voltage
rating, may be required. High performance tantalum or
electrolyticcapacitorscanbeusedfortheoutputcapacitor.
Bypass V and V with a ceramic capacitor of X7R or
IN
INS
X5Rtype.A10µFto22µFceramiccapacitorisadequatefor
bypassing. Note that a larger V bypass capacitor may
INS
be required if the input power supply source impedance
is high or there is significant inductance due to long wires
or cables. This can be provided with a lower performance
electrolyticcapacitorinparallelwiththeceramiccapacitor.
Low ESR is important, so choose one that is intended for
use in switching regulators. The ESR should be specified
by the supplier, and should be 0.05Ω or less. Table 2 lists
several capacitor vendors.
Buck regulators draw current from the input supply in
pulseswithveryfastriseandfalltimes.Theinputcapacitors
Table 2. Capacitor Vendors
VENDOR
URL
www.panasonic.com Ceramic, Polymer, EEF Series,
Tantalum POSCAP
PART SERIES
COMMANDS
are required to reduce the resulting voltage ripple at V
INS
Panasonic
and V and to force this very high frequency switching
IN
into a tight local loop, minimizing EMI. The capacitors
must be placed close to the LTC3355 pins.
Kemet
Murata
AVX
www.kemet.com
www.murata.com
www.avxcorp.com
Ceramic, Tantalum T494, T495
Ceramic
Ceramic, Tantalum TPS Series
Output Capacitor and Output Ripple
Taiyo Yuden www.taiyo-yuden.com Ceramic
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated by
the buck regulator to produce the DC output. In this role
it determines the output ripple, and low impedance at the
switchingfrequencyisimportant.Thesecondfunctionisto
storeenergyinordertosatisfytransientloadsandstabilize
the buck regulator control loop. Ceramic capacitors have
very low equivalent series resistance (ESR) and provide
the best ripple performance. A good starting value is:
Buck Catch Diode Selection
The catch diode (D1 in the Block Diagram) conducts cur-
rent only during the switch-off time. The average forward
current in normal operation can be calculated from:
I
= I (1 – DC)
OUT
D(AVG)
where DC is the duty cycle. The only reason to consider
a diode with a larger current rating than necessary for
nominal operation is for the case of shorted or overloaded
output conditions. For the worst case of shorted output
the diode average current will then increase to a value that
depends on the switch current limit.
⎛
⎞
100
COUT = fSW
⎜
⎟
V
⎝
⎠
OUT
where f is in MHz and C
is the recommended output
SW
OUT
capacitance in µF. Use X5R or X7R types. This choice will
If operating at high temperatures select a Schottky diode
with low reverse leakage current.
provide low output ripple and good transient response.
When choosing a capacitor look carefully through the
data sheet to find out what the actual capacitance is under
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LTC3355
APPLICATIONS INFORMATION
Audible Noise
Table 3. Schottky Diode Vendors
V AT 1A V AT 2A
I AT 5V
F
F
R
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can sometimes cause
problems when used with switching regulators. Both the
buck and boost can run in Burst Mode operation and the
switchingfrequencywilldependontheloadcurrentwhich
at very light loads can excite the ceramic capacitors at
audio frequencies, generating audible noise. Since the
buck and boost operate at lower current limits in Burst
Mode operation, the noise is typically very quiet. Use a
high performance tantalum or electrolytic at the output if
the noise level is unacceptable.
PART NUMBER
Diodes Inc.
B130
V (V)
I
(A) (mV)
AVE
(mV)
85°C (µA)
R
30
30
1
460
20
B230
2
430
100
Rohm
RSX201VA-30
Vishay
30
60
1
360
600
VS-20MQ060
2.1
Boost Inductor L2 Selection and
Maximum Output Current
Buck Soft-Start
The boost inductor L2 should be 3.3µH to ensure fast
transfer of power from the buck to the boost after a V
power outage. Refer to Table 1 for inductor vendors.
IN
When the buck is enabled soft-start is engaged. Soft-start
reduces the inrush current by taking more time to reach
the final output voltage. This is achieved by limiting the
buck output current over a 1ms period.
Boost Frequency Compensation
TheLTC3355boostswitchingregulatorusescurrentmode
Boost Rectifier Diode
control to regulate V . This simplifies loop compensa-
OUT
tionandceramicoutputcapacitorscanbeused. Theboost
regulator does not require the ESR of the output capaci-
tor for stability. Frequency compensation is provided by
A Schottky rectifier diode (D2 in the Block Diagram) is
recommended for the boost rectifier diode. The diode
should have low forward drop at the peak operating
current, low reverse current and fast reverse recovery
times. The current rating should take into account power
dissipation as well as output current requirements. The
diode current rating should be equal to or greater than the
average forward current which is normally equal to the
output current. The reverse breakdown voltage should be
the components connected to the V
pin. Generally a
CBST
capacitor (C ) and resistor (R ) in series to ground are
C
C
used as shown in the Block Diagram.
Loop compensation determines the stability and transient
performance. Optimizing the design of the compensation
network depends on the application and type of output
capacitor. A practical approach is to start with one of the
circuits in this data sheet that is similar to your applica-
tion and tune the compensation network to optimize the
performance. Stability should then be checked across all
greaterthantheV
voltageplusthepeakringingvoltage
OUT
that is generated at the SW2 pin. Generally higher reverse
breakdown diodes will have lower reverse currents. Refer
to Table 3 for Schottky diode vendors.
3355fb
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LTC3355
APPLICATIONS INFORMATION
operatingconditions, includingloadcurrent, inputvoltage
and temperature. Figure 2 shows an equivalent circuit for
the boost regulator control loop. The error amplifier is a
transconductanceamplifierwithafiniteoutputimpedance.
Thepowersectionconsistingofamodulator,powerswitch
and inductor, is modeled as a transconductance amplifier
generating an output current proportional to the voltage
Low Ripple Burst Mode Operation
To enhance efficiency at light loads the buck and boost
regulatorcanruninlowrippleBurstModeoperationwhich
keeps the output capacitor charged to the proper voltage
while minimizing the input quiescent current. Setting the
MODE pin high sets both the buck and boost into Burst
Modeoperation.DuringBurstModeoperation,theenabled
regulator delivers single cycle bursts of current to the out-
put capacitor followed by sleep periods where the power
is delivered to the load by the output capacitor. Since the
power to the output is delivered with single, low current
pulses, the output ripple is kept below 15mV for typical
applications. As the load current falls towards a no-load
condition, the percentage of time in sleep mode increases
and the average input current is greatly reduced resulting
in high efficiency even at very light loads. At higher load
currents the regulators will seamlessly transition into
PWM mode.
at the V
pin. Note that the output capacitor integrates
CBST
this current, and that the capacitor on the V
pin (C )
CBST
C
integrates the error amplifier output current, resulting in
two poles in the loop. In most cases a zero is required
and comes from either the ESR of the output capacitor or
from a resistor R in series with C . This simple model
C
C
works well as long as the inductor value is not too high
and the loop crossover frequency is much lower than the
switching frequency. A phase lead capacitor across the
feedback divider may improve the transient response. A
small capacitor from V
to ground may have to be
CBST
added if phase lead is used.
BOOST LOOP
SW2
CURRENT MODE POWER STAGE
= 4mhos
OUTPUT
g
m
C
R1
R2
ESR
PL
C
OUT
–
+
FB
C
OUT
g
= 27μS
GND
m
CERAMIC
POLYMER,
TANTALUM
OR
0.8V
32M
ELECTROLYTIC
V
CBST
R
C
C
F
C
C
3355 F02
Figure 2. Model for Boost Loop Response
3355fb
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LTC3355
APPLICATIONS INFORMATION
PCB Layout
High Temperature Considerations
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Large switched
The PCB must provide heat sinking to keep the LTC3355
cool. The exposed pad on the bottom of the package
may be soldered to a copper area which should be tied
to large copper layers below with thermal vias; these
layers will spread the heat dissipated by the LTC3355.
Place additional vias to reduce thermal resistance
further. With these steps, the thermal resistance from
the die (or junction) to ambient can be reduced to
currents flow in the V , SW1, SW2 and paddle ground
IN
pins, the buck catch diode, boost rectifier diode and the
input capacitor. The loop formed by these components
should be as small as possible. These components, along
with the inductors and output capacitor, should be placed
on the same side of the circuit board, and their connec-
tions should be made on that layer. All connections to
GND should be made at a common star ground point or
directly to a local, unbroken ground plane below these
components. SW1 and SW2 nodes should be laid out
θ
= 47°C/W or less. With 100 LFPM airflow, this resis-
JA
tance can fall by another 25%.
The LTC3355 has two thermal circuits. The first thermal
circuitisoperationalwhenthebuckandchargerareenabled.
If the die temperature exceeds 110°C the charge current
will be reduced. When the LTC3355 is in boost mode the
highcurrentthermalshutdownwillturntheboostoffwhen
the die temperature reaches 155°C. The high temperature
shutdown is active in all modes of operation.
carefully to avoid interference. Keep the FB, PFI, I
BSTPK CBST
,
CHG
I
, V
and CFB nodes small so that the ground
traces will shield them from the switching nodes. To
keep thermal resistance low, extend the ground plane as
much as possible and add thermal vias under and near the
paddle. Keep in mind that the thermal design must keep
the junctions of the LTC3355 below the specified absolute
maximum temperature.
TYPICAL APPLICATIONS
Tantalum Capacitor Charger and Ride-Through Backup Supply
L1
R
S
6.8µH
1Ω
V
V
IN
SW1
V
IN
5
6
4
7
C
12V
C
C
VIN
10µF
CAP
IN
D1
1µF
10µF
INM5
V
PFO
BUCK
V
OUT
OUT
FB
V
INS
5V
15
2
R1
523k
47µF 10mA
R7
2.49M
PFI
1
R2
R8
200k
D2
100k
LTC3355
BOOST
V
CAP
10 PFOB
13 RSTB
14
16
17
11
19
L2 3.3µH
SW2
5V
+
1000µF
6.3V
TANT
9
8
3
CPGOOD
R3
1.05M
EN_CHG
MODE
CFB
R4
200k
V
CBST
INTV
I
I
R
CC
CHG
BSTPK
C
154k
18
12
20
C
C
220pF
C1
1µF
R5
604k
R6
1M
3355 TA02
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17
For more information www.linear.com/LTC3355
LTC3355
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
UF Package
20-Lead Plastic QFN (4mm × 4mm)
(Reference LTC DWG # 05-08-ꢀ7ꢀ0 Rev A)
0.70 0.05
4.50 0.05
3.ꢀ0 0.05
2.45 0.05
2.00 REF
2.45 0.05
PACKAGE OUTLINE
0.25 0.05
0.50 BSC
PIN ꢀ NOTCH
R = 0.20 TYP
OR 0.35 × 45°
CHAMFER
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
BOTTOM VIEW—EXPOSED PAD
R = 0.05
TYP
R = 0.ꢀꢀ5
0.75 0.05
TYP
4.00 0.ꢀ0
ꢀ9 20
0.40 0.ꢀ0
PIN ꢀ
TOP MARK
(NOTE 6)
ꢀ
2
2.45 0.ꢀ0
2.00 REF
4.00 0.ꢀ0
2.45 0.ꢀ0
(UF20) QFN 0ꢀ-07 REV A
0.200 REF
0.25 0.05
0.50 BSC
0.00 – 0.05
NOTE:
ꢀ. DRAWING IS PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220
VARIATION (WGGD-ꢀ)—TO BE APPROVED
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.ꢀ5mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN ꢀ LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3355fb
18
For more information www.linear.com/LTC3355
LTC3355
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
A
08/14 Modified V
Overvoltage, Undervoltage Lockout section
11
12
12
12
3 and 4
4
OUT
Modified Input Voltage Range equation
Modified I
Modified I
Set Resistor section
CHG
Set Resistor section
BSTPK
B
4/15
Updated conditions for I
, I
and I
SW1 SW2 VOUT
Updated units for Boost Error Amplifier Transconductance
Updated units for Boost Error Amplifier Transconductance vs Temperature Graph
Update TSTB (Pin 13), CPGOOD (Pin 9), PFOB (Pin 10)
Updated Block Diagram
7
8
9
Updated CFB Resistor Network and PFI Resistor Network
Updated Table 2: Capacitor Vendors
12
14
16
Updated Boost Error Amplifier Transconductance unit in Figure 2
3355fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
19
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC3355
TYPICAL APPLICATION
NiMH Trickle Charger and Ride-Through Backup Supply
L1
R *
S
4.7µH
0.27Ω
V
V
IN
SW1
V
IN
5
6
4
7
C
5V
C
C
*
VIN
CAP
IN
D1
1µF
10µF
10µF
INM5
V
PFO
BUCK
V
OUT
OUT
FB
V
INS
3.3V
15
2
R1
316k
47µF 50mA (MAX)
R7
931k
PFI
1
R2
R8
200k
D2
100k
LTC3355
200Ω
V
CAP
14
10 PFOB
13 RSTB
L2 3.3µH
MICROPROCESSOR
24 HOURS
SW2
16
17
11
19
1.4V
+
9
8
3
CPGOOD
BOOST
R3
NiMH
499k
2000mAhr
EN_CHG
MODE
CFB
R4
499k
V
CBST
INTV
I
I
R
CC
CHG
BSTPK
C
*OPTIONAL
154k
C
18
12
20
C
220pF
3355 TA03
C1
1µF
R5
604k
R6
909k
RELATED PARTS
PART
NUMBER
DESCRIPTION
COMMENTS
LTC3225/
LTC3225-1
150mA Supercapacitor Charger
Low Noise, Constant Frequency Charging of Two Series Supercapacitors. Automatic
Cell Balancing Prevents Capacitor Overvoltage During Charging. Programmable Charge
Current (Up to 150mA). 2mm × 3mm DFN Package
LTC3226
LT3485
2-Cell Supercapacitor Charger with Backup
PowerPath™ Controller
1×/2× Multimode Charge Pump Supercapacitor Charger Ideal Diode Main PowerPath™
Controller, Internal 2A LDO Back-Up Supply, 16-Lead (3mm × 3mm) QFN Package
Photoflash Capacitor Chargers with Output
Voltage Monitor and Integrated IGBT Drive
Integrated IGBT Driver; Voltage Output Monitor; Uses Small Transformers: 5.8mm
× 5.8mm × 3mm. Operates from Two AA Batteries, Single Cell Li-Ion or Any Supply
from 1.8V Up to 10V. No Output Voltage Divider Needed; No External Schottky Diode
Required. Charges Any Size Photoflash Capacitor; 10-Lead (3mm × 3mm) DFN Package
LTC3625/
LTC3625-1
1A High Efficiency 2-Cell Supercapacitor
Charger with Automatic Cell Balancing
High Efficiency Step-Up/Step-Down Charging of Two Series Supercapacitors. Automatic
Cell Balancing Prevents Capacitor Overvoltage During Charging. Programmable
Charging Current Up to 500mA (Single Inductor), 1A (Dual Inductor). V = 2.7V to
IN
5.5V, Low No-Load Quiescent Current: 23µA. 12-lead 3mm × 4mm DFN Package
LT®3750
LT3751
Capacitor Charger Controller
Charges Any Size Capacitor; Easily Adjustable Output Voltage. Drives High Current
NMOS FETs; Primary-Side Sense—No Output Voltage Divider Necessary. Wide Input
Range: 3V to 24V; Drives Gate to V – 2V. 10-Lead MS Package
CC
High Voltage Capacitor Charger Controller with Charges Any Size Capacitor; Low Noise Output in Voltage Regulation Mode. Stable
Regulation
Operation Under a No-Load Condition; Integrated 2A MOSFET Gate Driver with
Rail-to-Rail Operation for V ≤ 8V. Wide Input V Voltage Range
CC
CC
(5V to 24V). 20-Pin QFN 4mm × 5mm and 20-Lead TSSOP Packages
LTC4425
Supercapacitor Charger with Current Limited
Ideal Diode
Constant-Current/Constant-Voltage Linear Charger for 2-cell Series Supercapacitor
Stack. V : Li-Ion/Polymer Battery, a USB Port, or a 2.7V to 5.5V Current-Limited
IN
Supply. 2A Charge Current, Auto Cell Balancing, 20µA Quiescent Current, Shutdown
Current <2µA. Low Profile 12-Pin 3mm × 3mm DFN or a 12-Lead MSOP Package
3355fb
LT 0415 REV B • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
20
●
●
LINEAR TECHNOLOGY CORPORATION 2014
(408)432-1900 FAX: (408) 434-0507 www.linear.com/LTC3355
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