TPS54521: TPS54521 S/C Output

paul humphreys

Part Number: TPS54521

Hello
We have been using the TPS54521 for approx 5 years without problems. - (approx 40K pieces)
On one design we are see a very high rate on failure in that the device fails and the output goes S/C - approx 1.6ohm
This design is on a 3G GSM Modem - Vin = +12V - Vout = 3.7V at 2A (max) - normal operation <50mA)

We are using the same design as used on other products - Vin = +12V - Vout = +5V @ 4A max

Anyone else seen a similar problem or can help

Kind Regards
Paul H

over 7 years ago

0 Andy Chen over 7 years ago

TI__Mastermind 34875 points

Hi
Did the failure occured on new design?
Pls upload your circuit design and PCB layout for checking

0 Vental Mao over 7 years ago

TI__Expert 5745 points

What's the mean of the device fails? Is the SW short to the GND? Or Vin short?

0 Vental Mao over 7 years ago

TI__Expert 5745 points

Hi
For the application of the 3.7Vout@2A. There have some problem.
1,Schematic: The value of the Comp pin is not good ,please calculate the data again(refer to the Datasheet); Add a o.1uF cap in the Vin
2 PCB: Move the input cap to the Vin pin closely; Move the Feed back resistors to the Vsense pin closely too.
Thank you!

0 paul humphreys over 7 years ago in reply to Vental Mao

Prodigy 60 points

Hello
Thank you for the reply.
We have 1000off PCBs that are in goods in. Awaiting test.

We have tested the first 20off and the devices are failing on about 50%. The output SW of the IC (TPS54521RHLR) is short circuit to GND .

We understood that the device was Short Circuit and Thermally protected

Questions

1. Will the values of the Comp allow the IC to get damaged and S/C the SW output
2. Will the input capacitors in their current position and connections allow the IC to get damaged and S/C the SW output
3. Will the position of the feedback resistors allow the IC to get damaged and S/C the SW output
4. Can you please suggest the correct components for the Comp Pin

Thank You

Kind Regards

Paul Humphreys

0 Vental Mao over 7 years ago in reply to paul humphreys

TI__Expert 5745 points

1，Yes,unstable loop will damage the IC easily.

2, For your application, the Cin is not a big problem

3, The feedback resistor is very sensitive, it can't keep Vout stable if some noise couple into, but not get damaged easily.

4, For the value ,you can use the WEBENCH to get the value quickly

0 paul humphreys over 7 years ago in reply to Vental Mao

Prodigy 60 points

Hello Vental

Thank You for your rapid reply

Webbench does not support the TPS54521 for some reason

So you know or an equivalent IC or other software that helps calculate the COMP values

I have attached a PDF with the values that I think are correct but it would be good for TI if you could confirm my calculations

The requirement is

Vin min = 11V

Vin max = 13V

Switching frequency = 700KHz

Iout max = 2.5A

Vout = 3.9V

Kind Regards

Paul Humphreys

0 paul humphreys over 7 years ago in reply to paul humphreys

Prodigy 60 points

3554.ti_support_suggested_values.pdfHello Vental

The COMP values uses were taken from the "Typical Application Note"

The only difference is Vout = 5V on application note and we require Vout = 3.9V

I have updated the PDF again with the typical application note added

Kind Regards

Paul

0 Vental Mao over 7 years ago in reply to paul humphreys

TI__Expert 5745 points

TPS54521.xlsx

Please refer to the attachment

For the layout, please refer to the datasheet and use 4-layers PCB

0 paul humphreys over 7 years ago in reply to Vental Mao

Prodigy 60 points

HI Vental

We modified 3off PCBs as per your recommendation and the first failed withing 5minutes

The output stage short circuit to Ground

I will email you for further instructions

Paul Humphreys

0 Vental Mao over 7 years ago in reply to paul humphreys

TI__Expert 5745 points

Step 1: Remove the inductor, check whether the Vout short to GND or SW

Step 2: If the Output short to the GND, check the output cap and feedback resistor, maybe they are bad. If the SW short to GND, check the waveform of the SW in new board, maybe the ring of the SW is too high. You can add a snubber(R=2ohm, C=2200pF) circuit to decrease the ring which will decrease the efficiency.

Step 3, upload your Layout, if the ring is too high, the main reason is the layout.

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TPS54521: TPS54521 S/C Output