TPS40210: TPS40210 overcurrent protection always starts at only 6 Watt output power

Constantin Wiesener

Part Number: TPS40210

Hi,

I've just used the simulator and realized now the circuit. But I am facing some issues.

webench.ti.com/.../webench5.cgi

In the simulation I can run all simulations quiet well, except the startup. There the output voltage does not reach the requested 95V.

Furthermore in the real circuit we can't reach the real output current. So the voltage never reaches 95 V if the load is 1.16 kOhm (= 7.78Watt). It stays at 75 mA for 1kOhm (5,9Watt).

So I can't reach the simulated output current. If I increase the input current the TPS goes into overcurrent protection and switches off.

Is there a reason for this behavior?

Best regards,

Constantin

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru 73120 points

It sounds like hitting the peak current limit at higher load: the duty cycle is cut short hence Vout setting at a lower voltage. Can you monitor the current sense waveform, and post it so we can review?

0 Constantin Wiesener over 7 years ago in reply to Youhao Xi

Intellectual 540 points

Sorry for the delay, but I was on short business trip.

Here is the plot of the scope of the ISNS pin.

Input voltage:

6.3 V

0.936 A RMS

Output:

67 V

67 mA

1 kOhm load.

Thanks.

Constantin

0 Youhao Xi over 7 years ago in reply to Constantin Wiesener

TI__Guru 73120 points

You can see there is a current pulse that exceeds the peak limit of about 150mV typical. Can you check if the inductor (120uH) and the current sense resistor (0.03Ohm) are installed with right component? The reason for this question is that the CS peak voltage should not be that high. Also, where is the RC filter at the CS pin located on your PCB? They should be closely placed by the CS pin.

0 Constantin Wiesener over 7 years ago in reply to Youhao Xi

Intellectual 540 points

Could it be that the reason is a non-shielded inductor. We ordered by mistake a non shielded one. We will replace it with the shielded version and try again.

Best regards,

constantin

0 Youhao Xi over 7 years ago in reply to Constantin Wiesener

TI__Guru 73120 points

Hi Constantin,

Thank for the info. It could be the reason. Please signal back after you test with the new inductor.

Best Regards,
Youhao

0 Constantin Wiesener over 6 years ago in reply to Youhao Xi

Intellectual 540 points

Hi,

with the shielded coil we improved the result but there is still a shutdown at only half the output and we cannot reach the stated efficiency. Furthermore I rerun the simulation and there I could not get the startup simulation running. Is there a way to say the simulation that the load is disabled and the EN pin is enabled after a certain time.
I guess that the reason.
We are still using a pinboard. Could this be the reason as well for the low output results.

Best regards,

Constantin

0 Constantin Wiesener over 6 years ago in reply to Youhao Xi

Intellectual 540 points

And what is the CS pin you referring to at the TPS40210?

0 Youhao Xi over 6 years ago in reply to Constantin Wiesener

TI__Guru 73120 points

I meant the ISNS pin, which is often called CS in most of our products. Sorry for the confusion.

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TPS40210: TPS40210 overcurrent protection always starts at only 6 Watt output power