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TIDA-01352: output ripple - mosfet date command burst

Part Number: TIDA-01352
Other Parts Discussed in Thread: LM5030

Tool/software:

Hello,

I observe voltage spikes on the negative output. Spikes frequency is a function of the output capacitive load. Vout TIDA 01352 = -70V.

Connecting 1x470uF at the output gives a pulse period of 2.2 seconds

Connecting 2x470uF at the output gives a pulse period of 5.6 seconds

Pulse period also decrease as the output current increase : 

Connecting Tida 01371 lower the pulse period to 0.6s

Connecting Tida 01371 plus adding 1mA on TIDA01352 throug an eload lower the period to 0.4s.

The regulation works by burst : mosfet gates are only driven during pulses:

Is the feedback path for the negative rail regulation fast enough ?

Can mosfet gating be better spread by acting on the board ? (feedback speed / LM5030 mode ...)

Best regards,

Nicolas.