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TPS548D22: EN_UVLO-PIN inside structure

Zhanpeng Li
Intellectual 2140 points
Part Number: TPS548D22
Other Parts Discussed in Thread: TPS7A7001

Hi team,

This is brandon. FAE from NWCMM.

For now, we met a problem in using TPS548D22 with enable by TPS7A7001.I post the schemtic below:

As you could see, we connect the output of TPS7A7001 with en_uvlo-pin of TPS548D22, so that we could control the power up sequence. The problem we met is that if we use the output of TPS7A7001 as the EN_UVLO, we found that the TPS548D22 could influence the output of TPS7A7001, we could not achieve 3.3v as output, the output voltage of TPS7A7001 was clamped to 4.2v. from our testing now, it seems that there has some Sink current from EN_UVLO-pin that may cause TPS7A7001 output abnormal. the funny thing is that if we change the LDO to DCDC to connect EN_UVLO, the system could run well. 

we would like to check the structure on this PIN of TPS548D22? could you give us some insights on this issue? really urgent on this.

also, the solution is really demanding for us to feedback to our customer. any question, we could also engage with email: brandon-li@ti.com

by the way, we try to add a resistant between EN-UVLO to GND, it doesn't change anything.

BR

Brandon

  • 0
    TI__Guru 52745 points

     

    It sounds like you are seeing a leakage current out of the TPS548D22's EN_UVLO pin that is driving the output voltage of the TPS7A7001 above it's regulation point.  Rather than connecting the output of the TPS7A7001 directly to the EN_UVLO input, try connecting them with a resistor divider.  A 10k resistor from the 3.3V output to the EN_UVLO pin and a 20k resistor to ground will give a maximum turn-on voltage of 2.625V while ensuring any leakage current from the UN_UVLO pull-up does not over-drive the LDO's output.