LTC6820 datasheet(49/92 Pages) AD

49 / 92 page

LTC6811-1/LTC6811-2

Rev. C

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OPERATION

REQUIRED

BIAS

68111 F22

MISO

MOSI

CLK

VDD

MPU

V+

C12

S12

C11

S11

C10

S10

IPB

IMB

ICMP

IBIAS

SDO(NC)

SDI(NC)

SCK(IPA)

CSB(IMA)

ISOMD

WDT

DRIVE

VREG

DTEN

VREF1

VREF2

GPIO5

GPIO4

V–

GPIO3

GPIO2

GPIO1

LTC6811-1

TERMINATED UNUSED PORT

100

20k

68111 F23

MISO

MOSI

CLK

VDD

MPU

V+

C12

S12

C11

S11

C10

S10

SDO(IBIAS)

SDI(ICMP)

SCK(IPA)

CSB(IMA)

ISOMD

WDT

DRIVE

VREG

DTEN

VREF1

VREF2

GPIO5

GPIO4

V–

GPIO3

GPIO2

GPIO1

LTC6811-1

ADDRESS = 0×0

Figure 22. Single Device LTC6811-1 Using 4-Wire Port A

Figure 23. Single Device LTC6811-2 Using 4-Wire Port A

isoSPI Pulse Detail

Two LTC6811 devices can communicate by transmitting

and receiving differential pulses back and forth through an

isolation barrier. The transmitter can output three voltage

levels: +VA, 0V and -VA. A positive output results from IP

sourcingcurrentandIMsinkingcurrentacrossloadresistor

RM. A negative voltage is developed by IP sinking and IM

sourcing. When both outputs are off, the load resistance

forces the differential output to 0V.

To eliminate the DC signal component and enhance reli-

ability, the isoSPI uses two different pulse lengths. This

allows four types of pulses to be transmitted, as shown in

Table 25. A +1 pulse will be transmitted as a positive pulse

followed by a negative pulse. A –1 pulse will be transmit-

ted as a negative pulse followed by a positive pulse. The

duration of each pulse is defined as t½PW, since each is

half of the required symmetric pair (the total isoSPI pulse

duration is 2·t½PW).

Table 25. isoSPI Pulse Types

PULSE TYPE

FIRST LEVEL

(t½PW)

SECOND LEVEL

(t½PW)

ENDING LEVEL

Long +1

+VA (150ns)

–VA (150ns)

Long –1

–VA (150ns)

+VA (150ns)

Short +1

+VA (50ns)

–VA (50ns)

Short –1

–VA (50ns)

+VA (50ns)

A host microcontroller does not have to generate isoSPI

pulses to use this 2-wire interface. The first LTC6811 in

the system can communicate to the microcontroller using

the 4-wire SPI interface on its Port A, then daisy-chain to

other LTC6811s using the 2-wire isoSPI interface on its

Port B. Alternatively, the LTC6820 can be used to translate

the SPI signals into isoSPI pulses.

LTC6820 Datasheet(PDF) 49 Page - Analog Devices

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