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LTC4261/LTC4261-2

42612fd

For more information www.linear.com/LTC4261

C Interface

The LTC4261/LTC4261-2 feature an I

C interface to pro-

vide access to the ADC data registers and four other regis-

ters for monitoring and control of the pass FET. Figure

shows a general data transfer format using the I

C. The

LTC4261/LTC4261-2 are read-write slave devices and

support SMBus bus Read Byte, Write Byte, Read Word and

Write Word commands. The second word in a Read Word

command will be identical to the ﬁrst word. The second

word in a Write Word command is ignored. The data for

mats for these commands are shown in Figures 12 to 15.

Using Opto-Isolators with SDA

The LTC4261/LTC4261-2 split the SDA line into SDAI (in

put) and SDAO (output) for convenience of opto-coupling

with the host. If opto-isolators are not used then tie SDAI

and SDAO together to form a normal SDA line. When us

ing opto-isolators, connect the SDAI pin to the output of

the incoming opto-isolator and connect the SDAO pin to

the input of the outgoing opto-isolator (see Figure 2). If

the SDAI and SDAO on the master controller are not tied

together, the ACK bit of SDAO must be returned back to

SDAI. If the ALERT line is used as an interrupt for the

host to respond to a fault in real time, connect the ALERT

pin to an opto-isolator in a way similar to that for the

SDAO pin as shown in Figure 2.

Figure 11. Data Transfer over I

C or SMBus

Figure 12. LTC4261 Serial Bus SDA Write Byte Protocol

Figure 13. LTC4261 Serial Bus SDA Write Word Protocol

Figure 14. LTC4261 Serial Bus SDA Read Byte Protocol

Figure 15. LTC4261 Serial Bus SDA Read Word Protocol

APPLICATIONS INFORMATION

SCL

SDA

START

CONDITION

STOP

CONDITION

ADDRESS R/W ACK DATA ACK DATA ACK

1 - 7 8 9

42612 F11

a6 - a0 b7 - b0 b7 - b0

1 - 7 8 9 1 - 7 8 9

S ADDRESS

0 0 1 a3:a0

42612 F12

FROM MASTER TO SLAVE

FROM SLAVE TO MASTER

A: ACKNOWLEDGE (LOW)

: NOT ACKNOWLEDGE (HIGH)

R: READ BIT (HIGH)

W: WRITE BIT (LOW)

S: START CONDITION

P: STOP CONDITION

COMMAND DATA

X X X X b3:b00

0 0 0b7:b0

A A A P

S ADDRESS

0 0 1 a3:a0

COMMAND DATA DATA

X X X X b3:b00

0 0 0 0

42612 F13

X X X X X X X Xb7:b0

A A A P

S ADDRESS

0 0 1 a3:a0 0 0 1 a3:a0 1 0

COMMAND S ADDRESS R A

b7:b0 1

DATA

X X X X b3:b00

0 0

42612 F14

A A A P

S ADDRESS

0 0 1 a3:a0 0 0 1 a3:a0 1 0

COMMAND S ADDRESS R A

b7:b0 1

DATA

X X X X b3:b00

0 0

42612 F15

b7:b0

DATA

A A P

MOSFET

TO SENSE PIN

–48V INPUT PLANE

PLANE

LTC4261 V

ALL CAPACITORS

ALL RESISTIVE DIVIDERS

ALL OPTO-ISOLATORS

C COMMON

VIAS

42612 F10

•

Figure 10. Layout Example of V

Plane, –48V Input Plane and

Sense Resistor Connection

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 33 34

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