LTC2990CMS datasheet(14/26 Pages) AD

14 / 26 page

LTC2990

Rev. F

For more information www.analog.com

APPLICATIONS INFORMATION

bit set to zero. The addressed LTC2990 acknowledges

the address and then the master sends a command byte

which indicates which internal register the master wishes

to write. The LTC2990 acknowledges the command byte

and then latches the lower four bits of the command byte

into its internal Register Address pointer. The master then

delivers the data byte and the LTC2990 acknowledges

once more and latches the data into its internal register.

The transmission is ended when the master sends a STOP

condition. If the master continues sending a second data

byte, as in a Write Word command, the second data byte

will be acknowledged by the LTC2990 and written to the

next register in sequence, if this register has write access.

Read Protocol

The master begins a read operation with a START condi-

tion followed by the seven bit slave address and the R/W#

bit set to zero. The addressed LTC2990 acknowledges

this and then the master sends a command byte which

indicates which internal register the master wishes to

read. The LTC2990 acknowledges this and then latches

the lower four bits of the command byte into its inter-

nal Register Address pointer. The master then sends a

repeated START condition followed by the same seven bit

address with the R/W# bit now set to one. The LTC2990

acknowledges and sends the contents of the requested

sends a STOP condition. The register pointer is automati-

cally incremented after each byte is read. If the master

acknowledges the transmitted data byte, as in a Read

Word command, the LTC2990 will send the contents

of the next sequential register as the second data byte.

The byte following register 0x0F is register 0x00, or the

status register.

Control Register

The control register (Table 5) determines the selected

measurement mode of the device. The LTC2990 can be

configured to measure voltages, currents and tempera-

tures. These measurements can be single-shot or repeated

measurements. Temperatures can be set to report in

Celsius or Kelvin temperature scales. The LTC2990 can

be configured to run particular measurements, or all pos-

sible measurements per the configuration specified by the

mode bits. The power-on default configuration of the con-

trol register is set to 0x00, which translates to a repeated

measurement of the internal temperature sensor, when

triggered. This mode prevents the application of remote

diode test currents on pins V1 and V3, and remote diode

terminations on pins V2 and V4 at power-up.

Status Register

The status register (Table 4) reports the status of a par-

ticular conversion result. When new data is written into a

particular result register, the corresponding DATA_VALID

bit is set. When the register is addressed by the I2C inter-

face, the status bit (as well as the DATA_VALID bit in the

respective register) is cleared. The host can then deter-

mine if the current available register data is new or stale.

The busy bit, when high, indicates a single-shot conver-

sion is in progress. The busy bit is always high during

repeated mode, after the initial conversion is triggered.

STOP

2990 F04

START

ADDRESS

R/W

1-7

a6-a0

b7-b0

DATA

ACK

Figure 4. Data Transfer Over I2C or SMBus

A DATA

ADDRESS

COMMAND

0 b7:b0

10011a1:a0

FROM MASTER TO SLAVE

XXXXXb3:b0

2990 F05

FROM SLAVE TO MASTER

A: ACKNOWLEDGE (LOW)

A#: NOT ACKNOWLEDGE (HIGH)

R: READ BIT (HIGH)

W#: WRITE BIT (LOW)

S: START CONDITION

P: STOP CONDITION

Figure 5. LTC2990 Serial Bus Write Byte Protocol

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