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LP38798: question about EN voltage

TS Yang
Genius 4800 points
Part Number: LP38798

Hi,

One of my customer is willing to use TI's LP38798SD-ADJ/NOPB for their new application.

Customer's schematic is as below.

Input power is 5V, and output AVDD is 3V.

Now EN pin is not conneted, but they are performing several test with EN pin.

Above waveform is screen capture of Vin, Vout, Enable voltage. (Yellow is Vin, Blue is Vout, Pupple is EN)

As you see, the Enable voltage is around 2.4V.

If the EN pin is open, does the EN voltage remain at 5V? or this 2.4V is right?

I found below at LP38798 datasheet.

I know that the datasheet says that the zener diode has been clamped by 5V.
Whether it is measured well or customer made the circuit or the PCB layout wrong?

thanks,

TS

  • 0
    TI__Guru 55940 points
    Hi TS,

    Since the internal current source that is pulling up EN is also being powered by your input voltage of 5 V, I would expect Ven to be ~4.8 V. Please confirm that you are measuring Ven using high impedance probes and that there are no unintentional leakage paths such as residual flux on your board that could be pulling down Ven.

    Very Respectfully,
    Ryan