AAT2552 [ANALOGICTECH]
Total Power Solution for Portable Applications; 用于便携式应用的总电源解决方案
| 型号： | AAT2552 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | Total Power Solution for Portable Applications |
| 文件： | 总33页 (文件大小：1050K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AAT2552
Total Power Solution for Portable Applications
™
SystemPower
General Description
Features
The AAT2552 is a fully integrated 500mA battery
charger, a 300mA step-down converter, and a
300mA low dropout (LDO) linear regulator. The
input voltage range is 4V to 6.5V for the battery
charger and 2.7V to 5.5V for the step-down con-
verter and linear regulator, making it ideal for appli-
cations operating with single-cell lithium-ion/poly-
mer batteries.
•
Battery Charger:
— Input Voltage Range: 4V to 6.5V
— Programmable Charging Current up to
500mA
— Highly Integrated Battery Charger
•
•
•
Charging Device
Reverse Blocking Diode
Current Sensing
•
Step-Down Converter:
The battery charger is a complete constant cur-
rent/constant voltage linear charger. It offers an
integrated pass device, reverse blocking protec-
tion, high accuracy current and voltage regulation,
charge status, and charge termination. The charg-
ing current is programmable via external resistor
from 30mA to 500mA. In addition to these stan-
dard features, the device offers over-voltage, cur-
rent limit, and thermal protection.
— Input Voltage Range: 2.7V to 5.5V
— Output Voltage Range: 0.6V to VIN
— 300mA Output Current
— Up to 96% Efficiency
— 45µA Quiescent Current
— 1.5MHz Switching Frequency
— 120µs Start-Up Time
•
•
Linear Regulator:
— 300mA Output Current
— Low Dropout: 400mV at 300mA
— Fast Line and Load Transient Response
— High Accuracy: 1.5%
— 85µA Quiescent Current
Short-Circuit, Over-Temperature, and Current
Limit Protection
TDFN34-16 Package
-40°C to +85°C Temperature Range
The step-down converter is a highly integrated
converter operating at a 1.5MHz switching fre-
quency, minimizing the size of external compo-
nents while keeping switching losses low. The out-
put voltage ranges from 0.6V to the input voltage.
The AAT2552 linear regulator is designed for high
speed turn-on and turn-off performance, fast tran-
sient response, and good power supply ripple
rejection. Delivering up to 300mA of load current,
it includes short-circuit protection and thermal
shutdown.
•
•
Applications
®
The AAT2552 is available in a Pb-free, thermally-
enhanced TDFN34-16 package and is rated over
the -40°C to +85°C temperature range.
•
•
•
•
•
•
•
Bluetooth Headsets
Cellular Phones
GPS
Handheld Instruments
MP3 and Portable Music Players
PDAs and Handheld Computers
Portable Media Players
Typical Application
Adapter/USB Input
INB
ADP
ENB
INA
STAT
Enable
EN_BAT
ENA
VOUTB
L1
LX
AAT2552
RFBB1
RFBB2
MODE
BATT+
BATT-
FBB
OUTA
BAT
COUTB
4.7μF
VOUTA
COUTA
RFBA1
RFBA2
COUT
ISET
FBA
GND
RSET
Battery
Pack
2552.2007.04.1.0
1
AAT2552
Total Power Solution for Portable Applications
Pin Descriptions
Pin # Symbol
Function
1
EN_BAT
Enable pin for the battery charger. When connected to logic low, the battery charger is dis-
abled and consumes less than 1µA of current. When connected to logic high, the charger
operates normally (pulled down internally).
2
ISET
Charge current set point. Connect a resistor from this pin to ground. Refer to typical charac-
teristics curves for resistor selection.
3
4
AGND
FBB
Analog ground.
Feedback input for the step-down converter. This pin must be connected directly to an exter-
nal resistor divider. Nominal voltage is 0.6V.
5
6
7
8
ENB
MODE
ENA
Enable pin for the step-down converter. When connected to logic low, the step-down convert-
er is disabled and consumes less than 1µA of current. When connected to logic high, the con-
verter operates normally (pulled up internally).
Pulled down internally for automatic PWM/LL operation. Connect to logic high for forced PWM.
Drive with external clock signal to synchronize step-down converter to external clock in PWM
mode.
Enable pin for the linear regulator. When connected to logic low, the regulator is disabled and
consumes less than 1µA of current. When connected to logic high, the LDO operates normal-
ly (pulled up internally).
Feedback input for the LDO. This pin must be connected directly to an external resistor divider.
Nominal voltage is 1.24V.
FBA
9
OUTA
INA
INB
LX
Linear regulator output. Connect a 2.2µF capacitor from this pin to ground.
Linear regulator input voltage. Connect a 1µF or greater capacitor from this pin to ground.
Input voltage for the step-down converter.
Output of the step-down converter. Connect the inductor to this pin. Internally, it is connected
to the drain of both high- and low-side MOSFETs.
10
11
12
13
14
15
16
EP
PGND
BAT
ADP
Power ground.
Battery charging and sensing. Connect to positive terminal of Lithium-ion/polymer battery.
Input from USB port or AC wall adapter.
Open drain status pin for charger.
STAT
Exposed paddle (bottom): connect to ground directly beneath the package.
Pin Configuration
TDFN34-16
(Top View)
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
STAT
ADP
BAT
PGND
LX
INB
INA
EN_BAT
ISET
AGND
FBB
ENB
MODE
ENA
FBA
OUTA
2
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
1
Absolute Maximum Ratings
Symbol
Description
Value
Units
VINA, VINB
VADP
VLX
Input Voltage to GND
Adapter Voltage to GND
LX to GND
FB to GND
ENA, ENB, EN_BAT to GND
BAT, ISET, STAT
6.0
-0.3 to 7.5
V
V
V
V
V
V
°C
°C
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-0.3 to 6.0
-0.3 to VADP + 0.3
-40 to 150
VFB
VEN
VX
TJ
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
TLEAD
300
Thermal Information
Symbol
Description
Value
Units
PD
θJA
Maximum Power Dissipation
Thermal Resistance
2.0
50
W
°C/W
2
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at condi-
tions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
2552.2007.04.1.0
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AAT2552
Total Power Solution for Portable Applications
1
Electrical Characteristics
VINB = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
Conditions
Min
Typ
Max Units
Step-Down Converter
VIN
Input Voltage
2.7
5.5
2.6
V
V
mV
VINB Rising
Hysteresis
IOUTB = 0 to 300mA,
VINB = 2.7V to 5.5V
VUVLO
UVLO Threshold
250
45
2
VOUT
Output Voltage Tolerance
-3.0
0.6
3.0
%
VOUT
IQ
ISHDN
Output Voltage Range
Quiescent Current
Shutdown Current
VINB
90
1.0
V
µA
µA
mA
Ω
Ω
µA
%
%/V
V
µA
MHz
No Load
VENB = GND
ILIM
P-Channel Current Limit
300
RDS(ON)H
RDS(ON)L
ILXLEAK
ΔVOUT/ΔVOUT Load Regulation
ΔVLinereg/ΔVIN Line Regulation
High-Side Switch On Resistance
Low-Side Switch On Resistance
LX Leakage Current
0.3
0.5
VINB = 5.5V, VLX = 0 to VINB
IOUTB = 0mA to 300mA
VINB = 2.7V to 5.5V
1.0
0.4
0.1
0.6
VFB
IFB
FOSC
Feedback Threshold Voltage Accuracy VINB = 3.6V
FB Leakage Current
Oscillator Frequency
0.591
0.609
0.2
VOUTB = 1.0V
1.5
From Enable to Output
Regulation
TS
Startup Time
120
µs
TSD
THYS
VEN(L)
VEN(H)
IEN
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Enable Threshold Low
Enable Threshold High
Input Low Current
140
15
°C
°C
V
V
µA
0.6
1.0
1.4
-1.0
VINB = VENB = 5.5V
1. The AAT2552 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2. Output voltage tolerance is independent of feedback resistor network accuracy.
4
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
1
Electrical Characteristics
VINA = VOUT(NOM) + 1V. IOUT = 1mA, COUT = 2.2µF, TA = -40°C to +85°C, unless otherwise noted. Typical val-
ues are TA = 25°C.
Symbol
Description
Conditions
Min Typ Max Units
Linear Regulator
I
OUTA = 1mA
TA = 25°C
TA = -40°C to +85°C
-1.5
-2.5
1.2
1.5
2.5
3.3
VOUT
Output Voltage Tolerance
%
to 300mA
VOUT
VFB
Output Voltage Range
Feedback Voltage Accuracy
V
V
1.22 1.24 1.26
VOUT
VDO
+
VIN
Input Voltage
5.5
650
0.09
V
2
3
VDO
ΔVOUT
VOUT*ΔVIN
Dropout Voltage
IOUTA = 300mA; VOUT = 3.3V
VINA = VOUTA + 1 to 5.0V
400
mV
%/V
/
Line Regulation
IOUT
ISC
IQ
ISHDN
Output Current
VOUTA > 2.0V
VOUTA < 0.4V
VINA = 5V; VENA = VIN
VINA = 5V; VENA = 0V
1kHz
300
mA
mA
µA
Short-Circuit Current
Quiescent Current
Shutdown Current
400
85
150
1.0
µA
70
50
30
Power Supply Rejection
Ratio
PSRR
IOUTA =10mA
10kHz
1MHz
dB
Over-Temperature
Shutdown Threshold
Over-Temperature
Shutdown Hysteresis
TSD
THYS
eN
140
15
95
8
°C
°C
µVRMS
√Hz
/
Output Noise
eNBW = 100Hz to 100kHz
Output Voltage
TC
ppm/°C
Temperature Coefficient
Enable Threshold Low
Enable Threshold High
Enable Input Current
VEN(L)
VEN(H)
IEN
0.6
1.0
V
V
µA
1.4
VINA = VENA = 5.5V
1. The AAT2552 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2. VDO is defined as VIN - VOUT when VOUT is 98% of nominal.
3. For VOUT <2.3V, VDO = 2.5V - VOUT
.
2552.2007.04.1.0
5
AAT2552
Total Power Solution for Portable Applications
1
Electrical Characteristics
VADP = 5V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
Conditions
Min Typ Max Units
Battery Charger
Operation
VADP
Adapter Voltage Range
Under-Voltage Lockout (UVLO)
UVLO Hysteresis
Operating Current
Shutdown Current
4.0
3
6.5
4
V
V
mV
mA
µA
µA
Rising Edge
VUVLO
150
0.5
0.3
0.4
IOP
Charge Current = 200mA
VBAT = 4.25V, VEN_BAT = GND
1
1
2
ISHUTDOWN
ILEAKAGE
Voltage Regulation
Reverse Leakage Current from BAT Pin VBAT = 4V, ADP Pin Open
VBAT EOC
VMIN
VRCH
End of Charge Accuracy
Preconditioning Voltage Threshold
Battery Recharge Voltage Threshold
4.158 4.20 4.242
V
V
V
_
2.8
3.0
3.2
Measured from VBAT EOC
-0.1
_
Current Regulation
ICH
ΔICH/ICH
VSET
Charge Current Programmable Range
Charge Current Regulation Tolerance ICHARGE = 200mA
ISET Pin Voltage
30
-10
500
10
mA
%
V
2
KI_A
Current Set Factor: ICH/ISET
800
Charging Devices
RDS(ON)
Charging Transistor On Resistance
VADP = 5.5V
0.5
0.8
Ω
Logic Control/Protection
VEN(H)
VEN(L)
VSTAT
ISTAT
VOVP
Enable Threshold High
Enable Threshold Low
Output Low Voltage
STAT Pin Current Sink Capability
Over-Voltage Protection Threshold
Pre-Charge Current
1.6
V
V
V
mA
V
%
%
0.4
0.4
8
STAT Pin Sinks 4mA
ICH = 100mA
4.4
10
10
ITK/ICHG
TERM/ICHG
I
Charge Termination Threshold Current
1. The AAT2552 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
6
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–Battery Charger
Constant Charging Current vs. Set Resistors
(VIN = 5.0V)
Operating Supply Current vs. RSET
(VIN = 5.0V)
10000
1000
100
1000
100
10
Constant Current Mode
Preconditioning Mode
10
1
10
100
1000
1
10
100
R
SET (kΩ)
R
SET (kΩ)
Operating Current vs. Temperature
(VIN = 5.0V; RSET = 8.06kΩ)
Sleep Mode Current vs. Input Voltage
(RSET = 8.06kΩ)
540
520
500
480
460
440
800
700
600
500
400
300
200
100
0
25°C
85°C
-40°C
-50
-25
0
25
50
75
100
4.0
4.5
5.0
5.5
6.0
6.5
Temperature (°C)
Input Voltage (V)
Battery Charging Current vs. Battery Voltage
Constant Charging Current vs. Temperature
(RSET = 8.06kΩ)
600
210
208
205
203
200
198
195
193
190
RSET = 3.24K
500
400
RSET = 5.62K
300
RSET = 8.06K
200
RSET = 16.2K
RSET = 31.6K
100
0
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
-50
-25
0
25
50
75
100
VBAT (V)
Temperature (°C)
2552.2007.04.1.0
7
AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–Battery Charger
End of Charge Voltage Regulation
End of Charge Battery Voltage
vs. Input Voltage
vs. Temperature
(VIN = 5V; RSET = 8.06kΩ)
4.206
4.204
4.202
4.200
4.198
4.196
4.194
4.215
4.210
4.205
4.200
4.195
4.190
4.185
RSET = 8.06kΩ
RSET = 31.6kΩ
-40
-15
10
35
60
85
4.5
5
5.5
6
6.5
Temperature (°C)
VIN (V)
Recharging Threshold Voltage vs. Temperature
(RSET = 8.06kΩ)
Constant Charging Current vs. Input Voltage
(VIN = 5.62V)
4.16
4.14
4.12
4.10
4.08
4.06
4.04
310
VIN = 3.3V
305
300
295
290
285
VIN = 4V
VIN = 3.6V
-40
-15
10
35
60
85
4
4.5
5
5.5
6
6.5
V
IN (V)
Temperature (°C)
Preconditioning Charge Current vs. Temperature
(RSET = 8.06kΩ)
Preconditioning Voltage Threshold vs. Temperature
(RSET = 8.06kΩ)
3.03
3.02
3.01
3.00
2.99
2.98
2.97
20.8
20.4
20.0
19.6
19.2
-40
-15
10
35
60
85
-40
-15
10
35
60
85
Temperature (°C)
Temperature (°C)
8
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–Battery Charger
Enable Threshold High vs. Input Voltage
Enable Threshold Low vs. Input Voltage
(RSET = 8.06kΩ)
(RSET = 8.06kΩ)
1.1
1.0
0.9
0.8
0.7
0.6
1.2
1.1
1.0
0.9
0.8
0.7
-40°C
-40°C
85°C
85°C
25°C
25°C
4.0
4.5
5.0
5.5
6.0
6.5
4.0
4.5
5.0
5.5
6.0
6.5
VIN (V)
VIN (V)
2552.2007.04.1.0
9
AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–Step-Down Converter
Efficiency vs. Load
(VOUT = 3.3V; L = 5.6µH)
DC Regulation
(VOUT = 3.3V; L = 5.6µH)
100
90
80
70
60
50
40
1.0
0.5
VIN = 3.6V
VIN = 5.0V
VIN = 5.0V
VIN = 4.2V
0.0
VIN = 4.2V
-0.5
-1.0
VIN = 3.6V
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 1.8V; L = 3.3µH)
DC Regulation
(VOUT = 1.8V; L = 3.3µH)
100
90
80
70
60
50
40
1.0
0.5
VIN = 3.6V
VIN = 2.7V
VIN = 3.6V
VIN = 5.0V
VIN = 4.2V
0.0
VIN = 5.0V
VIN = 4.2V
VIN = 2.7V
-0.5
-1.0
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 1.2V; L = 1.5µH)
DC Regulation
(VOUT = 1.2V; L = 1.5μH)
100
90
80
70
60
50
40
1.0
0.5
VIN = 3.6V
VIN = 3.6V
VIN = 5.0V
VIN = 2.7V
0.0
VIN = 5.0V
VIN = 2.7V
VIN = 4.2V
VIN = 4.2V
-0.5
-1.0
0.1
0.1
1
10
100
1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
10
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–Step-Down Converter
Line Regulation
(VOUT = 1.8V)
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 150mA)
4
3
2
1
0
0.2
0.1
0
VEN
IOUT = 10mA
VOUT
IOUT = 50mA
-0.1
-0.2
-0.3
-0.4
IL
0.3
0.2
0.1
0.0
IOUT = 150mA
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Time (100µs/div)
Output Voltage Accuracy vs. Temperature
(VIN = 3.6V; VO = 1.8V; IOUT = 150mA)
No Load Quiescent Current vs. Input Voltage
2.0
70
1.5
1.0
85°C
25°C
60
50
40
30
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-40°C
-40
-15
10
35
60
85
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Temperature (°C)
N-Channel RDS(ON) vs. Input Voltage
P-Channel RDS(ON) vs. Input Voltage
600
500
400
300
200
100
1000
900
800
700
600
500
400
300
85°C
85°C
100°C
120°C
100°C
120°C
25°C
25°C
2.5
3
3.5
4
4.5
5
5.5
6
2.5
3
3.5
4
4.5
5
5.5
6
VIN (V)
VIN (V)
2552.2007.04.1.0
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AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–Step-Down Converter
Load Transient Response
Line Transient Response
(VOUT = 1.8V @ 150mA, CFF = 100pF)
(10mA to 300mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7µF; C = 100pF)
2.0
1.90
1.85
1.80
1.75
1.9
VOUT
1.8
1.7
1.6
IOUT
300mA
10mA
4.6
4.1
3.6
3.1
0.2
0.0
-0.2
ILX
Time (20µs/div)
Time (25µs/div)
Output Voltage Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 300mA)
Output Voltage Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)
40
1.81
20
0
1.80
1.79
-20
0.4
0.05
0.3
0.2
0.1
0.00
-0.05
-0.10
Time (0.2µs/div)
Time (5µs/div)
12
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–LDO Regulator
Quiescent Current vs. Temperature
(VIN = 5V)
Dropout Voltage vs. Temperature
0.5
0.4
0.3
0.2
0.1
0.0
120
110
100
90
IL = 300mA
IL = 200mA
IL = 100mA
IL = 50mA
80
70
60
50
-40
-20
0
20
40
60
80
100
120
-40
-15
10
35
60
85
Temperature (°°C)
Temperature (°C)
Dropout Characteristics
Dropout Voltage vs. Output Current
3.8
0.5
0.4
0.3
0.2
0.1
0.0
IOUT = 0mA
85°C
25°C
3.6
3.4
3.2
3
IOUT = 50mA
IOUT = 300mA
2.8
2.6
2.4
IOUT = 100mA
-40°C
0
50
100
150
200
250
300
3
3.2
3.4
3.6
3.8
4
Output Current (mA)
Input Voltage (V)
Output Voltage vs. Temperature
(VIN = 3.6V; VO = 1.8V; IOUT = 150mA)
Enable Threshold Voltage vs. Input Voltage
3.301
3.300
3.299
3.298
3.297
3.296
0.96
0.94
VEN(H)
0.92
0.9
0.88
0.86
VEN(L)
0.84
0.82
-40
-15
10
35
60
85
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Temperature (°C)
2552.2007.04.1.0
13
AAT2552
Total Power Solution for Portable Applications
Typical Characteristics–LDO Regulator
Line Transient Response
(IOUT = 300mA)
Load Transient Response
(1mA to 300mA; VIN = 5.0V; VOUT = 3.3V)
3.40
3.35
3.30
3.6
3.4
3.2
VOUT
VOUT
5.0
4.5
4.0
VIN
0.4
0.2
0.0
-0.2
IL
Time (100µs/div)
Time (100µs/div)
Turn-Off Response Time
(VIN = 4.2V; IOUT = 300mA)
Turn-On Time From Enable
(VIN = 4.2V; IOUT = 300mA)
VEN = 2V/div
VEN = 2V/div
VOUT = 1V/div
VOUT = 1V/div
Time (50µs/div)
Time (100µs/div)
LDO Output Noise
(COUT = 4.7µF; IOUT = 10mA; RLOAD = 330; 98.33µVrms)
10000
1000
100
10
0.01
0.1
1
10
100
1000
Frequency (kHz)
14
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Functional Block Diagram
Reverse Blocking
ADP
BAT
Current Compare
CV/Pre-Charge
Charge
Control
Constant Current
ISET
UVLO
STAT
FBB
INB
Charge Status
EN_BAT
Err.
DH
Amp
.
LX
Voltage
Reference
Logic
DL
ENB
Input
MODE
PGND
OUTA
Over-Temperature
Protection
From
Charger Section
INA
Active Feedback
Control
Over-Current
Protection
Err.+
FBA
Amp
Voltage
Reference
Fast Start
Control
-
ENA
AGND
Battery Charger
Functional Description
The battery charger is designed for single-cell lithi-
um-ion/polymer batteries using a constant current
and constant voltage algorithm. The battery charg-
er operates from the adapter/USB input voltage
range from 4V to 6.5V. The adapter/USB charging
current level can be programmed up to 500mA for
rapid charging applications. A status monitor out-
put pin is provided to indicate the battery charge
state by directly driving one external LED. Internal
device temperature and charging state are fully
monitored for fault conditions. In the event of an
over-voltage or over-temperature failure, the
device will automatically shut down, protecting the
charging device, control system, and the battery
under charge. Other features include an integrat-
ed reverse blocking diode and sense resistor.
The AAT2552 is a high performance power man-
agement IC comprised of a lithium-ion/polymer
battery charger, a step-down converter, and a lin-
ear regulator. The linear regulator is designed for
high-speed turn-on and fast transient response,
and good power supply ripple rejection. The step-
down converter operates in both fixed and variable
frequency modes for high efficiency performance.
The switching frequency is 1.5MHz, minimizing
the size of the inductor. In light load conditions,
the device enters power-saving mode; the switch-
ing frequency is reduced and the converter con-
sumes 45µA of current, making it ideal for battery-
operated applications.
2552.2007.04.1.0
15
AAT2552
Total Power Solution for Portable Applications
Switch-Mode Step-Down Converter
Under-Voltage Lockout
The step-down converter operates with an input
voltage of 2.7V to 5.5V. The switching frequency is
1.5MHz, minimizing the size of the inductor. Under
light load conditions, the device enters power-sav-
ing mode; the switching frequency is reduced, and
the converter consumes 45µA of current, making it
ideal for battery-operated applications. The output
voltage is programmable from VIN to as low as
0.6V. Power devices are sized for 300mA current
capability while maintaining over 96% efficiency at
full load. Light load efficiency is maintained at
greater than 80% down to 1mA of load current. A
high-DC gain error amplifier with internal compen-
sation controls the output. It provides excellent
transient response and load/line regulation.
The AAT2552 has internal circuits for UVLO and
power on reset features. If the ADP supply voltage
drops below the UVLO threshold, the battery
charger will suspend charging and shut down.
When power is reapplied to the ADP pin or the
UVLO condition recovers, the system charge con-
trol will automatically resume charging in the
appropriate mode for the condition of the battery. If
the input voltage of the step-down converter drops
below UVLO, the internal circuit will shut down.
Protection Circuitry
Over-Voltage Protection
An over-voltage protection event is defined as a
condition where the voltage on the BAT pin
exceeds the over-voltage protection threshold
(VOVP). If this over-voltage condition occurs, the
charger control circuitry will shut down the device.
The charger will resume normal charging operation
after the over-voltage condition is removed.
The AAT2552 synchronous step-down converter
can be synchronized to an external clock signal
applied to the MODE pin.
Linear Regulator
The advanced circuit design of the linear regulator
has been specifically optimized for very fast start-
up. This proprietary CMOS LDO has also been tai-
lored for superior transient response characteris-
tics. These traits are particularly important for appli-
cations that require fast power supply timing.
Current Limit, Over-Temperature Protection
For overload conditions, the peak input current is lim-
ited at the step-down converter. As load impedance
decreases and the output voltage falls closer to zero,
more power is dissipated internally, which causes the
internal die temperature to rise. In this case, the ther-
mal protection circuit completely disables switching,
which protects the device from damage.
The high-speed turn-on capability is enabled
through implementation of a fast-start control cir-
cuit which accelerates the power-up behavior of
fundamental control and feedback circuits within
the LDO regulator. The LDO regulator output has
been specifically optimized to function with low-
cost, low-ESR ceramic capacitors; however, the
design will allow for operation over a wide range
of capacitor types.
The battery charger has a thermal protection circuit
which will shut down charging functions when the
internal die temperature exceeds the preset ther-
mal limit threshold. Once the internal die tempera-
ture falls below the thermal limit, normal charging
operation will resume.
The regulator comes with complete short-circuit
and thermal protection. The combination of these
two internal protection circuits gives a comprehen-
sive safety system to guard against extreme
adverse operating conditions.
Control Loop
The AAT2552 contains a compact, current mode
step-down DC/DC controller. The current through
the P-channel MOSFET (high side) is sensed for
current loop control, as well as short-circuit and
overload protection. A fixed slope compensation
signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak
current mode loop appears as a voltage-pro-
grammed current source in parallel with the output
capacitor. The output of the voltage error amplifier
programs the current mode loop for the necessary
The regulator features an enable/disable function.
This pin (ENA) is active high and is compatible with
CMOS logic. The LDO regulator will go into the dis-
able shutdown mode when the voltage on the ENA
pin falls below 0.6V. If the enable function is not
needed in a specific application, it may be tied to INA
to keep the LDO regulator in a continuously on state.
16
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
peak switch current to force a constant output volt-
rent level for this mode is programmed using a sin-
gle resistor from the ISET pin to ground.
Programmed current can be set from a minimum
15mA up to a maximum of 500mA. Constant cur-
rent charging will continue until the battery voltage
reaches the voltage regulation point, VBAT. When
the battery voltage reaches VBAT, the battery charg-
er begins constant voltage mode. The regulation
voltage is factory programmed to a nominal 4.2V
( 0.5%) and will continue charging until the charg-
ing current has reduced to 10% of the programmed
current.
age for all load and line conditions. Internal loop
compensation terminates the transconductance
voltage error amplifier output. The error amplifier
reference is fixed at 0.6V.
Battery Charging Operation
Battery charging commences only after checking
several conditions in order to maintain a safe charg-
ing environment. The input supply (ADP) must be
above the minimum operating voltage (UVLO) and
the enable pin must be high (internally pulled down).
When the battery is connected to the BAT pin, the
charger checks the condition of the battery and
determines which charging mode to apply. If the bat-
tery voltage is below VMIN, the charger begins bat-
tery pre-conditioning by charging at 10% of the pro-
grammed constant current; e.g., if the programmed
current is 150mA, then the pre-conditioning current
(trickle charge) is 15mA. Pre-conditioning is purely a
safety precaution for a deeply discharged cell and
will also reduce the power dissipation in the internal
series pass MOSFET when the input-output voltage
differential is at its highest.
After the charge cycle is complete, the pass device
turns off and the device automatically goes into a
power-saving sleep mode. During this time, the
series pass device will block current in both direc-
tions, preventing the battery from discharging
through the IC.
The battery charger will remain in sleep mode,
even if the charger source is disconnected, until
one of the following events occurs: the battery ter-
minal voltage drops below the VRCH threshold; the
charger EN pin is recycled; or the charging source
is reconnected. In all cases, the charger will mon-
itor all parameters and resume charging in the
most appropriate mode.
Pre-conditioning continues until the battery voltage
reaches VMIN (see Figure 1). At this point, the
charger begins constant-current charging. The cur-
Preconditioning
Trickle Charge
Constant Current
Charge Phase
Constant Voltage
Charge Phase
Phase
Charge Complete Voltage
I = Max CC
Regulated Current
Constant Current Mode
Voltage Threshold
Trickle Charge and
Termination Threshold
I = CC / 10
Figure 1: Current vs. Voltage Profile During Charging Phases.
2552.2007.04.1.0
17
AAT2552
Total Power Solution for Portable Applications
Battery Charging System Operation Flow Chart
Enable
Power On Reset
No
Yes
Power Input
Voltage
VADP > VUVLO
Yes
Fault Conditions
Monitoring
OV, OT
Charge
Control
Shut Down
Yes
No
Preconditioning
Test
Preconditioning
(Trickle Charge)
Yes
V
MIN > VBAT
No
No
Constant
Current Charge
Mode
Recharge Test
Current Phase Test
BAT_EOC > VBAT
Yes
Yes
V
RCH > VBAT
V
No
Constant
Voltage Charge
Mode
Voltage Phase Test
IBAT > ITERM
Yes
No
Charge Completed
18
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
the fast charge, as well as the preconditioning trick-
le charge current, is dominated by the tolerance of
the set resistor used. For this reason, a 1% toler-
ance metal film resistor is recommended for the set
resistor function. Fast charge constant current lev-
els from 30mA to 500mA may be set by selecting
the appropriate resistor value from Table 1.
Application Information
Soft Start / Enable
The EN_BAT pin is internally pulled down. When
pulled to a logic high level, the battery charger is
enabled. When left open or pulled to a logic low level,
the battery charger is shut down and forced into the
sleep state. Charging will be halted regardless of the
battery voltage or charging state. When it is re-
enabled, the charge control circuit will automatically
reset and resume charging functions with the appro-
priate charging mode based on the battery charge
state and measured cell voltage from the BAT pin.
Normal
Set Resistor
ICHARGE (mA)
Value R1 (kΩ)
500
400
300
250
200
150
100
50
40
30
20
15
3.24
4.12
5.36
6.49
8.06
10.7
16.2
31.6
38.3
53.6
78.7
105
Separate ENA and ENB inputs are provided to
independently enable and disable the LDO and
step-down converter, respectively. This allows
sequencing of the LDO and step-down outputs dur-
ing startup.
The LDO is enabled when the ENA pin is pulled
high. The control and feedback circuits have been
optimized for high-speed, monotonic turn-on char-
acteristics.
The step-down converter is enabled when the ENB
pin is pulled high. Soft start increases the inductor
current limit point in discrete steps when the input
voltage or ENB input is applied. It limits the current
surge seen at the input and eliminates output voltage
overshoot. When pulled low, the ENB input forces the
AAT2552 into a low-power, non-switching state. The
step-down converter input current during shutdown is
less than 1µA.
Table 1: RSET Values.
1000
100
10
1
Adapter or USB Power Input
1
10
100
1000
Constant current charge levels up to 500mA may
be programmed by the user when powered from a
sufficient input power source. The battery charger
will operate from the adapter input over a 4.0V to
6.5V range. The constant current fast charge cur-
rent for the adapter input is set by the RSET resistor
connected between ISET and ground. Refer to
Table 1 for recommended RSET values for a desired
constant current charge level.
RSET (kΩ)
Figure 2: Constant Charging Current
vs. Set Resistor Values.
Charge Status Output
The AAT2552 provides battery charge status via a
status pin. This pin is internally connected to an N-
channel open drain MOSFET, which can be used to
drive an external LED. The status pin can indicate
several conditions, as shown in Table 2.
Programming Charge Current
The fast charge constant current charge level is
user programmed with a set resistor placed
between the ISET pin and ground. The accuracy of
2552.2007.04.1.0
19
AAT2552
Total Power Solution for Portable Applications
First, the maximum power dissipation for a given
Event Description
Status
OFF
situation should be calculated:
No battery charging activity
Battery charging via adapter
or USB port
ON
(TJ(MAX)
-
TA)
PD(MAX)
=
θJA
Charging completed
OFF
Where:
PD(MAX) = Maximum Power Dissipation (W)
θJA = Package Thermal Resistance (°C/W)
Table 2: LED Status Indicator.
The LED should be biased with as little current as
necessary to create reasonable illumination; there-
fore, a ballast resistor should be placed between
the LED cathode and the STAT pin. LED current
consumption will add to the overall thermal power
budget for the device package, hence it is good to
keep the LED drive current to a minimum. 2mA
should be sufficient to drive most low-cost green or
red LEDs. It is not recommended to exceed 8mA
for driving an individual status LED.
TJ(MAX) = Maximum Device Junction Temperature
(°C) [135°C]
TA
= Ambient Temperature (°C)
Figure 3 shows the relationship of maximum
power dissipation and ambient temperature of the
AAT2552.
The required ballast resistor values can be esti-
mated using the following formulas:
3.00
2.50
2.00
1.50
1.00
0.50
0.00
(VADP
- VF(LED)
ILED
)
R6 =
Example:
0
20
40
60
80
100
TA (°C)
(5.5V - 2.0V)
2mA
R6 =
= 1.75kΩ
Figure 3: Maximum Power Dissipation.
Next, the power dissipation of the battery charger
can be calculated by the following equation:
Note: Red LED forward voltage (VF) is typically
2.0V @ 2mA.
Thermal Considerations
PD = [(VADP - VBAT) · ICH + (VADP · IOP)]
The AAT2552 is offered in a TDFN34-16 package
which can provide up to 2W of power dissipation
when it is properly bonded to a printed circuit board
and has a maximum thermal resistance of 50°C/W.
Many considerations should be taken into account
when designing the printed circuit board layout, as
well as the placement of the charger IC package in
proximity to other heat generating devices in a given
application design. The ambient temperature around
the IC will also have an effect on the thermal limits of
a battery charging application. The maximum limits
that can be expected for a given ambient condition
can be estimated by the following discussion.
Where:
PD
= Total Power Dissipation by the Device
VADP = ADP/USB Voltage
VBAT = Battery Voltage as Seen at the BAT Pin
ICH = Constant Charge Current Programmed for
the Application
IOP = Quiescent Current Consumed by the
Charger IC for Normal Operation [0.5mA]
20
2552.2007.04.1.0
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Total Power Solution for Portable Applications
By substitution, we can derive the maximum
IQ is the step-down converter quiescent current.
The term tsw is used to estimate the full load step-
down converter switching losses.
charge current before reaching the thermal limit
condition (thermal cycling). The maximum charge
current is the key factor when designing battery
charger applications.
For the condition where the step-down converter is
in dropout at 100% duty cycle, the total device dis-
sipation reduces to:
(PD(MAX)
-
VIN
VIN - VBAT
· IOP)
ICH(MAX)
=
PTOTAL = IO2 · RDSON(H) + IQ · VIN
(TJ(MAX)
θJA
VIN - VBAT
- TA)
-
VIN · IOP
Since RDS(ON), quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range.
ICH(MAX)
=
In general, the worst condition is the greatest volt-
age drop across the IC, when battery voltage is
charged up to the preconditioning voltage thresh-
old. Figure 4 shows the maximum charge current in
different ambient temperatures.
Given the total losses, the maximum junction tem-
perature can be derived from the θJA for the
TDFN34-16 package which is 50°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
500
450
TA = 60°C
400
350
TA = 45°C
300
250
Capacitor Selection
Linear Regulator Input Capacitor (C6)
TA = 85°C
200
An input capacitor greater than 1µF will offer supe-
rior input line transient response and maximize
power supply ripple rejection. Ceramic, tantalum,
or aluminum electrolytic capacitors may be select-
ed for CIN. There is no specific capacitor ESR
requirement for CIN. However, for 300mA LDO reg-
ulator output operation, ceramic capacitors are rec-
ommended for CIN due to their inherent capability
over tantalum capacitors to withstand input current
surges from low impedance sources such as bat-
teries in portable devices.
150
100
50
0
4.25 4.5 4.75
5
5.25 5.5 5.75
6
6.25 6.5 6.75
VIN (V)
Figure 4: Maximum Charging Current Before
Thermal Cycling Becomes Active.
There are three types of losses associated with the
step-down converter: switching losses, conduction
losses, and quiescent current losses. Conduction
losses are associated with the RDS(ON) characteris-
tics of the power output switching devices.
Switching losses are dominated by the gate charge
of the power output switching devices. At full load,
assuming continuous conduction mode (CCM), a
simplified form of the losses is given by:
Battery Charger Input Capacitor (C1)
In general, it is good design practice to place a
decoupling capacitor between the ADP pin and
GND. An input capacitor in the range of 1µF to
22µF is recommended. If the source supply is
unregulated, it may be necessary to increase the
capacitance to keep the input voltage above the
under-voltage lockout threshold during device
enable and when battery charging is initiated. If the
adapter input is to be used in a system with an
external power supply source, such as a typical
AC-to-DC wall adapter, then a CIN capacitor in the
range of 10µF should be used. A larger input
IO2 · (RDSON(H) · VO + RDSON(L) · [VIN - VO])
PTOTAL
=
VIN
+ (tsw · FS · IO + IQ) · VIN
2552.2007.04.1.0
21
AAT2552
Total Power Solution for Portable Applications
capacitor in this application will minimize switching
or power transient effects when the power supply is
"hot plugged" in.
IO
2
IRMS(MAX)
=
VO
VIN
⎛
⎝
VO
VIN
⎞
⎠
·
1 -
Step-Down Converter Input Capacitor (C6)
Select a 4.7µF to 10µF X7R or X5R ceramic capac-
itor for the input. To estimate the required input
capacitor size, determine the acceptable input rip-
ple level (VPP) and solve for CIN. The calculated
value varies with input voltage and is a maximum
when VIN is double the output voltage.
The term
appears in both the input
voltage ripple and input capacitor RMS current
equations and is a maximum when VO is twice VIN.
This is why the input voltage ripple and the input
capacitor RMS current ripple are a maximum at
50% duty cycle.
The input capacitor provides a low impedance loop
for the edges of pulsed current drawn by the step-
down converter. Low ESR/ESL X7R and X5R
ceramic capacitors are ideal for this function. To
minimize stray inductance, the capacitor should be
placed as closely as possible to the IC. This keeps
the high frequency content of the input current
localized, minimizing EMI and input voltage ripple.
VO
VIN
⎛
VO ⎞
VIN ⎠
· 1 -
⎝
CIN =
⎛ VPP
⎝ IO
⎞
⎠
- ESR ·FS
VO
VIN
⎛
VO ⎞
VIN ⎠
1
· 1 -
=
for VIN = 2 · VO
⎝
4
The proper placement of the input capacitor (C6)
can be seen in the evaluation board layout in
Figure 7.
1
CIN(MIN)
=
⎛ VPP
⎝ IO
⎞
⎠
- ESR · 4 · FS
A laboratory test set-up typically consists of two
long wires running from the bench power supply to
the evaluation board input voltage pins. The induc-
tance of these wires, along with the low-ESR
ceramic input capacitor, can create a high Q net-
work that may affect converter performance. This
problem often becomes apparent in the form of
excessive ringing in the output voltage during load
transients. Errors in the loop phase and gain meas-
urements can also result.
Always examine the ceramic capacitor DC voltage
coefficient characteristics when selecting the prop-
er value. For example, the capacitance of a 10µF,
6.3V, X5R ceramic capacitor with 5.0V DC applied
is actually about 6µF.
The maximum input capacitor RMS current is:
Since the inductance of a short PCB trace feeding
the input voltage is significantly lower than the
power leads from the bench power supply, most
applications do not exhibit this problem.
VO
VIN
⎛
VO ⎞
VIN ⎠
IRMS = IO ·
· 1 -
⎝
The input capacitor RMS ripple current varies with
the input and output voltage and will always be less
than or equal to half of the total DC load current.
In applications where the input power source lead
inductance cannot be reduced to a level that does
not affect the converter performance, a high ESR
tantalum or aluminum electrolytic capacitor should
be placed in parallel with the low ESR, ESL bypass
ceramic capacitor. This dampens the high Q net-
work and stabilizes the system. The linear regula-
tor and the step-down convertor share the same
input capacitor on the evaluation board.
VO
VIN
⎛
VO ⎞
VIN ⎠
1
2
· 1 -
⎝
=
D · (1 - D) = 0.52 =
for VIN = 2 · VO
22
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Linear Regulator Output Capacitor (C5)
current demand. The relationship of the output volt-
For proper load voltage regulation and operational
stability, a capacitor is required between OUT and
GND. The COUT capacitor connection to the LDO
regulator ground pin should be made as directly as
practically possible for maximum device perform-
ance. Since the regulator has been designed to
function with very low ESR capacitors, ceramic
capacitors in the 1.0µF to 10µF range are recom-
mended for best performance. Applications utilizing
the exceptionally low output noise and optimum
power supply ripple rejection should use 2.2µF or
greater for COUT. In low output current applications,
where output load is less than 10mA, the minimum
value for COUT can be as low as 0.47µF.
age droop during the three switching cycles to the
output capacitance can be estimated by:
3 · ΔILOAD
=
COUT
V
DROOP · FS
Once the average inductor current increases to the
DC load level, the output voltage recovers. The
above equation establishes a limit on the minimum
value for the output capacitor with respect to load
transients.
The internal voltage loop compensation also limits
the minimum output capacitor value to 4.7µF. This
is due to its effect on the loop crossover frequency
(bandwidth), phase margin, and gain margin.
Increased output capacitance will reduce the
crossover frequency with greater phase margin.
Battery Charger Output Capacitor (C2)
The battery charger of the AAT2552 only requires a
1µF ceramic capacitor on the BAT pin to maintain
circuit stability. This value should be increased to
10µF or more if the battery connection is made any
distance from the charger output. If the AAT2552 is
to be used in applications where the battery can be
removed from the charger, such as with desktop
charging cradles, an output capacitor greater than
10µF may be required to prevent the device from
cycling on and off when no battery is present.
The maximum output capacitor RMS ripple current
is given by:
1
V
OUT · (VIN(MAX) - VOUT
)
IRMS(MAX)
=
·
L · FS · VIN(MAX)
2 · 3
Step-Down Converter Output Capacitor (C3)
The output capacitor limits the output ripple and
provides holdup during large load transitions. A
4.7µF to 10µF X5R or X7R ceramic capacitor typi-
cally provides sufficient bulk capacitance to stabi-
lize the output during large load transitions and has
the ESR and ESL characteristics necessary for low
output ripple. For enhanced transient response and
low temperature operation applications, a 10µF
(X5R, X7R) ceramic capacitor is recommended to
stabilize extreme pulsed load conditions.
Dissipation due to the RMS current in the ceram-
ic output capacitor ESR is typically minimal,
resulting in less than a few degrees rise in hot-
spot temperature.
Inductor Selection
The step-down converter uses peak current mode
control with slope compensation to maintain stabil-
ity for duty cycles greater than 50%. The output
inductor value must be selected so the inductor
current down slope meets the internal slope com-
pensation requirements. The internal slope com-
pensation for the AAT2552 is 0.45A/µsec. This
equates to a slope compensation that is 75% of the
inductor current down slope for a 1.8V output and
3.0µH inductor.
The output voltage droop due to a load transient is
dominated by the capacitance of the ceramic out-
put capacitor. During a step increase in load cur-
rent, the ceramic output capacitor alone supplies
the load current until the loop responds. Within two
or three switching cycles, the loop responds and
the inductor current increases to match the load
2552.2007.04.1.0
23
AAT2552
Total Power Solution for Portable Applications
0.75 ⋅ VO 0.75 ⋅ 1.8V
= 0.45
A
µsec
R3 = 59kΩ
R2 (kΩ)
R3 = 221kΩ
R2 (kΩ)
m =
=
L
3.0µH
VOUT (V)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
75
113
150
187
221
261
301
332
442
464
523
715
1000
0.75 ⋅ VO
0.75
⋅
VO
A
µsec
A
L =
=
≈
1.67
⋅ VO
m
0.45A
µsec
For most designs, the step-down converter operates
with inductor values from 1µH to 4.7µH. Table 6 dis-
plays inductor values for the AAT2552 for various
output voltages.
Manufacturer's specifications list both the inductor
DC current rating, which is a thermal limitation, and
the peak current rating, which is determined by the
saturation characteristics. The inductor should not
show any appreciable saturation under normal load
conditions. Some inductors may meet the peak and
average current ratings yet result in excessive loss-
es due to a high DCR. Always consider the losses
associated with the DCR and its effect on the total
converter efficiency when selecting an inductor.
Table 3: Adjustable Resistor Values For
Step-Down Converter.
Adjustable Output Voltage for the LDO
The output voltage for the LDO can be pro-
grammed by an external resistor divider network.
The 3.0µH CDRH2D09 series inductor selected
from Sumida has a 150mΩ DCR and a 470mA DC
current rating. At full load, the inductor DC loss is
9.375mW which gives a 2.08% loss in efficiency for
a 250mA, 1.8V output.
As shown below, the selection of R4 and R5 is a
straightforward matter. R5 is chosen by considering
the tradeoff between the feedback network bias cur-
rent and resistor value. Higher resistor values allow
stray capacitance to become a larger factor in circuit
performance whereas lower resistor values increase
bias current and decrease efficiency. To select appro-
priate resistor values, first choose R5 such that the
feedback network bias current is reasonable. Then,
according to the desired VOUT, calculate R4 according
to the equation below. An example calculation follows.
Adjustable Output Voltage for the Step-
down Converter
Resistors R2 and R3 of Figure 5 program the out-
put of the step down converter and regulate at a
voltage higher than 0.6V. To limit the bias current
required for the external feedback resistor string
while maintaining good noise immunity, the sug-
gested value for R3 is 59kΩ. Decreased resistor
values are necessary to maintain noise immunity
on the FBB pin, resulting in increased quiescent
current. Table 3 summarizes the resistor values for
various output voltages.
⎛ VOUT
⎝ VREF
⎞
R4 =
- 1 · R5
⎠
An R5 value of 59kΩ is chosen, resulting in a small
feedback network bias current of 1.24V/59kΩ ≈
21µA. The desired output voltage is 1.8V. From this
information, R4 is calculated from the equation below.
The result is R4 = 26.64kΩ. Since 26.64kΩ is not a
standard 1%-value, 26.7kΩ is selected. From this
example calculation, for VOUT = 1.8V, use R5 = 59kΩ
and R4 = 26.7kΩ. Example output voltages and cor-
responding resistor values are provided in Table 4.
V
V
3.3V
0.6V
⎛
⎝
⎞
⎛
⎝
⎞
⎠
R2 =
OUT -1 · R3 =
- 1 · 59kΩ = 267kΩ
⎠
REF
With enhanced transient response for extreme
pulsed load application, an external feed-forward
capacitor (C8 in Figure 5) can be added.
24
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
1. The input capacitors (C1, C6) should connect as
closely as possible to ADP, INA, and INB. It is pos-
R4 Standard 1% Values
(R5 = 59kΩ)
sible to use two input capacitors for INA and INB.
2. C4 and L1 should be connected as closely as
possible. The connection of L1 to the LX pin
should be as short as possible. Do not make the
node small by using narrow trace. The trace
should be kept wide, direct, and short.
VOUT (V)
R4 (kΩ)
3.3
2.8
2.5
2.0
1.8
1.5
97.6
75.0
60.4
36.5
26.7
12.4
3. The feedback pin should be separate from any
power trace and connect as closely as possible
to the load point. Sensing along a high-current
load trace will degrade DC load regulation.
Feedback resistors should be placed as closely
as possible to the FBB pin to minimize the length
of the high impedance feedback trace. If possi-
ble, they should also be placed away from the
LX (switching node) and inductor to improve
noise immunity.
4. The resistance of the trace from PGND should
be kept to a minimum. This will help to minimize
any error in DC regulation due to differences in
the potential of the internal signal ground and
the power ground.
Table 4: Adjustable Resistor Values for the LDO.
Printed Circuit Board Layout
Considerations
For the best results, it is recommended to physi-
cally place the battery pack as close as possible to
the AAT2552 BAT pin. To minimize voltage drops
on the PCB, keep the high current carrying traces
adequately wide. Refer to the AAT2552 evaluation
board for a good layout example (see Figures 6
and 7). The following guidelines should be used to
help ensure a proper layout.
5. A high density, small footprint layout can be
achieved using an inexpensive, miniature, non-
shielded, high DCR inductor.
2552.2007.04.1.0
25
AAT2552
Total Power Solution for Portable Applications
JP1
EN_BAT
2
1
3 2 1
Power Selection
JP2
BAT
ADP
D1
RED
LED
C6
10μF
(at bottom layer)
C1
10μF
1
2
R6
EN_LDO
U1
JP3
1.5K
Sync/Mode
15
16
1
10
11
7
ADP
INA
1
2
STAT
INB
ENA
ENB
EN_BAT
MODE
6
5
EN_BUCK
VoB
L1
14
2
12
4
BAT
LX
C4
100pF
(Optional)
ISET
FBB
VoA
C2
10μF
R2
3
9
8
AGND
PGND
OUTA
FBA
R1
8.06K
13
R4
C3
4.7μF
R3
59k
C5
4.7μF
R5
59k
VOUTB (V) R2 (Ω)
L1
VOUTA (V)
R4 (Ω)
0.6
13
R2 short, R3 open
1.24
1.5
1.8
2.0
2.5
2.8
3.0
R4 short, R5 open
12.4K
9.2K
59K
1.5μH (CDRH2D09/HP; DCR 88mΩ; 730mA @ 20°C)
2.2μH (CDRH2D09/HP; DCR 115mΩ; 600mA @ 20°C)
3.0μH (CDRH2D09/HP; DCR 150mΩ; 470mA @ 20°C)
3.9μH (CDRH2D09/HP; DCR 180mΩ; 450mA @ 20°C)
4.7μH (CDRH2D09/HP; DCR 230mΩ; 410mA @ 20°C)
5.6μH (CDRH2D09/HP; DCR 260mΩ; 370mA @ 20°C)
1.2
1.8
2.5
3.0
3.3
26.7K
118K
187K
237K
267K
36.5K
60.4K
75.0K
97.6K
Figure 5: AAT2552 Evaluation Board Schematic.
Figure 6: AAT2552 Evaluation Board
Top Side Layout.
Figure 7: AAT2552 Evaluation Board
Bottom Side Layout.
26
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Component Part Number
Description
Manufacturer
U1
C1, C2
C3, C5
C6
AAT2552IRN
ECJ-1VB0J106M
GRM188R60J475KE19
GRM319R61A106KE19
Total Power Solution for Portable Applications AnalogicTech
CER 10μF 6.3V X5R 0603
CER 4.7μF 6.3V X5R 0603
CER 10μF 10V X5R 1206
Panansonic
Murata
Murata
C4
GRM1886R1H101JZ01J CER 100pF 50V 5% R2H 0603
Murata
L1
R6
R1
R2
CDRH2D09
Shielded SMD, 3x3x1mm
1.5KΩ, 5%, 1/4W 0603
8.06KΩ, 1%, 1/4W 0603
118KΩ, 1%, 1/4W 0603
59KΩ, 1%, 1/4W 0603
60.4KΩ, 1%, 1/4W 0603
Conn. Header, 2mm zip
Sumida
Vishay
Vishay
Vishay
Vishay
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
PRPN401PAEN
R3, R5
R4
JP1, JP2,
JP3, JP4
D1
Vishay
Sullins Electronics
CMD15-21SRC/TR8
Red LED 1206
Chicago Miniature Lamp
Table 5: AAT2552 Evaluation Board Component Listing.
2552.2007.04.1.0
27
AAT2552
Total Power Solution for Portable Applications
Step-Down Converter Design Example (to be updated)
Specifications
VO
VIN
FS
= 1.8V @ 250mA, Pulsed Load ΔILOAD = 200mA
= 2.7V to 4.2V (3.6V nominal)
= 1.5MHz
TAMB = 85°C
1.8V Output Inductor
µsec
µsec
⋅ 1.8V = 3µH
A
L1 = 1.67
⋅ VO2 = 1.67
(use 3.0µH; see Table 3)
A
For Sumida inductor CDRH2D09-3R0, 3.0µH, DCR = 150mΩ.
⎛
⎞
⎠
VO
L1 ⋅ FS
VO
VIN
1.8
V
1.8V
4.2V
⎛
⎞
⎠
ΔIL1 =
⋅ 1 -
⎝
=
⋅ 1 -
= 228mA
⎝
3.0µH ⋅ 1.5MHz
ΔIL1
2
IPKL1 = IO +
= 250mA + 114mA = 364mA
2
PL1 = IO ⋅ DCR = 250mA2 ⋅ 150mΩ = 9.375mW
1.8V Output Capacitor
VDROOP = 0.1V
3 · ΔILOAD
VDROOP · FS
3 · 0.2A
COUT
=
=
= 4µF (use 4.7µF)
0.1V · 1.5MHz
(VO) · (VIN(MAX) - VO)
L1 · FS · VIN(MAX)
1
1.8V · (4.2V - 1.8V)
1
·
= 66mArms
IRMS
=
·
=
3.0µH · 1.5MHz · 4.2V
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (66mA)2 = 21.8µW
28
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Input Capacitor
Input Ripple VPP = 25mV
1
1
CIN =
=
= 1.38µF (use 4.7µF)
⎛ VPP
⎝ IO
⎞
⎛ 25mV
⎝ 0.2A
⎞
⎠
- ESR · 4 · FS
- 5mΩ · 4 · 1.5MHz
⎠
IO
IRMS
=
= 0.1Arms
2
P = esr · IRMS2 = 5mΩ · (0.1A)2 = 0.05mW
AAT2552 Losses
IO2 · (RDSON(H) · VO + RDSON(L) · [VIN -VO])
PTOTAL
=
VIN
+ (tsw · FS · IO + IQ) · VIN
0.22 · (0.59Ω · 1.8V + 0.42Ω · [4.2V - 1.8V])
4.2V
=
+ (5ns · 1.5MHz · 0.2A + 30µA) · 4.2V = 26.14mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 26.14mW = 86.3°C
2552.2007.04.1.0
29
AAT2552
Total Power Solution for Portable Applications
Output Voltage
VOUTB (V)
R3 = 59kΩ
R3 = 221kΩ
R1 (kΩ)
L1 (µH)
R3 (kΩ)
0.6
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3
R2 short, R3 open
R2 short, R3 open
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2.2
2.7
3.0/3.3
3.0/3.3
3.0/3.3
3.9/4.2
4.9
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
237
267
75
113
150
187
221
261
301
332
442
464
523
715
887
1000
3.3
5.6
Table 6: Step-Down Converter Component Values.
Inductance
(µH)
Max DC
DCR
Size (mm)
LxWxH
Manufacturer
Part Number
Current (mA)
(mΩ)
Type
Sumida
Sumida
Sumida
Sumida
Sumida
Sumida
Sumida
Sumida
Sumida
Sumida
Sumida
Taiyo Yuden
Taiyo Yuden
Taiyo Yuden
Taiyo Yuden
FDK
CDRH2D09-1R5
CDRH2D09-2R2
CDRH2D09-2R5
CDRH2D09-3R0
CDRH2D09-3R9
CDRH2D09-4R7
CDRH2D09-5R6
CDRH2D11-1R5
CDRH2D11-2R2
CDRH2D11-3R3
CDRH2D11-4R7
NR3010T1R5N
NR3010T2R2M
NR3010T3R3M
NR3010T4R7M
MIPWT3226D-1R5
MIPWT3226D-2R2
MIPWT3226D-3R0
MIPWT3226D-4R2
1.5
2.2
2.5
3.0
3.9
4.7
5.6
1.5
2.2
3.3
4.7
1.5
2.2
3.3
4.7
1.5
2.2
3.0
4.2
730
600
530
470
450
410
370
900
780
600
500
1200
1100
870
750
1200
1100
1000
900
110
144
150
194
225
287
325
68
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
3.2x3.2x1.2
3.2x3.2x1.2
3.2x3.2x1.2
3.2x3.2x1.2
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
3.2x2.6x0.8
3.2x2.6x0.8
3.2x2.6x0.8
3.2x2.6x0.8
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Chip shielded
Chip shielded
Chip shielded
Chip shielded
98
123
170
80
95
140
190
90
100
120
140
FDK
FDK
FDK
Table 7: Suggested Inductors and Suppliers.
1. For reduced quiescent current, R3 = 221kΩ.
30
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
Value
(µF)
Voltage
Rating
Temp.
Co.
Case
Size
Manufacturer
Part Number
Murata
Murata
Murata
Murata
Murata
Murata
GRM21BR61A106KE19
GRM188R60J475KE19
GRM188R61A225KE34
GRM188R60J225KE19
GRM188R61A105KA61
GRM185R60J105KE26
10
4.7
2.2
2.2
1.0
1.0
10
6.3
10
6.3
10
X5R
X5R
X5R
X5R
X5R
X5R
0805
0603
0603
0603
0603
0603
6.3
Table 8: Surface Mount Capacitors.
2552.2007.04.1.0
31
AAT2552
Total Power Solution for Portable Applications
Ordering Information
1
2
Package
Marking
Part Number (Tape and Reel)
TDFN34-16
UVXYY
AAT2552IRN-CAE-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
Legend
Voltage
Code
Adjustable
(0.6)
0.9
Adjustable
(1.2)
1.5
A
B
E
G
I
1.8
1.9
2.5
2.6
2.7
2.8
2.85
2.9
Y
N
O
P
Q
R
S
T
3.0
3.3
4.2
W
C
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
32
2552.2007.04.1.0
AAT2552
Total Power Solution for Portable Applications
1
Package Information
TDFN34-16
3.000 0.050
1.600 0.050
Detail "A"
Index Area
0.350 0.100
Top View
Bottom View
C0.3
(4x)
Pin 1 Indicator
(optional)
0.050 0.050
0.229 0.051
Side View
Detail "A"
All dimensions in millimeters.
1. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the
lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required
to ensure a proper bottom solder connection.
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work
rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service with-
out notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied war-
ranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent,
copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the
customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty.
Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated.
All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
2552.2007.04.1.0
33
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