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BQ25798: BQ25798 When using PMID as a system load in Backup mode, is it possible to detect a short in PMID PIN?

Part Number: BQ25798

Tool/software:

Hello

This is a question about applying BQ25798.

I want to apply the power block of our system as shown in the figure below.

Input power: 12~24V Adapter

Output power:

System load1: 24V, 40mA (PMID)
System load2: 3.3V 300mA (SYS)

In backup mode without input power, power should be supplied to system load1 and 2 at the same time.

Detailed questions
1)Can I charge a 14.8V (4S cell) battery using a 12~24V charging adapter?

2)Can I supply 24V to system load1 (PMID pin) and 3.3V to system load2 (SYS pin) at the same time in backup mode without charging power?

2-1) Can I detect a short when supplying 24V power to system load1 (PMID pin) in backup mode?

2-2) Can I detect a short circuit when the PMID pin is shorted? How can the BQ25798 detect a short circuit and inform me as SW or HW?

3) In backup mode, should I apply an additional BUCK IC to supply 3.3V power to system load2 (SYS pin)?

    If I need to add a BUCK IC, please tell me why.

Thank you, your support.

  • Hi Jonghyo,

    Regarding 1, yes.

    Regarding 2, yes to PMID.  V(SYS)=higher of V(BAT) or MINSYS voltage in the event of discharged battery. You will need a 3.3V dc/dc converter after SYS.

    Regarding 2-1 and 2-2, in backup (OTG) mode, the only short protections available

    1. cycle-by-cycle current limit

    2.  OTG Under-voltage Protection (OTG_UVP)

    3. System Short Protection (VSYS_SHORT)

    There is a BAT discharge current clamp that can be enabled to clamp battery current to the converter in reverse mode.

    Regarding 3, yes.  There is only one dc/dc converter that operates in forward/charge or reverse/OTG/backup mode.  So only one node, SYS/BAT or VBUS/PMID can be regulated.  Even then, the NVDC architecture requires V(SYS)=higher of V(BAT) or MINSYS voltage in the event of discharged battery.

    Regards,

    Jeff