LTC2990
9
2990fe
For more information www.linear.com/LTC2990
operaTion
The LTC2990 monitors voltage, current, internal and
remote temperatures. It can be configured through an
I
2
C interface to measure many combinations of these pa-
rameters. Single or repeated measurements are possible.
Remote temperature measurements use a transistor as
a temperature
sensor, allowing the remote sensor to be a
discrete NPN (ex. MMBT3904) or an embedded PNP device
in a microprocessor or FPGA. The internal ADC reference
minimizes the number of support components required.
The Functional Diagram displays the main components of
the device. The input signals are selected with an input
MUX, controlled by the control logic block. The control
logic uses the mode bits in the control register to manage
the sequence and types of data acquisition. The control
logic also controls the variable current sources during
remote temperature acquisition. The order of acquisitions
is fixed: T
INTERNAL
, V1, V2, V3, V4 then V
CC
. The ADC
performs the necessary conversion(s) and supplies the
data to the control logic for further processing in the case
of temperature measurements, or routing to the appropri
-
ate data register for voltage and current measurements.
Current and temperature measurements, V1
– V2 or V3
– V4, are sampled differentially by the internal ADC. The
I
2
C interface supplies access to control, status and data
registers. The ADR1 and ADR0 pins select one of four
possible I
2
C addresses (see Table 2). The undervoltage
detector inhibits I
2
C communication below the specified
threshold. During an undervoltage condition, the part is in
a reset state, and the data and control registers are placed
in the default state of 00h.
Remote diode measurements are conducted using multiple
ADC conversions and source currents to compensate for
sensor series resistance. During temperature measure
-
ments, the V2 or V4 terminal of the LTC2990 is terminated
with a diode. The
LTC2990
is calibrated to yield the correct
temperature for a remote diode with an ideality factor of
1.004. See the applications section for compensation of
sensor ideality factors other than the factory calibrated
value of 1.004.
The LTC2990 communicates through an I
2
C serial in-
terface. The serial interface provides access to control,
status and data registers. I
2
C defines a 2-wire open-drain
interface supporting multiple slave devices and masters
on a single bus. The LTC2990 supports 100kbits/s in the
standard mode and up to 400kbit/s in fast mode. The
four physical addresses supported are listed in Table 2.
The I
2
C interface is used to trigger single conversions, or
start repeated conversions by writing to a dedicated trig-
ger register. The data registers contain a destructive-read
status bit (data valid), which is used in repeated mode to
determine if the register
’s contents have been previously
read. This bit is set when the register is updated with new
data, and cleared when read.
V
CC
V1
LTC2990
2.5V
2-WIRE
I
2
C
INTERFACE
5V
GND
SDA
SCL
ADR0
ADR1
V3
V4
V2
470pF
MMBT3904
R
SENSE
15mΩ
I
LOAD
2990 F01
0.1µF
Figure 1 is the basic LTC2990 application circuit.
Figure 1
applicaTions inForMaTion
Power Up
The V
CC
pin must exceed the undervoltage (UV) thresh-
old of 2.5V to keep the LTC2990 out of power-on reset.
Power-on reset will clear all of the data registers and the
control register
.
Temperature Measurements
The LTC2990 can measure internal temperature and up
to two external diode or transistor sensors. During tem
-
perature conversion, current is sourced through either the
V1 or the V3 pin to forward bias the sensing diode. The
