AN2208 datasheet(47/51 Pages) STMICROELECTRONICS

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AN2208

7 Test results

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The output voltage can be adjustable by voltage divider. In Figure 9 can be seen voltage divider

by resistors R26 and R27. The value of resistor R26 is equal to:

Note:

VFB = 1.235 V

For more information and technical data about L5970D, refer to the L5970D datasheet.

C.2

L5970D layout recommendations

A optimized layout is on of the key factors to operate the DC/DC converter. It reduce noise and

interference. Power-generating portions of the layout are the main cause of noise, therefore, the

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

has to be kept short as possible.

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

and so they should be as far as possible from the high current paths.

Below there is a layout example on Figure 57. The input and output loops are minimized to

avoid radiation and high frequency resonance problems. The feedback pin connections to the

external divider are very close to the device to avoid pick up noise. Moreover the GND pin of the

device is connected to the ground plane directly with VIA on the bottom side of the PCB.

Figure 57. L5970 DC/DC converter layout example

R26

R27

OUT

–

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AN2208 Datasheet(PDF) 47 Page - STMicroelectronics