REF3112: Oscillation of VOUT in REF3112

REF3112 oscillation.pptx

Hi Wenting,

Thanks you for the detailed description of the problem you are seeing. Can you help me out by answering these questions?

1. Can you confirm that the failed chip and the okay chip are both REF3112-Q1?

2. Can you provide the ESR of the output capacitor being used?

3. Does the issue persist if the output capacitor is disconnected from the circuit?

4. On slide 3, is it correct to say that REF3112 works correctly when it is not on the motherboard, but incorrectly when it is soldered onto the motherboard? I'm confused because on slide 3 the failed chip seems to be acting normally when it is on the breadboard but then in slide 6, the failed chip is not working well on the breadboard. Can you clarify when REF3112 is seen as having an issue and when it is not?

Thanks,

Jackson

Hello Jackson,

1. Both chis are REF3112-Q1.

2. Let me check with the customer and feedback to you. Are there some influence related to ESR or the output capacitor?

3. If the output capacitor is not used, the issue will not happen.

3. In page 3, REF3112-Q1 is soldered on a breadboard without 10uF capacitor and the breadboard is connected to the motherboard. There is no other REF3112-Q1 in motherboard.

In page 6, the difference between the circuit in page 3 is an 10uF capacitor added. For GOOD REF3112-Q1, the output wave still is good. For failured REF3112-Q1, the output wave becomes oscillated. 

Best regards,

Wenting 

Hi Wenting,

Thanks for helping with those questions. Here is some additional feedback and other questions that I have.

Wenting Wu said:

Why ESR of capacitor needs to be considered here?

It is recommended that low ESR output capacitors are used for the best performance as is described in section 11.1 of the datasheet REF31-Q1. Why have you selected a 10µF capacitor? Is this issue happening for any capacitive load, or only 10µF?

Wenting Wu said:

The customer thinks it's a FA issue, because when the customer try other REF3112-Q1 in their boards, the oscillation issue can be solved. But CQE doesn't think so.

Is the issue you are seeing happening with one device or many devices?

Thanks,

Jackson

Hello Jackson,

The link of capacitor, https://www.digikey.com/en/products/detail/samsung-electro-mechanics/CL10Z106MQ9VPNC/16615641.

Sorry to add one more information. 

The failure device is happening in 1 device after the customer did high temperature test for their boards.

As the slides shown, if the customer add a 2Ohm before Cout, the Vout will become normal. 

In page 3, the customer only move REF3112 chip to a breadboard and leave other REF3112-Q1 surround circuits (including 10uF COUT) in motherboard. And use wires to connect mother board and breadboard together.

...

Best regards,

Wenting

Are there some situation can cause over current during high temperature test?

Does REF3112-Q1 include a over current protection inside it?

The customer tested 6 boards and only 1 boards happen the issue.