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BQ76930: Put PTC on BAT pin

Arking Chiu
Intellectual 790 points
Part Number: BQ76930

Hi Team,

Customer would like put a PTC on below red block, is there any risk?

Customer reason:

In order to prevent internal fault causing an over-current condition, leading a thermal event PTC resistor are placed at the power feed points associated with the internal control circuitry.

PTC_OC_SMD_0402_0603_1210_24V_230V.pdf

  • 0
    TI__Guru 54715 points

    Hi Arking,

    The PTC at R43 would need to handle the normal current for REGSRC which includes the load from REGOUT, otherwise should be fine.

    A PTC at the BAT pin will isolate the power pin of the IC from the filter capacitor potentially making the part more susceptible to noise. If the IC were to fault with BAT short to GND the PTC would open allowing BAT to fall much below VC10 which the VC10 to BAT diode is intended to prevent. That could allow damage, but the part would already be damaged from the fault causing the PTC to open.  One might consider if it serves the purpose to have the PTC in series with the power filter resistor (R35?) allowing the filter cap to remain at the power pin and adjusting the power filter resistance for the Rr of the PTC.  Current could still flow through through the VC10 to BAT diode in that case.  Moving the power filter cap (C25?) connection to the IC side of the PTC might also be considered.