TPS73201 Reverse Current Issue

I am assuming you are considering connecting the EN pin to VIN so that the TPS73201 is always enabled when power is applied.  This will not damage the TPS73201.  The TPS73201 output voltage may overshoot on power up with the EN pin connected to VIN which is not a problem for the TPS73201 but could be a problem for the load it is powering.

I am not connecting EN pin to Vin. I am using EN separately since I need to power on the TPS73201 after some other power is stable.

The datasheet recommends that EN be driven low before VIN is removed and I am just wondering if this doesn't happen in this order, is there a problem?

Matty, for your case the order EN is pulled low is actually not the issue. The only requirement is that the EN pin be held low when there is power to the part.

When the part is powered but disabled, the gate of the NMOS pass transistor is discharged. We recommend EN low before power is removed to insure that reverse current can't flow from OUT to IN when power is absent (ie: OUT is high and IN is low).

Hi .

I have an issue with TPS73201 powered from +5.1 V input curent limit 90mA , ENABLE connected to In , V out set to 1,25

Problem :

Device powered up , tested - output voltage OK , device turned of by remove IN voltage ,   after that device has been powered up again and , damage of TPS73201 was observed . ( Input shorted to GND , voltage drop about 600...700mV - current limited to 90 by external regulator that power up TPS 73201 .

I assume that problem is caused by EN tied to IN .

Am I right that if gate is charged during power down , than during next power up  ( a few seconds after power down) it is posible that curent limit doesn't work .

Because have no explanations for damage of TPS73201 in that circiut ( because IC is powered up from current limited source)

Please let me know what do you think , preferably let's continue via email .

Regards Grzegorz

Hi Grzegorz,

I am not sure what is occurring in your application.  My first thought was that the reverse current might be damaging the part during shutdown.  I cannot account for the fact that the part is damaged by a "short to ground" - I would have thought instead that the input to output would be shorted or open (but not shorted to gnd).  You could add a diode in series with the input to see if this prevents the problem -  by preventing the reverse current.  Note - this reverse current is due to the gate charge holding "on" the pass FET (and the pass FET's body diode) to effectively short  Vout to the ground at Vin.

If there is an internal charge remaining on the gate of the pass fet before the next turnon then what happens is that the input is shorted to the output for the time it takes for the part to start up properly. I suppose that large currents could flow in this case as well except that the current is limited to 90mA - which would not damage the part.

Bill

Bill's answer is correct. I might add:

If there is a large cap on the output, when input power is removed and if the input is low impedance, reverse current could damage the part. Like Bill says, it seems more likely that this would give an input-output short, but might not.

Also, if there is a large cap on the output, when power is re-applied the part a very large current can flow before the current limit on either the TPS732 or the power supply can engage. The turn-on time for current limit is often in the 10's to 100's of us.

Dave H

Hi

thanks a lot for help : Please have look on details:

1. IC removed from circuit tested using standard multimeter , diode test:

voltage drop betwen pin 1 (+) and other (-):

1-2 760mV

1-3 1,43V

1-4 1,42V

1-5 0,39V

 reversed polarity PIN 1 (-)

1-5 infinity

1-2 500mV

1-4 800mV

Please have o look on schematics - I placed is here :  http://e-stewia.pl/screenshot.24.jpg because have no idea if possible to attach file to this post
there are no large cap's there so it must be something interesting if such damage was observed , right now I have about 120 units damaged that way , and most of them works fine when IC is replaced

I connected external power supply to IC11 PIN 1 (5V1 ) and I was trying to simulate power loss / power up - no damege was observed , even if TPS had addirional load (20R on TP43)

If you have any suggestion - will be happy to discuus it .

Grzegorz

Hi Grzegorz,

I still don't see what might be causing your problem. Assuming that the enable occurs after Vin is applied and disable occurs before Vin is removed, then we have experienced no problems.  However, despite what is said about "large capacitors," I would encourage the use of 10uF minimum for the output caps (C32, C52, and C78) and not more than 10nF for the feedforward capacitors ( C61,62,63).

It might be a good idea to start the failure analysis process, but I warn you that it takes several weeks for the process to work itself through.  This is the only way to possibly discover whether your diode readings are correct - though I am not entirely sure this is tested.  Attached here you will find a failure analysis report for you to fill out as well as possible.  Send this document along with several failed units to the attention of Halimah Yusof at the address found at the end of the document.

7713.FVF_Dallas.doc

Bill