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TPS65217: Vsys drop down abnormally when power on

Zoe Yang
Intellectual 2210 points
Part Number: TPS65217
Other Parts Discussed in Thread: AM3352

Dear experts,

My customer have some issues when using TPS65217 to power for AM3352. there is a strange sign that Vsys drop down abnormally when power on vac.

Below capture is shown below;

Ch1 is SYS waveform powered by 5Vdc. Drop down to 1V in 80ms.

Ch2 is LDO2 output.

Ch3 is LDO1 output.

Questions:

1. Checking from the circuit schematic diagram, what would cause VSYS power on abnormally?

2.According to our datasheet block diagram, I see customer connect VINLDO directly to VSYS. Why LDO1/2 react different voltage waveforms in below capture?  

3. If VINLDO has input voltage(ignore actual connect to SYS), would LDO1/2 has regular output?

  • 0
    TI__Mastermind 19130 points

    Hi Zoe,

    We are experiencing high support volumes at this time. I'll provide an update within the next 3 business days.

    Thanks,

    James

  • 0 in reply to James Steenbock
    TI__Mastermind 19130 points

    Hi Zoe,

    After looking at your schematic, there are some concerns I have. I recommend following the TPS65217x Schematic Checklist for proper device function:

    • I recommend you increase the capacitor at VINLDO to 4.7uF
    • The BAT and BAT_SENSE pins need to be connected together and pulled to GND through a pull-down resistor if you do not intend to use these pins
    • I would increase the capacitance at the SYS pin to match our recommended 22uF
    • The USB pin needs a GND connection if not being used
    • I do not see a pull-up resistor pictured on the nWAKEUP pin, perhaps it is off screen? A 10k pull-up resistor to 3.3V will suffice. 
    • For L1 pin, I recommend increasing the capacitor to 22uF
    • For VIN_DCDC2 I recommend increasing the capacitor to 10uF
    • For L2 increase capacitance to 22uF
    • For L3 increase capacitance to 22uF
    • For VIN_DCDC3 I recommend increasing the capacitor to 10uF
    • ISINK1 and ISINK2 should both be connected to GND when not in use
    • LS1_OUT and LS2_OUT only need to be tied to a higher than expected voltage if they are not used.
    • nRESET will need a connection to the processor for proper function

    If you still have issues with the power up sequence after these adjustments, let us know here on the forums.

    Regards,

    James