LM134 datasheet(9/26 Pages) AD

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LTC2990

Rev. F

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OPERATION

The LTC2990 monitors voltage, current, internal and

remote temperatures. It can be configured through an

I2C interface to measure many combinations of these

parameters. Single or repeated measurements are pos-

sible. 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 2). 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 mul-

tiple ADC conversions and source currents to compen-

sate for sensor series resistance. During temperature

measurements, 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 inter-

face. The serial interface provides access to control, sta-

tus 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 2.

The I2C 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.

VCC

LTC2990

2.5V

2-WIRE

I2C

INTERFACE

GND

SDA

SCL

ADR0

ADR1

470pF

MMBT3904

RSENSE

15m

ILOAD

2990 F01

0.1µF

Figure 1 is the basic LTC2990 application circuit.

Figure 1.

APPLICATIONS INFORMATION

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. The

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