TPS82130: minimum effective Cout

Kazuhiko Hirano

Genius 15578 points

Part Number: TPS82130
Other Parts Discussed in Thread: TIDA-01457

Hello,

My customer is considering to use TPS82130 as an inverting buck-boost referencing to TIDA-01457.

Their design requirements are as follows.

Vin = 3.3V+/-5%

Vout = -3.2V+/-2%

Iout(max) = 1.1A

Since their app requires very small size, they would like to use as small size Cout as much as possible.

Could you tell them how much minimum effective capacitance is required for the Cout from design point of view, please?

Best regards,

K.Hirano

over 5 years ago

0 Gerold Dhanabalan - High Performance Radar over 5 years ago

TI__Genius 14455 points

What are the ripple and transient requirements on Vout?

Regards,

Gerold

0 Kazuhiko Hirano over 5 years ago in reply to Gerold Dhanabalan - High Performance Radar

TI__Genius 15578 points

Gerold,

Since they remove the Vout ripple by LC filter located at later stage, they do not care about the Vout ripple at all.

Also, they do not care about load transient at all?

Anyway, they would like to know not only minimum effective Cout but also minimum effective Cin.

Please let them know the required minimum effective capacitance for Cin and Cout.

Best regards,

K.Hirano

0 Gerold Dhanabalan - High Performance Radar over 5 years ago in reply to Kazuhiko Hirano

TI__Genius 14455 points

Jean will do the calculations and get back to you.

Regards

Gerold

0 Jean Picard over 5 years ago

TI__Intellectual 1125 points

Kazuhiko Hirano

The inverting topology introduces a right half plane zero, as explained in TIDA-01457 literature.

That imposes restrictions on Cout selection that are much more stringent than from output ripple requirement. Please refer to literature indicating how to calculate the RHPZ frequency. To avoid stability issue, you need to limit the loop gain crossover frequency to sufficiently lower than fRHPZ. The amount used in the literature is a good starting point, then refer to SLVA381 to check stability and potentially fine-tune it.

Regarding input capacitance, you need to at least use a 10uF as indicated in TPS82130 data sheet. More capacitance may be needed depending on input network impedance and the amount of input ripple considered acceptable for the application.

Regards

Jean

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TPS82130: minimum effective Cout