Hello,
I am running some tests on a 5031/4232 PD combination. The “power supply” runs more or less fine, but I encounter an issue with the transition from Boost mode to Buck mode. I find the Vout/Vin differential way to large, but maybe I am missing something.
The board is powered by a 19V PSU and I have measured the input voltage at the Vin pin of the 4232 with my scoop and it reads 18.1Vmin and 18.4Vmax at full load. The Fs = 600Khz.
At full load (15V-2.6A) the 4232 runs perfectly fine in Buck mode. When the output voltage is increased to 15.3V, then the unit starts to run in Boost mode. To make the transition to Buck mode again, the output voltage needs to be decreased to somewhere between 12 – 14V, even without a load.
Is this normal behavior and do I mis reed the spec sheet? Is there an option available in the config to optimize this setting?
Hi,
Thank you for posting on the MPS Technical Forum.
This sounds like normal behavior. The converter will transition from buck to boost before the output voltage reaches its input. 100% duty cycle is uncommon in converters above 6V. To transition back to a buck, the converter will want the input voltage significantly higher to ensure the output is still regulated.
What output voltage(s) are you looking to use in your system?
Thanks,
Allison
Hello Allison,
Thank you for your reply.
The PDO’s are 5/9/12/15/20V. The unit is powered by a 19V external power supply and the voltage measured at the Vin pin of the 4232 does not drop below 18.10V. The Fs = 600Khz
In the specsheet is stated following:
Mode Transition Threshold
Buck-boost to buck transition threshold VMODE_TH2 VIN / VOUT 120 %
Buck-boost to boost transition hysteresis VMODE_HYS2 VIN / VOUT 82 %
When the PD switches from 5 - 15V, the unit runs trouble free in Buck mode. When 20V is selected then the unit start to run in Boost mode. When you go back from 20V to 15V, then the unit keeps the Boost mode for 15V regardless of the output current (low current = high Vin). I have to go back to 12V or power cycle the circuit to get the 15V output in (pure) Buck mode again.
Now going back from 20V to 15V is rare, but the unit goes in Boost mode also with a over-current event when running on 15V. That is fine, but is doesn’t go back to Buck-mode even with disconnecting the load.
Maybe you can give me your estimated value for Vin when the unit should make the transition from Boost to Buck with Vout = 15V, so I can double check this.
Is there a configuration option for the threshold, maybe the setting is wrong in the config?