TPS7H4001-SP: TPS7H4001-SP

I will check the caps around the device and get back to you ....

by the way, I did not get an email from e2e when I submitted this question nor when you replied .....

Hey Rajan,

Okay please keep me updated.

Thanks,
Daniel

Daniel,

I have checked the three TMPU 680uF tantalums at the output and they have been fitted in the correct polarity, as have the two TMPU 470 uF input caps. The board looks perfect, all the other rails have high resistance or open circuit to GND, it's the just the output from the TPS7H4001 that is low resistance ...

There is some sort of static short that is causing the output resistance to measure 22 ohms, it's not a dead short! The TPS7H4001 is used to generate 1V and powers an FPGA and an MCU, I am double checking their power and GND pins ....

Hey Rajan,

Please check to make sure  there are not solder issues with the device.
If you still see the issue you can go through our returns process:
https://www.ti.com/productreturns/docs/createReturn.tsp

Thanks,
Daniel

I have powered up the board and the TPS7H4001 is outputting 1.1V using a 12.1k resistor to set the desired output voltage.

I have noticed the PGOOD output is only 2.4V, even though it is pulled up to the input of +5V, can you explain this?

PGOOD has a value of 10k

Hey Rajan,

Please make sure there is no damage to the device or the board.
There is not a situation where the TPS7H4001-SP should output 2.4 V in that situation.

Thanks,
Daniel

I have increased the voltage setting resistor and the part is outputting the required 1V, however, PGOOD is still around 2.5V

The part is functioning, however, I am surprised the resistance between the 1V output and GND is only 14 ohms ....

Hey Rajan,

Is the device drawing current with no load on it?
If that is the case the output minor short might be effecting it.

As far as PGOOD is concerned I will reiterate that there should not be a situation where PGOOD outputs 2.5 V.
PGOOD can sink up to 5 mA and thus should be able to pull the node all the way down if it wanted to be low.
Its possible there is a partial short on the node causing the issue.

Thanks,
Daniel

Daniel,

It's not possible to disconnect the loads from the regulator, which is supplying the 1V core voltage for an fpga and an mcu. Neither are currently being used at the moment, but both loads are powered. 

The current being drawn from the TPS7H4001 is low, it goes through a 5 milli ohm current-sense resistor and the voltage across this is amplified by 20 and is presently producing an output voltage of 70 mV. Therefore, the sense voltage is 70 mV/20 = 3.5 mV which means the current being supplied by the regulator must be 3.5 mV/5milli ohms = 0.7A

Hey Rajan,

Understood

Thanks,
Daniel

0.7A is quite a lot of static current, I'll have a look with the thermal camera to see where the heat is, but nothing is hot and there is no aromatic perfume

Hey Rajan,

I assumed 0.7 A was with the load applied.
I agree with your assessment, the most likely cause would be a solder short.

Thanks,
Daniel

It is, both the FPGA and MCU are powered and, therefore, drawing some current, however, neither are running an application, hence my last comment, 0.7A seems a lot for doing nothing ....

had a look at both sides with a thermal camera and there is nothing abnormal, e.g. a short-circuit current path, and I will check the datasheets to understand how much static power the FPGA and MCU dissipate when they are powered but not executing code.

The fact the TPS7H4001 is functioning correctly, apart from its PGOOD output level, is interesting.

Upstream of the TPS7H4001 is a TI TPS22997RYZR load switch, however, I think this got damaged during the initial power-up and I am now bypassing it using a wire ...

Hey Rajan,

Its quite possible the PGOOD got damaged during your testing.
A thermal camera might not see a "short" at this level of power.

Thanks,
Daniel