Detailed Description

The MAX8845Z/MAX8845Y chargers use voltage, cur-

rent, and thermal-control loops to charge a single Li+

cell and protect the battery (Figure 1). When a Li+ bat-

tery with a cell voltage below 2.5V is inserted, the

MAX8845Z/MAX8845Y chargers enter a prequalifica-

tion stage where it precharges that cell with 10% of the

user-programmed fast-charge current (Figure 2). The

CHG indicator is driven low to indicate entry into the

prequalification state. When the battery voltage

exceeds 2.5V, the charger soft-starts as it enters the

fast-charge stage. The fast-charge current level is pro-

grammed through a resistor from SETI to GND. As the

battery voltage approaches 4.2V, the charging current

28V Linear Li+ Battery Chargers with Battery

Detection and Overvoltage Protected Output

_______________________________________________________________________________________

7

OUTPUT DRIVER,

CURRENT SENSE,

AND LOGIC

TEMPERATURE

SENSOR

VL

REGULATOR

REF

REFOK

OVLO

VL

UVLO

LOGIC

BATT

DETBAT

ABI

ABO (MAX8845Z ONLY)

ABO (MAX8845Y ONLY)

EN

POK

IN

BATT

IN

BATT

POK

200k

Ω

GND

EP

+115

°C

4.2V

Li+

200k

Ω

CHG

MAX8845Z

MAX8845Y

DETBAT

LINEAR

REGULATOR

WITH OVP

SETI

MIN

SAFEOUT

Figure 1. MAX8845Z/MAX8845Y Functional Diagram