TPS2491 enable and pgood behaviour

Arndt Kritzner

Intellectual 720 points

Other Parts Discussed in Thread: TPS2491

In my circuit I experience some unexpected behaviour:

- MOSFET gate voltage (blue) and output power (pink) are switched on before EN (green) signal

- PGOOD (yellow) never reaches HIGH (good) level

- TPS2491 VCC is ~11V (as output voltage)

- EN is switched by microcontroller (3.5V)

- PGOOD is pulled against the microcontrollers VCC (3.5V) over a 100k resistor

- my test was with no load or very light load (10mA)

I'd expect the load to be switched on when enabled and vice versa and PGOOD to come up with a small delay after load power. Or do I misunderstand the intended devices behaviour (possible)?

Kind regards

Arndt

over 11 years ago

0 Darwin Fernandez over 11 years ago

TI__Mastermind 41770 points

Arndt,

This is unusual behavior. The enable pin turns off the gate driver so you should expect the FET to be off when it is low. Is the FET or IC damaged? Can you attach a schematic? Have you tried testing the EVM in your system?

0 Arndt Kritzner over 11 years ago in reply to Darwin Fernandez

Intellectual 720 points

Darwin,

Thanks for your reply. Attached the schematic snippet. The rails are:

+V_INTERN: 3.3V (µC Supply)

V+ and VOUT_BUF: ORed external end internal ACCU voltage, 11V

~LOAD_OFF: from µC (3,3V logic)

PG_LOAD: to µC

FET is a AUIRF540ZS. A second device shows exactly the same behaviour, so it's not very likely that IC or FET are defective.

Kind regards

Arndt

Bordspannungs-USV.pdf

0 Naveen Bevara over 11 years ago in reply to Arndt Kritzner

TI__Intellectual 1970 points

Hi Arndt,

Have you tried this on a regular EVM of TPS2491? Instead of controlling from a microcontroller, use an external source and test on a regural EVM with changes made in it accordingly. Also could you confirm that all the components are correct in the layout and there is no layout mistake.

0 Arndt Kritzner over 11 years ago in reply to Naveen Bevara

Intellectual 720 points

Hi,

we found a pin direction mistake in our controller programming, so 2 output pins were on the same net. Sorry. After fixing this PG acts as expected.

Thanks and Regards

Arndt

Power management

Power management forum

TPS2491 enable and pgood behaviour