AAT2552IRN-CAE-T1 - AnalogicTech

General Description

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.

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.

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.

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.

Features

• 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:

— 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

Applications

• Bluetooth®Headsets

• Cellular Phones

• GPS

• Handheld Instruments

• MP3 and Portable Music Players

• PDAs and Handheld Computers

• Portable Media Players

AAT2552

Total Power Solution for Portable Applications

Typical Application

BATT-

ADP

GND

BAT

MODE

ISET

INB

INA

ENB

ENA

BATT+

AAT2552

dapter/USB Input

STAT

EN_BAT

Enable

RSET

Battery

Pack

OUT

System

FBB

RFBB2

RFBB1

RFBA2

RFBA1

COUTB

4.7μF

VOUTB

OUTA

FBA

COUTA

VOUTA

2552.2007.04.1.0 1

SystemPower™

Pin Descriptions

Pin Configuration

TDFN34-16

(Top View)

AGND

FBB

ENB

EN_BAT

ISET

MODE

ENA

FBA

BAT

PGND

STAT

ADP

INB

INA

OUTA

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 AGND Analog ground.

4 FBB 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 ENB 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).

6 MODE 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.

7 ENA 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).

8 FBA Feedback input for the LDO. This pin must be connected directly to an external resistor divider.

Nominal voltage is 1.24V.

9 OUTA Linear regulator output. Connect a 2.2µF capacitor from this pin to ground.

10 INA Linear regulator input voltage. Connect a 1µF or greater capacitor from this pin to ground.

11 INB Input voltage for the step-down converter.

12 LX 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.

13 PGND Power ground.

14 BAT Battery charging and sensing. Connect to positive terminal of Lithium-ion/polymer battery.

15 ADP Input from USB port or AC wall adapter.

16 STAT Open drain status pin for charger.

EP Exposed paddle (bottom): connect to ground directly beneath the package.

AAT2552

Total Power Solution for Portable Applications

22552.2007.04.1.0

Absolute Maximum Ratings1

Thermal Information

Symbol Description Value Units

PDMaximum Power Dissipation 2.0 W

θJA Thermal Resistance250 °C/W

Symbol Description Value Units

VINA, VINB Input Voltage to GND 6.0 V

VADP Adapter Voltage to GND -0.3 to 7.5 V

VLX LX to GND -0.3 to VIN + 0.3 V

VFB FB to GND -0.3 to VIN + 0.3 V

VEN ENA, ENB, EN_BAT to GND -0.3 to 6.0 V

VXBAT, ISET, STAT -0.3 to VADP + 0.3 V

TJOperating Junction Temperature Range -40 to 150 °C

TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300 °C

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 3

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.

Electrical Characteristics1

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 V

VINB Rising 2.6 V

VUVLO UVLO Threshold Hysteresis 250 mV

VOUT Output Voltage Tolerance2IOUTB = 0 to 300mA, -3.0 3.0 %

VINB = 2.7V to 5.5V

VOUT Output Voltage Range 0.6 VINB V

IQQuiescent Current No Load 45 90 µA

ISHDN Shutdown Current VENB = GND 1.0 µA

ILIM P-Channel Current Limit 300 mA

RDS(ON)H High-Side Switch On Resistance 0.3 Ω

RDS(ON)L Low-Side Switch On Resistance 0.5 Ω

ILXLEAK LX Leakage Current VINB = 5.5V, VLX = 0 to VINB 1.0 µA

ΔVOUT/ΔVOUT Load Regulation IOUTB = 0mA to 300mA 0.4 %

ΔVLinereg/ΔVIN Line Regulation VINB = 2.7V to 5.5V 0.1 %/V

VFB Feedback Threshold Voltage Accuracy VINB = 3.6V 0.591 0.6 0.609 V

IFB FB Leakage Current VOUTB = 1.0V 0.2 µA

FOSC Oscillator Frequency 1.5 MHz

TSStartup Time From Enable to Output 120 µs

Regulation

TSD Over-Temperature Shutdown Threshold 140 °C

THYS Over-Temperature Shutdown Hysteresis 15 °C

VEN(L) Enable Threshold Low 0.6 V

VEN(H) Enable Threshold High 1.4 V

IEN Input Low Current VINB = VENB = 5.5V -1.0 1.0 µA

AAT2552

Total Power Solution for Portable Applications

42552.2007.04.1.0

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.

Electrical Characteristics1

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

VOUT Output Voltage Tolerance IOUTA = 1mA TA= 25°C -1.5 1.5 %

to 300mA TA= -40°C to +85°C -2.5 2.5

VOUT Output Voltage Range 1.2 3.3 V

VFB Feedback Voltage Accuracy 1.22 1.24 1.26 V

VIN Input Voltage VOUT + 5.5 V

VDO2

VDO Dropout Voltage3IOUTA = 300mA; VOUT = 3.3V 400 650 mV

ΔVOUT/Line Regulation VINA = VOUTA + 1 to 5.0V 0.09 %/V

VOUT*ΔVIN

IOUT Output Current VOUTA > 2.0V 300 mA

ISC Short-Circuit Current VOUTA < 0.4V 400 mA

IQQuiescent Current VINA = 5V; VENA = VIN 85 150 µA

ISHDN Shutdown Current VINA = 5V; VENA = 0V 1.0 µA

1kHz 70

PSRR Power Supply Rejection IOUTA =10mA 10kHz 50 dB

Ratio 1MHz 30

TSD

Over-Temperature 140 °C

Shutdown Threshold

THYS

Over-Temperature 15 °C

Shutdown Hysteresis

eNOutput Noise eNBW = 100Hz to 100kHz 95 µVRMS/

√Hz

Output Voltage 8 ppm/°C

Temperature Coefficient

VEN(L) Enable Threshold Low 0.6 V

VEN(H) Enable Threshold High 1.4 V

IEN Enable Input Current VINA = VENA = 5.5V 1.0 µA

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 5

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.

AAT2552

Total Power Solution for Portable Applications

62552.2007.04.1.0

Electrical Characteristics1

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 4.0 6.5 V

VUVLO

Under-Voltage Lockout (UVLO) Rising Edge 3 4 V

UVLO Hysteresis 150 mV

IOP Operating Current Charge Current = 200mA 0.5 1 mA

ISHUTDOWN Shutdown Current VBAT = 4.25V, VEN_BAT = GND 0.3 1 µA

ILEAKAGE Reverse Leakage Current from BAT Pin VBAT = 4V, ADP Pin Open 0.4 2 µA

Voltage Regulation

VBAT_EOC End of Charge Accuracy 4.158 4.20 4.242 V

VMIN Preconditioning Voltage Threshold 2.8 3.0 3.2 V

VRCH Battery Recharge Voltage Threshold Measured from VBAT_EOC -0.1 V

Current Regulation

ICH Charge Current Programmable Range 30 500 mA

ΔICH/ICH Charge Current Regulation Tolerance ICHARGE = 200mA -10 10 %

VSET ISET Pin Voltage 2 V

KI_ACurrent 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) Enable Threshold High 1.6 V

VEN(L) Enable Threshold Low 0.4 V

VSTAT Output Low Voltage STAT Pin Sinks 4mA 0.4 V

ISTAT STAT Pin Current Sink Capability 8 mA

VOVP Over-Voltage Protection Threshold 4.4 V

ITK/ICHG Pre-Charge Current ICH = 100mA 10 %

ITERM/ICHG Charge Termination Threshold Current 10 %

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.

Typical Characteristics–Battery Charger

Battery Charging Current vs. Battery Voltage

VBAT (V)

ICH (mA)

100

200

300

400

500

600

2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3

RSET = 3.24K

RSET = 5.62K

RSET = 8.06K

RSET = 16.2K RSET = 31.6K

Constant Charging Current vs. Temperature

(RSET = 8.06kΩ

)

Temperature (

ICH (mA)

190

193

195

198

200

203

205

208

210

-50 -25 0 25 50 75 100

Operating Current vs. Temperature

(VIN = 5.0V; RSET = 8.06kΩ

)

Temperature (

IOP (µA)

440

460

480

500

520

540

-50 -25 0 25 50 75 100

Sleep Mode Current vs. Input Voltage

(RSET = 8.06kΩ

)

Input Voltage (V)

ISLEEP (nA)

100

200

300

400

500

600

700

800

4.0 4.5 5.0 5.5 6.0 6.5

85°C25°C

-40°C

Constant Charging Current vs. Set Resistors

(VIN = 5.0V)

RSET (kΩ

)

ICH (mA)

100

1000

10000

1 10 100 1000

Operating Supply Current vs. RSET

(VIN = 5.0V)

RSET (kΩ

)

IOP (µA)

100

1000

1 10 100

Constant Current Mode

Preconditioning Mode

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 7

Typical Characteristics–Battery Charger

Preconditioning Charge Current vs. Temperature

(RSET = 8.06kΩ

)

Temperature (

ITK (mA)

19.2

19.6

20.0

20.4

20.8

-40 -15 10 35 60 85

Preconditioning Voltage Threshold vs. Temperatur

(RSET = 8.06kΩ

)

Temperature (

VMIN (V)

2.97

2.98

2.99

3.00

3.01

3.02

3.03

-40 -15 10 35 60 85

Recharging Threshold Voltage vs. Temperature

(RSET = 8.06kΩ

)

Temperature (

VRCH (V)

4.04

4.06

4.08

4.10

4.12

4.14

4.16

-40 -15 10 35 60 85

Constant Charging Current vs. Input Voltage

(VIN = 5.62V)

VIN (V)

ICH (mA)

285

290

295

300

305

310

4 4.5 5 5.5 6 6.5

VIN = 3.6V

VIN = 4V

VIN = 3.3V

End of Charge Voltage Regulation

vs. Temperature

(VIN = 5V; RSET = 8.06kΩ

)

Temperature (

VBAT_EOC (V)

4.185

4.190

4.195

4.200

4.205

4.210

4.215

-40 -15 10 35 60 85

End of Charge Battery Voltage

vs. Input Voltage

VIN (V)

VBAT_EOC (V)

4.194

4.196

4.198

4.200

4.202

4.204

4.206

4.5 5 5.5 6 6.5

RSET = 8.06kΩ

RSET = 31.6kΩ

AAT2552

Total Power Solution for Portable Applications

82552.2007.04.1.0

Typical Characteristics–Battery Charger

Enable Threshold High vs. Input Voltage

(RSET = 8.06kΩ

)

VIN (V)

VEN(H) (V)

0.7

0.8

0.9

1.0

1.1

1.2

4.0 4.5 5.0 5.5 6.0 6.5

-40°C

85°C

25°C

Enable Threshold Low vs. Input Voltage

(RSET = 8.06kΩ

)

VIN (V)

VEN(L) (V)

0.6

0.7

0.8

0.9

1.0

1.1

4.0 4.5 5.0 5.5 6.0 6.5

-40°C

25°C

85°C

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 9

Typical Characteristics–Step-Down Converter

Efficiency vs. Load

(VOUT = 1.2V; L = 1.5µH)

Output Current (mA)

Efficiency (%)

100

0.1 1 10 100 1000

VIN = 2.7V

VIN = 3.6V

VIN = 5.0V

VIN = 4.2V

DC Regulation

OUT

= 1.2V; L = 1.5μH)

Output Current (mA)

Output Error (%)

-1.0

-0.5

0.0

0.5

1.0

0.1 1 10 100 1000

= 5.0V

= 2.7V

= 4.2V

= 3.6V

Efficiency vs. Load

(VOUT = 1.8V; L = 3.3µH)

Output Current (mA)

Efficiency (%)

100

0.1 1 10 100 1000

VIN = 2.7V

VIN = 3.6V

VIN = 5.0V

VIN = 4.2V

DC Regulation

(VOUT = 1.8V; L = 3.3µH)

Output Current (mA)

Output Error (%)

-1.0

-0.5

0.0

0.5

1.0

0.1 1 10 100 1000

VIN = 4.2V

VIN = 5.0V

VIN = 3.6V

VIN = 2.7V

Efficiency vs. Load

(VOUT = 3.3V; L = 5.6µH)

Output Current (mA)

Efficiency (%)

100

0.1 1 10 100 1000

VIN = 5.0V

VIN = 4.2V

VIN = 3.6V

DC Regulation

(VOUT = 3.3V; L = 5.6µH)

Output Current (mA)

Output Error (%)

-1.0

-0.5

0.0

0.5

1.0

0.1 1 10 100 1000

VIN = 5.0V

VIN = 4.2V

VIN = 3.6V

AAT2552

Total Power Solution for Portable Applications

10 2552.2007.04.1.0

Typical Characteristics–Step-Down Converter

N-Channel RDS(ON) vs. Input Voltage

VIN (V)

RDS(ON)L (mΩ

)

300

400

500

600

700

800

900

1000

2.5 3 3.5 4 4.5 5 5.5 6

25°C

85°C

100°C120°C

P-Channel RDS(ON) vs. Input Voltage

VIN (V)

RDS(ON)H (mΩ

)

100

200

300

400

500

600

2.5 3 3.5 4 4.5 5 5.5 6

25°C

85°C100°C120°C

Output Voltage Accuracy vs. Temperature

(VIN = 3.6V; VO = 1.8V; IOUT = 150mA)

Temperature (°

Output Accuracy (%)

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

-40 -15 10 35 60 85

No Load Quiescent Current vs. Input Voltage

Input Voltage (V)

IQ (mA)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.

85°C 25°C

-40°C

Line Regulation

(VOUT = 1.8V)

Input Voltage (V)

Accuracy (%)

-0.4

-0.3

-0.2

-0.1

0.1

0.2

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.

IOUT = 10mA

IOUT = 50mA

IOUT = 150mA

Soft Start

(VIN = 3.6V; VOUT = 1.8V; IOUT = 150mA)

Time (100µs/div)

Enable and Output Voltage

(top) (V)

Inductor Current (bottom) (A)

0.0

0.1

0.2

0.3

VEN

VOUT

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Total Power Solution for Portable Applications

2552.2007.04.1.0 11

Typical Characteristics–Step-Down Converter

Output Voltage Ripple

(VIN = 3.6V; VOUT = 1.8V; IOUT = 300mA)

Time (0.2µs/div)

Output Voltage (AC coupled)

(top) (V)

Inductor Current (bottom) (A)

1.79

1.80

1.81

0.1

0.2

0.3

0.4

Output Voltage Ripple

(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)

Time (5µs/div)

Output Voltage (AC coupled)

(top) (V)

Inductor Current (bottom) (A)

-20

-0.10

-0.05

0.00

0.05

Load Transient Response

(10mA to 300mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7µF; C = 100pF)

Time (20µs/div)

Output Voltage (top) (V)

Load and Inductor Current

(bottom) (A)

1.6

1.7

1.8

1.9

2.0

-0.2

0.0

0.2

VOUT

IOUT

ILX

10mA

300mA

Line Transient Response

(VOUT = 1.8V @ 150mA, CFF = 100pF)

Time (25µs/div)

Output Voltage (top) (V)

Input Voltage (bottom) (V)

1.75

1.80

1.85

1.90

3.1

3.6

4.1

4.6

AAT2552

Total Power Solution for Portable Applications

12 2552.2007.04.1.0

Typical Characteristics–LDO Regulator

Output Voltage vs. Temperature

(VIN = 3.6V; VO = 1.8V; IOUT = 150mA)

Temperature (°

Output Voltage (V)

3.296

3.297

3.298

3.299

3.300

3.301

-40 -15 10 35 60 85

Enable Threshold Voltage vs. Input Voltage

Input Voltage (V)

VENABLE (V)

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.

VEN(H)

VEN(L)

Dropout Characteristics

Input Voltage (V)

Output Voltage (V)

2.4

2.6

2.8

3.2

3.4

3.6

3.8

3 3.2 3.4 3.6 3.8 4

IOUT = 0mA

IOUT = 300mA

IOUT = 100mA

IOUT = 50mA

Dropout Voltage vs. Output Current

Output Current (mA)

Dropout Voltage (V)

0.0

0.1

0.2

0.3

0.4

0.5

0 50 100 150 200 250 300

-40°C

85°C

25°C

Quiescent Current vs. Temperature

(VIN = 5V)

Temperature (°

IQ (µA)

100

110

120

-40 -15 10 35 60 85

Dropout Voltage vs. Temperature

Temperature (°

Dropout Voltage (V)

0.0

0.1

0.2

0.3

0.4

0.5

-40 -20 0 20 40 60 80 100 120

IL = 300mA

IL = 200mA

IL = 100mA

IL = 50mA

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 13

AAT2552

Total Power Solution for Portable Applications

14 2552.2007.04.1.0

Typical Characteristics–LDO Regulator

LDO Output Noise

(COUT = 4.7µF; IOUT = 10mA; RLOAD = 330; 98.33µVrms)

Frequency (kHz)

nVrms/sqrt (Hz)

100

1000

10000

0.01 0.1 1 10 100 1000

Turn-Off Response Time

(VIN = 4.2V; IOUT = 300mA)

Time (50µs/div)

Enable and Output Voltage

VEN = 2V/div

VOUT = 1V/div

Turn-On Time From Enable

(VIN = 4.2V; IOUT = 300mA)

Time (100µs/div)

Enable and Output Voltage

VEN = 2V/div

VOUT = 1V/div

Line Transient Response

(IOUT = 300mA)

Time (100µs/div)

Output Voltage (top) (V)

Input Voltage (bottom) (V)

3.30

3.35

3.40

4.0

4.5

5.0

VOUT

VIN

Load Transient Response

(1mA to 300mA; VIN = 5.0V; VOUT = 3.3V)

Time (100µs/div)

Output Voltage (top) (V)

Output Current (bottom) (A)

3.2

3.4

3.6

-0.2

0.0

0.2

0.4

VOUT

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Total Power Solution for Portable Applications

2552.2007.04.1.0 15

Functional Block Diagram

Charge

Control

Current Compare

Reverse Blocking

ADP

ISET UVLO

Err.

Amp

STAT

EN_BAT

Logic

Voltage

Reference

Input

Voltage

Reference

INA OUTA

AGND

Fast Start

Control

Active Feedback

Control

BAT

INB

FBB

PGND

ENB

ENA

MODE

FBA

From

Charger Section

Constant Current

Charge Status

CV/Pre-Charge

Over-Temperature

Protection

Over-Current

Protection

Err.

Amp

Functional Description

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.

Battery Charger

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.

AAT2552

Total Power Solution for Portable Applications

16 2552.2007.04.1.0

Switch-Mode Step-Down Converter

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 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.

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 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.

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.

Under-Voltage Lockout

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.

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 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.

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

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 17

peak switch current to force a constant output volt-

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.

Pre-conditioning continues until the battery voltage

reaches VMIN (see Figure 1). At this point, the

charger begins constant-current charging. The cur-

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.

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.

Figure 1: Current vs. Voltage Profile During Charging Phases.

Constant Current

Charge Phase

Constant Voltage

Charge Phase

Preconditioning

Trickle Charge

Phase

Charge Complete Voltage

Constant Current Mode

Voltage Threshold

Regulated Current

Trickle Charge and

Termination Threshold

I = CC / 10

I = Max CC

AAT2552

Total Power Solution for Portable Applications

18 2552.2007.04.1.0

Battery Charging System Operation Flow Chart

Power On Reset

Power Input

Voltage

VADP > VUVLO

Fault Conditions

Monitoring

OV, OT

Preconditioning

Test

VMIN > VBAT

Current Phase Test

VBAT_EOC

> VBAT

Voltage Phase Test

IBAT > ITERM

Yes

Preconditioning

(Trickle Charge)

Constant

Current Charge

Mode

Constant

Voltage Charge

Mode

Yes

Charge Completed

Charge

Control

Recharge Test

VRCH > VBAT

Yes

Shut Down Yes

Enable

Yes

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 19

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.

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.

Adapter or USB Power Input

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.

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

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.

Table 1: RSET Values.

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.

RSET (kΩ

)

ICH (mA)

100

1000

1 10 100 1000

Normal Set Resistor

ICHARGE (mA) Value R1 (kΩ)

500 3.24

400 4.12

300 5.36

250 6.49

200 8.06

150 10.7

100 16.2

50 31.6

40 38.3

30 53.6

20 78.7

15 105

AAT2552

Total Power Solution for Portable Applications

20 2552.2007.04.1.0

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.

The required ballast resistor values can be esti-

mated using the following formulas:

Example:

Note: Red LED forward voltage (VF) is typically

2.0V @ 2mA.

Thermal Considerations

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.

First, the maximum power dissipation for a given

situation should be calculated:

Where:

PD(MAX) = Maximum Power Dissipation (W)

θJA = Package Thermal Resistance (°C/W)

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.

Figure 3: Maximum Power Dissipation.

Next, the power dissipation of the battery charger

can be calculated by the following equation:

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]

PD = [(VADP - VBAT) · ICH + (VADP · IOP)]

TA (°

PD(MAX) (mW)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 2040608010

J(MAX) -

)

D(MAX)

= θ

(5.5V

- 2.0

= = 1.75kΩ

2mA

ADP -

F(LED)

)

= I

LED

Event Description Status

No battery charging activity OFF

Battery charging via adapter ON

or USB port

Charging completed OFF

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 21

By substitution, we can derive the maximum

charge current before reaching the thermal limit

condition (thermal cycling). The maximum charge

current is the key factor when designing battery

charger applications.

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.

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:

IQis the step-down converter quiescent current.

The term tsw is used to estimate the full load step-

down converter switching losses.

For the condition where the step-down converter is

in dropout at 100% duty cycle, the total device dis-

sipation reduces to:

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.

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.

Capacitor Selection

Linear Regulator Input Capacitor (C6)

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.

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

TJ(MAX) = PTOTAL · ΘJA + TAMB

PTOTAL = IO

2 · RDSON(H) + IQ · VIN

PTOTAL

2 · (RDSON(H) · VO + RDSON(L) · [VIN - VO])

VIN

+ (tsw · FS · IO + IQ) · VIN

VIN (V)

ICH(MAX) (mA)

100

150

200

250

300

350

400

450

500

4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25 6.5 6.7

TA = 60°C

TA = 85°C

TA = 45°C

J(MAX) -

)

- V

BAT

CH(MAX)

D(MAX) -

)

- V

BAT

CH(MAX)

AAT2552

Total Power Solution for Portable Applications

22 2552.2007.04.1.0

capacitor in this application will minimize switching

or power transient effects when the power supply is

"hot plugged" in.

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.

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:

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.

for VIN = 2 · VO

The term appears in both the input

voltage ripple and input capacitor RMS current

equations and is a maximum when VOis 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.

The proper placement of the input capacitor (C6)

can be seen in the evaluation board layout in

Figure 7.

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.

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.

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.

⎛⎞

· 1 -

⎝⎠

VIN

RMS(MAX)

⎛⎞

· 1 - = D · (1 - D) = 0.52 =

⎝⎠

VIN

⎛⎞

IRMS = IO · · 1 -

⎝⎠

VIN

CIN(MIN) = 1

⎛⎞

- ESR · 4 · FS

⎝⎠

VPP

⎛⎞

· 1 - = for VIN = 2 · V

⎝⎠

VIN

⎛⎞

· 1 -

⎝⎠

VIN

CIN =

VIN

⎛⎞

- ESR · FS

⎝⎠

VPP

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 23

Linear Regulator Output Capacitor (C5)

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.

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.

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.

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

current demand. The relationship of the output volt-

age droop during the three switching cycles to the

output capacitance can be estimated by:

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.

The maximum output capacitor RMS ripple current

is given by:

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.

VOUT · (VIN(MAX) - VOUT)

RMS(MAX)

IL · FS · VIN(MAX)

=·

COUT =

3 · ΔILOAD

VDROOP · FS

AAT2552

Total Power Solution for Portable Applications

24 2552.2007.04.1.0

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.

The 3.0µH CDRH2D09 series inductor selected

from Sumida has a 150mΩDCR 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.

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.

With enhanced transient response for extreme

pulsed load application, an external feed-forward

capacitor (C8 in Figure 5) can be added.

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.

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.

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.

⎛⎞

· R5

- 1R4 = ⎝⎠

VOUT

VREF

R3 = 59kΩR3 = 221kΩ

VOUT (V) R2 (kΩ) R2 (kΩ)

0.8 19.6 75

0.9 29.4 113

1.0 39.2 150

1.1 49.9 187

1.2 59.0 221

1.3 68.1 261

1.4 78.7 301

1.5 88.7 332

1.8 118 442

1.85 124 464

2.0 137 523

2.5 187 715

3.3 267 1000

⎛⎞

⎝⎠

R2 = -1 · R3 = - 1 · 59kΩ = 267kΩ

VOUT

VREF

⎛⎞

⎝⎠

3.3V

0.6V

0.75 ⋅ V

L = =

≈

1.67

⋅ V

0.75

⋅

0.45A

µsec

0.75 ⋅ V

m = = = 0.45

0.75 ⋅ 1.8V

3.0µH

µsec

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 25

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.

1. The input capacitors (C1, C6) should connect as

closely as possible to ADP, INA, and INB. It is pos-

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.

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.

5. A high density, small footprint layout can be

achieved using an inexpensive, miniature, non-

shielded, high DCR inductor.

R4 Standard 1% Values

VOUT (V) (R5 = 59kΩ)

R4 (kΩ)

3.3 97.6

2.8 75.0

2.5 60.4

2.0 36.5

1.8 26.7

1.5 12.4

AAT2552

Total Power Solution for Portable Applications

26 2552.2007.04.1.0

Figure 5: AAT2552 Evaluation Board Schematic.

Figure 6: AAT2552 Evaluation Board Figure 7: AAT2552 Evaluation Board

Top Side Layout. Bottom Side Layout.

ADP

RED

LED

1.5K

10μF

8.06K

10μF

59k

4.7μF

59k

100pF

(Optional)

4.7μF

VoA

VoB

123 Power Selection BAT

Sync/Mode

12 EN_BAT

JP1

EN_LDO

JP2

EN_BUCK

JP3

ENB 5

EN_BAT

MODE

ISET 2

AGND

INB 11

FBB

PGND

BAT 14

ADP

STAT

16 INA 10

OUTA 9

ENA 7

FBA 8

VOUTB (V) VOUTA (V)R2 (Ω)R4 (Ω)

13 9.2K

1.8 118K

3.0 237K

1.2 59K

2.5 187K

3.0μH (CDRH2D09/HP; DCR 150mΩ; 470mA @ 20°C)

1.5μH (CDRH2D09/HP; DCR 88mΩ; 730mA @ 20°C)

4.7μH (CDRH2D09/HP; DCR 230mΩ; 410mA @ 20°C)

2.2μH (CDRH2D09/HP; DCR 115mΩ; 600mA @ 20°C)

3.9μH (CDRH2D09/HP; DCR 180mΩ; 450mA @ 20°C)

10μF

(at bottom layer)

1.24 R4 short, R5 open

1.8 26.7K

2.0 36.5K

2.8 75.0K

1.5 12.4K

2.5 60.4K

0.6 R2 short, R3 open

3.0 97.6K

3.3 267K 5.6μH (CDRH2D09/HP; DCR 260mΩ; 370mA @ 20°C)

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 27

Table 5: AAT2552 Evaluation Board Component Listing.

Component Part Number Description Manufacturer

U1 AAT2552IRN Total Power Solution for Portable Applications AnalogicTech

C1, C2 ECJ-1VB0J106M CER 10μF 6.3V X5R 0603 Panansonic

C3, C5 GRM188R60J475KE19 CER 4.7μF 6.3V X5R 0603 Murata

C6 GRM319R61A106KE19 CER 10μF 10V X5R 1206 Murata

C4 GRM1886R1H101JZ01J CER 100pF 50V 5% R2H 0603 Murata

L1 CDRH2D09 Shielded SMD, 3x3x1mm Sumida

R6 Chip Resistor 1.5KΩ, 5%, 1/4W 0603 Vishay

R1 Chip Resistor 8.06KΩ, 1%, 1/4W 0603 Vishay

R2 Chip Resistor 118KΩ, 1%, 1/4W 0603 Vishay

R3, R5 Chip Resistor 59KΩ, 1%, 1/4W 0603 Vishay

R4 Chip Resistor 60.4KΩ, 1%, 1/4W 0603 Vishay

JP1, JP2, PRPN401PAEN Conn. Header, 2mm zip Sullins Electronics

JP3, JP4

D1 CMD15-21SRC/TR8 Red LED 1206 Chicago Miniature Lamp

AAT2552

Total Power Solution for Portable Applications

28 2552.2007.04.1.0

Step-Down Converter Design Example (to be updated)

Specifications

VO= 1.8V @ 250mA, Pulsed Load ΔILOAD = 200mA

VIN = 2.7V to 4.2V (3.6V nominal)

FS= 1.5MHz

TAMB = 85°C

1.8V Output Inductor

(use 3.0µH; see Table 3)

For Sumida inductor CDRH2D09-3R0, 3.0µH, DCR = 150mΩ.

1.8V Output Capacitor

VDROOP = 0.1V

1 1.8V · (4.2V - 1.8V)

3.0µH · 1.5MHz · 4.2V

RMS

IL1 · FS · VIN(MAX)

= ·

3 · ΔILOAD

VDROOP · FS

3 · 0.2A

0.1V · 1.5MHz

COUT = = = 4µF (use 4.7µF)

· = 66mArms

(VO) · (VIN(MAX) - VO)=

Pesr = esr · IRMS2 = 5mΩ · (66mA)2 = 21.8µW

1.8

1.8V

ΔI

⋅ 1 - = ⋅ 1 - = 228m

L1 ⋅ F

3.0µH ⋅ 1.5MHz

4.2V

PKL1

= I

+ ΔI

= 250mA + 114mA = 364mA

= I

⋅ DCR = 250mA

⋅ 150mΩ = 9.375mW

⎛

⎝⎞

⎠

⎛

⎝⎞

⎠

L1 = 1.67 ⋅ V

= 1.67 ⋅ 1.8V = 3µH

µsec

Input Capacitor

Input Ripple VPP = 25mV

AAT2552 Losses

TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 26.14mW = 86.3°C

PTOTAL

+ (tsw · FS · IO + IQ) · VIN

2 · (RDSON(H) · VO + RDSON(L) · [VIN -VO])

VIN

+ (5ns · 1.5MHz · 0.2A + 30µA) · 4.2V = 26.14mW

0.22 · (0.59Ω · 1.8V + 0.42Ω · [4.2V - 1.8V])

4.2V

RMS

P = esr · IRMS

2 = 5mΩ · (0.1A)2 = 0.05mW

= = 0.1Arms

CIN = = = 1.38µF (use 4.7µF

)

⎛⎞

- ESR · 4 · FS

⎝⎠

VPP

⎛⎞

- 5mΩ · 4 · 1.5MHz

⎝⎠

25mV

0.2A

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 29

AAT2552

Total Power Solution for Portable Applications

30 2552.2007.04.1.0

Table 6: Step-Down Converter Component Values.

Table 7: Suggested Inductors and Suppliers.

Inductance Max DC DCR Size (mm)

Manufacturer Part Number (µH) Current (mA) (mΩ) LxWxH Type

Sumida CDRH2D09-1R5 1.5 730 110 3.0x3.0x1.0 Shielded

Sumida CDRH2D09-2R2 2.2 600 144 3.0x3.0x1.0 Shielded

Sumida CDRH2D09-2R5 2.5 530 150 3.0x3.0x1.0 Shielded

Sumida CDRH2D09-3R0 3.0 470 194 3.0x3.0x1.0 Shielded

Sumida CDRH2D09-3R9 3.9 450 225 3.0x3.0x1.0 Shielded

Sumida CDRH2D09-4R7 4.7 410 287 3.0x3.0x1.0 Shielded

Sumida CDRH2D09-5R6 5.6 370 325 3.0x3.0x1.0 Shielded

Sumida CDRH2D11-1R5 1.5 900 68 3.2x3.2x1.2 Shielded

Sumida CDRH2D11-2R2 2.2 780 98 3.2x3.2x1.2 Shielded

Sumida CDRH2D11-3R3 3.3 600 123 3.2x3.2x1.2 Shielded

Sumida CDRH2D11-4R7 4.7 500 170 3.2x3.2x1.2 Shielded

Taiyo Yuden NR3010T1R5N 1.5 1200 80 3.0x3.0x1.0 Shielded

Taiyo Yuden NR3010T2R2M 2.2 1100 95 3.0x3.0x1.0 Shielded

Taiyo Yuden NR3010T3R3M 3.3 870 140 3.0x3.0x1.0 Shielded

Taiyo Yuden NR3010T4R7M 4.7 750 190 3.0x3.0x1.0 Shielded

FDK MIPWT3226D-1R5 1.5 1200 90 3.2x2.6x0.8 Chip shielded

FDK MIPWT3226D-2R2 2.2 1100 100 3.2x2.6x0.8 Chip shielded

FDK MIPWT3226D-3R0 3.0 1000 120 3.2x2.6x0.8 Chip shielded

FDK MIPWT3226D-4R2 4.2 900 140 3.2x2.6x0.8 Chip shielded

1. For reduced quiescent current, R3 = 221kΩ.

Output Voltage R3 = 59kΩ R3 = 221kΩ

L1 (µH)

VOUTB (V) R3 (kΩ) R1 (kΩ)

0.6 R2 short, R3 open R2 short, R3 open 1.5

0.8 19.6 75 1.5

0.9 29.4 113 1.5

1.0 39.2 150 1.5

1.1 49.9 187 1.5

1.2 59.0 221 1.5

1.3 68.1 261 1.5

1.4 78.7 301 2.2

1.5 88.7 332 2.7

1.8 118 442 3.0/3.3

1.85 124 464 3.0/3.3

2.0 137 523 3.0/3.3

2.5 187 715 3.9/4.2

3 237 887 4.9

3.3 267 1000 5.6

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 31

Table 8: Surface Mount Capacitors.

Value Voltage Temp. Case

Manufacturer Part Number (µF) Rating Co. Size

Murata GRM21BR61A106KE19 10 10 X5R 0805

Murata GRM188R60J475KE19 4.7 6.3 X5R 0603

Murata GRM188R61A225KE34 2.2 10 X5R 0603

Murata GRM188R60J225KE19 2.2 6.3 X5R 0603

Murata GRM188R61A105KA61 1.0 10 X5R 0603

Murata GRM185R60J105KE26 1.0 6.3 X5R 0603

AAT2552

Total Power Solution for Portable Applications

32 2552.2007.04.1.0

Ordering Information

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.

Package Marking1Part Number (Tape and Reel)2

TDFN34-16 UVXYY AAT2552IRN-CAE-T1

1. XYY = assembly and date code.

2. Sample stock is generally held on part numbers listed in BOLD.

Legend

Voltage Code

Adjustable A

(0.6)

0.9 B

Adjustable

(1.2) E

1.5 G

1.8 I

1.9 Y

2.5 N

2.6 O

2.7 P

2.8 Q

2.85 R

2.9 S

3.0 T

3.3 W

4.2 C

AAT2552

Total Power Solution for Portable Applications

2552.2007.04.1.0 33

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

Package Information1

TDFN34-16

All dimensions in millimeters.

3.000

0.050 1.600

0.050

0.050 0.229

0.051

(4x)

0.850 MAX

4.000

0.050

3.300

0.050

Index Area

Detail "A"

Top View Bottom View

Side View

0.350

0.100

0.230

0.0500.450

0.050

Detail "A"

Pin 1 Indicator

(optional)

C0.3

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.