LMR62421: Problems with the PWM signal of the LMR62421

Hi Martin,

What's the voltage of VBAT1? Please also measure and provide the voltage at the EN pin.

Regards

Lei

Hi Lei,

The voltage on VBAT1 is 4.1V and on VIN it is 4.1V as expected, but I don't understand why the voltage on the EN pin is 2.1V, so I thought that there should be 2V on resistor R53, but when I measure the voltage on resistor R53 (between EN and VBAT1) there is 0V

Hi Martin,

I remembered that you've replaced the chip of LMR62421 and had the same issue. Could you have a try to replace the R53 as well?

Another trying is to remove R53 and connect EN to VBAT, then measure the Vout.

Regards

Lei

Hi Lei,

OK, I'll do it when I'm in the lab and I'll tell you the results.

Regards.

Martin

Hi Martin,

Thank you. Let's check again when you have the results.

Regards

Lei

Hi Lei Zhong,

Everything remains the same, now there is already 4.1 V on the EN pin but Vout is still equal to Vin and there is no PWM signal on the SW pin.

Could there be a faulty component? Why does it not generate the PWM signal on the SW pin if the EN pin is high and Vin is in the established range?

Regards,

Martin.

Hi Martin,

Please help take a clear photo of the top surface of this device. I'd like to check the top markings and confirm it's a real TI device.

And is there no load at the Vout as the picture you attached?

Regards

Lei

Hi @Lei Zhon , I acquired the device I'm using from Mouser, so I'm confident about its origin. However, I'm still sending you the best image:

Hi @Lei Zhon , I acquired the device I'm using from Mouser, so I'm confident about its origin. However, I'm still sending you the best image:

I could take. What I do think is important is the arrangement of the circuit components.

The previous image is of the PCB

and I'll also provide a simplified image with the most important components of the entire power circuit.

Regards,

Martin.

Hi Martin,

In the previous setup, was the SW1 in open-status? If not, please have a try. The purpose is to make a empty load.

As for the top markings, I do see some difference compared with the samples I have at hand. Please see below. The first picture was taken from the fresh sample. The second one taken from the units after ~1 min 400C air flow.

And in the left-up corner, I saw that there was exposed copper. Was the device broken?

Are you available to demount the unit and take photo of the bottom markings? Sorry I just realized that the lot trace code of this device was on the bottom side.

I've sent the pictures you attached to our quality team for checking. Will let you know as soon as I have the feedback.

Regard

Lei