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TIDA-01093: Low side FET design considerations

Eddie Koh
Genius 10645 points

Part Number: TIDA-01093

In TIDA-01093, it was noted that the DSG/CHG controlled FETs are on the PACK- / Low side.

Customer's system designs usually put the FETs on the high side, so that the PACK- / GND is not disconnected from system. Is there a reason for TI to prefer putting FETs on low side?

Using TIDA-01093 as starting point, if customer changes DSG/CHG to control FETs on PACK+ / high side, is there any concerns? (Customer will add charge pump to drive the high side FETs)

  • 0
    TI__Guru 54715 points

    Hi Eddie,

    The selection of high side vs low side often depends on the system or industry.  High side switching makes communications with PACK- reference easier. But high side switching is harder requiring either P-ch FETs or a charge pump driver as you mention.  Any driver will take current which can be part of the electronics power budget.  High current applications will sometimes prefer to use low side FETs for simpler drive and deal with the more complex communication path.

    For the TIDA-01093 and modifying for high side switching the following come to mind:

    1. The protection signaling is designed to flow down to drive the low side FETs.  Consider if a circuit should have the signal flow up or level shift the low side signal to the charge pump driver.
    2. The boot circuit will need to respond to signaling appropriate for the high side FETs.  It could be sensed from the PACK+ terminal movement or from a PACK- referenced input.
    3. Load detection would likely change, it would seem simpler since PACK+ would be moving with respect to the MCU ground. 
    4. Communication interface. Generally this should be easier since many are GND referenced and PACK- would always be available.

    Of course review the design guide for TIDA-01093 for a discussion of the design and your system requirements.