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TPS62130A-Q1: output Voltage stability

Lidong Yu
Intellectual 1756 points
Part Number: TPS62130A-Q1
Other Parts Discussed in Thread: TPS62130

We are using 2 TPS62130 in a low voltage regulator in order to drive an ir source (1.3V) and for 5V board power

All components are aligned with power designer except additional filtering capacitors on the output.

2 problems were observed :

- pulsating output voltage when small load - 20mA. This was fixed with 2 1oouF tantalum caps. Observed on both 5V an 1.3V circuit.

- Output voltage drop upon load. Only 1.V supply is affected. 

--- No-load voltage is stable at 1.3V

--- Output voltage drops to 1V @ 80mA load

Any suggestion how to troubleshoot this issue will be appreciated.

Thanks!

  • 0
    TI__Mastermind 21755 points

    Hi Lidong,

    The schematic looks fine with just the 22uF ceramic caps and you should not require adding any additional tantalum caps. I would increase the soft-start cap to higher values as this device has lower current limit during startup and that could cause voltage foldback.

    • What is the measurement technique for output voltage ripple you are using? Please make sure to use AC coupling/1Mohm termination with a 1x/10x scope probe and a tip and barrel technique. Please check this video: https://training.ti.com/power-tips-measuring-vout-ripple-dcdc-converters At no load or even 80mA, the device will operate in PFM mode and a typical waveform of output ripple should look like Figure 36 in datasheet.
    • Is it possible to share your ripple waveform that you are observing?
    • Also, with increasing load from no load, the output can dip as shown in load regulation plot in Figure 25 of datasheet. For the output voltage measurement (DC value), you would need to use a DMM.

    Thanks,
    Amod

  • 0 in reply to Amod Vaze
    TI__Intellectual 1756 points

    Thanks for your support! I am trying to calculate the Soft Start capacitor and I am not able to follow the units in the datasheet - 10.2.1.2.7
    - my guess is if charging current is in uA then the result will be in uF. This way for 10mS delay i will need 2nF capacitor.

     I tested with 10nF capacitor and with 100nF - no improvement. With a load of 200mA the output voltage drops to 1.04V. It is a strange situation as my load is resistive 0.8ohm and looks like the current is limited.

  • 0 in reply to Lidong Yu
    TI__Mastermind 21755 points

    Hi Lidong,

    You can check the inductor current (lifting COUT side of inductor and adding a wire between inductor and the board pad) and check its waveform during startup to confirm if there is current limit being hit or not. This device does have a reduced current limit during startup so that is possible. For a 10ms soft-start time, you would need a 20nF Css cap. The charge current is in uA already but the tss and Css units are seconds and Farads. 

    Thanks,
    Amod