TPS54340B-Q1: Jitter in switching frequency of TPS54340B-Q1

Jagdish,

Please share the layout as well. I'd like to see if you could have some noise coupling to your RT pin.

-Sam

Hi Sam,

Please find attached layout.

Regards,

jagdish

LAYOUT OF iSLC3500-C REV.3.pdf

Hi Sam,

Apart from above issue, I would appreciate answers to below mentioned queries,

1. What could be impact on application with this jitter? As such we are fine with ripple we are getting. Any other impact..?

2. Could this impact reliability of TPS54340B-Q1 in long run?

3. Any other impact this jitter can have on any other parameter you think?

Regards,
jagdish

Hi Sam,

Thanks for your response. Did you got the chance to look into the layout for any noise issue?

Your statement " I have no evidence to suggest this will impact reliability of TPS54340-Q1 in the long run" , do you mean here that this jitter can't have any long term reliability impact on IC. Do I understand correct? or you mean something other way, please clarify.

Regards,
jagdish

Hi Sam,

Thanks for response, it will help me at least to release this PCB version since IC has no long term reliability impact.

However, apart from layout what else could be reason for this issue. Any idea?

Regards,

jagdish

Hi Sam,

We found the issue to be noise pickup from nearby SMPS. Now having 240pF capacitor on 107K RT resistor makes switching frequency stable. We checked following after adding capacitor on RT pin.

=> Power on waveforms at 1.6A load appears clean.
=> No jitter at switching node.
=> Transient response slightly degraded from 126mV to 148mV but quite enough for our application. Slew rate for transient was 25000A/s.

=> So do you see any issues in having 240pF in parallel with RT capacitor?
Awaiting your response.

Regards,
jagdish

Sorry,

Forgot to attach waveforms for your review.

Regards,

jagdish