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LTC2990CMS

I2C Temperature, Voltage and Current Monitor

Linear Technology 

LTC2990

Operation

The LTC2990 monitors voltage, current, internal and

remote temperatures. It can be configured through an

I2C 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: TINTERNAL, V1, V2, V3, V4 then VCC. 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

I2C interface supplies access to control, status and data

registers. The ADR1 and ADR0 pins select one of four

possible I2C addresses (see Table 1). The undervoltage

detector inhibits I2C 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 I2C serial interface.

The serial interface provides access to control, status and

data registers. I2C 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 1. The I2C interface

is used to trigger single conversions, or start repeated

conversions by writing to a dedicated trigger 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.

Applications Information

Figure 1 is the basic LTC2990 application circuit.

2.5V

5V

0.1µF

RSENSE

15mΩ

2-WIRE

I2C

INTERFACE

VCC V1

V2

SDA

V3

SCL LTC2990

ADR0

ADR1 GND

V4

ILOAD

MMBT3904

470pF

2990 F01

Figure 1



Power Up

The VCC 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.

2990f

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