Datasheet

GENERAL OPERATIONAL OVERVIEW
Stand-Alone Mode and Host Control Mode
bq77PL900
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The bq77PL900 has two operational modes, stand-alone mode and host-control mode. The mode is switched by
STATE_CONTROL [HOST]. In stand-alone mode, the battery protection is managed by the bq77PL900 without
the need for any external control. In this mode, the CHG and DSG FETs are driven ON and OFF automatically
and cell balancing is processed by a fixed algorithm if enabled by OCDELAY[CBEN]). In this mode, I
2
C
communication is enabled, and a host can read the registers and set STATE_CONTROL [HOST] but cannot
control any output or function such as Vcell AMP enable.
In host control mode, a host microcontroller can obtain battery information such as voltage and current from the
bq77PL900 analog interface. This allows the host, such as a microcontroller, to calculate remaining capacity or
implement an alternative cell balancing algorithm. In this mode, the bq77PL900 still detects cell protection faults
and acts appropriately, although the recovery method is different from that in stand-alone mode. The host
controller has control over the recovery method and FET action after the protection state has been entered.
Table 3 contains further details of the protection action differences.
Table 3. Stand-Alone Mode and Host Control Mode Protection Summary
Stand-Alone Mode Host-Control Mode
FUNCTION MODE
(HOST = L) (HOST = H)
Automatic
The bq77PL900 detects an OV voltage and
Detection
turns OFF the CHG FET. Must turn off cell
OV protection
balancing for correct voltage detection.
Recovery Host Control
Host Control
The bq77PL900 detects a UV voltage but no
Detection
FET action is taken. Must turn off cell
Automatic
UV protection
balancing for correct voltage detection.
The bq77PL900 detects and recovers from
protection states and controls the FETs.
Recovery Host Control
Automatic
Detection The bq77PL900 detects OCD and turns CHG
OCD/SCD
and DSG FETs OFF.
protection
Recovery Host Control
Detection Host must turn ON.
Overtemperature
protection
Recovery Host Control
Host Control
CHG/DSG FET Automatic
— The bq77PL900 cannot release from
control Host cannot drive the FETs
protection state automatically.
Host Control
CBEN = 1: Automatic
Cell balancing — The host can balance any cells at any time
CBEN = 0: No function
CBEN = Don ’ t care
PMS = High, Automatic
Zero-volt charge1 Automatic
ZVC = X (0-V charge current flows through CHG FET)
PMS = Low,
Zero-volt charge2 No support for 0-V charge
ZVC = 0
Host Control
Host should control precharge FET by using
Automatic
PMS = Low,
GPOD pin.
Zero-volt charge3 (0-V charge current flows through FET that is
ZVC = 1
driven by GPOD)
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