UCC28600: Distrust of counterfeit chip

Valdecir Saccomano

Part Number: UCC28600

Dear sirs,

For over a year now we are using UCC28600D in our power supply without any problem. But a week ago we encountered a problem. The voltage output, after thirty minutes, decays from 12,3V (normal value) to 11,0V. Analyzing with a scope, this voltage shows a ripple with 3 V peak-to-peak and a waveform like a sawtooth. For this case, power supply is only energized by AC power, without any load on this output.

Then, we note that replacing UCC28600D for another, output remains without any ripple and voltage doesn´t decays.

But, if we use a “type” of UCC28600D (event though it is a new part, picked up from the reel), the defective behavior remains. If the top mark of this part have a Texas logo filled, our power supply works without any problem. If this logo isn´t filled, we have this problem.

This test was realized in 10 boards. The defective behavior follows the chip with “not-filled” logo. We are thinking that this component may be counterfeit.

This part was supplied by an authorized distributor in Brazil (Arrow).

Is there someone here with any problem like this? Even if it´s with another part number. And, is there someone can say if two logo´s drawing are used by Texas Instruments?

Below, some photos with the two “types” of chip and another photo of this reel.

Best regards.

Valdecir

over 8 years ago

0 Bernard Keogh over 8 years ago

TI__Genius 9130 points

Valdecir

Thank you for posting this message.

First of all, I would doubt very much if you have a counterfeit part, this is highly unlikely.

To summarise your findings, the UCC28600 with date code marking "37M AJG5" works ok in your system. But parts with date code marking "62M A331" do not. Is this correct?

In the last picture, can you confirm, is this a picture of the label on the reel of parts that do not function correctly for you (marked "62M A331")?

I will check these codes internally to determine the details of when and where they were manufactured, and will come back to you in a couple of days.

Thanks,
Bernard

0 Valdecir Saccomano over 8 years ago in reply to Bernard Keogh

Prodigy 50 points

Bernard,

thank you for reply.

Yes, it´s correct. This part is marked with "62M A331" and this is the defective part that I have on the reel.

Best regards.

Valdecir

0 Mike O' over 8 years ago

TI__Guru* 85736 points

Hello Valdecir,

Could you send us a copy of your schematic to review?

The failure happens under no load condition. Is the ripple voltage sinusoidal or triangular?

Do you have a scope plot of the misbehavior?

Under no load conditions the UCC28600 will be operating in burst mode. I wonder if the two devices have different Idd current during these conditions. If one device has more Idd current than the other it could cause the VDD capacitor to discharge faster and might trigger a UVLO. This can be checked by studding Vdd voltage and output voltage. Could you check this on your design to see if the converter is entering UVLO?

Regards,

Mike