TPS54291 Output Stability: Minimum output current

leinho

Other Parts Discussed in Thread: TPS54291, SWITCHERPRO

Hi,

I use a TPS54291 for the electronic supply of my robot. I use 3.3 Volts for internal supply with around 300 mA of consumption and 5 Volts for external supply. I mean with external that I left a pin with 5 Volts in order to add external PCB to the robot.

The problem arrives when a have only one PCB connected (around 20 mA load). The output voltage isn't stable. It's around 5 V but with a notorius ripple. With 3 PCB (around 100 mA load) the Voltage becomes stable. I have tested with an oscilloscope.

Is this telling me that I need a minimum load in order to assure the stability of the circuit?

Regards!

over 11 years ago

0 JohnTucker over 11 years ago

TI__Guru**** 191445 points

Do you have a schematic you camn post? And a waveform of the ripple shoeing both Vout and SW of the affeceted rail?

0 leinho over 11 years ago in reply to JohnTucker

Expert 1230 points

Hi John,

I am testing my robot right now. Here is the schematic and the oscilloscope pictures that you have asked:

We are testing the dc/dc converter without load and here is the oscilloscope pictures of Vout and SW (in this order):

(this is not periodic)

As you can see, Vout isn't stable. This also affects the 3.3 Volts line.

And these are the tests with one PCB as load (it's okay but "more okay" with more PCBs)

What do you suggest?

0 JohnTucker over 11 years ago in reply to leinho

TI__Guru**** 191445 points

The compensation resistors seem high. Where did you get the component values? I recommend that you input your parameters to Switcherpro software, then post the reults.

0 leinho over 11 years ago in reply to JohnTucker

Expert 1230 points

I got them using the equation proposed in the datasheet of the ic.

Adding one capacitor ( 4700 uF 16V electrolytic) in Vout seems to be solving our issues...

Power management

Power management forum

TPS54291 Output Stability: Minimum output current