LM51561: why the LM51561 does not have output

Hi Bowen, 

Thank you for using e2e forum.

Could you also please share the waveforms like SW, CS vs Vout and Vin?

Best regards,

Mounika

Hi Mounika,

The SW pin is a DC value (Vsw=Vin), which means the device is not switching, the pin3 GATE is 0, CS I did not test since Vsw is not switching, it should be 0. Vin is a constant DC value by power supply.

From the schematic, did you find any errors?

Thanks!

Best Regards,

Bowen

Hi Bowen, 

Please allow me some time to look into this. Thank you for your patience. 

Best regards,

Mounika

Hi Bowen,

Can you please specify the voltage you measure at VCC and BIAS pin?

Best Regards,

Hassan 

Hi Hassan,

I am out of office this and next week, after i go back to office, i will test these 2 pins and let you know.

Thanks!

Bowen

Hi Bowen,

Sure, I will wait for your response.

Best Regards,

Hassan

Hi Hassan,

I did some test. When input 20V, the bias pin is 18.4V, VCC is 6.8V. PIN12 UVLO is 2.69V.

GATE has no output.

The D1 diode is not conducting. So the power from VCC should be generated by this controller.

TP12 has 0.29V.

Thanks!

Best Regards,

Bowen

Hi Bowen,

Thanks for the information. I will come back to you tomorrow.

Best Regards,

Hassan 

Hi Bowen,

Based on your schematic and voltage levels at BIAS, UVLO, and VCC, your device need to be active and should perform the switching.

Can you please try to run the converter with R35 = 100Ohms?

Moreover, check the solder connection of R25 gate resistor.

If possible, can you please measure the gate signal on the gate pin of LM51561 IC to confirm that it is not a soldering issue. 

Best Regards,

Hassan