UCC28061：Channel B single phase operation in light-load condition

Hello user,

during the start up, Phase B will have pulse output even that PHB is connected to VREF with high threshold. this is normal.

after start up, if the PHB is connected with Comp, then it is possible that comp pin voltage is less than the threshold of outputting pulses, at this condition, you have a chance with GDA no pulses GDB outputting pulses. if the PHB is connected with Vref, GDB should not output any pulse.

After startup, the PHB is not connected to the COMP, but 5V is applied to the PHB.

Is it possible that only GDB will always be turned on in this situation?

"If the PHB is connected with Vref, GDB should not output any pulse."

I don't understand the meaning of this sentence.

I haven't connected the VREF terminal to any other pin.

if the PHB is connected to 5v, when comp pin below 5V, GDB should keep off  after start up.

is it possible that customer mis-match the channel A and channel B?

I suggest you can use a new samples for the debug, and double confirm whether ZCDB /GDB for the same channel and zcda/gdb for the other channel.

I checked the terminal connections, but there was no mismatch the channels A and B.

After booting, V (COMP) = 2.5V and V (PHB) = 5V, so GDB should stop, but it is a single operation.

Is it strange that V (COMP) = 2.5V even though there is no load?

As pointed out, only the GDB output is pulsed with no or very light load, and with a little load, the GDA outputs a pulse.

Is the "regulated voltage" the reference voltage inside the IC?

Hi Mukaide,

if you slightly increase the load, Does GDA still only output one pulse?

I think at no load or very light load for GDA it maybe only one pulse, the pulse number depends on how long the Comp pin voltage over the 222mV threshold.

once the Comp pin voltage goes higher than 222mV when you increase the load, GDA should not only output one pulse.

the requlated voltage here is the PFC output voltage(PFC bus cap voltage)

As explained, when the COMP voltage exceeded 222 mV, both GDA and GDB output pulses.

[that is because at no load condition if the Comp Voltage is lower than 222mV, then both GDA and GDB will stop the pulse. And at this condition,

GDB output some pulses to allow the regulated voltage to be stable, and in the Phase A On time Control diagram, still phase A is stopped because it still do not achieve Comp pin higher than 222mV requirement.]

↑Does the above explanation refer to the hysteretic control mode on page 21 of the manual?

If yes, is there a mode in which hysteretic control mode operates only GDA under no load?

When the parts were replaced during the experiment（Q1,Q2,UCC28061）, the mode of the pulse output under no load changed to GDA single operation.

Please tell me the details of the operation of the hysteresis control mode.

(Relationship between COMP voltage and GDA and GDB operation)

The answer is that GDA or GDB may operate independently in the hysteresis control mode, but is it determined by the individual parts of UCC28061 whether GDA or GDB operates independently?

Or does it work randomly by turning the circuit on and off?