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LM5156H-Q1: layout questions

Sherry Liang
Genius 10255 points
Part Number: LM5156H-Q1

Dear team,

1. In below layout recommendation, we suggest separate PGND and AGND, and PGND and AGND should be connected together at the exposed pad. Do these two pins require additional single point connections?

2. In our datasheet, it describes "Do not connect input and output capacitor grounds underneath the device". It means we need to separate PGND and AGND, and connect input and output capacitor grounds to PGND directly, and then PGND make the single connections with AGND at EP, right?

3. If we don't separate PGND and AGND. What are the potential risks? Are there any cases to share?

4. The customer has concerns for the separation GND. In the power side, there will be high frequency voltage and current, which may result in voltage difference between the two GNDs. Is there such a risk? If so, how does our device solve this?

Thanks & Best Regards,

Sherry

  • 0
    TI__Genius 11215 points

    Hello Sherry, 

    Thanks for reaching out. Let me share some comments here: 

    • No, the exposed pad is the right point for this connection as suggested in the datasheet. No further connection points are required.
    • Correct. 
    • It is not a good practice not to separate the AGND and the PGND. The reason is that the power stage is very noisy and has high currents flowing while the components that usually belong on the AGND need to be kept quite (e.g. feedback divider, compensation...). 
    • No, actually this issue happens if the two grounds (analog and power) are not connected at all. 

    Let us know if you have further questions. 

    Kind regards,
    EM