LTC6820 datasheet(80/92 Pages) AD

80 / 92 page

LTC6811-1/LTC6811-2

Rev. C

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APPLICATIONS INFORMATION

Connecting Multiple LTC6811-1s on the Same PCB

WhenconnectingmultipleLTC6811-1devicesonthesame

PCB, only a single transformer is required between the

LTC6811-1 isoSPI ports. The absence of the cable also

reduces the noise levels on the communication lines and

often only a split termination is required. Figure 48 shows

an example application that has multiple LTC6811-1s

on the same PCB, communicating to the bottom MCU

through an LTC6820 isoSPI driver. If a transformer with

a center tap is used, a capacitor can be added for better

noise rejection. Additional noise filtering can be provided

with discrete common mode chokes (not shown) placed

to both sides of the single transformer.

On single board designs with low noise requirements, it

is possible for a simplified capacitor-isolated coupling as

shown in Figure 49 to replace the transformer.

In this circuit, the transformer is directly replaced by two

10nF capacitors. A common mode choke (CMC) pro-

vides noise rejection similar to application circuits using

transformers. The circuit is designed to use IBIAS/ICMP

settings identical to the transformer circuit.

Figure 49. Capacitive Isolation Coupling for LTC6811-1s on the Same PCB

10nF

GNDB

10nF

GNDB

10nF

GNDA

10nF

GNDA

68111 F49

10nF

IPA

IBIAS

ICMP

LTC6811-1

IMA

49.9

IPB

IMB

V–

IPA

IBIAS

ICMP

LTC6811-1

IMA

49.9

IPB

IMB

V–

ACT45B-101-2P-TL003

LTC6820 Datasheet(PDF) 80 Page - Analog Devices

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