TPS62063 SW Node stops switching

Aaron Burnie

Other Parts Discussed in Thread: TPS62063

Hello all,

I was wondering if someone would be able to help me out with a strange issue I have with the TPS62063 Step Down Converter. My schematic is as below and I have put a 150 ohm load on the output to draw a little bit of current.

Initially all seems to be working properly and the SW node has a PWM output of ~3.2MHz

However after ~126usec the switcher stops switching and the output voltage regulates to the input voltage. It seems that the FB pin is no longer sensing the output voltage and hence it stops regulating.

This last image just shows a little more close up of the PWM waveform which then stops switching and becomes the input voltage.

Is it because I need a greater load on the output to actually see any more switching? If this is the case I would have thought the output would still regulate to the 3V3 that I wanted.

Thanks

Aaron

over 9 years ago

0 Chris Glaser over 9 years ago

TI__Guru*** 142710 points

The TPS62063 is a fixed output voltage version, so the FB pin needs to connect directly to the output without any FB resistors per the D/S. Assuming everything is soldered down well, this will give 3.3V as the input voltage varies.

0 Aaron Burnie over 9 years ago in reply to Chris Glaser

Prodigy 140 points

Thanks Chris,

Seems like I overlooked this bit in the datasheet in the pin description section.
Is there generally any instability issues with the fixed voltage output versions and hence would I need to add a feed forward capacitor between Vout and the FB pin?

0 Chris Glaser over 9 years ago in reply to Aaron Burnie

TI__Guru*** 142710 points

Nope, they are perfectly stable just like the adjustable. The Cff is taken care of inside the IC.

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TPS62063 SW Node stops switching