LM61460-Q1: Question about the start up test

Hi,

In order to better solve the problem, please provide the circuit schematic diagram. Also, may I ask if this phenomenon occurred in the test on the LM61460EVM? Or on the customer's own board? Looking forward to your reply. Thanks.

Aurora

Hello expert,

    This issue happened on my board.Here are the schematic,now MCU is no function about the CPU_CV_REF so I think this is high impedance and no impact. And will the R1711 and C1718 slow down the loop and cause this issue?

Hello,

Due to the US holiday, responses may be delayed. Our team will get back to you soon.

Hi,

Can you test the waveform of SW pin, I want to see the work condition of the chip.  And can you remove R1711 and C1718? Thanks.

Aurora

Hello expert,

    I remove R1711 and C1718 and there is nod voltage drop issue now. But the delay from the EN=1 to output voltage start to ramp up is the same.Is it due to the CV BUCK loop?

Hi,

Normally, the start-up waveform should be as shown in the figure below. You can see it in the datasheet. Can you try to disconnect the front and rear stages of the circuit, and then use Vin to supply power to EN, and test the startup waveform of LM61460 alone? In addition, do you have a sequence when you power on? Does Vin exist before the EN voltage? Thanks.

Aurora

Hello Expert,

    I confirm that the Vin is always present even before and after the enable is pulled high. It is strange that the device need such a long time to start the output voltage ramp up when EN=1. Do you have a maximum value defined for this? From your data the time is less than 1ms

Hi,

The data I gave above was tested with EVM. May I ask if you have an EVM that can move the customer's parameters to the EVM to see if this phenomenon still exists? In addition, please test the waveform of Vin. Pay attention to the waveform at the Vin pin of LM61460. I'm still concerned that the actual Vin pin waveform isn't always there.

Thanks