ADP2108 layout considerations (high frequency switching regulator layout considerations)

Document created by power-layout-guy Employee on Aug 5, 2014
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Improper layout can cause some IC's not to operate correctly, as an example let’s use the ADP2108.

 

 

The part has a 3Mhz fixed operating frequency. You will want to place the input cap, output cap and inductor as close as physically possible to the corresponding pins on the IC. Failure to do so will result in the circuit malfunctioning. We have seen this with some customers. Here is what is stated in the ADP2108 data sheet

 

 

Below is a typical schematic for the ADP2108

2108-sch.png

 

The layout below is not an optimal layout for the ADP2108, and can cause the 2108 not to work correctly. C7 is the input cap. Reference (A) is pointing to the long trace from the input cap to the Vin pin of the IC.   This makes for a large current loop and the increased inductance in that trace can cause the circuit to be unstable.   C7 needs to be across the Vin and GND pins of the IC

 

2108-bad 1 - Copy.jpg

 

 

L1 is placed in a good position. However, C8 is not in a good position and should be located closer to the IC and L1. Look at reference B, the output trace. Placing the output cap (C8) that far away from the IC will result in a large current loop, which will cause problems with the ADP2108 circuit. Ultimately you want keep the GND nodes of the Input cap, Output cap and the IC close together as possible.

 

Also instead of using 10 mil traces, it is recommended to use larger connection and or copper fills.


2108-bad 2.jpg





The layout below is a known working layout for the ADP2108. Component placement is ideal and use of large copper connections helps with reducing parasitic inductance

 

2108-good1.jpg

 

 

Below is another example of a known working layout. In this case although copper fill was not used the traces remain short and the components are very close to the IC. Traces can be routed under the IC between the pins to achieve low inductance connections.



2108-good 2.png

 

This FAQ was generated from the following discussion: ADP2108 layout considerations (high frequency switching regulator layout considerations)

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