LT8640 datasheet(16/32 Pages) AD

16 / 32 page

LT8640S/LT8643S/

LT8640SA/LT8643SA

Rev. D

For more information www.analog.com

APPLICATIONS INFORMATION

GROUND VIA

VIN VIA

VOUT VIA

OTHER SIGNAL VIAS

8640S F01a

COPT2

CIN3

COPT1

CSS

COUT

GROUND VIA

VIN VIA

VOUT VIA

OTHER SIGNAL VIAS

8640S F01b

COPT2

CIN3

COPT1

CSS

COUT

(a) LT8640S/LT8640SA

(b) LT8643S/LT8643SA

Figure 1. Recommended PCB Layouts for the LT8640S/LT8640SA and LT8643S/LT8643SA

Low EMI PCB Layout

The LT8640S/LT8643S/LT8640SA/LT8643SA is specifi-

cally designed to minimize EMI emissions and also to

maximize efficiency when switching at high frequen-

cies. For optimal performance the LT8640S/LT8643S/

LT8640SA/LT8643SA should use multiple VIN bypass

capacitors.

Two small <1µF capacitors can be placed as close as pos-

sible to the LT8640S/LT8643S/LT8640SA/LT8643SA, one

capacitor on each side of the device (COPT1, COPT2). A third

capacitor with a larger value, 2.2µF or higher, should be

placed near COPT1 or COPT2.

See Figure 1 for recommended PCB layouts.

For more detail and PCB design files refer to the Demo Board

guide for the LT8640S/LT8643S/LT8640SA/LT8643SA.

Note that large, switched currents flow in the LT8640S/

LT8643S/LT8640SA/LT8643SA VIN and GND pins and the

input capacitors. The loops formed by the input capacitors

should be as small as possible by placing the capacitors

adjacent to the VIN and GND pins. Capacitors with small

case size such as 0603 are optimal due to lowest parasitic

inductance.

The input capacitors, along with the inductor and out-

put capacitors, should be placed on the same side of the

circuit board, and their connections should be made on

that layer. Place a local, unbroken ground plane under the

application circuit on the layer closest to the surface layer.

LT8640 Datasheet(PDF) 16 Page - Analog Devices

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