TPS51125 is commonly used main regulator IC in laptops and macbooks. This guide will help you identify if this IC needs to be replaced. Use the image as a reference of a normal working 3v/5v main regulator IC.
TPS51125 chip should have the following voltage readings for normal operations:
Make sure you are getting approximately 19V in VIN
Check if EN0 is present
If EN0 is present, then you must have normal voltages at VREF, VREG3 and VREG5
ENTRIP1 and ENTRIP2 must be within normal voltage range.
If ENTRIP1 and ENTRIP2 is normal, then you should have 3.3V and 5V at VOUT1 and VOUT 2
PGOOD should have 3.3V indicating a normal operation.
Note: Sometimes, ENTRIPx, VOUTx, and PGOOD will only have voltage readings when power button is pressed.
PGOOD:
PGOOD signal is an indicator that the circuit is operating normally. The absence of 3.3v provides a clear confirmation that there is a problem with this circuit that you need to focus on. Sometimes, the power button must be pressed before the PGOOD signal becomes present.
EN0:
EN0 is responsible for turning on VREF, VREG3 and VREG5. If these signals are not present, check EN0 if voltage is normal (see the reference image). Replace TPS51125 base on the following conditions:
Supply voltage at VIN is present
Voltage at EN0 pin is normal
Resistance of VREF, VREG3, and VREG5 pins with respect to ground is in the range of kilo ohms or higher
Any of the output voltage on VREF, VREG3 and VREG5 pin is missing.
ENTRIP1/ENTRIP2:
Normal voltage for these control signal will turn on the 2-channel output for 3.3V and 5V (V01 and V02). Replace this chip if ENTRIPx has normal voltages but VOx is missing. Make sure that the load resistance is normal.
DRVL1/DRVL2:
if any of the load circuit that is connected to VOx is shorted, the TPS51125 will force DRVLx to have 5V to protect the load from over current. if this is the case, check the load for short, as well as the high-side and low-side MOSFET for leaks.
SUMMARY
In summary, the absence of output voltage at VOx may be caused by missing ENTRIPx signals. If ENTRIPx signals are present but there is no VOx, then the TPS51125 may need a replacement.
If PGOOD signal is normal but any of the VOx is missing, then you may replace the TPS51125. The absence of PGOOD signal might also indicates a problem with the external circuits feeding input signals (EN0, ENTRIPx) for this chip, or this chip is busted, or any of the load circuit is faulty, including the low-side and high-side MOSFET it drives. Whatever the case, It is a good practice to perform voltage and resistance measurements to isolate and confirm the problem.
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