This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS65217: Vsys drop down abnormally when power on

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.


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?

  • Hi Zoe,

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



  • 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.