BODE plot measurement for TPS650832

Antony Lin

Genius 13480 points

Other Parts Discussed in Thread: TPS650832

Hi,

My customer needs to measure BODE plot for their TPS650832 project, and I have some related questions as below.

Besides the BUCK rails, can they measure BODE plot for the VTT LDO? How? The same way as BUCK rails?
When we measure one of the rail, does it matter that the other rails needs to be turned off or not?
Which GND point is preferred to be connected to the tester for each rail during the measurement?

Thanks!

Antony

over 8 years ago

0 Kevin LaRosa over 8 years ago

TI__Genius 17380 points

Hi Antony,

They can take a Bode plot of the VTT LDO if they want. It should not be any different than the BUCKs. The other rails being enabled/disabled should have no effect. GND connection should be a solid connection to the board GND, I don't think there is any particular spot necessary.

0 Antony Lin over 8 years ago in reply to Kevin LaRosa

TI__Genius 13480 points

Hi Kevin,

Just to double confirm, the GND point just need to be a solid GND on their board, and it does not need to be anyy specific GND pin for each rail, right? So, all the power rail measurement can actually share the same GND point for such measurement?
THanks!
Antony

0 Kevin LaRosa over 8 years ago in reply to Antony Lin

TI__Genius 17380 points

Hi Antony,

We don't perform Bode plot testing here, we prefer to rely on step response instead as it is more practical, so I am not an expert on Bode plot techniques. However, we would expect that a good connection to GND plane should provide sufficient GND connection.

0 Kevin LaRosa over 8 years ago in reply to Kevin LaRosa

TI__Genius 17380 points

Hi Antony,

I discussed it with Jay and he actually ran a test and found the testing should be done connected to either the input capacitor GND or output capacitor GND and that connecting away from the rail under test can have some effect on the crossover frequency.

0 Antony Lin over 8 years ago in reply to Kevin LaRosa

TI__Genius 13480 points

Hi Kevin,

Regarding the BODE test, customer would like to know if our buck rails in TPS65083x is constant on time technology or not. Besides, if the test result is not good, what can customer do to compensate it?

Thanks!

Antony

0 Kevin LaRosa over 8 years ago in reply to Antony Lin

TI__Genius 17380 points

Hi Antony,

The controllers are DCAP2. You can find more information on this architecture on the DCAP2 page on ti.com: www.ti.com/.../designing-dcap2.html

Let me know if customer finds any irregularity, but I don't expect it for DCAP2 architecture. They may try adding more capacitance.

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BODE plot measurement for TPS650832