LM7332: Unity gain buffer problem

Hello Panos,

We will check with our quality and manufacturing teams to understand if anything has changed recently with this product.  Would it be possible to share the full part number for the LM7332 you're purchasing along with images of the two different devices showing the top-side markings?

The LM7332 has a max input bias current of +/-2uA and with a 1MOhm biasing resistor I would expect +/-2V of input bias current related output error which is likely what you're seeing.  The input signal likely has a lower source impedance and when it is connected to the IN+ pin the input bias current flows through it instead of the 1M resistor resulting in a smaller output error.

Can you replace the 1M resistor with a 1k resistor for testing purposes to see if the output error is reduced?

Hi Collin, many thanks for your reply.

I understand your point about the 1M resistor bias to ground, however this circuit has been working perfectly well up to now. Original package IC measured voltage output (pin 1) is 0.875V; New package IC output (pin 1) is 1.398V.

All products with the latter package have failed production test. The IC in question is used in two different boards of the instrument, resulting in both boards failing production test.

Please see below the package that works, and those that do not (Marked X). These are: LM7332MAX.

Many thanks for your help

Panos

Panos,

Thank you for the fast images. We should be able to pull the date codes and work with our internal teams to understand if anything has changed.

Can you confirm if the voltages you've mentioned are measured with the input signal connected, or disconnected? What is the source impedance of the input source? Is it from a high-Z sensor, or is it from a low-Z source like the output of an op amp or lab equipment?

Panos,

We've looked into this inquiry and the beveled edge doesn't match our records for this device. I'm going to send you a "friend request" so we can share private messages off the public forum.

I'll be asking you also send us images of the bottom of the trouble IC's, an image of the barcode for the reel/tube/ESD bag, and the shipping/purchasing information if you'd like to start getting this information together.

Panos,

In order for TI to begin the verification process all of the following information is required. Please review the attached customer letter and provide the required information to ti-counterfeit@list.ti.com.
Required information
1) Completed Counterfeit Request Form.
2) High quality pictures of the bottom & top of the device(s)
3) High quality pictures of the 2D bar code labels.
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5) Provide device application.
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Hi Collin. Did you get my private message in response to your bevel enquiry?

Panos

Hi Panos,

I was out of the office yesterday but received your message.  I'll reply on the private thread to explain what's going on.