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TPS65320-Q1: TPS65320D-Q1 inrush current issue

TzuYang WU
Prodigy 90 points
Part Number: TPS65320-Q1
Other Parts Discussed in Thread: TPS65320D-Q1

In the current design, TPS65320D-Q1 is used to convert 12V to 3.3V by buck regulator and the LDO is used to convert 3.3v to 1.2V.

1. There is currently an inrush current issue with the 1.2V output, which has been measured at 1.8A. Is there a maximum limit for inrush current on the LDO_OUT pin?

2. As shown in the diagram below, when the 1.2V enable is activated, the inrush current value is 1.8A at LDO_OUT pin. Could inrush current cause the enable pin to be pulled low?

3. how to reduce the inrush current for LDO output

singnal 1: LDO enable pin

singnal 2: LDO output voltage

singnal 3: LDO output current

Derek

  • 0
    TI__Intellectual 1921 points

    Hi.

    Sorry for the delay. I'll look into your issue and provide a response by tomorrow.

    Thanks,

    David Martinez

  • 0 in reply to David Martinez
    TI__Intellectual 1921 points

    Hey Derek.

    1) It is difficult to define a maximum limit for the inrush current. Nonetheless, this E2E post discusses more about how to define the limit. I'd set the limit as the short-circuit threshold of this device (1A), though the actual limit is obviously higher than this given that inrush currents are in the microsecond range.

    2) Inrush current is known for decreasing input voltage when the input power supply cannot handle the spike in current. However, I see that LDO Enable are being driven by 3.3V and not 12V(Battery), so it is strange to me that this signal is dropping. There is no protection feature in this device that forces EN1/EN2 low. Which enable pin is this? What source is driving this enable pin? If this signal was EN2 (LDO Enable) then signal 2 should drop eventually because the enable low level threshold is 0.7V, disabling the LDO.

    3) There are many ways to decrease inrush current including reducing the output capacitance. However, if this is not an option, then this document goes over the common solutions to increase the output voltage rise time, effectively decreasing inrush current.

    Solutions:

    • Integrated Soft-start feature: If Buck and LDO turn on at the same time, then an option would be to increase the soft-start time of the buck regulator. Increasing the rise time of the buck regulator will increase the rise time of the LDO output. The soft-start time is dependent on the soft-start capacitor (Css) which can be varied from 1nF to 0.47uF. Equations for the soft-start feature are in section 7.3.1.8 of the datasheet.
    • Add load switch to increase the rise time.

    Best,

    David Martinez