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LM3409HVEVAL: Start Up delay at 20kHz PWM

Part Number: LM3409HVEVAL
Other Parts Discussed in Thread: LM3409EVAL, LM3409, LM3409HV

Hi TI,

we have a problem with the LM3409EVAL Board.

The LM3409 operates at 1MHz with a 33uH inductor.  We use the external PWM with EN coupled and external 5V.

With 20kHz PWM is takes 2us to reach the 1,5A LED current.

With 100kHz PWM it only takes 70ns to reach the 1,5A but with a large ringing of the current.

We need a response time << 100ns up to 1,5A stable current.

What design changes are needed?

Martin Hermann