ADP5350 Lose I2C with LDO Discharge

Hi Robert,

Kevin responded to you on other question also about the LDO. Did that fix the issue of this LDO discharge?

Hi Fil,

Who is Kevin and can you give us the answer here?

Thanks

Charly

Hi Charly,

Im referring to this post: https://ez.analog.com/power/f/q-a/534611/adp5350-ldo1-with-usb. The fix was about schematic connection. Is this a different issue?

Yes it is a different issue. 

The VDD123 is connected now but the problem is still there!

Charly 

Hi Charly,

Did you tie VIN1234 together? VIN4 is the power supply of the LDO controller. 

Let me confirm with your issue. The I2C pull up supply is LDO1. When you turn off LDO2/3 with discharge function enabled, LDO1 output would be 1.2V and I2C cannot communicate. Is that correct?

BRs,

Kevin

Yes to tying them together and yes to the 1.2V :)

I tried on the demo board and did not see this issue. Vout1 is still 3.3V and Vout2/3 are zero when I disable LDO2/3. What board did you work on?

This is for a customer, not me. 

I'll ask him to answer you here.

Charly

Hi Charly / Kevin,

We were finally able to solve the issue, which was an error in our schematic, by sourcing a MUX with LDO2, and using LDO1 for the pull up resistors on the MUX Select pins.  Seems that a diode or FET in the MUX was creating a path for LDO1 with a voltage divider, and of course, when we turned on the 500 Ohm Discharge on LDO2 we end up with a voltage divider on the I2C lines.

Thanks,

RM

Hi Charly / Kevin,

We were finally able to solve the issue, which was an error in our schematic, by sourcing a MUX with LDO2, and using LDO1 for the pull up resistors on the MUX Select pins.  Seems that a diode or FET in the MUX was creating a path for LDO1 with a voltage divider, and of course, when we turned on the 500 Ohm Discharge on LDO2 we end up with a voltage divider on the I2C lines.

Thanks,

RM