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LM5032 (minimum duty cycle)

Paulin LEDESERT
Prodigy 75 points
Other Parts Discussed in Thread: LM5032

Hi,

I used LM5032 to drive 2 interleaved Buck converters, with a 200kHz switching frequency.

The COMP1 and COMP2 pins are connected together on the PCB. I have noticed a problem when I tried to have low duty cycles : the voltage on the pin COMP is about 1.6V, I measured a duty cycle of 6% on the OUT1 pin (about 300ns of conduction time), and on the OUT2 pin, I measured 0V during all the period.

I did not found any information on the datasheet which explains this problem. Do you have any idea of what can happen?

Best regards.

  • 0
    TI__Guru* 78400 points

    What you saw is not a problem.  The interleaved configuration is intended for high power, by which the two channels share the current.  It seems you ran the circuit with very light load.  Note that owing to tolerance, the two channels are not perfectly matched, and the PWM comparators may have slightly different parameter deviations.  When COMP voltage is low (usually the case at light load), the channel that have slightly higher internal down-shift of voltage (represented by the diode inside the COMP pin) may cut off the output, while the other having lower internal down-shift may still produce a small duty cycle.  When COMP voltage increases at higher load, both OUT's will operate, in the interleaved mode.