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bq24155

SLUS942 – FEBRUARY 2010

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Charge Status Output, STAT Pin

The STAT pin is used to indicate operation conditions for bq24155. STAT is pulled low during charging when

EN_STAT bit in control register (00H) is set to "1". Under other conditions, the STAT pin acts as a high

impedance (open-drain) output. Under fault conditions, a 128-ms pulse is sent out to notify the host. The status of

STAT pin at different operation conditions is summarized in Table 1. The STAT pin can be used to drive an LED

or communicate to the host processor.

Table 1. STAT Pin Summary

CHARGE STATE

STAT

Charge in progress and EN_STAT = 1

Low

Other normal conditions

Open-drain

Charge mode faults: Timer fault, sleep mode, VBUS 128-ms pulse, then open-drain

or battery overvoltage, poor input source, VBUS

UVLO, no battery, thermal shutdown

Control Bits in Charge Mode

CE Bit (Charge Mode)

The bit of CE in control register is used to disable or enable the charge process. A low logic level (0) on this bit

enables the charge and a high logic level (1) disables the charge.

RESET Bit

The bit of RESET in control register is used to reset all the charge parameters. Writing '1" to RESET bit resets all

the charge parameters to default values and RESET bit is automatically cleared to zero once the charge

parameters are reset. It is designed for charge parameter reset before charge starts, and it is not recommended

to set the RESET bit when charging or boosting in progress.

OPA_Mode Bit

OPA_MODE is the operation mode control bit. When OPA_MODE = 0, the bq24155 operates as a charger if

HZ_MODE is set to "0", refer to Table 2 for detail.

Table 2. Operation Mode Summary

OPA_MODE

HZ_MODE

OPERATION MODE

0

0

Charge (no fault)

1

0

NA

X

1

High impedance

High Impedance Mode

When control bit of HZ-MODE is set to "1", the bq24155 operates in high impedance mode, with the impedance

in VBUS pin higher than 165 k

Ω. In high impedance mode, a crude 32-second timer is enabled when the battery

bq24155 operates in 32 minute mode and the crude 32 second timer is disabled. In 32 minute mode, when

VBUS is below UVLO, the bq24155 operates in high impedance mode regardless of the setting of the HZ_MODE

bit.

Output Inductor and Capacitance Selection Guidelines

The bq24155 provides internal loop compensation. With this scheme, the best stability occurs when the LC

(1)

16

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