MAX8903A View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX8903A

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

Maxim Integrated 

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

and Adapter Power

Table 1. External Components List for Figures 2 and 3

COMPONENT

(FIGURES 2 AND 3)

CDC, CUSB

CVL

CSYS

CBAT

CCT

RPU (X4)

THM

RT

RIDC

RISET

L1

FUNCTION

Input filter capacitor

VL filter capacitor

SYS output bypass capacitor

Battery bypass capacitor

Charger timing capacitor

Logic output pullup resistors

Negative TC thermistor

THM pullup resistor

DC input current-limit programming resistor

Fast-charge current programming resistor

DC input step-down inductor

PART

4.7µF ceramic capacitor

1.0µF ceramic capacitor

10µF ceramic capacitor

10µF ceramic capacitor

0.15µF low TC ceramic capacitor

100kΩ

Phillips NTC thermistor, P/N 2322-640-63103, 0kΩ

±5% at +25°C

10kΩ

3kΩ ±1%, for 2A limit

1.2kΩ ±1%, for 1A charging

1µH inductor with ISAT > 2A

step-down output current programmed at IDC, maxi-

mum charger current programmed at ISET, and maxi-

mum die temperature. The feedback signal requiring

the smallest current controls the average output current

in the inductor. This scheme minimizes total power dis-

sipation for battery charging and allows the battery to

absorb any load transients with minimum system volt-

age disturbance.

If the battery voltage is below VSYSMIN, the charger

does not directly connect the system voltage to the bat-

tery. VSYS pin is held at a fixed point slightly above

VSYSMIN, and does not track the battery. The battery

charger independently controls the battery charging

current. VSYSMIN is set to 3.0V in the MAX8903A, for

other VSYSMIN values, please contact the factory.

After the battery charges to 50mV above VSYSMIN, the

system voltage is connected to the battery. The battery

fast-charge current then controls the step-down con-

verter to set the average inductor current so that both

the programmed input current limit and fast-charge cur-

rent limit are satisfied.

DC-DC Step-Down Control Scheme

A proprietary hysteretic current PWM control scheme

ensures fast switching and physically tiny external com-

ponents. 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.

VSYSMIN

4.4V

4.2V

VSYS

IBAT x RON

VBAT

Figure 4. SYS Tracking VBAT to the Minimum System Voltage

Similarly, when the input voltage is too high to allow

4MHz operation due to the minimum on-time, the con-

troller becomes a minimum on-time, valley current regu-

lator. 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

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