TPS563211: Is that the must to measure the Bode plot for TPS563211 to confirm the stability?

Hi Zixu,

 Please see Page8 of the attachment, It measure the bode plot for AECM topology and the result is not over 45 degree & 10dB. So that's why  I post this question. Could you help to double confirm this or could someone provide the TPS563211EVM test result for bode plot.

 By the way, from you opinion 45 deg and 10dB is good for buck converter. Does this include the DCAP topology?

AECM DCDC Control Topology.pdf

Hi Shihchin,

For stable work, PM is recommended to be greater than 45deg, but it does not mean that converter works unstably if PM is less than 45deg.

If you want to know whether the converter could work stably, some tests should also be included apart from bode plot：

1. load transient performance. Check whether there exists ringing in Vout

2. Steady state SW waveforms and Vout ripple. Check whether there exists multipulse in SW waveforms and extreme high vout ripple.

The recommendation rule for PM and GM is also suitable for DCAP.

BRs

Zixu

Hi Zixu,

For TPS563211,

  If from our test PM & GM can not meet 45deg & 10dB, do you have suggestion that how to imrove the PM & GM?

Since it doesn't have compensation pin.

Thanks. 

Hi Shhchin,

The feedforward capacitor (Cff) could be added to improve PM.

Since the bode plot of AECM is quite similar with DCAP, the following application note could be used to select Cff

Stability Analysis and Design of D-CAP2 and D-CAP3 Converter – Part 2 (ti.com)

BRs

Zixu

Hi Zixu,

  If use Cff, PM would be improved but GM would have chance to be decreased, right?

Hi Shihchin,

I suppose it depends on the value of Cff added in the circuit.  The GM would have chance to be decreased. But it should be tested on bench for verification.

BRs

Zixu