PMP7282: Slave not turning ON condition

Dear Sir,

The Soft Start Capacitor Value of the Slave should be less than the master?

Is that mandatory for Master -Slave configuration for proper functionality at No load conditions etc.?

Thanks and Regards,

Nesh

Hi Johny,

I don't recall seeing this behavior, so will have to run some tests here. There should not be any issue with the soft-start values.

Best Regards,

Bob Sheehan

Power Design Services

Dear Sir,

Thanks for the reply, what should be the minimum COMP pin voltage required for the slave (LM5116 controller) to operate in No load condition, Once the No load condition happens then master will work and, If the slave (COMP pin) is just below the required voltage, then it will not generate the PWM signals?

To make sure slave board it runs in No load condition. Any fine tuning is required?

Thanks & Regards,

Nesh

Hi Johny,

I made measurements on my prototype. At 48V in and no load, the input current draw is 35mA. Both phases are switching in deep discontinuous conduction mode. The slave has slightly wider switch pulses. Measuring at both error amplifiers, the master FB voltage is 1.220V, while the slave is 1.218V. COMP voltage on the master is 1.42V, while the slave is 1.46V. Since the salve COMP is slightly higher, there is a little more switching from the slave.

In your case I expect the COMP voltage on the slave is slightly lower than the master, resulting in no switching at all. There is nothing wrong, just a mismatch in component values resulting in some offset. To match precisely, the FB voltages and the external reference need to be the same. The gain resistors of 10K and 4.99K between the master and slave COMP through the external amplifier must also match.

Best Regards,

Bob Sheehan