TPS53355: A question about ripple injection circuit

Genie Hsu

Part Number: TPS53355

1. In slva453 equation (4), it requires Cr must be larger than Cc, but in slva653 page 5, it states that AC coupling cap (Cc) should be 3 to 4 times larger than the integrator capacitor (Cr). Which one is correct?

2. In slva453 page 4, reagrding the selection of RrCr, why RrCr>L/DCR can get a good transient performance but have havier PWM jitter?

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

I'll look into this, It may be a few days

0 JohnTucker over 7 years ago in reply to JohnTucker

TI__Guru**** 191445 points

Genie,

SLVA453 is authored specifically for DCAP devices such as TPS53355. The authors of that application note have detailed knowledge of DCAP mode operation. The SLVA653 is authored by another group within TI for COT devices. COT is similar to DCAP, but it apparently has slightly different requirements with respect to ripple injection. For TPS53355, please follow SLVA453 and the TPS53355 datasheet for ripple injection design

The amplitude of the ripple injection determines the transient response and jitter. Higher amplitude has lower jitter as the slew rate is faster. Lower amplitude provides faster transient response at the expense of higher jitter.

0 Genie Hsu over 7 years ago in reply to JohnTucker

Intellectual 360 points

Dear John,

Regarding question 2, does it exist in COT mode, DCAP mode, or both?

0 JohnTucker over 7 years ago in reply to Genie Hsu

TI__Guru**** 191445 points

Genie,

I would suppose that transient and jitter are related the same for COT devices as DCAP as the operating principles are similar. However I have never personally worked with any COT type devices. Our operating group has never developed one. They come from other groups within TI.

0 Genie Hsu over 7 years ago in reply to JohnTucker

Intellectual 360 points

Thank you, John.

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TPS53355: A question about ripple injection circuit