LED2000PUR datasheet(26/40 Pages) STMICROELECTRONICS

26 / 40 page

Application information

LED2000

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DocID023432 Rev 4

7.2

Layout considerations

The layout of switching DC-DC converters is very important to minimize noise and

interference. Power-generating portions of the layout are the main cause of noise and so

high switching current loop areas should be kept as small as possible and lead lengths as

short as possible.

High impedance paths (in particular the feedback connections) are susceptible to

interference, so they should be as far as possible from the high current paths. A layout

example is provided in Figure 16.

The input and output loops are minimized to avoid radiation and high frequency resonance

problems. The feedback pin to the sensing resistor path must be designed as short as

possible to avoid pick-up noise. Another important issue is the ground plane of the board.

As the package has an exposed pad, it is very important to connect it to an extended ground

plane in order to reduce the thermal resistance junction-to-ambient.

To increase the design noise immunity, different signal and power ground should be

implemented in the layout (see Section 7.5: Application circuit). The signal ground serves

the small signal components, the device analog ground pin, the exposed pad and a small

filtering capacitor connected to the VINA pin. The power ground serves the device ground pin

and the input filter. The different grounds are connected underneath the output capacitor.

Neglecting the current ripple contribution, the current flowing through this component is

constant during the switching activity and so this is the cleanest ground point of the buck

application circuit.

Figure 16. Layout example

LED2000PUR Datasheet(PDF) 26 Page - STMicroelectronics