LM5037 - Maximum Frequency Operation?

Kurt,

The maximum freq of LM5037 is 2 MHz Fosc, which is then 1 MHz at each output driver, at up to 50% Dmax.

The main considerations would be the effects of dead-time on Dmax, and prop delays on Dmin.

The deadtime is programmed with RT2 - with 15 k-ohm, dead-time is 75 ns typ, 105 ns max. At 2 MHz, this sets Dmax of ~40% for each output - a significant reduction. From Fig. 7, the minimum typ dead-time is ~20 ns, so with tolerance upper limit will be ~30 ns (from ratio of 105 to 75 ns). So with 30 ns dead-time, Dmax will be 47% - however, such short dead-time may be problematic, depending on how fast your external FET's turn on and off. It may be wise to design the power stage for a conservative Dmax.


Ton min will depend on the PWM comparator prop delays, which is 65 ns typ (tdly(pwm)). So this limits the minimum practical duty cycle to 6.5%, or somewhat higher to allow for some margin on the typ prop delay. At high line, light load, at the burst-mode boundary, toy need to check that the required pulse-width or duty cycle is achievable, i.e. more than this Dmin level plus some margin.


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Thanks,
Bernard