TPS63060: Oscillation stop section at startup

HI  Dice,

Suepect your input voltage is not stable in your picture and there is some mode transition, yes, in pure boost mode, you will not see switching signal at L1 and no switching signal at L2 in pure buck mode.

Anyway, you can see Vout is keep rising even there is no switching. But of cource if there is actually no switching, Vout will decrease but not increase, right?

Regards

Tao

Hi Tao,
Thank you for your reply.

ch1: Input voltage of 7.2V is stable.
ch4: SW waveform is L1.

Is it working without any problems?

Best regards,
Dice-K

Hi Dice,

I am afraid it does not make sense if Vin is constant 7.2V in start-up phase.

Then, device should always work in BUCK mode, no mode transition will be observed.

Could you let me the SW signal in your picture is which node? L1 or L2?

Also, could you help to capture another screenshot with Vin included?

Regards

Tao

Hi Tao,
Thank you for your reply.

As I wrote in my previous reply, the SW waveform is L1.
Figure 9-24 only shows step-down operation, but the inductor current appears to have stages.

The output current of the waveform I first showed seems small, so I think it would be interesting to investigate how the SW starts up if the output current is increased.

Best regards,
Dice-K

Hi  Dice,

Apologize. 

I think you mean it is interesting that the SW disappeared when Vout is increasing in your waveforms, right?

From your waveform, i am pretty sure Vin is actually not stable at 7.2V, yes, may be you set a 7.2V output of your power source, but actually, device need time to approch this target.

In your waveform, you can see the high voltage of SW in beginning is much lower then 7.2V which means your input voltage is actually not 7.2V here. After Vout is little higher than Vin, device change mode to boost, then no switching  observed, that is make sense.

Regards

Tao

Hi Tao,
Thank you for your support.

I checked the VIN start-up state again.

There is a FET placed before the 7.2V VIN input, and what had been reported as "stable VIN" until now was the voltage before this FET.
The actual VIN input to the DCDC gradually rose from 0V because the FET opened slowly, and the voltage stagnated along the way (until the input capacitor was fully charged).
As a result, from the time the DCDC started up, the mode progressed from buck mode to boost mode to buck mode, and because the SW waveform was viewed at the L1 terminal, it appeared that there was an area where the SW stopped, but in fact the L2 side was oscillating (boosting) and raising the output level.

The above waveform is the Buck region.
Ch1: VIN
Ch2: VOUT
Ch4: L1

The above waveform is the Boost region.
Ch1: VIN
Ch2: VOUT
Ch4: L2

Therefore, I think that the device is operating correctly.
Is it okay for the device to stagnate during VIN startup like this?

Best regards,
Dice-K