TPS56528: Power Dissipation

Parag Bisen

Part Number: TPS56528

Tool/software:

Hello Team,

In our project we are using 8 TPS56528DDA Buck converter .Schematic is uploaded on the Drive Link
input voltage : 16V
Output Voltage : 5.3V
output Current : 3A

There are total 8 Buck with same configuration as mentioned above .
We calculate the Power dissipation across one buck when all the buck are running at full load (3A).
We found PD across 1 buck = 2.68W

Overall PD = 21.44W (across 8 buck).
Efficiency of buck = 85.5%. Efficiency is low , we were expecting to have efficiency around 93%.
Buck input section waveform and output section waveform are added in the drive link
inductor part used is XAL4030-332MEC ,Datasheet is in drive .
Please suggest how to reduce the Power dissipation across the buck .Buck should provide 90 to 93% efficiency .

Drive link : drive.google.com/.../1jh4OPAcHO5qq5Aef539kjCUtgRDSdXy8

4 months ago

0 Himanshu Nigudkar 4 months ago

TI__Intellectual 1850 points

Hi Parag,

Can you please elaborate on how you arrived on 2.68W power loss?

Regards,

Himanshu

0 Parag Bisen 4 months ago in reply to Himanshu Nigudkar

Prodigy 65 points

Hello Himanshu,

We measured the Buck input voltage and current at the vin pin and output voltage and current at TP126.Active load is connected at the output of the buck at TP126

Check the input and output waveform attached in the drive link.
Measured input voltage vin=15.35V
Measured input current at vin pin =1.21A
Power = 18.06W

Measured output voltage at active load = 5.33V

Measured output current at active load =2.982A
Power= 15.925

PD=18.06-15.925 =2.68W.

Voltage and current are measured with Oscilloscope

0 Himanshu Nigudkar 4 months ago in reply to Parag Bisen

TI__Intellectual 1850 points

Hi Parag,

Can you please re-check the calculations once? 18.06 - 15.925 = 2.135. Also, how long is the trace from input/output connector to the device? If the trace has significant resistance, you can expect some voltage drop across it. We recommend to measure the voltages near to the device (maybe on input/output capacitors), with an accurate DMM. Also, if possible can you attach the schematic directly? I am unable to open the drive link.

Regards,

Himanshu

0 Parag Bisen 4 months ago in reply to Himanshu Nigudkar

Prodigy 65 points

Hello Himanshu ,

Sorry ,writing mistake its 18.60-15.925 = 2.68. We have measured input directly on the Vin pin and output on TP which is very close to output cap (both are in same plane).

sch_501-1-03918_a1.pdf

0 Himanshu Nigudkar 4 months ago in reply to Parag Bisen

TI__Intellectual 1850 points

Can you please share the schematic and BOM?

0 Parag Bisen 4 months ago in reply to Himanshu Nigudkar

Prodigy 65 points

Hello Himanshu,

Schematic: sch_501-1-03918_a1 (1).pdf

BOM: 5V SWITCHER_CORE_ENG BILL OF MATERIALS.xlsx

0 Parag Bisen 4 months ago in reply to Parag Bisen

Prodigy 65 points

Hello Himanshu,

Please provide your feedback

0 Himanshu Nigudkar 4 months ago in reply to Parag Bisen

TI__Intellectual 1850 points

Hi Parag,

I dont see anything wrong with the schematic. It maybe be because of inaccuracy in test setup. Can you please share the details of the test setup?

0 Parag Bisen 4 months ago in reply to Himanshu Nigudkar

Prodigy 65 points

Hello Himanshu,

Please find setup details,

Test Setup for Buck Efficiency Check:
1. DC Power Supply with 16V/15A output configuration was connected on the VCC_16V0 power rail
2. Active DC load with 3A constant current configuration was connected at point B
3. Pin 8 of U49 buck was isolated from the PCB, a short wire of length ~6cm was connected between Pin 8 of U49 buck and pad 8 of U49 on the PCB. This was done to probe the buck input current.
4. DC supply was turned ON first, then the active load was turned ON. Other loads from point B were isolated.
5. After stable operation for 5 mins, the voltage and current at point A was probed.
6. The voltage and current at point B was also probed. Efficiency was calculated from these power numbers measured.