MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
top-off current threshold set by R
MIN
, the charger
enters top-off mode and the CHG indicator goes high
impedance signaling that the battery is fully charged.
Overvoltage-Protected Output (SAFEOUT)
SAFEOUT is a linear regulator that provides an output
voltage of 4.7V (MAX8845Z/MAX8845Y/MAX8845W) or
4.85V (MAX8845X) and can be used to supply low volt-
age- rated USB systems. The SAFEOUT linear regulator
turns on when V
IN
≥ 4.25V regardless of EN and is dis-
abled when V
IN
is greater than the overvoltage thresh-
old (7.5V typ) (8.0V typ for MAX8845X only).
Battery-Pack Detection Input (DETBAT)
DETBAT is a battery-pack ID resistor detector that
enables the battery charger if pulled low through a
resistor that is less than 51kΩ. If DETBAT is left uncon-
nected or the pulldown resistor is 51kΩ or greater the
battery charger is disabled. If DETBAT is not used con-
nect DETBAT to GND for normal operation.
POK
Output
The open-drain POK output asserts low when 2.35V ≤
V
IN
≤ 7V (7.5V for MAX8845X only) and (V
IN
- V
BATT
) ≥
40mV (typ V
IN
rising). POK is high impedance during
shutdown. When interfacing with a microprocessor
logic input, a pullup resistor to the microprocessor’s I/O
voltage may be required.
Autobooting Assistant
The MAX8845Z/MAX8845Y/MAX8845X/MAX8845W con-
tain autobooting assistant circuits that generate an
enable signal for system booting (ABO—MAX8845Z,
ABO—MAX8845Y/MAX8845X/MAX8845W). For the
MAX8845Z, the booting assistant functions as an internal
OR gate (Figure 1). The first input is dependant on the
input voltage (V
IN
) and DETBAT while the second input
is an external signal applied to ABI. The first input (POK)
is driven high once DETBAT is pulled low through a
resistor less than 51kΩ, 2.35V ≤ V
IN
≤ 7V (7.5V for only
MAX8845X), and (V
IN
- V
BATT
) ≥ 40mV (typ V
IN
rising).
The second input signal (ABI) is driven by an external
source (Table 1). ABI enables an autoboot signal when
a battery is connected at BATT and is independent of
POK. If POK is pulled low, the booting assistant always
drives ABO high regardless of ABI. ABI is pulled to GND
through an internal 200kΩ resistor. If ABI is supplied
from an outside exposed pin, a RC filter (Figure 4) is
required for ESD protection and noise filtering. If ABI is
supplied by a system’s internal GPIO, or logic, the RC
filter is not required. For the MAX8845Y/MAX8845X/
MAX8845W, the output ABO is only dependent on the
state of ABI (Table 1).
CHG
Charge Indicator Output
CHG is an open-drain output that indicates charge sta-
tus. Table 2 describes the state of CHG during different
stages of operation. CHG is suitable for driving a charge
indication LED. If the MAX8845Z/MAX8845Y/MAX8845X/
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
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