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Original question:

TPS62172 EN pin

TPS62175: Inverting Power Supply Issues

Kevin11
Prodigy 50 points
Part Number: TPS62175

Hello, we are using the TPS62175 as an inverting power supply. We are using it in two configurations. One of the configurations is working and the other is not.

Below is a configuration that is working. That is:

VIN = 12V

Expected Output = -2.0V

We are reaching ~-1.995 volts with this R1 / R2 configuration with no issues, The voltage output stays steady with or without a load. This configuration is working nicely. 

We are trying to use this same configuration, and only changing the value of R1 / R2 to try and achieve a -3.3V output but we cannot seem to get it to work. 

Below are the different R1 / R2 configurations we are trying for an inverted output of -3.3V. Both configurations result in a Voltage starting at -3.0V and as the device is powered over time, the voltage output changes to -2.6 and then stays there. 

Attempted Resistor R1 / R2 Configurations for output of -3.3V

R1: 68k

R2: 200k

R1:115k

R2:357k

We have double checked the calculations for the -3.3V output as well as the -2.0V output, why would this work at -2V and not -3.3V?

  • 0
    TI__Guru*** 142610 points
    Hi Kevin,

    Thanks for posting your circuit schematic.

    With SLEEP tied to GND, sleep mode is activated. This will strongly limit the output current. Can you cut that connection and tie SLEEP to GND (0V)?

    Finally, the EP needs to tie to the same potential as the IC's GND pins--this is Vout, not GND.

    Also, since you just changed a resistor maybe the soldering is not good or the resistor was damaged during installation. You might try replacing both FB resistors.
  • 0 in reply to Chris Glaser
    TI__Guru*** 142610 points
    Hi Kevin,

    Did you have a chance to cut the connection to the exposed thermal pad to separate it from GND?

    I just noticed that SLEEP is tied high, being tied to GND (0V). So, this should be ok.

    The resistor divider on the EN pin should be referenced to -Vout.

    It is key to remember that the logic levels are shifted in the inverting configuration.