Rainbow Electronics MAX8903A User Manual

General Description

The MAX8903A is an integrated 1-cell Li+ charger and
Smart Power Selector™ with dual (AC adapter and
USB) power inputs. The switch mode charger uses a
high switching frequency to eliminate heat and allow
tiny external components. It can operate with either
separate inputs for USB and AC adapter power, or from
a single input that accepts both. All power switches for
charging and switching the load between battery and
external power are included on-chip. No external
MOSFETs, blocking diodes, or current-sense resistors
are required.

The MAX8903A features optimized smart power control
to make the best use of limited USB or adapter power.
Battery charge current and SYS output current limit are
independently set. Power not used by the system
charges the battery. Charge current and SYS output
current limit can be set up to 2A while USB input cur­rent can be set to 100mA or 500mA. Automatic input
selection switches the system from battery to external
power. The DC input operates from 4.15V to 16V with
up to 20V protection, while the USB input has a range
of 4.1V to 6.3V with up to 8V protection.

The MAX8903A internally blocks current from the bat­tery and system back to the DC and USB inputs when
no input supply is present. Other features include pre­qual charging and timer, fast charge timer, overvoltage
protection, charge status and fault outputs, power-OK
monitors, and a battery thermistor monitor. In addition,
on-chip thermal limiting reduces battery charge rate
and AC adapter current to prevent charger overheat­ing. The MAX8903A is available in a 4mm x 4mm, 28-pin
thin QFN package.

Applications

PDAs, Palmtops, and Wireless Handhelds

Personal Navigation Devices

Smart Cell Phones

Portable Multimedia Players

Mobile Internet Devices

Ultra Mobile PCs

Features

♦ Efficient DC-DC Converter Eliminates Heat

♦ 4MHz Switching for Tiny External Components

♦ Instant On—Works with No Battery or Low

Battery

♦ Dual Current-Limiting Input Circuits—AC Adapter

or USB

Automatic Adapter/USB/Battery Switchover to

Support Load Transients
50mΩ System-to-Battery Switch
Supports USB Spec

♦ Thermistor Monitor

♦ Integrated Current-Sense Resistor

♦ No External MOSFETS or Diodes

♦ 4.1V to 16V Input Operating Voltage Range

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

________________________________________________________________

Maxim Integrated Products

1

19-4410; Rev 0; 12/08

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

Pin Configuration appears at end of data sheet.

Typical Operating Circuit

*Protected by US Patent #6,507,172.

Smart Power Selector is a trademark of Maxim Integrated
Products, Inc.

Ordering Information

+

Denotes a lead(Pb)-free/RoHS-compliant package.

**

EP = Exposed pad.

PART TEMP RANGE PIN-PACKAGE

MAX8903AETI+ -40°C to +85°C

28 Thin QFN-EP**

AC

ADAPTER

OR USB

USB

DC

USB

LX

PWM

STEP-DOWN

CS

SYS

LOAD

CHARGE
CURRENT

CURRENT

CHARGE AND
SYS LOAD
SWITCH

BAT

SYSTEM

LOAD

BATTERY

MAX8903A

GND

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

2 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(VDC= V

USB

= 5V, V

BAT

= 4V, circuit of Figure 2, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

(Note 1)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

ABSOLUTE MAXIMUM RATINGS

DC, LX, DCM to GND .............................................-0.3V to +20V

DC to SYS .................................................................-6V to +20V

BST to GND ...........................................................-0.3V to +26V

BST TO LX ................................................................-0.3V to +6V

USB to GND .............................................................-0.3V to +9V

USB to SYS..................................................................-6V to +9V

VL to GND ................................................................-0.3V to +6V

THM, IDC, ISET, CT to GND .........................-0.3V to (VL + 0.3V)

DOK, FLT, CEN, UOK, CHG, USUS,

BAT, SYS, IUSB, CS to GND ................................-0.3V to +6V

SYS to BAT ...............................................................-0.3V to +6V

PG, EP (exposed pad) to GND .............................-0.3V to +0.3V

DC Continuous Current (total in two pins)......................2.4A

RMS

USB Continuous Current.......................................................1.6A

LX Continuous Current (total in two pins).......................2.4A

RMS

CS Continuous Current (total in two pins) ......................2.4A

RMS

SYS Continuous Current (total in two pins) .......................3A

RMS

BAT Continuous Current (total in two pins) .......................3A

RMS

Continuous Power Dissipation (TA= +70°C)

28-Pin Thin QFN-EP

Multilayer (derate 28.6mW/°C above +70°C) ..........2286mW

28-Pin Thin QFN-EP

Single-Layer (derate 20.8mW/°C above +70°C)...1666.7mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature Range ............................-40°C to +150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

DC INPUT

DC Operating Range 4.15 16 V

DC Undervoltage Threshold

DC Overvoltage Threshold

DC Supply Current

DC High-Side Resistance 0.15 Ω

DC Low-Side Resistance 0.15 Ω

DC-to-BAT Dropout Resistance 0.31 Ω

DC-to-BAT Dropout Voltage

Switching Frequency

DC Step-Down Output Current­Limit Step Range

DC Step-Down Output Current
Limit

DC Soft-Start Time

PARAMETER CONDITIONS MIN TYP MAX UNITS

When V
rising, 500mV typical hysteresis

When V
hysteresis

Charger enabled, no switching, V

Charger enabled, f = 3MHz, VDC = 5V 15

C har g er enab l ed , V

C har g er enab l ed , V

V

DCM

When SYS regulation and charging stops, V
200mV hysteresis

VDC = 8V, V

V

DC

V

DC

No valid USB input 1 ms

Valid USB input before soft-start 20 µs

goes low, V

DOK

goes high, VDC rising, 500mV typical

DOK

= 0V, V

USUS

= 4V 4

BAT

= 5V, V

= 6V, V

= 3V 3

BAT

= 4V

SYS

DC

= 0V , 100m A U S B m od e ( N ote 2) 1 2

C E N

= 5V , 100m A U S B m od e ( N ote 2) 1 2

C E N

= 5V 0.10 0.25

No valid USB input 3.9 4.0 4.1

Valid USB input 4.0 4.3 4.4

16.5 17 17.5 V

= 5V 2.3 4

SYS

falling,

DC

R

= 3kΩ 1900 2000 2100

IDC

R

= 6kΩ 950 1000 1050

IDC

= 12kΩ 450 500 550

R

IDC

01530mV

0.5 2 A

V

mA

MHz

mA

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDC= V

USB

= 5V, V

BAT

= 4V, circuit of Figure 2, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

(Note 1)

DC Output Current
500mA USB Mode
(Note 3)

DC Output Current
100mA USB Mode
(Note 2)

SYS to DC Reverse Current
Blocking

USB INPUT

USB Operating Range 4.1 6.3 V

USB Standoff Voltage 8V

USB Undervoltage Threshold When V

USB Overvoltage Threshold When V

USB Current Limit

Minimum USB to BAT Headroom 0 15 30 mV

USB to SYS Dropout Resistance 0.2 0.35 Ω

USB Soft-Start Time

SYS OUTPUT

Minimum SYS Regulation Voltage I

Regulation Voltage I

Load Regulation I

CS to SYS Resistance VDC = 6V, V

SYS to CS Leakage V

BAT to SYS Resistance VDC = V

BAT to SYS Reverse Regulation
Voltage

SYS Undervoltage Threshold SYS falling, 200mV hysteresis (Note 4) 1.8 1.9 2.0 V

BATTERY CHARGER

BAT Regulation Voltage I

Charger Restart Threshold Change in V

BAT Prequal Threshold V

Prequal Charge Current Percentage of fast-charge current set at ISET 10 %

PARAMETER CONDITIONS MIN TYP MAX UNITS

V

= 0V, V

DCM

V

= 0V, V

DCM

V

= 5.5V, VDC = 0V 0.01 µA

SYS

UOK

UOK

V

= 0V (100mA setting) 90 95 100

IUSB

V

= 5V (500mA setting) 450 475 500

IUSB

I

= I

SYS

BAT

I

= I

SYS

BAT

= 5V (USB suspend mode) 0.115 0.25

V

USUS

V

rising 1 ms

USB

falling below DC UVLO to initiate USB soft-start 20 µs

V

DC

= 1A, V

SYS

= 0A 4.3 4.4 4.5 V

SYS

= 0 to 2A 40 mV/A

SYS

= 5.5V, VDC = VCS = 0V 0.01 µA

SYS

USB

V

= 5V, VDC = 0V, V

USB

= 0mA

BAT

rising, 180mV hysteresis 2.9 3 3.1 V

BAT

= 5V 450 475 500 mA

IUSB

= 0V 90 95 100 mA

IUSB

goes low, V

goes high, V

= 0mA, V

= 0mA, V

< V

BAT

SYS_MIN

= 5V, V

DCM

= 0V, V

BAT

rising, 500mV hysteresis 3.95 4.0 4.05 V

USB

rising, 500mV hysteresis 6.8 6.9 7.0 V

USB

= 0V 1.3 3

CEN

= 5V 0.8 2USB Supply Current

CEN

3.0 V

= 4V, ICS = 1A 0.07 Ω

SYS

= 4.2V, I

IUSB

= 1A 0.05 0.1 Ω

SYS

= 0V, I

= 200mA 50 75 100 mV

SYS

TA = +25°C 4.179 4.2 4.221

= -40°C to +85°C 4.158 4.2 4.242

T

A

from DONE to fast-charge -150 -100 -60 mV

BAT

mA

mA

V

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VDC= V

USB

= 5V, V

BAT

= 4V, circuit of Figure 2, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

(Note 1)

DONE Threshold Percentage of fast-charge, I

R

ISET

ISET Output Voltage 1.5 V

ISET Current Monitor Gain 1.25 mA/A

BAT Leakage Current

Charger Soft-Start Time 1.0 ms

Charger Thermal Limit
Temperature

Charger Thermal Limit Gain Charge current = 0 at + 120°C 5 %/°C

CHARGER TIMER

Prequalification Time CCT = 0.15µF 33 min

Fast-Charge Time CCT = 0.15µF 660 min

Timer Accuracy -15 +15 %

Timer Extend Current Threshold

Timer Suspend Current Threshold

Charge Done Delay Time

THERMISTOR MONITOR

THM Threshold, Hot When charging is suspended, 1% hysteresis

THM Threshold, Cold When charging is suspended, 1% hysteresis

THM Threshold, Disabled THM function is disabled below this voltage

THM Input Leakage

THERMAL SHUTDOWN, VL, AND LOGIC I/O: CHG, FLT, DOK, UOK, DCM, CEN, USUS, IUSB

Logic-Input Thresholds
(DCM, CEN, USUS, IUSB)

Logic-Input Leakage Current
(DCM, CEN, USUS, IUSB)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Resistor Range 0.6 2.4 kΩ

R

= 600Ω 1800 2000 2200

ISET

R

= 1.2kΩ 900 1000 1100Fast-Charge Current

ISET

= 2.4kΩ 450 500 550

R

ISET

decreasing 10 %

BAT

No DC or USB input 0.05 4

With valid input power, V

Percentage of fast-charge current below which the timer
clock operates at half-speed

Percentage of fast-charge current below which timer
clock pauses

From done threshold detection until charger turns off and
CHG goes high

THM = GND or VL; TA = +25°C -0.1 +0.001 +0.2

THM = GND or VL; T

High level 1.3

Low level 0.4

Hysteresis 50 mV

= 0 to 5.5V

V

INPUT

= 5V 1 6

CEN

40 50 60 %

16 20 24 %

0.27 x
V

0.73 x
V

0.0254
x V

= +85°C 0.01

A

TA = +25°C 0.001 1

T

= +85°C 0.01

A

0.28 x

VL

0.74 x

VL

0.03 x

VL

100 °C

15 s

0.29 x

V

V

V

VL

VL

VL

V

0.75 x
V

0.036 x
V

VL

VL

VL

mA

µA

V

V

V

µA

V

µA

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

(VDC= V

USB

= 5V, V

BAT

= 4V, circuit of Figure 2, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

(Note 1)

Note 1: Limits are 100% production tested at T

A

= +25°C. Limits over the operating temperature range are guaranteed by design.

Note 2: For the 100mA USB mode using the DC input, the step-down regulator is turned off and a low-dropout linear regulator is

connected from DC to SYS.

Note 3: For the 500mA USB mode, the actual current drawn from USB is less than the output current due to the input/output current

ratio of the DC-DC converter.

Note 4: For short-circuit protection, SYS sources 25mA below V

SYS

= 400mV, and 50mA for V

SYS

between 400mV and 2V.

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

Logic Output Voltage, Low
(CHG, FLT, DOK, UOK)

Open-Drain Output Leakage
C ur rent, Hi g h (CHG , FLT, DOK, UOK)

VL Output Voltage VDC = V

VL UVLO Threshold VVL falling; 200mV hysteresis 3.2 V

Thermal Shutdown Temperature 160 °C

Thermal Shutdown Hysteresis 15 °C

PARAMETER CONDITIONS MIN TYP MAX UNITS

Sinking 1mA 8 50

Sinking 10mA 80

V

OUT

= 5.5V

= 6V, I

USB

= 0 to 1mA 4.6 5 5.4 V

VL

TA = +25°C 0.001 1

T

= +85°C 0.01

A

mV

µA

BATTERY CHARGER EFFICIENCY

vs. BATTERY VOLTAGE

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

VDC = 5V

VDC = 8V

VDC = 12V

I

= 0.15A

BATT

1.0 2.0 2.51.5 3.0 3.5 4.0 4.5 5.0
BATTERY VOLTAGE (V)

I

BATT

I

BATT

= 1.5A

= 1.5A

4.5

4.0

MAX8903A toc01

3.5

3.0

2.5

2.0

1.5

1.0

SWITCHING FREQUENCY (MHz)

0.5

0.0
486 10121416

SWITCHING FREQUENCY

vs. V

DC

V

= 3V

BAT

V

= 4V

BAT

R

ISET

CEN = 0V

DC VOLTAGE (V)

= 1.2kΩ

100

MAX8903A toc02

SYS EFFICIENCY (%)

SYS EFFICIENCY vs. DC VOLTAGE

90

80

70

60

50

40

30

20

10

0

1 10,000

SYS OUTPUT CURRENT (mA)

VDC = 16V

VDC = 11V

VDC = 6V

VDC = 4.5V

100010010

MAX8903A toc03

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

0

0.4

0.2

0.8

0.6

1.4

1.2

1.0

1.6

021 34567

USB QUIESCENT CURRENT

vs. USB VOLTAGE

MAX8903A toc04

USB VOLTAGE (V)

USB QUIESCENT CURRENT (mA)

CHARGER
ENABLED

CHARGER
DISABLED

0

40

20

80

60

120

100

140

0231 4567

USB QUIESCENT CURRENT

vs. USB VOLTAGE

MAX8903A toc05

USB VOLTAGE (V)

USB QUIESCENT CURRENT (μA)

USB SUSPEND

0

1.5

1.0

0.5

2.5

2.0

4.5

4.0

3.5

3.0

5.0

01234567

SYS VOLTAGE vs. USB VOLTAGE

MAX8903A toc12

USB VOLTAGE (V)

SYS VOLTAGE (V)

V

USB

FALLING

V

USB

RISING

R

SYS

= 1MΩ

80

70

60

50

40

30

20

BATTERY LEAKAGE CURRENT (nA)

10

BATTERY LEAKAGE CURRENT

vs. BATTERY VOLTAGE

MAX8903A toc06

USB UNCONNECTED

0

0456321

BATTERY VOLTAGE (V)

BATTERY LEAKAGE CURRENT

vs. AMBIENT TEMPERATURE

90

80

70

60

50

40

30

20

BATTERY LEAKAGE CURRENT (nA)

10

0

-40 35 60-15 10 85

NORMALIZED CHARGE CURRENT

vs. AMBIENT TEMPERATURE

1.015
V

= 5V, V

USB

1.010

1.005

1.000

0.995

NORMALIZED CHARGE CURRENT

0.990

0.985

-40 85

TEMPERATURE (°C)

= 4V

BATT

TEMPERATURE (°C)

CHARGE CURRENT

vs. BATTERY VOLTAGE—DC MODE

SET TO 1.5A

BAT

SET TO 1A

DC

BATTERY VOLTAGE (V)

MAX8903A toc09

500

450

400

MAX8903A toc07

350

300

250

200

150

CHARGE CURRENT (mA)

100

50

0

CHARGE CURRENT

vs. BATTERY VOLTAGE—USB

CHARGER ENABLED

SET TO 1.5A

I

BAT

V

= V

IUSB

USB

V

= 0V

IUSB

042135

BATTERY VOLTAGE (V)

1000

900

800

MAX8903A toc08

700

600

500

400

300

CHARGE CURRENT (mA)

200

100

0

CHARGER ENABLED
I
I

042315

BATTERY REGULATION VOLTAGE

vs. AMBIENT TEMPERATURE

4.205

4.200

MAX8903A toc10

4.195

4.190

4.185

BATTERY REGULATION VOLTAGE (V)

4.180

603510-15

-40 85
TEMPERATURE (°C)

603510-15

MAX8903A toc11

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

_______________________________________________________________________________________ 7

Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

4.355

4.365

4.360

4.375

4.370

4.380

4.385

4.395

4.390

4.400

0 10050 200150 300250 400350 500450

SYS VOLTAGE

vs. SYS OUTPUT CURRENT, USB INPUT

MAX8903A toc15

SYS OUTPUT CURRENT (mA)

SYS VOLTAGE (V)

V

USB

= 5V

0

1

2

3

4

5

6

042 6 8 1012141618

VL VOLTAGE vs. DC VOLTAGE

MAX8903A toc16

DC VOLTAGE (V)

VL VOLTAGE (V)

DC SWITCHING

WAVEFORMS—HEAVY LOAD

MAX8903A toc20

200ns/div

V

LX

V

OUT

I

LX

5V/div
0V

20mV/div
AC-COUPLED

500mA/div

0A

R

SYS

= 5Ω

SYS VOLTAGE

vs. DC VOLTAGE

5.0

4.5

4.0

3.5

3.0

2.5

2.0

SYS VOLTAGE (V)

1.5

1.0

0.5

0

0 4682 1012141618

VDC RISING

VDC FALLING

DC VOLTAGE (V)

MAX8903A toc13

vs. SYS OUTPUT CURRENT, DC INPUT

4.50

4.40

4.30

4.20

4.10

SYS VOLTAGE (V)

4.00

3.90

3.80
0 0.3 0.50.1 0.7 0.9 1.1 1.3 1.5

CHARGE PROFILE—1400mAh BATTERY

6.0

5.5

5.0

4.5

4.0

3.5

(V)

3.0

BAT

V

2.5

2.0

1.5

1.0

0.5
0

0 140

SYS VOLTAGE

VDC = 5.75V

USB AND DC UNCONNECTED

= 4V

V

BATT

SYS OUTPUT CURRENT (A)

ADAPTER INPUT—1A CHARGE

IDC SET TO 1A

SET TO 2A

I

BAT

I

BAT

TIME (min)

V

MAX8903A toc17

BAT

MAX8903A toc14

CHARGE PROFILE—1400mAh BATTERY

USB INPUT—500mA CHARGE

1.2

1.0

0.8

0.6

0.4

0.2

0.0

12010060 804020

5.0

4.5

4.0

3.5

3.0

(V)

(A)

2.5

BAT

BAT

I

V

2.0

1.5

1.0

0.5

0

0 200

V

BAT

I

SET TO 500mA

USB

SET TO 2A

I

BAT

TIME (min)

I

MAX8903A toc18

BAT

180160120 14040 60 80 10020

0.500

0.450

0.400

0.350

0.300
(A)

0.250

BAT

I

0.200

0.150

0.100

0.050

0

V

OUT

V

DC SWITCHING WAVEFORMS—LIGHT LOAD

LX

I

LX

200ns/div

MAX8903A toc19

R

SYS

= 44Ω

20mV/div
AC-COUPLED

5V/div

0V

500mA/div
0A

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

400μs/div

DC CONNECT WITH NO USB

(R

SYS

= 25Ω)

2V/div

MAX8903A toc22

5V/div

1A/div

1A/div

3.6V

3.84V

3.6V

3.44V

C

DC

CHARGING

C

SYS

CHARGING

850mA

-1A

BATTERY
CHARGER
SOFT-START

144mA

0A

V

SYS

V

BAT

I

DC

I

BAT

-I

BAT

= CHARGING

40μs/div

DC DISCONNECT WITH NO USB

(R

SYS

= 25Ω)

2V/div

MAX8903A toc23

5V/div

1A/div

1A/div

3.6V

3.68V

850mA

-1A

144mA

0A

V

SYS

V

BAT

I

DC

I

BAT

3.6V

-I

BAT

= CHARGING

100μs/div

USB DISCONNECT WITH NO DC

(R

SYS

= 25Ω)

2V/div

MAX8903A toc26

5V/div

500mA/div

500mA/div

3.6V

475mA

V

SYS

V

USB

I

USB

I

BAT

5V

144mA

-330mA

DC CONNECT WITH

USB CONNECTED (R

SYS

= 25Ω)

MAX8903A toc21

3.6V

V

SYS

I

DC

475mA

I

USB

-I

BAT

I

-335mA

BAT

200μs/div

SYS LOAD TRANSIENT

(0 TO 1A)

V

SYS

I

SYS

100µs/div

347mA

= CHARGING

MAX8903A toc24

2V/div

500mA/div

500mA/div

0A
500mA/div

50mV/div
AC COUPLED

500mA/div

0A

USB CONNECT WITH NO DC

(R

= 25Ω)

SYS

144mA

3.6V

C
CHARGING

3.5V

USB

BATTERY
CHARGER
SOFT-START

400μs/div

V

SYS

V

USB

I

USB

I

BAT

3.75V

5V

475mA

MAX8903A toc25

2V/div

5V/div

500mA/div

500mA/div

-330mA

V

USUS

V

I

USB

SYS

I

BAT

0V

475mA

3.7V

-475mA

USB SUSPEND

3V

0A

0A

200μs/div

MAX8903A toc27

5V/div

500mA/div

2V/div

500mA/div

V

USUS

I

USB

V

SYS

I

BAT

3V

0A

3.6V

0A

C

USB

CHARGING

BATTERY
CHARGER
SOFT-START

USB RESUME

0V

3.8V

200μs/div

MAX8903A toc28

475mA

3.6V

-475mA

5V/div

500mA/div

2V/div

500mA/div

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

_______________________________________________________________________________________ 9

Pin Description

PIN NAME FUNCTION

1, 2 PG

3, 4 DC

5 DCM

6 BST High-Side MOSFET Driver Supply. Bypass BST to LX with a 0.1µF ceramic capacitor.

7 IUSB

8 DOK

9VL

10 CT

11 IDC

12 GND Ground. GND is the low-noise ground connection for the internal circuitry.

13 ISET

14 CEN

15 USUS

Power Ground for Step-Down Low-Side Synchronous n-Channel MOSFET. Both PG pins must be
connected together externally.

DC Power Input. DC is capable of delivering up to 2A to SYS. DC supports both AC adapter and USB
inputs. The DC current limit is set through DCM, IUSB, or IDC depending on the input source used. See
Table 2. Both DC pins must be connected together externally. Connect at least a 4.7µF ceramic capacitor
from DC to PG.

Current-Limit Mode Setting for the DC Power Input. When logic-high, the DC input current limit is set by
the resistor at IDC. When logic-low, the DC input current limit is internally programmed to 500mA or
100mA, as set by the IUSB pin.

USB Current-Limit Set Input. Drive IUSB logic-low to set the USB current limit to 100mA. Drive IUSB logic­high to set the USB current limit to 500mA.

DC Power-OK Output. Active-low open-drain output pulls low when a valid input is detected at DC. DOK
is still valid when the charger is disabled (CEN high).

Logic LDO Output. VL is the output of an LDO that powers the MAX8903A internal circuitry and charges
the BST capacitor. Connect a 1µF ceramic capacitor from VL to GND.

Charge Timer Set Input. A capacitor (C
Connect to GND to disable the timer.

DC Current-Limit Set Input. Connect a resistor (R
step-down regulator from 0.5A to 2A when DCM is logic-high.

Charge Current Set Input. A resistor (R
The prequal charge current is 10% of the fast-charge current.

Charger Enable Input. Connect CEN to GND to enable battery charging when a valid source is connected
at DC or USB. Connect to VL, or drive high to disable battery charging.

USB Suspend Input. Drive USUS logic-high to enter USB suspend mode, lowering USB current to 115µA,
and internally shorting SYS to BAT.

) from CT to GND sets the fast-charge and prequal fault timers.

CT

) from IDC to GND to program the current limit of the

IDC

) from ISET to GND programs the fast-charge current up to 2A.

ISET

16 THM

17 USB

18 FLT

19 UOK

20, 21 BAT

Thermistor Input. Connect a negative temperature coefficient (NTC) thermistor from THM to GND.
Connect a resistor equal to the thermistor +25°C resistance from THM to VL. Charging is suspended
when the thermistor is outside the hot and cold limits. Connect THM to GND to disable the thermistor
temperature sensor.

USB Power Input. USB is capable of delivering 100mA or 500mA to SYS as set by the IUSB logic input.
Connect a 4.7µF ceramic capacitor from USB to GND.

Fault Output. Active-low, open-drain output pulls low when the battery timer expires before prequal or
fast-charge completes.

USB Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at USB.
UOK is still valid when the charger is disabled (CEN high).

Battery Connection. Connect to a single-cell Li+ battery. The battery charges from SYS when a valid
source is present at DC or USB. BAT powers SYS when neither DC nor USB power is present, or when the
SYS load exceeds the input current limit. Both BAT pins must be connected together externally.

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

10 ______________________________________________________________________________________

Pin Description (continued)

PIN NAME FUNCTION

22 CHG

23, 24 SYS

25, 26 CS

Charger Status Output. Active-low, open-drain output pulls low when the battery is in fast-charge or
prequal. Otherwise, CHG is high impedance.

System Supply Output. SYS connects to BAT through an internal 50mΩ system load switch when DC or
USB are invalid, or when the SYS load is greater than the input current limit.
When a valid voltage is present at DC or USB, SYS is limited to 4.4V. When the system load (I
exceeds the DC or USB current limit, SYS is regulated to 50mV below BAT, and both the powered input
and the battery service SYS.
Bypass SYS to GND with a 10µF X5R or X7R ceramic capacitor. Both SYS pins must be connected
together externally.

70mΩ Current-Sense Input. Connect the step-down inductor from LX to CS. When the step-down
regulator is on, there is a 70mΩ current-sense MOSFET from CS to SYS. When the step-down regulator is
off, the internal CS MOSFET turns off to block current from SYS back to DC.

SYS

)

27, 28 LX

—EP

Inductor Connection. Connect the inductor between LX and CS. Both LX pins must be connected together
externally.

Exposed Pad. Connect the exposed pad to GND. Connecting the exposed pad does not remove the
requirement for proper ground connections to the appropriate pins.

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

MAX8903A

ADAPTER

USB

PG

DC POWER

EMENT

MANAG

DOK

USB

UOK

DC

PWR

OK

STEP-DOWN

REGULA

USB POWER

EMENT

MANAG

PWR

OK

CURRENT-

REGULATOR

AC

LX

PWM

TOR

SET
INPUT
LIMIT

LIMITED

VOLTAGE

SET
INPUT
LIMIT

BST

CS

IC

THERMAL

REGULATION

MAX8903A

Li+ BATTERY

CHARGER

AND SYS LOAD SWITCH

CHARGER

CURRENT-

VOLTAGE

CONTROL

THERMISTOR

MONITOR

(SEE FIGURE 7)

CHARGE

TERMINATION

AND MONITOR

SYS

ISET

BAT

THM

VL

CHG

TO
SYSTEM
LOAD

BATTERY

CONNECTOR

BAT+

BAT-

NTC

+

T

USB

SUSPEND

DC

LIMIT

DCM

IUSB

USUS

IDC

USB
LIMIT

DC MODE

500mA

100mA

Figure 1. Functional Block Diagram

______________________________________________________________________________________ 11

INPUT AND

CHARGER

CURRENT-LIMIT

SET LOGIC

FLT

CHARGE

TIMER

EP

CT

CEN

GND

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

12 ______________________________________________________________________________________

Circuit Description

The MAX8903A is a dual input charger with a 16V input
for a wide range of DC sources and USB inputs. The IC
includes a high-voltage (16V) input DC-DC step-down
converter that reduces charger power dissipation while
also supplying power to the system load. The step­down converter supplies up to 2A to the system, the
battery, or a combination of both.

A USB charge input can charge the battery and power
the system from a USB power source. When powered
from USB or the DC input, system load current peaks
that exceed what can be supplied by the input are sup­plemented by the battery.

The MAX8903A also manages load switching from the
battery to and from an external power source with an
on-chip 50mΩ MOSFET. This switch also helps support
load peaks using battery power when the input source
is overloaded.

Figure 2. Typical Application Circuit Using a Separate DC and USB Connector

R

PU

4 x 100kΩ

1

PG

2

ADAPTER

USB

VBUS

GND

C

4.7μF

C

0.1μF

L1

1μH

DC

BST

C

USB

4.7μF

PG

3

DC

DC

4

6

BST

LX

27

LX

28

CS

25

CS

26

17 USB

MAX8903A

FLT

UOK

DOK

CHG

ISET

IDC

SYS

SYS

BAT

BAT

18

19

8

22

R

ISET

13

R

IDC

11

24

C

23

21

20

10μF

C

BAT

10μF

SYS

TO VL

FAULT
OUTPUT

USB PWR OK

DC PWR OK

CHARGE
INDICATOR

TO SYSTEM
LOAD

1-CELL
LI+

5

OFF

CHARGE ON

500mA

100mA

USB SUSPEND

C

0.15μF

TO VL

CT

DCM

14

CEN

7

IUSB

15

USUS

10

CT

THM

GND

9

VL

RT

16

12

10kΩ

NTC
10kΩ

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

______________________________________________________________________________________ 13

The IC includes a full-featured charger with thermistor
monitor, fault timer, charger status, and fault outputs.
Also included are power-OK signals for both USB and
DC. Flexibility is maintained with adjustable charge
current, input current limit, and a minimum system volt­age (when charging is scaled back to hold the system
voltage up).

The MAX8903A prevents overheating during high ambi­ent temperatures by limiting charging current when the
die temperature exceeds +100°C.

DC Input—Fast Hysteretic

Step-Down Regulator

If a valid DC input is present, the USB power path is
turned off and power for SYS and battery charging is
supplied by the high-frequency step-down regulator
from DC. If the battery voltage is above the minimum
system voltage (V

SYSMIN

, Figure 4), the battery charger
connects the system voltage to the battery for lowest
power dissipation. The step-down regulation point is
then controlled by three feedback signals: maximum

Figure 3. Typical Application Circuit Using a Mini 5 Style Connector or Other DC/USB Common Connector

SERIES
MINI-B

VBUS

GND

D-

D+

ID

4.7μF

TO SYSTEM LOGIC

OFF

CHARGE ON

500mA

100mA

USB SUSPEND

C

DC

C

BST

0.1μF

L1

1μH

0.15μF

R

PU

4 x 100kΩ

1

PG

2

PG

MAX8903A

3

DC

DC

4

6

BST

LX

27

LX

28

CS

25

CS

26

17 USB

5

DCM

14

CEN

7

IUSB

15

USUS

10

C

CT

CT

FLT

UOK

DOK

CHG

ISET

SYS

SYS

BAT

BAT

THM

GND

IDC

18

19

8

22

R

ISET

13

R

IDC

11

24

C

C
1μF

SYS

10μF

C

BAT

10μF

VL

23

21

20

9

VL

16

12

RT
10kΩ

NTC
10kΩ

TO VL

FAULT
OUTPUT

USB PWR OK

DC PWR OK

CHARGE
INDICATOR

TO SYSTEM
LOAD

1-CELL
LI+

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

14 ______________________________________________________________________________________

step-down output current programmed at IDC, maxi­mum charger current programmed at ISET, and maxi­mum die temperature. The feedback signal requiring
the smallest current controls the average output current
in the inductor. This scheme minimizes total power dis­sipation for battery charging and allows the battery to
absorb any load transients with minimum system volt­age disturbance.

If the battery voltage is below V

SYSMIN

, the charger
does not directly connect the system voltage to the bat­tery. V

SYS

pin is held at a fixed point slightly above

V

SYSMIN

, and does not track the battery. The battery
charger independently controls the battery charging
current. V

SYSMIN

is set to 3.0V in the MAX8903A, for

other V

SYSMIN

values, please contact the factory.

After the battery charges to 50mV above V

SYSMIN

, the
system voltage is connected to the battery. The battery
fast-charge current then controls the step-down con­verter to set the average inductor current so that both
the programmed input current limit and fast-charge cur­rent limit are satisfied.

DC-DC Step-Down Control Scheme

A proprietary hysteretic current PWM control scheme
ensures fast switching and physically tiny external com­ponents. The feedback control signal that requires the
smallest input current controls the center of the peak
and valley currents in the inductor. The ripple current is
internally set to provide 4MHz operation. When the
input voltage decreases near the output voltage, very
high duty cycle occurs and, due to minimum off-time,
4MHz operation is not achievable. The controller then
provides minimum off-time, peak current regulation.

Similarly, when the input voltage is too high to allow
4MHz operation due to the minimum on-time, the con­troller becomes a minimum on-time, valley current regu­lator. In this way, ripple current in the inductor is always
as small as possible to reduce ripple voltage on SYS for
a given capacitance. The ripple current is made to vary
with input voltage and output voltage in a way that
reduces frequency variation. However, the frequency
still varies somewhat with operating conditions. See the

Typical Operating Characteristics

.

DC Input—USB mode

When powering from DC with DCM set to logic-low, the
DC input is set to USB mode. The input current limit from
DC is then internally set to 500mA max if IUSB is high
and 100mA max if IUSB is low. For the 500mA case, the
DC input continues to operate as a step-down regulator
to minimize thermal heating. For the 100mA case, the

Table 1. External Components List for Figures 2 and 3

Figure 4. SYS Tracking V

BAT

to the Minimum System Voltage

COMPONENT

(FIGURES 2 AND 3)

CDC, C

USB

C

VL

C

SYS

C

BAT

C

CT

RPU (X4) Logic output pullup resistors 100kΩ

THM Negative TC thermistor

R

T

R

IDC

R

ISET

L1 DC input step-down inductor 1µH inductor with I

Input filter capacitor 4.7µF ceramic capacitor

VL filter capacitor 1.0µF ceramic capacitor

SYS output bypass capacitor 10µF ceramic capacitor

Battery bypass capacitor 10µF ceramic capacitor

Charger timing capacitor 0.15µF low TC ceramic capacitor

THM pullup resistor 10kΩ

DC input current-limit programming resistor 3kΩ ±1%, for 2A limit

Fast-charge current programming resistor 1.2kΩ ±1%, for 1A charging

FUNCTION PART

Phillips NTC thermistor, P/N 2322-640-63103, 0kΩ
±5% at +25°C

SAT

> 2A

4.4V

4.2V

V

SYS

I

x R

BAT

V

SYSMIN

V

BAT

ON

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

______________________________________________________________________________________ 15

step-down regulator is turned off and a low-dropout lin­ear regulator is connected between DC and SYS.

USB Input—Linear Regulator

If a valid USB input is present with no valid DC input,
current for SYS and battery charging is supplied by a
low-dropout linear regulator connected from USB to
SYS. The SYS regulation voltage shows the same char­acteristic as when powering from the DC input (see
Figure 4). The battery charger operates from SYS with
any extra available current, while not exceeding the
maximum-allowed USB current. If both USB and DC
inputs are valid, power is only taken from the DC input.
The maximum USB input current is set by the logic
state of the IUSB input to either 100mA or 500mA.

Power Monitor Outputs (

UOK, DOK

)

DOK is an open-drain, active-low output that indicates
the DC input power status. With no source at the USB
pin, the source at DC is considered valid and DOK is
driven low when: 4.15V < VDC< 16V. When the USB
voltage is also valid, the DC source is considered valid
and DOK is driven low when: 4.45V < VDC< 16V. The
higher minimum DC voltage with USB present helps
guarantee cleaner transitions between input supplies. If
the DC power-OK output feature is not required, con­nect DOK to ground.

UOK is an open-drain, active-low output that indicates
the USB input power status. UOK is low when a valid
source is connected at USB. The source at USB is valid
when 4.1V < V

USB

< 6.6V. If the USB power-OK output

feature is not required, connect UOK to ground.
Both the UOK and the DOK circuitry remain active in

thermal overload, USB suspend, and when the charger
is disabled. DOK and UOK can also be wire-ORed
together to generate a single power-OK (POK) output.

Thermal Limiting

When the die temperature exceeds +100°C, a thermal
limiting circuit reduces the input current limit by 5%/°C,
bringing the charge current to 0mA at +120°C. Since
the system load gets priority over battery charging, the
battery charge current is reduced to 0mA before the
input limiter drops the load voltage at SYS. To avoid
false charge termination, the charge termination detect
function is disabled in this mode. If the junction temper­ature rises beyond +120°C, no current is drawn from
DC or USB, and V

SYS

regulates at 50mV below V

BAT

.

System Voltage Switching

DC Input

When charging from the DC input, if the battery is
above the minimum system voltage, SYS is connected

to the battery. Current is provided to both SYS and the
battery, up to the maximum program value. The step­down output current sense and the charger current
sense provide feedback to ensure the current loop
demanding the lower input current is satisfied. The
advantage of this approach when powering from DC is
that power dissipation is dominated by the step-down
regulator efficiency, since there is only a small voltage
drop from SYS to BAT. Also, load transients can be
absorbed by the battery while minimizing the voltage
disturbance on SYS. If both the DC and USB inputs are
valid, the DC input takes priority and delivers the input
current, while the USB input is off.

After the battery is done charging, the charger is turned
off and the SYS load current is supplied from the DC
input. The SYS voltage is regulated to 4.4V. The charg­er turns on again after the battery drops to the restart
threshold. If the load current exceeds the input limiter,
SYS drops down to the battery voltage and the 50mΩ
SYS-to-BAT PMOS switch turns on to supply the extra
load current. The SYS-to-BAT switch turns off again
once the load is below the input current limit. The 50mΩ
PMOS also turns on if valid DC input power is removed.

USB Input

When charging from the USB input, the DC input step­down regulator turns off and a linear regulator from
USB to SYS powers the system and charges the bat­tery. If the battery is greater than the minimum system
voltage, the SYS voltage is connected to the battery.
The USB input then supplies the SYS load and charges
the battery with any extra available current, while not
exceeding the maximum-allowed USB current. Load
transients can be absorbed by the battery while mini­mizing the voltage disturbance on SYS. When battery
charging is completed, or the charger is disabled, SYS
is regulated to 4.4V. If both USB and DC inputs are
valid, power is only taken from the DC input.

USB Suspend

Driving USUS high turns off charging as well as the SYS
output and reduces input current to 170µA to accom­modate USB suspend mode.

Charge Enable (

CEN

)

When CEN is low, the charger is on. When CEN is high,
the charger turns off. CEN does not affect the SYS out­put. In many systems, there is no need for the system
controller (typically a microprocessor) to disable the
charger, because the MAX8903A smart power selector
circuitry independently manages charging and
adapter/battery power hand-off. In these situations,
CEN may be connected to ground.

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

16 ______________________________________________________________________________________

Soft-Start

To prevent input transients that can cause instability in
the USB or AC adapter power source, the rate of
change of the input current and charge current is limit­ed. When an input source is valid, SYS current is
ramped from zero to the set current-limit value in typi­cally 50µs. This also means that if DC becomes valid
after USB, the SYS current limit is ramped down to zero
before switching from the USB to DC input. At some
point, SYS is no longer able to support the load and
may switch over to BAT. The switchover to BAT occurs
when V

SYS

< V

BATT

. This threshold is a function of the
SYS capacitor size and SYS load. The SYS current limit
then ramps from zero to the set current level and SYS
supports the load again as long as the SYS load current
is less than the set current limit.

When the charger is turned on, the charge current ramps
from 0A to the ISET current value in typically 1.0ms.
Charge current also soft-starts when transitioning to fast­charge from prequal, when the input power source is
switched between USB and DC, and when changing the

USB charge current from 100mA to 500mA with the IUSB
logic input. There is no di/dt limiting, however, if R

ISET

is

changed suddenly using a switch.

Battery Charger

While a valid input source is present, the battery charg­er can attempt to charge the battery with a fast-charge
current determined by the resistance at the ISET pin:

R

ISET

= 1200/I

CHG-MAX

Monitoring Charge Current

The voltage from ISET to GND is a representation of the
battery charge current and can be used to monitor the
current charging the battery. A voltage of 1.5V repre­sents the maximum fast-charge current.

If necessary, the charge current is reduced automati­cally to prevent the SYS voltage from dropping.
Therefore, a battery never charges at a rate beyond the
capabilities of a 100mA or 500mA USB input, or over­loads an AC adapter. See Figure 5.

Table 2. Input Limiter Control Logic

**

Charge current cannot exceed the input current limit. Charge may be less than the maximum charge current if the total SYS load

exceeds the input current limit.

X = Don’t care.

DC STEP-DOWN

POWER SOURCE DOK UOK DCM IUSB USUS

AC Adapter at DC Input L X H X X 6000/R

OUTPUT

CURRENT LIMIT

IDC

USB INPUT

CURRENT LIMIT

MAXIMUM

CHARGE

CURRENT**

Lesser of

1200/R

ISET

6000/R

and

IDC

USB Power at DC Input

USB Power at USB Input,
DC Unconnected

DC and USB Unconnected H H X X X

L X L L L 100mA

L X L H L 500mA

L X L X H USB suspend

H L X L L 100mA

H L X H L 500mA

H L X X H USB suspend 0

No DC input

USB input off. DC

input has priority.

No USB input 0

1200/R

1200/R

1200/R

1200/R

Lesser of

ISET

100mA

Lesser of

ISET

500mA

0

Lesser of

ISET

100mA

Lesser of

ISET

500mA

and

and

and

and

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

______________________________________________________________________________________ 17

When V

BATT

is below 3V, the charger enters prequal
mode and the battery charges at 10% of the maximum
fast-charge rate until the voltage of the deeply dis­charged battery recovers. When the battery voltage
reaches 4.2V and the charge current drops to 10% of
the maximum fast-charge current, the charger enters
the DONE state. The charger restarts a fast-charge
cycle if the battery voltage drops by 100mV.

Charge Termination

When the charge current falls to the termination thresh­old (I

TERM

) and the charger is in voltage mode, charg­ing is complete. Charging continues for a brief 15s
top-off period and then enters the DONE state where
charging stops.

Note that if charge current falls to I

TERM

as a result of
the input or thermal limiter, the charger does not enter
DONE. For the charger to enter DONE, charge current
must be less than I

TERM

, the charger must be in volt­age mode, and the input or thermal limiter must not be
reducing charge current.

Charge Status Outputs

Charge Output (CHG)

CHG is an open-drain, active-low output that indicates
charger status. CHG is low when the battery charger is
in its prequalification and fast-charge states. CHG goes
high impedance if the thermistor causes the charger to
go into temperature suspend mode.

When used in conjunction with a microprocessor (µP),
connect a pullup resistor between CHG and the logic
I/O voltage to indicate charge status to the µP.
Alternatively, CHG can sink up to 20mA for an LED
charge indicator.

Fault Output (FLT)

FLT is an open-drain, active-low output that indicates
charger status. FLT is low when the battery charger has
entered a fault state when the charge timer expires.
This can occur when the charger remains in its prequal
state for more than 33 minutes or if the charger remains
in fast-charge state for more than 660 minutes (see
Figure 6). To exit this fault state, toggle CEN or remove
and reconnect the input source.

When used in conjunction with a microprocessor (µP),
connect a pullup resistor between FLT and the logic I/O
voltage to indicate charge status to the µP.
Alternatively, FLT can sink up to 20mA for an LED fault
indicator. If the FLT output is not required, connect FLT
to ground or leave unconnected.

Charge Timer

A fault timer prevents the battery from charging indefi­nitely. The fault prequal and fast-charge timers are con­trolled by the capacitance at CT (CCT).

While in fast-charge mode, a large system load or device
self-heating may cause the MAX8903A to reduce charge
current. Under these circumstances, the fast-charge
timer is slowed by 2x if the charge current drops below
50% of the programmed fast-charge level, and suspend­ed if the charge current drops below 20% of the pro­grammed level. The fast-charge timer is not affected at
any current if the charger is regulating the BAT voltage
at 4.2V (i.e., the charger is in voltage mode).

Thermistor Input (THM)

The THM input connects to an external negative tem­perature coefficient (NTC) thermistor to monitor battery
or system temperature. Charging is suspended when
the thermistor temperature is out of range. The charge
timers are suspended and hold their state but no fault is
indicated. When the thermistor comes back into range,

Figure 5. Monitoring the Battery Charge Current with the
Voltage from ISET to GND

MONITORING THE BATTERY

CHARGE CURRENT WITH V

1.5

(V)

V

ISET

0

DISCHARGING

0

BATTERY CHARGING CURRENT (A)

ISET

1200/R

ISET

C

t

PREQUAL

t

FST CHG

−

ts

TOP OFF

−

min

=×

33

min

660

=×

15

=

CT

.

015

C
.μμ

015

F

CT

F

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

18 ______________________________________________________________________________________

charging resumes and the charge timer continues from
where it left off. Connecting THM to GND disables the
thermistor monitoring function. Table 4 lists the fault
temperature of different thermistors.

Since the thermistor monitoring circuit employs an
external bias resistor from THM to VL (R

TB

, Figure 7),

the thermistor is not limited only to 10kΩ (at +25°C).

Any resistance thermistor can be used as long as the
value is equivalent to the thermistor’s +25°C resistance.
For example, with a 10kΩ at +25°C thermistor, use
10kΩ at R

TB

, and with a 100kΩ at +25°C thermistor,

use 100kΩ .

For a typical 10kΩ (at +25°C) thermistor and a 10kΩ
RTBresistor, the charger enters a temperature suspend

Figure 6. MAX8903A Charger State Flow Chart

V

< 2.8V

BATT

RESET TIMER

ANY CHARGING

STAT E

THM OK

TIMER RESUME

TEMPERATURE SUSPEND

UOK OR DOK PREVIOUS STATE

= 0mA

I

CHG

CHG = HIGH IMPEDANCE

FLT = HIGH IMPEDANCE

THM NOT OK
TIMER SUSPEND

NOT READY

UOK AND DOK = HIGH IMPEDANCE

CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE

= 0mA

I

CHG

PREQUALIFICATION

UOK AND/OR DOK = LOW

CHG = LOW

FLT = HIGH IMPEDANCE

0 < V

BAT

≤ I

I

CHG

CHGMAX

V

< 2.82V

BATT

RESET TIMER = 0

FAST-CHARGE

UOK AND/OR DOK = LOW

CHG = LOW

FLT = HIGH IMPEDANCE

3V < V

BAT

≤ I

I

CHG

CHGMAX

> I

I

CHG

TERM

RESET TIMER

TOP-OFF

UOK AND/OR DOK = LOW
CHG = HIGH IMPEDANCE

FLT = HIGH IMPEDANCE

VBAT = 4.2V

= I

I

CHG

DONE

UOK AND/OR DOK = 0

CHG = HIGH IMPEDANCE

FLT = HIGH IMPEDANCE

4.1V < V

BAT

= 0mA

I

CHG

UOK AND/OR DOK = LOW
CEN = 0
RESET TIMER

< 3V

/10

V

> 3.0V

BATT

RESET TIMER

< 4.2V

I

CHG

AND V
AND THERMAL
OR INPUT LIMIT
NOT EXCEEDED;
RESET TIMER

TERM

TIMER > 15s

< 4.2V

CEN = HI OR
REMOVE AND RECONNECT
THE INPUT SOURCE(S)

TIMER > t

< I

TERM

= 4.2V

BAT

PREQUAL

V

< 4.1V

BAT

RESET TIMER

ANY STATE

TOGGLE CEN OR

REMOVE AND RECONNECT

THE INPUT SOURCE(S)

FAULT

UOK AND/OR DOK = LOW
CHG = HIGH IMPEDANCE

FLT = LOW

= 0mA

I

CHG

TIMER > t

FSTCHG

(TIMER SLOWED BY 2x IF

< I

CHGMAX

CHG

/2, AND

< I

CHGMAX

I

CHG

PAUSED IF I

/5 WHILE V

BAT

< 4.2V)

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*

and Adapter Power

______________________________________________________________________________________ 19

state when the thermistor resistance falls below 3.97kΩ
(too hot) or rises above 28.7kΩ (too cold). This corre­sponds to a 0°C to +50°C range when using a 10kΩ
NTC thermistor with a beta of 3500. The general relation
of thermistor resistance to temperature is defined by
the following equation:

where:

R

T

= The resistance in Ω of the thermistor at tempera-

ture T in Celsius

R25= The resistance in Ω of the thermistor at +25°C

ß = The material constant of the thermistor, which typi­cally ranges from 3000K to 5000K

T = The temperature of the thermistor in °C

Table 4 shows the MAX8903A THM temperature limits
for different thermistor material constants.

Some designs might prefer other thermistor tempera­ture limits. Threshold adjustment can be accommodat­ed by changing RTB, connecting a resistor in series
and/or in parallel with the thermistor, or using a thermis­tor with different ß. For example, a +45°C hot threshold
and 0°C cold threshold can be realized by using a ther­mistor with a ß of 4250 and connecting 120kΩ in paral­lel. Since the thermistor resistance near 0°C is much
higher than it is near +50°C, a large parallel resistance
lowers the cold threshold, while only slightly lowering
the hot threshold. Conversely, a small series resistance

Figure 7. Thermistor Monitor Circuitry

Table 3. Fault Temperatures for Different
Thermistors

CEN

THERMISTOR

CIRCUITRY

VL

VL

MAX8903A

ALTERNATE
THERMISTOR
CONNECTION

RTS

R

T

RTP

RTB

0.74 VL

THM

0.28 VL

R

T

0.03 VL

GND

Thermistor ß (K) 3000 3250 3500 3750 4250

RTB (kΩ) (Figure 7) 10 10 10 10 10

Resistance at +25°C
(kΩ)

Resistance at +50°C
(kΩ)

Resistance at 0°C (kΩ) 25.14 27.15 29.32 31.66 36.91

Nominal Hot Trip
Temperature (°C)

Nominal Cold Trip
Temperature (°C)

10 10 10 10 10

4.59 4.30 4.03 3.78 3316

55 53 50 49 46

-3 -1 0 2 4.5

COLD

THM
OUT OF
RANGE

DISABLE
CHARGER

⎧

β

⎨

25

⎩

RR e

=×

T

⎛
⎜

⎝

T

+

1

−

2731298

⎫

⎞
⎟

⎬

⎠

⎭

ALL COMPARATORS
60mV HYSTERESIS

HOT

ENABLE THM

MAX8903A

2A 1-Cell Li+ DC-DC Charger for USB*
and Adapter Power

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

20

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

raises the cold threshold, while only slightly raising the
hot threshold. Raising RTBlowers both the hot and cold
thresholds, while lowering R

TB

raises both thresholds.

Note that since VL is active whenever valid input power
is connected at DC or USB, thermistor bias current
flows at all times, even when charging is disabled (CEN
= high). When using a 10kΩ thermistor and a 10kΩ
pullup to VL, this results in an additional 250µA load.
This load can be reduced to 25µA by instead using a
100kΩ thermistor and 100kΩ pullup resistor.

Power Dissipation

PCB Layout and Routing

Good design minimizes ground bounce and voltage
gradients in the ground plane, which can result in insta­bility or regulation errors. The GND and PGs should
connect to the power-ground plane at only one point to
minimize the effects of power-ground currents. Battery
ground should connect directly to the power-ground
plane. The ISET and IDC current-setting resistors
should connect directly to GND to avoid current errors.
Connect GND to the exposed pad directly under the IC.
Use multiple tightly spaced vias to the ground plane
under the exposed pad to help cool the IC. Position
input capacitors from DC, SYS, BAT, and USB to the
power-ground plane as close as possible to the IC.
Keep high current traces such as those to DC, SYS,
and BAT as short and wide as possible. Refer to the
MAX8903A Evaluation Kit for a suitable PCB layout
example.

Table 4. Package Thermal Characteristics

Pin Configuration

Chip Information

PROCESS: BiCMOS

Package Information

For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages

.

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

28 TQFN-EP T2844-1

21-0139

28-PIN 4mm x 4mm THIN QFN

SINGLE-LAYER PCB MULTILAYER PCB

Continuous
Power
Dissipation

θ

JA

θ

JC

1666.7mW

Derate 20.8mW/°C
above +70°C

48°C/W 35°C/W

3°C/W 3°C/W

2286mW

Derate 28.6mW/°C
above +70°C

TOP VIEW

22

CHG

SYS

23

24

SYS

25

26

CS

27

LX

28

LX

*EXPOSED PAD

+

12CS4567

UOK

BAT

FLT

BAT

2021 19 17 16 15

MAX8903A

3

PG

PG

THIN QFN

4mm x 4mm

USB

18

DC

DC

DCM

*EP

THM

BST

USUS

IUSB

14

CEN

ISET

13

12

GND

IDC

11

10

CT

VL

9

8

DOK