LM22677: IC were damage after first power on or in burn-in test.

Jeff Chen71

Part Number: LM22677

Hi ,

Picture 1 is customer's last generation product and they had produced 10 kilo units without problem. Because they want to change brown-in voltage in new product,

as picture 2 they modify the EN pin from a 470kohm pull-up to a voltage divider, and the other circuit is same as picture 1. Before they had faced voltage oscillation on

EN pin,it is solved by remove the cap connect on EN pin. Now voltage on EN pin is good ,but the chip still damage and the failure rate is 32pcs/192pcs.

Because customer using the same real of chips on mass product and new design so we don't think it is quality issue. Please help me to figure out what will cause this.

Thanks

over 5 years ago

0 Jeff Chen71 over 5 years ago

Expert 1345 points

Attached picture 2 again

0 Neal Zhang over 5 years ago in reply to Jeff Chen71

TI__Expert 4720 points

Hi Jeff,

1. Do they use the same layout for the first and second design? I found the input loop which is composed by IC, diode, C106 is big in your layout.

2. In pic 2, SN1 and SN2, both of them are broken? So VIN, SW, BOOT are all short to GND for the broken IC, right?

0 Jeff Chen71 over 5 years ago in reply to Neal Zhang

Expert 1345 points

Hi Neal,

1. Do they use the same layout for the first and second design? I found the input loop which is composed by IC, diode, C106 is big in your layout.

As below picture1 and picture2, two layout and placement are almost the same,they increase SW node copper area in new design.

2. In pic 2, SN1 and SN2, both of them are broken? So VIN, SW, BOOT are all short to GND for the broken IC, right?

Yes, both SN1 and SN2 are broken. In FA report the VIN of SN2 was open, but in customer factory most of broken chip are short to ground.

Thanks

Picture 1: First Design Layout without issue.

Picture 2 : Second Design

0 Neal Zhang over 5 years ago in reply to Jeff Chen71

TI__Expert 4720 points

Hi Jeff,

For the original layout, I can't find C106. But I guess the input loop which is composed by IC, diode, C106 is also big.

Does the device work in a condition, when the IC power off, the input voltage drops very quickly? I'm thinking that during power off, if Vin is lower than Vo, current will flow the high side MOS's parasitic diode, and may damage the IC.

0 Jeff Chen71 over 5 years ago in reply to Neal Zhang

Expert 1345 points

Hi Neal,

As below picture, we don't see the voltage VIN less then vout condition on test fixture. And customer say they had many failure board happened

during burn-in test. They do not have power on and power off during burn-in test. The ambiance temp is 55°C and they measure the top of the chip temp

is about 77°C ~79°C. The total test time are 4 hours.

They want to reproduce the failure phenomenon, so they rework the failure board. And do some testing like short vout、heating the chip (using heat gun)、

full load power on、light load power on and ESD ,after all the testing the chip still work well. They could not reproduce failure phenomenon. I had checked

the smt manufacture is the same as first design. Do you have any idea to reproduce that?

Picture 1 and 2 were measurement from customer's board .

Picture 3 and 4 were measurement from EVM board .

They didn't using tip-and-barrel method to measurement so the waveform have glitch.

CH1: BOOT

CH2: SW

CH3: VIN

CH4: VOUT

Customer's Board Power On