LTC2990_15 Datasheet, PDF (13/24 Pages) Linear Technology – Quad I2C Voltage, Current and Temperature Monitor

LTC2990
Applications Information
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 condition
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 internal 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 register. The transmission
is ended when the master sends a STOP condition. The
register pointer is automatically 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 possible
measurements per the configuration specified by the mode
bits. The power-on default configuration of the control
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 determine
if the current available register data is new or stale. The
busy bit, when high, indicates a single-shot conversion is
in progress. The busy bit is always high during repeated
mode, after the initial conversion is triggered.
a6-a0
b7-b0
b7-b0
S
START
1-7
ADDRESS
8
9
R/W ACK
1-7
8
9
DATA
ACK
1-7
8
9
DATA
ACK
Figure 4. Data Transfer Over I²C or SMBus
P
STOP
2990 F04
S ADDRESS W# A COMMAND A DATA A P
10011a1:a0 0 0 XXXXXb3:b0 0 b7:b0 0
FROM MASTER TO SLAVE
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
2990 F05
Figure 5. LTC2990 Serial Bus Write Byte Protocol
For more information www.linear.com/LTC2990
2990fd
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