THS4631: About the effect of R3 in peak detector

Yatao Ling1

Expert 1840 points

Part Number: THS4631

Dear Ti expert,

I consulted you a problem about the configuration of peak detector several months ago.

e2e.ti.com/.../940064

I followed the circuit shown by Kai in the thread above, and it worked perfectly.

When I remove the R3 in the circuit proposed by Kai in the thread above, the output willl obviously oscillate a bit and deviate from the input when the input rises. This happend in both simulations and experiments.

I wonder why this R3 is so important?

Best Regards

Yatao

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

A happy New Year, dear Yatao :-)

R3 just improves the phase margin and by this avoids instability resulting in overshot:

yatao_ths4631_3.TSC

The crystal resistance of BAT17 additionally improves the phase margin by effectively increasing R3.

Kai

0 kai klaas69 over 4 years ago in reply to kai klaas69

Guru 140200 points

Also see the transient analysis:

yatao_ths4631_4.TSC

Kai

0 Yatao Ling1 over 4 years ago in reply to kai klaas69

Expert 1840 points

Dear Kai,

U r so nice!

Wish u have a good, healthy and happy year 2021. Take care!

Thx for your explanations! I have much to learn from u!

BTW, I hope my threads have not brought too much work load for u!

Best Regards

Yatao

0 kai klaas69 over 4 years ago in reply to Yatao Ling1

Guru 140200 points

It's a pleasure :-)

Kai

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THS4631: About the effect of R3 in peak detector