TPS51200: Capacitance on REFOUT pin

Shota Mago

Part Number: TPS51200
Other Parts Discussed in Thread: TL431

Hi team,

According to PCN notification which my customer received recently, "keep total REFOUT capacitance below 0.47 μF" was added on pin function table.

The customer assumes having greater than 0.47uF would cause REF oscillation .

Could you provide more detail about what if the capacitor is greater than 0.47uF?

I'm looking forward to hearing back from you.

Best regards,

Shota Mago

over 5 years ago

0 Qian Chen over 5 years ago

TI__Mastermind 24075 points

Hi Shota,

In recent simulation we see lower phase margin with higher capacitance on REFOUT. This is precautions move for the future design.

TPS51200 is being used by many customer in large quantity, We know the refout capacitance is larger than 0.47uF in some customer's design. So far no customer report REFOUT issue.

In typical DIMM application, the REFOUT current is only a few uA, so it is low risk to keep the existing cap on the released project. For future projects we would recommend customer to stay at or below 0.47uF.

Thanks

Qian

0 Shota Mago over 5 years ago in reply to Qian Chen

TI__Expert 8130 points

Hi Qian,

Sorry for positing additional question whereas I clicked "resolved" button.

My customer is asking another question.

At some devices, having larger capacitor enters stable region.

e.g. TL431 figure 16.

https://www.tij.co.jp/lit/ds/symlink/tl431.pdf?ts=1591695645185&ref_url=https://www.tij.co.jp/product/jp/TL431#page=17

Is there no condition like above(having larger capacitor enters stable region) at TPA51200?

Does having large capacitor just decrease phase margin since REFOUT is output of internal simple opamp?

Best regards,

Shota Mago

0 Qian Chen over 5 years ago in reply to Shota Mago

TI__Mastermind 24075 points

Hi Shota,

The REFOUT internal design is different from TL431.

It is a linear output with control loop.

Thanks

Qian

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TPS51200: Capacitance on REFOUT pin