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TPS7A8300: Startup issue with TPS7A8300RGRR

Part Number: TPS7A8300

Hi TI experts,

For the design of TPS7A8300RGRR, we use external resistors to set output voltage.

The design parameters are as follows, Vbias=5V, Vin=1.2V, Vout=0.9V,and using an external power supply to control the EN of TPS7A8300RGRR.

But we found a startup issue:

(1)When the startup sequence of the device is Vbias--->EN--->Vin, Vout will rise to Vin(1.2V) and remain unchanged, instead of 0.9V, the test waveform is shown in the Figure 1.

(2)When the startup sequence of the device is Vbias--->Vin--->EN, Vout will rise to 0.9V, the startup is normal, the test waveform is shown in the Figure 2.

(3)But, as described in (1) above, when we heat up the chip, and  the startup sequence of the device is Vbias--->EN--->Vin, Vout will rise to 0.9V, the startup is normal, the problem described in (1) does not occur.

Figure 1:

Figure 2:

Thanks

  • Hey Liu,

    would you be able to send us the schematic for your application? 

    do you have an NR cap?

    Best,

    Juliette

  • Hi Juliette,

    Thank you for helping to analyze and solve this problem.

    The schematic is as follows.

    Thanks

    Yanwei

  • Hey Yanwei, 

    is there any change to the start-up behavior if the NR cap or the CFF cap are changed?

    Best,

    Juliette

  • Hi Juliette,

    We tried two debugging solutions,as shown below,but the startup issue still exists 

    (1) We changed the NR cap from 10nF to 22nF;

    (2)We removed CFF cap.

    Thanks

    Yanwei

  • Hey Yanwei,

    Unfortunately, it seems like this device has sequencing requirements and the datasheet is very unclear about it:

    we typically include EN(MAX) = VIN on the ROC table on page 5 and a sequencing sectioning the applications section. The device will behave outside of how it is characterized if sequencing is not followed. 

    The device might work when heated because there's more energy in the IC. 

    Actions on our end - Update the datasheet to be more clear. 

    Would you like me to loop in marketing to find a part that will be more suitable for your sequencing requirements?

    Best,

    Juliette