Precharge Current

The MAX1551/MAX1555 feature a precharge current to

the device enters precharge mode where charging cur-

rent is limited to 40mA.

Package Thermal Limiting

On-chip thermal limiting in the MAX1551/MAX1555 sim-

plifies PC board layout and allows charging rates to be

optimized without the limits imposed by worst-case bat-

tery and input voltages. The device reduces the power

dissipation at BAT to prevent overheating. This allows

the board design to be optimized for compact size and

typical thermal conditions. When the MAX1551/

MAX1555 thermal limits are reached, the chargers do

not shut down, but progressively reduce charging cur-

rent by 17mA/

°C above a die temperature of +110°C.

Solder the MAX1551/MAX1555s’ GND to a large

ground plane to help dissipate power and keep the die

temperature below the thermal limit. The USB charge

current of 100mA is unlikely to induce thermal limiting.

Bypass Capacitors

Use ceramic bypass capacitors at DC, USB, and BAT.

Mount these capacitors within 1cm of their respective

pins. X7R and X5R dielectrics are recommended.

Chip Information

TRANSISTOR COUNT: 541

PROCESS: BiCMOS

SOT23 Dual-Input USB/AC Adapter 1-Cell Li+

Battery Chargers

6

_______________________________________________________________________________________

MAX1551

(MAX1555)

DC

USB

BAT

AC ADAPTER

3.7V TO 7V

USB

3.7V TO 6V

TO SYSTEM

LOAD

Li+

GND

TO LOGIC RAIL

CHARGE

CONTROL

POK

(CHG)

LOGIC

CONTROL

C1

1

µF

C2

1

µF

C3

1

µF

R1

100k

Ω

INDICATES

THAT POWER

IS PRESENT

(EITHER DC

OR USB)

Typical Application Circuit