TPS7H1101A-SP: Does power good need to be pulled up to VOUT?

Hey Matty,

When you say "Multiple TPS7H1101 on power good pin" do you mean you are sequencing the LDOs or paralleling the LDOs?

Thanks,
Daniel

Hi Daniel,

Here are the two setups that I have. I think a picture might show you better on what I am doing. Thx

Hey Matty,

The PG pin is an open-drain output.
This means that it will not pull the voltage high without a pull-up resistor.

The pictures that you have will not work as you need some way to pull the voltage up.
You would have to connect the gate of the FET high through a resistor in order for it to work.

Thanks,
Daniel

Hi Daniel,

Sorry about my picture. The FET is internal to the TPS parts. I think I confused you by placing them outside the part. So just assume where you see the FETS they are all internal to the LDOs. So my question still stands as drawn. Do I need to adhere to the pullup being only being pulled up to VOUT?

Thanks!

Hey Matty,

I now understand.

What you are doing is fine as long as you dont violate the voltage ratings for the pin
Note that the EN pin is referenced to the input of the TPS7H1101A-SP, so the VCC would have to be equal to or lower than the input voltage of the part.

(EN voltage rating listed as VIN + 0.3 V)

Thanks,
Daniel

Thanks Daniel. So even though it says in the TPS7H1101 the following, I should be ok, since it will be greater than the Vout pin

Hey Matty,

You can pull it up to a different voltage, as long as you dont violate the ratings of the pin.
Note that this also means if the voltage its being pulled up to is high before the input voltage is applied to the part, it will also cause damage.

Thanks,
Daniel

Hey Matty,

I would like to elaborate on my explanation briefly.

The PG pin does not have the same rating as the EN pin.
With the EN pin you need to make sure the voltage does not exceed the VIN voltage, however this is not the case for the PG pin.

The PG pin has a 7.5 V ABS MAX rating.

Thanks,
Daniel

Ok makes sense. So just to be clear on your earlier statement: "Note that this also means if the voltage its being pulled up to is high before the input voltage is applied to the part, it will also cause damage."

I am assuming you are referring to the EN input and the Vin when you mention this. You are saying you do not want the Enable pin active before power is applied to the part, correct?

I am also assuming it is ok to have the enable pin and the vin pin tied to the same voltage source? So I am pulling up a power good from the previous LDO to +3.3V which is the enable for the next LDO which also has its Vin pin = 3.3V, so it gets enabled the same time as the Vin is applied?

Hey Matty,

Pulling the EN pin high before power is applied to VIN could damage the part.
Tying them to the same voltage node is a common solution.

Looking at your first picture:
Having the VCC be the 1.8 V input to the TPS7H1101A-SP on the right is something that would work.

Thanks,
Daniel

Welcome