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Part Number: TPS51120
Circuit for design of regulation using TPS51120 is similar to the datasheet. It is working in 2 of the boards.
But in 3rd board, CH-1 output of 5V is generated for 100msec and is dropping to 0V. EN1 is still high during this time and PGOOD1 is going low.
What is the current sense mechanism that you are using in your design? If you are using external sense resistor for sensing, can you please probe the voltage on the current sense resistor and send us the waveform? If you are using Rdson sensing, can you please give us the value of the threshold setting resistor. Also, please give us the part numbers of the FETs that you are using.
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1, upload your schematic
2, try more boards to confirm it is single board issue or not. If it is single board issue, swap the IC to double check the issue follows IC or the board.
Attached the schematic and CRO images of 5V, DRVH and CS1.
In reply to shiridi sai manikant chunchurupu:
Can you upload schematic and waveforms with the pictures instead of zip file? And have you confirmed my second question?
I have tested 3 boards and the design is working. I am having this issue in 4th board.
(1) VCC_5SB_F (yellow) and DRVH1(Green)
(2) CS1 (yellow)
Seems no weak in schematic to cause it can’t start up.
Since you have 3boards working well, only one issue board found.
1, About the issue board, if 3.3Vout works well, you can disconnect F7, the fuse of the 5Vout, to double check whether it can work normally..
2, if no found from item1, suggest to swap IC between good borad and issue board to check the issue follows board or IC?
The waveforms show that the TPS51120 is not achieving regulation and appears to be shutting down before it an reach regulation.
1) Over Current
my calculation show the current limit should be about 17A, but if there is excessive load on the output, the part wont be able to achieve the target output voltage and will shut-down to prevent damage t the device.
The TPS51120 has a minimum off-time between on-time pulses, which limits the switching frequency is can operate at while generating 5V on the output, it's possible that the minimum on-time is preventing the part from reaching regulation and triggering a shut-down due to under voltage protection.
I current mode control, the stability of the control loop is always a concern, if the loop is unstable, that could trigger UVP and shut-down the part.
Peter James Miller
Senior Applications Engineer
TI Power - Buck Switching Regulators - Mid Voltage
Senior Member Technical Staff 2020
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