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# LMZ31704: Need help debugging problem

Part Number: LMZ31704

Hi,

.  I need help with an issue I have using the LMZ31704RVQT.  I think I know the solution, but I need to confirm with you.  First let me tell you what we have set up on our board:

Vin = 5V

Vout = 1.0V

Imax ~ 3A

Pvin = Vin

We have an input of 5V (4.75V to 5.25V) that we send through a filter that is dropping the voltage by about 0.4V.  When we use 4.75V as our input and drop it 0.4V we end up with 4.35V which is less than the 4.5V input voltage min required at the Vin, but not required at the Pvin which requires a min of 2.95V or (Vout + 0.7), whichever is greater.  It seems to me that we simply remove our present connection from Vin (pin 3) and connect it to the input voltage to our board (5V), bypassing the large filter so that we are guaranteed at least 4.75V there.  Please let me know if this makes sense or if you need other information.

Also, I’m assuming that the Vin pin 3 is using a lot less current than the Pvin pins (1, 11, 12, 39, 40).  Can you tell me what that ratio is?

Thanks,

David

• Hi David,

I believe you are correct. The internal VIN UVLO is turning off the device. If possible, connect the VIN to your board input voltage of 5V. The current draw for the VIN is < 20mA.