The bq77904 and bq77905 devices are low-power battery pack protectors that implement a
suite of voltage, current, and temperature protections without microcontroller (MCU) control. The
devices stackable interface provides simple scaling to support battery cell applications from 3 S
to 20 S or more. Protection thresholds and delays are factory-programmed and available in a variety
of configurations. Separate overtemperature and undertemperature thresholds for discharge (OTD and
UTD) and charge (OTC and UTC) are provided for added flexibility.
The device achieves pack protection through the integrated independent CHG and DSG
low-side NMOS FET drivers, which may be disabled through two control pins. These control pins may
also be used to achieve cell protection solutions for higher series (6 S and beyond) in a simple
and economical manner. To do this, simply cascade a higher device CHG and DSG outputs to the
immediate lower device control pins. For reduced component count, all protection faults use
internal delay timers.
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