Issue with Logic Level Shifter HV/LV Connections

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1

Hi Pololu Team,

I’m having an issue with a batch of the logic level shifters product # 2595. I have quantity 16 of these shifters, with the HV pins connected to a common 5V bus, and the LV pins connected to common a 3.3V bus. 7 of these shifters have a soft shorting resistance between the HV and LV of anywhere between 2 kohm to 16 kohm, whereas on the remaining 9, I measured the resistance between HV and LV to be ~1.6 Mohm. It seems like the short between the HV and LV is causing my 5V and 3.3V bus to short together, in this case, blowing a 1A fuse connected in series to my 5V power supply (just my current theory). This issue was repeated even without the Lx and Hx lines connected to anything.

Can you advise what is the nominal and appropriate resistance range between the HV and LV pins, and maximum allowable current?

Thank you,
Tim

2

Hi, Tim.

When all the MOSFETs are off, the resistance between LV and HV should be in the Mohms, and when a FET is on, it should be around 20kohms per channel. If all 4 channels are on, that resistance could be as low as 5kohms. The circuit for each channel is shown on the bottom of the shifter’s product page. The MOSFET on each channel is rated for about 800mA. If you would like help troubleshooting, please post some information about what you have connected to the shifter as well as pictures that show all connections.

-Claire