TPS923653DYYREVM: TPS923653DYYREVM Change to Buck-Boost Mode

Vadim Konradi

Part Number: TPS923653DYYREVM
Other Parts Discussed in Thread: TPS923654, TPS923655

The TPS923653DYYREVM is originally configured for boost mode.

Boost Mode Sanity Check:

I'm testing with a ~26V LED load. When input voltage is near 26V, input current is a little over 2A. Seems right for output 2A and Vout ~= Vin.

When I decrease input voltage, the input current goes up. OK, normal boost behavior.

Configuring for Boost-Buck Mode:

I disconnected LED minus from GND and connected to Vin. This configures buck-boost topology.

I decreased the value of R6 to 31.3k. So I'm expecting overvoltage protect at theoretical 52.7V (Vin + V_LED).

I apply input voltage. Works with no fault between 11V ... 27.5V.

11V fault is maybe FET overcurrent, ok. 27.5V fault is probably OVP (Vin + V_LED), ok.

But in this ok voltage region, indicating no fault, the input current is low. At Vin = 26V the input current is 1.16A. It should be above 2A.

I haven't put a meter in the output yet, but obviously it is lower than the 2A output current EVM set point which worked correctly in boost mode.

Is there some other change required to configure buck-boost mode on this EVM? Thank you.

over 1 year ago

0 Patrick Yao over 1 year ago

TI__Mastermind 34840 points

Hi,

Our expert is out of office and will give you feedback when comes back.

0 Vadim Konradi over 1 year ago

Prodigy 90 points

Patrick, thank you for the quick response. When is the expert expected back in the office? Should I be working through my local FAE?

I connected a scope and a current meter in series with the LED output.

In Boost mode I see good output current regulation ~ 1% at 2A over 22V < Vin < 29V. Output current falls off fast below Vin=22V.

Now Buck-Boost configuration, with LED minus connected to Vin. Stable operation over 11V < Vin < 29V. Observing 639mA < I_out < 985mA over same Vin range.

So in buck-boost mode the current is wrong, less than half of the setpoint, and not well regulated.

0 Steven Li over 1 year ago in reply to Vadim Konradi

TI__Mastermind 23200 points

Hi Vadim,

I am currently out of office. I will reply to you on May 6th when I am back to office. Thanks for your understanding.

Best Regards,

Steven

0 Vadim Konradi over 1 year ago in reply to Steven Li

Prodigy 90 points

OK, just finished a schematic review and we are starting layout. If there is some additional application note or layout guidance regarding buck-boost mode for this part, please advise. We are working from the datasheet which has a buck-boost schematic, and the EVM which is buck mode.

I appreciate your help upon return to the office. Thank you.

0 Steven Li over 1 year ago in reply to Vadim Konradi

TI__Mastermind 23200 points

Hi Vadim,

First of all, you should use TPS923654 / TPS923655 in VSON package for Vin = 26V, Vout = 26V, Iout = 2A in Buck-boost mode due to higher internal switching FET cycle-by-cycle current limit and better thermal performance of the package.

Vadim Konradi said:
Now Buck-Boost configuration, with LED minus connected to Vin. Stable operation over 11V < Vin < 29V. Observing 639mA < I_out < 985mA over same Vin range.

Please check if you modify the thermal foldback resistor R_TEMP (R7 on EVM)? If not, then most likely this is due to both thermal foldback and internal switching FET cycle-by-cycle current limit.

You can disable the thermal foldback (Please refer to this E2E FAQ - [FAQ] Is there a way to disable the thermal foldback function of TPS923655 / TPS923654 / TPS923653 / TPS923652? - Power management forum - Power management - TI E2E support forums) to have another try but most likely you will see the LED flickers due to thermal shutdown. Again, please use VSON package for better thermal performance.

Best Regards,

Steven