UCC28C54-Q1: Crossover frequency and mid-frequency gain selection?

Thomas Nilsson

Part Number: UCC28C54-Q1

In the datasheet page 35 a crossover frequency of 625 Hz is selected for the typcial application design exemplified in the datasheet, and then the error amplifier mid-frequency gain is determined to 14,6 V/V.

How do I choose a suitable crossover frequency for a design that I am making, and how shall I go about to determine the mid-frequency gain?

6 months ago

0 Hong Huang 6 months ago

TI__Guru 55865 points

Hi,

Crossover frequency usually is picked up by the load transient response. In this application, the load transient response does not need to be fast so around 0.5kHz to 1kHz is ok. For faster load transient response, it is better to use some other tools to estimate such as simulation, or using feedback control theory to get a first "guess", then test to see if good enough, if not increase the crossover frequency retry and reiterate until ok.

Fig 5, shows the measured plant Bode Plot. If 625Hz was picked up by the designer as crossover, so +23.3dB needed to get total = 0dB based on Bode Plot addition operation. Why he picked up 625Hz, likely he did this and found the design was ok to meet the load transient. Some near by ok to pick up as well - no fixed ok or wrong. You could pickup 500Hz, then 20dB is needed to get crossover at 500Hz.

0 Thomas Nilsson 6 months ago in reply to Hong Huang

Prodigy 190 points

Ok, so is this the procedure I should go through to get the plant bode plot?

https://www.ti.com/lit/an/snva364a/snva364a.pdf?ts=1712341507080&ref_url=https%253A%252F%252Fwww.google.com%252F

0 Hong Huang 6 months ago in reply to Thomas Nilsson

TI__Guru 55865 points

Hi,

Yes, the plant bode plot is from COMP to VOUT.

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UCC28C54-Q1: Crossover frequency and mid-frequency gain selection?