TPS5430: TPS5430 cann't start

zhou zhx

Part Number: TPS5430

Tool/software:

The power supply circuit I designed using TPS5430 cannot start correctly when the supply current is below 800mA, regardless of the voltage, but it can start correctly when the current exceeds 900mA. What can I do to solve this problem (given the current design of the circuit)?

5 months ago

0 Onkar Bhakare 5 months ago

TI__Mastermind 20482 points

Hello Zhou

Could you please share some waveform which hep describe the issue you are facing. Kindly probe following points

PH
VOUT
BOOT

It would really help if you could capture these waveforms at 700mA load and 1A load. Let me know Vin, Vout conditions and kindly share your schematic for review.

Thank you

Regards

Onkar Bhakare

0 zhou zhx 5 months ago in reply to Onkar Bhakare

Prodigy 40 points

Here my load is not 700mA and 1A, my load is 5V/3A. It cannot start normally, which is due to the 800mA current at the input (Vin) preventing normal startup. Both 12V/800mA and 24V/800mA inputs cannot start normally. It is just that the input end requires a higher startup pulse current, but the source end limits the current to 800mA, which prevents the DC/DC from starting.

0 zhou zhx 5 months ago in reply to zhou zhx

Prodigy 40 points

This is 24V Input setting 800mA current limiting，The DC/DC converter is not working properly. Probe 1 is BOOT，Probe 2 is PH（SW），Probe 3 is OUTPUT （5V）

0 zhou zhx 5 months ago in reply to zhou zhx

Prodigy 40 points

This is 24V Input setting 1A current limiting，The DC/DC converter is working properly. Probe 1 is BOOT，Probe 2 is PH（SW），Probe 3 is OUTPUT （5V），Normal work actual input 360mA/24V.

0 Onkar Bhakare 5 months ago in reply to zhou zhx

TI__Mastermind 20482 points

Hello Zhou

As you correctly identified, the issue is likely your power supply’s 800mA current limit. Buck converters can demand higher initial current during startup to charge the output capacitor and supply load component

Let’s calculate the expected input current:

Output Power (Po): 5V * 3A = 15W
Efficiency (η): Let’s assume 80% (0.8)
Input Power (Pin): Po / η = 15W / 0.8 = 18.75W
Input Voltage (Vin): Assuming 12V
Input Current (Iin): Pin / Vin = 18.75W / 12V = 1.5625A

Therefore, the issue is likely a limitation of your power supply, rather than a device issue. Your power supply must provide current higher than required, especially during startup.

Thank you

Regards

Onkar Bhakare

0 zhou zhx 5 months ago in reply to Onkar Bhakare

Prodigy 40 points

What methods can I use to delay the startup of the DC/DC in this design?

+1 Onkar Bhakare 5 months ago in reply to zhou zhx

TI__Mastermind 20482 points

Hello Zhou

Delaying the startup won't help here as even in steady state, current requirements from input side is 1.5625A. So, input power has to supply required current demanded by the converter

Thank you

Regards

Onkar Bhakare

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TPS5430: TPS5430 cann't start