LMZM23601: How to deal with small metal pad

Noriyuki Takahashi

Genius 9245 points

Part Number: LMZM23601

Hi team

We found that there is a metal pad that is not described in datasheet.

Please see the green circle of the attached.

What is this and how should we deal with this?

Regards,

Noriyuki Takahashi

over 5 years ago

0 JohnTucker over 5 years ago

TI__Guru**** 191445 points

Takahashi-san,

That is the pin 1 identifier. It is shown in the mechanical data on page 42 of the datasheet. You can ignore it for the footprint per land pattern and stencil examples shown on page 43 and page 44 of the datasheet.

0 Noriyuki Takahashi over 5 years ago in reply to JohnTucker

TI__Genius 9245 points

John

Do you mean that it is no problem the pin 1identifier is connected to other pins?

Regards,
Noriyuki Takahashi

0 JohnTucker over 5 years ago in reply to Noriyuki Takahashi

TI__Guru**** 191445 points

Takahashi-san,

It does not need to be connected to anything.

0 Noriyuki Takahashi over 5 years ago in reply to JohnTucker

TI__Genius 9245 points

John,

Sorry for confusing question.
In customer board, the identifier is likely connected to other pins at mass production. That's why I am asking whether it is ok that the identifier is connected to other pins.

Regards,
Noriyuki Takahashi

0 Jimmy Hua over 5 years ago in reply to Noriyuki Takahashi

TI__Mastermind 47060 points

Hi Takahashi-san,

As John Tucker has pointed out, that is the pin 1(GND) indicator. During PCB design, the customer will most likely pour a GND plane between PIN 1, that Pin 1 indicator, and the thermal pad. Please take a look at Figure 71. Notice how GND polygon pour covers the Pin 1 indicator and also taps into the thermal pad.

Regards,

Jimmy

0 Noriyuki Takahashi over 5 years ago in reply to Jimmy Hua

TI__Genius 9245 points

Please let me confirm again.

- The pin 1 indicator is not connected to anything inside module, right?
- So, it is no problem that the indicator happens to be bridged to other pins?

Regards,
Noriyuki Takahashi

0 Jimmy Hua over 5 years ago in reply to Noriyuki Takahashi

TI__Mastermind 47060 points

Hi Takahashi-san,

My apologies if I wasn't clear in my response.

The indicator is actually a small dot of exposed GND plane. Pin 1 indicator is tied to Pin 1 internally.

Regards,

Jimmy

0 Noriyuki Takahashi over 5 years ago in reply to Jimmy Hua

TI__Genius 9245 points

Jimmy,

This fact leads customers to have concerns like below about how to deal with the pin 1 indicator.
e.g. If they don't care it for the footprint per land pattern and stencil, the indicator is accidentally connected/unconnected to GND plane. Then, LMZM23601 will be broken or can't work properly....

Could you give any comments on this concern?

Regards,
Noriyuki Takahashi

0 Jimmy Hua over 5 years ago in reply to Noriyuki Takahashi

TI__Mastermind 47060 points

Hi Takahashi-san,

If you have a PCB layout that you want me to review please attach it. As stated above, Figure 71 provides the customer with what a typical PCB layout would look like when using the LMZM23601. Following this layout helps ensure functionality of the part.

If your concern is the Pin1 indicator causing issues, perhaps you could leave the Pin 1 indicator floating on the top side of the board. This indicator pin does not need to be connected to anything.

Regards,
Jimmy

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LMZM23601: How to deal with small metal pad