LTC2991IMS#PBF - Linear Technology

LTC2991

2991fa

TYPICAL APPLICATION

FEATURES DESCRIPTION

Octal I2C Voltage, Current,

and Temperature Monitor

The LTC

2991 is used to monitor system temperatures,

voltages and currents. Through the I2C serial interface, the

eight monitors can individually measure supply voltages

and can be paired for differential measurements of cur-

rent sense resistors or temperature sensing transistors.

Additional measurements include internal temperature

and internal VCC. The internal 10ppm reference minimizes

the number of supporting components and area required.

Selectable address and configurable functionality give the

LTC2991 flexibility to be incorporated in various systems

needing temperature, voltage or current data. The LTC2991

fits well in systems needing submillivolt voltage resolution,

1% current measurement and 1°C temperature accuracy

or any combination of the three.

Temperature Total Unadjusted Error

APPLICATIONS

n Measures Voltage, Current, Temperature

n Measures Four Remote Diode Temperatures

n 0.7°C (Typ) Accuracy, 0.06°C Resolution

n 1°C (Typ) Internal Temperature Sensor

n Series Resistance Cancellation

n 14-Bit ADC Measures Voltage/Current

n PWM Temperature Output

n 3V to 5.5V Supply Operating Voltage

n Eight Selectable Addresses

n Internal 10ppm/°C Voltage Reference

n V1 to V8 Inputs ESD Rated to 6kV HBM

n 16-Lead MSOP Package

n Temperature Measurement

n Supply Voltage Monitoring

n Current Measurement

n Remote Data Acquisition

n Environmental Monitoring

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Easy Drive

is a trademark of Linear Technology Corporation. All other trademarks are the property of their

respective owners.

VCC

2-WIRE

I2C INTERFACE

LTC2991

TAMBIENT

RSENSE

3.3V

1.2V

2.5V

GND

SDA

SCL

ADR0

ADR1

ADR2

3.3V I/O

2.5V I/O

1.2V CORE

FPGA

TEMPERATURE

BOARD

TEMPERATURE

V3 V4

PWM TO FAN

2991 TA01a

TAMBIENT (°C)

–50

TERROR (°C)

0.25

0.50

0.75

25 50 75 100 125

2991 TA01b

–0.50

–0.25

–25 0 150

–0.75

–1.00

1.00

TREMOTE

TINTERNAL

LTC2991

2991fa

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS

Supply Voltage (VCC) ................................ –0.3V to 6.0V

Input Voltages V1, V2, V3, V4, V5, V6, V7, V8,

SCL, ADR0, ADR1, ADR2 ..............–0.3V to (VCC + 0.3V)

Output Voltage PWM ....................–0.3V to (VCC + 0.3V)

Output Voltage SDA ..................................... –0.3V to 6V

Operating Temperature Range

LTC2991C ................................................ 0°C to 70°C

LTC2991I .............................................–40°C to 85°C

Storage Temperature Range .................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

MS Package .......................................................... 300°C

(Note 1)

VCC

ADR2

ADR1

ADR0

PWM

SCL

SDA

GND

TOP VIEW

MS PACKAGE

16-LEAD PLASTIC MSOP

TJMAX = 125°C, θJA = 120°C/W

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC2991CMS#PBF LTC2991CMS#TRPBF 2991 16-Lead Plastic MSOP 0°C to 70°C

LTC2991IMS#PBF LTC2991IMS#TRPBF 2991 16-Lead Plastic MSOP –40°C to 85°C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

General

VCC Input Supply Range l2.9 5.5 V

ICC Input Supply Current During Conversion, I2C Inactive l1.1 1.5 mA

ISD Input Supply Current Shutdown Mode, I2C Inactive l16 μA

VCC(UVL) Input Supply Undervoltage Lockout l1.3 2.0 2.6 V

Measurement Accuracy

TINTERNAL(TUE) Internal Temperature Total Unadjusted Error ±1 ±3.5 °C

TRMT(TUE) Remote Diode Temperature Total Unadjusted

Error

η = 1.004 l±0.7 ±1.5 °C

VCC(TUE) VCC Voltage Total Unadjusted Error 2.9V ≤ 5.5V l±0.05 ±0.25 %

VN(TUE) V1 Through V8 Total Unadjusted Error 0V ≤ 4.9V l±0.05 ±0.25 %

VDIFF(TUE) Differential Voltage Total Unadjusted Error

V1 – V2 ,V3 – V4, V5 – V6, V7 – V8

–300mV≤ VD ≤300mV l±0.1 ±0.75 %

VDIFF(MAX) Full-Scale Differential Voltage l–312.5 312.5 mV

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.

LTC2991

2991fa

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VDIFF(CMR) Differential Voltage Common Mode Range l0V

CC V

VLSB(DIFF) Differential Voltage LSB Weight 19.075 μV

VLSB(SINGLE_ENDED) Single-Ended Voltage LSB Weight 305.18 μV

VLSB(TEMP) Temperature LSB Weight Celsius or Kelvin 0.0625 Deg

VLSB(DIODE_VOLTAGE) Diode Voltage LSB Weight Includes Series Resistance IR Drop 38.15 μV

TNOISE Temperature Noise Celsius or Kelvin Filter Disengaged 0.2 °RMS

TNOISE Temperature Noise Celsius or Kelvin Filter Engaged 0.07 °RMS

RES Resolution (No Missing Codes) (Note 2) l14 Bits

INL Integral Nonlinearity 2.9V ≤ VCC ≤ 5.5V, VIN(CM) = 1.5V

(Note 2)

Single-Ended

Differential

–2

LSB

CIN V1 Through V8 Input Sampling Capacitance (Note 2) 0.35 pF

IIN(AVG) V1 Through V8 Input Average Sampling

Current

(0 ≤ VN ≤ 4.9V) (Note 2) 0.6 μA

IDC_LEAK(VIN) V1 Through V8 Input Leakage Current (0 ≤ VN ≤ VCC)l–10 10 nA

PWM

FPWM PWM Period l0.9 1.2 ms

DCPWM Duty Cycle Range l0 99.8 %

SCALEPWM 0% to 100% PWM Temperature Range 32 Deg

Measurement Delay

TINTERNAL, TR1, TR2,

TR3, TR4

Per Configured Temperature

Measurement

l37 46 55 ms

V1, V2, V3, V4, V5,

V6, V7, V8

Single-Ended Voltage Measurement l0.9 1.5 1.8 ms

V1 – V2, V3 – V4,

V5 – V6, V7 – V8

Differential Voltage Measurement l0.9 1.5 1.8 ms

VCC VCC Measurement l0.9 1.5 1.8 ms

Max Delay Mode[4:0] = 11101, TINTERNAL, TR1, TR2, TR3,

TR4 VCC

l277 ms

V1, V3, V5, V7 OUTPUT (Remote Diode Mode Only)

IOUT Output Current Remote Diode Mode l260 350 μA

VOUT Output Voltage l0V

CC V

I2C Interface

VADR(L) ADR Input Low Threshold Voltage Falling l0.3•VCC V

VADR(H) ADR Input High Threshold Voltage Rising l0.7•VCC V

VOL1 SDA Low Level Maximum Voltage IO = –3mA, VCC 2.9V to 5.5V l0.4 V

VIL Maximum Low Level Input Voltage SDA and SCL Pins l0.3 •VCC V

VIH Minimum High Level Input Voltage SDA and SCL Pins l0.7 •VCC V

ISDAI, SCLI SDA, SCL Input Current 0 < VSDA, SCL < VCC l±1 μA

IADR(MAX) Maximum ADR0, ADR1, ADR2 Input Current ADR0, ADR1 or ADR2 Tied to VCC

or GND

l±1 μA

LTC2991

2991fa

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I2C Timing (Note 2)

fSCL(MAX) Maximum SCL Clock Frequency 400 kHz

tLOW Minimum SCL Low Period 1.3 μs

tHIGH Minimum SCL High Period 600 ns

tBUF(MIN) Minimum Bus Free Time Between Stop/Start

Condition

1.3 μs

tHD, STA(MIN) Minimum Hold Time After (Repeated) Start

Condition

600 ns

tSU, STA(MIN) Minimum Repeated Start Condition Set-Up

Time

600 ns

tSU, STO(MIN) Minimum Stop Condition Set-Up Time 600 ns

tHD, DATI(MIN) Minimum Data Hold Time Input 0ns

tHD, DATO(MIN) Minimum Data Hold Time Output 300 900 ns

tSU, DAT(MIN) Minimum Data Set-Up Time Input 100 ns

tSP(MAX) Maximum Suppressed Spike Pulse

Width

50 250 ns

CXSCL, SDA Input Capacitance 10 pF

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: Guaranteed by design and not subject to test.

Note 3: Integral nonlinearity is defined as the deviation of a code from a

straight line passing through the actual endpoints of the transfer curve.

The deviation is measured from the center of the quantization band.

LTC2991

2991fa

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, VCC = 3.3V, unless otherwise noted.

TINTERNAL Error

Remote Diode Error with LTC2991

at 25°C

Remote Diode Error with LTC2991

at Same Temperature as Diode

Supply Current vs TemperatureShutdown Current vs Temperature

Measurement Delay Variation

vs T Normalized to 3.3V, 25°C

VCC TUE Single-Ended VX TUE Differential Voltage TUE

TAMB (°C)

–50

ICC (μA)

2.0

2.5

3.0

25 50 75 100 125

2991 G01

1.5

1.0

–25 0 150

0.5

3.5

VCC = 5V

VCC = 3.3V

TAMB (°C)

–50

ICC (μA)

1050

1100

1150

25 50 75 100 125

2991 G02

–25 0 150

1000

950

1200

VCC = 5V

VCC = 3.3V

TAMB (°C)

–50

MEASUREMENT DELAY VARIATION (%)

25 50 75 100 125

2991 G03

–25 0 150

–1

VCC = 5V

VCC = 3.3V

TAMB (°C)

–50

VCC TUE (%)

25 50 75 100 125

2991 G04

–25 0 150

–0.25

–0.50

0.25

TAMB (°C)

–50

VX TUE (%)

0.25

25 50 75 100 125

2991 G05

–25 0 150

–0.25

–0.50

0.50

TAMB (°C)

–50

VDIFF TUE (%)

25 50 75 100 125

2991 G06

–25 0 150

–0.25

–0.50

0.25

TAMB (°C)

–50

ERROR (°C)

1.0

1.5

25 50 75 100 125

2991 G07

0.5

–25 0 150

–0.5

–1.0

2.0

BATH TEMPERATURE (°C)

–50

LTC2990 TRX ERROR (°C)

0.2

0.4

25 50 75 100 125

2991 G08

–0.2

–25 0 150

–0.4

–0.6

0.6

TAMB (°C)

–50

LTC2991 TRX ERROR (DEG)

0.25

0.50

0.75

25 50 75 100 125

2991 G09

–0.25

–25 0 150

–0.50

–1.00

–0.75

1.00

LTC2991

2991fa

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, VCC = 3.3V, unless otherwise noted.

LTC2991 Differential Noise Differential Transfer Function Differential INL

TINTERNAL Noise Remote Diode Noise

LSBs (19.42μV/LSB)

–4

COUNTS

300

400

500 800 READINGS

–1 1

2991 G13

200

100

–3 –2 023

V1-V2 (V)

–0.4

LTC2990 V1-V2 (V)

0.2

0.4

2991 G14

–0.2

–0.4 –0.2 00.2

–0.3 –0.1 0.1 0.3

0.4

–0.1

0.1

–0.3

0.3

VIN (V)

–0.4

INL (LSBs)

0.4

2991 G15

–1

–2 –0.2 00.2

(°C)

–0.75 –0.5

COUNTS

200

500 1000 READINGS

–0.25 0.25 0.5

2991 G16

100

400

300

00.75

(°C)

–0.75 –0.5

COUNTS

200

600 1000 READINGS

500

–0.25 0.25 0.5

2991 G17

100

400

300

00.75

Single-Ended Transfer Function Single-Ended INL

VX (V)

–1

2991 G11

–0 1 356

–1

LTC2990 VALUE (V)

VCC = 5V

VCC = 3.3V

VX (V)

–1.0

INL (LSBs)

–0.5

0.5

1.0

1234

2991 G12

VCC = 5V

VCC = 3.3V

Single-Ended Noise

LSBs (305.18μV/LSB)

–3

COUNTS

3500

2991 G10

2000

1000

–2 –1 1

500

4000 4800 READINGS

3000

2500

1500

LTC2991

2991fa

Digital Filter Step Response

CPARALLEL (pF)

TERROR (°C)

2991 G20

0.4

0.2

010 100 1k 10k 100k 1000k

1.2

1.0

0.8

0.6

TERROR vs CPARALLEL

TERROR vs RSERIES

ITERATION

% FULL-SCALE

200

2991 G18

050 100 150

100

RSERIES (Ω)

TERROR (°C)

5000

2991 G19

0.1 1000 2000 3000 4000

100

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, VCC = 3.3V, unless otherwise noted.

LTC2991

2991fa

PIN FUNCTIONS

V1 (Pin 1): First Monitor Input. This pin can be configured

as a single-ended input (0V to 4.9V) or the positive input

for a differential or remote diode temperature measurement

(in combination with V2). Differential common mode range

is 0V to VCC, ±300mV differential. When configured for

remote diode temperature, this pin will source a current.

V2 (Pin 2): Second Monitor Input. This pin can be config-

ured as a single-ended input (0V to 4.9V) or the negative

input for a differential or remote diode temperature mea-

surement (in combination with V1). Differential common

mode range is 0V to VCC, ±300mV differential. When

configured for remote diode temperature, this pin will have

an internal termination, while the measurement is active.

V3 (Pin 3): Third Monitor Input. This pin can be configured

as a single-ended input (0V to 4.9V) or the positive input

for a differential or remote diode temperature measurement

(in combination with V4). Differential common mode range

is 0V to VCC, ±300mV differential. When configured for

remote diode temperature, this pin will source a current.

V4 (Pin 4): Fourth Monitor Input. This pin can be configured

as a single-ended input (0V to 4.9V) or the negative input

for a differential or remote diode temperature measurement

(in combination with V3). Differential common mode range

is 0V to VCC, ±300mV differential. When configured for

remote diode temperature, this pin will have an internal

termination, while the measurement is active.

V5 (Pin 5): Fifth Monitor Input. This pin can be configured

as a single-ended input (0V to 4.9V) or the positive input

for a differential or remote diode temperature measurement

(in combination with V6). Differential common mode range

is 0V to VCC, ±300mV differential. When configured for

remote diode temperature, this pin will source a current.

V6 (Pin 6): Sixth Monitor Input. This pin can be configured

as a single-ended input (0V to 4.9V) or the negative input

for a differential or remote diode temperature measurement

(in combination with V5). Differential common mode range

is 0V to VCC, ±300mV differential. When configured for

remote diode temperature, this pin will have an internal

termination, while the measurement is active.

V7 (Pin 7): Seventh Monitor Input. This pin can be

configured as a single-ended input (0V to 4.9V) or the

positive input for a differential or remote diode tempera-

ture measurement (in combination with V8). Differential

common mode range is 0V to VCC, ±300mV differential.

When configured for remote diode temperature, this pin

will source a current.

V8 (Pin 8): Eighth Monitor Input. This pin can be configured

as a single-ended input (0V to 4.9V) or the negative input

for a differential or remote diode temperature measurement

(in combination with V7). Differential common mode range

is 0V to VCC, ±300mV differential. When configured for

remote diode temperature, this pin will have an internal

termination, while the measurement is active.

GND (Pin 9): Device Ground. Connect this pin through a

low impedance connection to system ground.

SDA (Pin 10): Serial Bus Data Input and Output. In the

transmitter mode (read), the conversion result is output

through the SDA pin, while in the receiver mode (write),

the device configuration bits are input through the SDA

pin. At data input mode, the pin is high impedance; while

at data output mode, it is an open-drain N-channel driver

and, therefore, an external pull-up resistor or current

source to VCC is needed.

SCL (Pin 11): Serial Bus Clock Input of the I2C Interface.

The LTC2991 can only act as a slave and the SCL pin

only accepts external serial clock. The LTC2991 does not

implement clock stretching.

PWM (Pin 12): PWM Output. The PWM pin provides a

CMOS output level with a duty cycle proportional to the

remote diode temperature of the sensor connected to

pins V7 and V8.

ADR0, ADR1, ADR2 (Pins 13, 14, 15): Serial Bus Address

Control Input. The ADR pins are address control bits for

the device I2C address. See Table 1.

VCC (Pin 16): Chip Power. Connect to 2.9V to 5.5V low

noise supply. A 0.1μF decoupling capacitor to GND is

required for this pin.

LTC2991

2991fa

FUNCTIONAL DIAGRAM

ADC

MUX

MODE

REFERENCE

I2C

UNDERVOLTAGE

DETECTOR

V7 UV

REMOTE

DIODE

SENSORS

POWER

MONITORING

RSENSE 4

SCL

2991 FD

CONTROL

LOGIC

SDA 10

PWM 12

ADR0 13

ADR1 14

ADR2 15

GND 9

VCC 16

PULSE WIDTH

DETECTOR

VCC

VCC VCC VCC VCC VCC

INTERNAL

SENSOR

+–

–

VOLTAGE

MONITORING

TIMING DIAGRAM

tSU, DAT

tSU, STO

tSU, STA tBUF

tHD, STA

tSP

tHD, DATO,

tHD, DATI

tHD, STA

START

CONDITION

STOP

CONDITION

REPEATED START

CONDITION

START

CONDITION

2991 TD

SDAI/SDAO

SCL

LTC2991

2991fa

OPERATION

The LTC2991 monitors voltage, current, internal and remote

temperatures. It can be configured through an I2C inter-

face to measure many combinations of these parameters.

Single or repeated measurements can be configured.

Remote temperature measurements use transistors as

temperature sensors, 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 functional com-

ponents of the device. The input signals are selected with an

input mux, controlled by the control logic block. The control

logic block uses the mode bits in the control registers to

manage the sequence and types of data acquisition. The

control logic block also controls the current sources during

remote temperature acquisition. The order of acquisitions

is fixed: V1, V2, V3, V4, V5, V6, V7, V8, TINTERNAL then

VCC. The ADC performs the necessary conversion(s) and

supplies the data to the control logic for routing to the ap-

propriate data register. The I2C interface supplies access

to control, status and data registers. The ADR2, ADR1 and

ADR0 pins select one of eight possible I2C addresses (see

Table 1). The UVLO 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. The V2, V4, V6 or V8 terminals of

the LTC2991 are terminated with a diode if that channel is

configured for temperature measurements. It is acceptable

to ground these pins, but increased noise may result on

the temperature measurements. The LTC2991 is calibrated

to yield the correct temperature for a remote diode with an

ideality factor of 1.004. See the Applications Information

section for compensation of sensor ideality factors other

than the factory calibrated value of 1.004.

The LTC2991 communicates through an I2C serial in-

terface. 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 LTC2991 supports 100kbit/s in the

standard mode and up to 400kbit/s in fast mode. The

eight 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 trig-

ger register. The data registers contain a destructive read

status bit (data valid), which is used in repeated mode to

determine if the registers contents have been previously

read. This bit is set when the register is updated with new

data, and cleared when read.

LTC2991

2991fa

The basic LTC2991 application circuit is shown in Figure 1.

APPLICATIONS INFORMATION

Figure 1.

Power Up

The VCC pin must exceed the undervoltage (UV) thresh-

old of 2.5V to keep the LTC2991 out of power-on reset.

Power-on reset will clear all of the data registers and the

control registers.

Temperature Measurements

The LTC2991 can measure internal temperature and up

to four external diode or transistor sensors. During tem-

perature conversion, current is sourced through the V1,

V3, V5 or the V7 pin to forward bias the remote sensing

diode. The change in sensor voltage per degree temperature

change is hundreds of μV/°C, so environmental noise must

be kept to a minimum. Recommended shielding and PCB

trace considerations are illustrated in Figure 2.

The diode equation:

VkT

BE C

=⎛

⎝

⎜⎞

⎠

⎟

ηtttMn

(1)

can be solved for T, where T is Kelvin degrees, IS is a

process dependent factor on the order of 1E-13, η is the

diode ideality factor, k is Boltzmann’s constant and q is

the electron charge.

TVq

kInI

=⎛

⎝

⎜⎞

⎠

⎟

ttη

(2)

The LTC2991 makes differential measurements of diode

voltage to calculate temperature. Proprietary techniques

allow for cancellation of error due to series resistance.

Ideality Factor Scaling

The LTC2991 is calibrated to yield the correct temperature

for a remote diode with an ideality factor of 1.004. While

this value is typical of target sensors, small deviations can

yield significant temperature errors. The ideality factor of

the diode sensor can be considered a temperature scaling

factor. The temperature error for a 1% accurate ideality fac-

tor error is 1% of the Kelvin temperature. Thus, at 25°C, or

298°K, a +1% accurate ideality factor error yields a +2.98

degree error. At 85°C, or 358°K, a +1% error yields a 3.6

degree error. It is possible to scale the measured Kelvin

or Celsius temperature measured using the LTC2991 with

a sensor ideality factor other than 1.004, to the correct

value. The scaling Equations (3) and (4), are simple, and

can be implemented with sufficient precision using 16-bit

fixed point math in a microprocessor or microcontroller.

Factory ideality calibration value:

ηCAL = 1.004

Actual sensor ideality value:

ηACT

Figure 2. Recommended PCB Layout

VCC

2-WIRE

I2C INTERFACE

LTC2991

TAMBIENT

RSENSE

3.3V

1.8V

2.5V

GND

SDA

SCL

ADR0

ADR1

ADR2

3.3V I/O

2.5V I/O

1.8V CORE

FPGA

TEMPERATURE

BOARD

TEMPERATURE

V3 V4

PWM TO FAN

2991 F01

VCC

ADR2

ADR1

ADR0

PWM

SCL

SDA

GND

LTC2991

2991 F01

GND SHIELD

TRACE

NPN SENSOR

470pF 0.1μF

LTC2991

2991fa

APPLICATIONS INFORMATION

Compensated Kelvin temperature:

TK_COMP =ηCAL

ηACT

tTK_MEAS

(3)

Compensated Celsius temperature:

C COMP ACT

CAL CMEAS

η273.15 273.15TT=–+

()

(4)

A 16-bit unsigned number is capable of representing the

ratio ηCAL/ηACT in a range of 0.00003 to 1.99997, by

multiplying the fractional ratio by 215. The range of scal-

ing encompasses every conceivable target sensor value.

The ideality factor scaling granularity yields a worst-case

temperature error of 0.01° at +125°C. Multiplying this

16-bit unsigned number and the measured Kelvin (un-

signed) temperature represented as a 16-bit number, yields

a 32-bit unsigned result. To scale this number back to a

13-bit temperature (9-bit integer part, and a 4-bit fractional

part), divide the number by 215. Similarly, Celsius coded

temperature values can be scaled using 16-bit fixed-point

arithmetic, using Equation (4). In both cases, the scaled

result will have a 9-bit integer (d[12:4]) and the four LSB’s

(d[3:0]) representing the 4-bit fractional part. To convert

the corrected result to decimal, divide the final result by

24, or 16, as you would the register contents. If ideality

factor scaling is implemented in the target application, it

is beneficial to configure the LTC2991 for Kelvin coded

results to limit the number of math operations required

in the target processor.

(UNSIGNED)

K COMP ACT

CAL KMEAS

⎛

⎝

⎜⎞

⎠

⎟

η2

(5)

(6)

Sampling Currents

Single-ended voltage measurements are directly sampled

by the internal ADC. The average ADC input current is a

function of the input applied voltage as follows:

SAMPLE = (VIN – 1.49V) • 0.17[μA/V]

Inputs with source resistance less than 500Ω will yield

full-scale gain errors due to source impedance of < ½ LSB

for 14-bit conversions. The nominal conversion time is

1.5ms for single-ended conversions.

Current Measurements

The LTC2991 has the ability to perform 14-bit current

measurements with the addition of a current sense resis-

tor (see Figure 3).

(UNSIGNED) T

CCOMP ACT

CAL CMEAS

⎛

⎝

⎜⎞

⎠

⎟+

(

η2 273.15 t2

15 4

)

273 15 2

– t

Figure 3. Simplified Current Sense Schematic

In order to achieve 13-bit current sensing a few details

must be considered. Differential voltage or current mea-

surements are directly sampled by the internal ADC. The

average ADC input current for each leg of the differential

input signal during a conversion is:

SAMPLE = (VIN – 1.49V) • 0.34[μA/V]

The maximum source impedance to yield 14-bit results

with ½ LSB full-scale error is ~50Ω.

In order to achieve 14-bit accuracy, 4-point, or Kelvin

connected measurements of the sense resistor differential

voltage are necessary.

V1 V2

LTC2991

0V – VCC

RSENSE

ILOAD

2991 F03

LTC2991

2991fa

APPLICATIONS INFORMATION

In the case of current measurements, the external sense

resistor is typically small, and determined by the full-scale

input voltage of the LTC2991. The full-scale differential

voltage is 0.300V. The external sense resistance, is then a

function of the maximum measurable current, or REXT_MAX

= 0.300V/IMAX. For example, if you wanted to measure a

current range of ±5A, the external shunt resistance would

equal 0.300V/5A = 60mΩ.

There exists a way to improve the sense resistor’s precision

using the LTC2991. The LTC2991 measures both differential

voltage and remote temperature. It is therefore, possible

to compensate for the absolute resistance tolerance of the

sense resistor and the temperature coefficient of the sense

resistor in software. The resistance would be measured

by running a calibrated test current through the discrete

resistor. The LTC2991 would measure both the differential

voltage across this resistor and the resistor temperature.

From this measurement, RO and TO in the following equa-

tion would be known. Using the two equations, the host

microprocessor could compensate for both the absolute

tolerance and the TCR.

T = RO • [1 + α(T – TO)],where

α = 3930ppm/°C for copper trace

α = ±2 to ~200ppm/°C for discrete R (7)

I = (V1 – V2)/RT (8)

Device Configuration

The LTC2991 is configured by writing the channel control

registers through the serial interface. Refer to Tables 5, 6

and 7 for control register bit definition. The device is ca-

pable of many application configurations including voltage,

temperature and current measurements. It is possible to

configure the device for single or repeated acquisitions. For

repeated acquisitions, only the initial trigger is required,

and new data is written over the old data. Acquisitions

are frozen during serial read data transfers, to prevent the

upper and lower data bytes for a particular measurement

from becoming out of sync. Internally, both the upper and

lower bytes are written at the same instant. Since serial data

transfer timeout is not implemented, failure to terminate a

read operation will yield an indefinitely frozen wait state.

The device can also make single measurements, or with

one trigger, all of the measurements for the configuration.

When the device is configured for multiple measurements,

the order of measurements is fixed. As each new data

result is ready, the MSB of the corresponding data reg-

ister is set, and the corresponding status register bit is

set. These bits are cleared when the corresponding data

power-up yields the measurement of the internal tempera-

ture sensor and V1 through V8 as single-ended voltages,

if triggered. The eight input pins V1 through V8 will be in

a high impedance state, until configured otherwise, and

a measurement triggered.

Data Format

The data registers are broken into 8-bit upper and lower

bytes. Voltage and temperature conversions are 13-bits.

The upper bits in the MSB registers provide status on the

resulting conversions. These status bits are different for

temperature and voltage conversions.

Temperature

Temperature conversions are reported as Celsius or Kelvin

results described in Tables 11 and 12, each with 0.0625

degree weighted LSBs. The format is controlled by the

control registers, xxx. The temperature MSB result register

most significant bit (Bit 7) is the DATA_VALID bit, which

indicates whether the current register contents have been

accessed since the result was written to the register. This

bit will be set when new data is written to the register,

and cleared when accessed. The LTC2991 internal bias

circuitry maintains this voltage above this level during

normal operating conditions. Bit 4 through bit 0 of the

MSB register are the conversion result bits D[12:8], in

two’s compliment format. Note in Kelvin results, the

result will always be positive. The LSB register contains

temperature result bits D[7:0]. To convert the register

contents to temperature, use the following equation: T =

D[12:0]/16. See Table 16 for conversion value examples.

Remote diode voltage is digitized at ~50μA of bias current.

The ADC LSB value during these conversions is typically

38.15μV. Voltages are only available for the remote di-

odes, not the internal sensor. This code repeats at a diode

voltage of approximately 0.625V (see Tables 13 and 14).

The absolute temperature of the diode can be used to

detect whether the diode is operating (≤0.62501V or

≥ 0.62505V). This mode is useful for testing small relative

LTC2991

2991fa

APPLICATIONS INFORMATION

changes in temperature using the approximate relation-

ship of –2.1mV/°C of voltage dependence on temperature.

With an LSB weight of 38.15μV and a diode temperature

relationship of –2.1mV/°C this yields ~0.018 degree resolu-

tion. For sensor applications involving heaters, the ability

to sense small changes in temperature with low noise

can yield significant power savings, allowing the heater

power to be reduced. Table 16 has some conversion result

examples for various diode voltages.

Voltage/Current

Voltage results are reported in two respective registers,

an MSB and LSB register. The Voltage MSB result register

most significant bit (bit 7) is the DATA_VALID bit, which

indicates whether the current register contents have been

accessed since the result was written to the register. This

bit will be set when the register contents are new, and

cleared when accessed. Bit 6 of the MSB register is the

sign bit, bits 5 though 0 represent bits D[13:8] of the

two’s complement conversion result. The LSB register

holds conversion bits D[7:0]. The LSB value is different

for single-ended voltage measurements V1 through V8,

and differential (current measurements) V1 – V2 , V3 – V4,

V5 – V6 and V7 – V8. Single-ended voltages are limited

to positive values in the range 0V to 4.9V or VCC + 0.2V,

whichever is smaller. Differential voltages can have input

values in the range of –0.300V to 0.300V.

Use the following equations to convert the register values

(see Table 16 for examples):

VSINGLE_ENDED = D[13:0] • 305.18μV

VDIFFERENTIAL = D[13:0] • 19.0735μV, if sign = 0

VDIFFERENTIAL = (D[13:0] +1) • –19.0735μV, if sign = 1

Current = D[13:0] • 19.0735μV/RSENSE, if sign = 0

Current = (D[13:0] +1) • –19.0735μV/RSENSE, if sign = 1,

Where RSENSE is the current sensing resistor, typically

< 1Ω.

VCC

The LTC2991 measures VCC. To convert the contents of

the VCC register to voltage, use the following equation:

VCC = 2.5 + (D[13:0] • 305.18μV).

PWM Output

A 9-bit, 1kHz PWM output proportional to temperature V7

is available for controlling fans or heaters. PWM_Thresh-

old is a 9-bit value with an LSB weighting of one degree

Kelvin. PWM_Threshold is subtracted from V7 and a

pulse width proportional to the difference is produced.

Note that the PWM threshold is split among two regis-

ters, with PWM_Threshold[8:1] in register 09h[7:0] and

PWM_Threshold[0] in register 08h[7]. Equation 9 shows

the registers involved. The PWM frequency is ~1kHz. The

PWM output can be disabled or inverted with the PWM

enable and PWM invert bits is register 08h, respectively.

Figure 9 illustrates the PWM transfer function. The equa-

tion for the duty cycle is:

(9)

PWM_DUTY_CYCLE %

(

)

=100 • (REG7 – PWM • 16)

512

Where REG7 is bits [12:0] and

PWM is PWM Threshold bits [8:0]

A 50% duty cycle PWM signal would occur, for example,

if the PWM threshold was set to 10h (16°C) and register

7 contained 200h (32°C). If channel 7 is configured for

Kelvin temperatures, the PWM threshold must also be a

Kelvin temperature. The registers are two’s compliment

numbers. When calculating the duty cycle above for

Celsius temperatures care should be taken to sign extend

the register 7 and PWM threshold values. For temperatures

below the PWM Threshold, the PWM output pin will be a

constant logic level 0. For temperatures 32 degrees above

Figure 9. PWM Transfer Function

REG7[12:4]-PWM_THRESHOLD[8:0]

PWM DC (%)

50%

16 32

2991 F09

99.8%

PWM INVERT = LOGIC 0

LTC2991

2991fa

APPLICATIONS INFORMATION

the PWM Threshold, the PWM output pin will be a constant

logic level 1. This relationship is opposite if the PWM

invert bit is set. If the filter is enabled for the V7/V8 pair,

the filtered result is routed to the PWM block; otherwise,

the unfiltered version is used. The PWM CMOS output

drive is intended to be buffered to drive large (>100pF)

external capacitances or resistors <10k. A recommended

noninverting buffer is a NC7SZ125 to increase the drive

capability of the PWM signal.

Digital Filter

Each conversion result can be filtered using an on-chip

digital filter. The filter equation is:

OUTPUT[X] = (15 • (OUTPUT[X – 1]) + SAMPLE[X])/16

where output[x] is the register value when enabled. The

filter step response is illustrated in the Typical Perfor-

mance Characteristics section. The filter can be seeded

by triggering an unfiltered conversion of each configured

measurement, then subsequently enabling the filter. This

will cause the filter to converge instantaneously to the value

of the initial unfiltered sample. The filter can be enabled

or disabled for each channel pair and internal temperature

measurements. VCC measurements cannot be filtered.

Digital Interface

The LTC2991 communicates with a bus master using

a 2-wire interface compatible with the I2C Bus and the

SMBus, an I2C extension for low power devices.

The LTC2991 is a read write slave device and supports

SMBus bus read byte data and write byte data, read word

data and write word data commands. The data formats

for these commands are shown in Tables 3 though 15.

The connected devices can only pull the bus wires LOW

and can never drive the bus HIGH. The bus wires are

externally connected to a positive supply voltage via a

current source or pull-up resistor. When the bus is free,

both lines are HIGH. Data on the I2C bus can be transferred

at rates of up to 100kbit/s in the standard mode and up to

400kbit/s in the fast mode. Each device on the I2C bus is

recognized by a unique address stored in that device and

can operate as either a transmitter or receiver, depending

on the function of the device. In addition to transmitters

and receivers, devices can also be considered as masters

or slaves when performing data transfers. A master is

the device which initiates a data transfer on the bus and

generates the clock signals to permit that transfer. At the

same time any device addressed is considered a slave.

The LTC2991 can only be addressed as a slave. Once ad-

dressed, it can receive configuration bits or transmit the

last conversion result. Therefore the serial clock line SCL

is an input only and the data line SDA is bidirectional. The

device supports the standard mode and the fast mode for

data transfer speeds up to 400kbit/s. The Timing Diagram

shows the definition of timing for fast/standard mode

devices on the I2C bus. The internal state machine cannot

update internal data registers during an I2C read operation.

The state machine pauses until the I2C read is complete.

It is therefore, important not to leave the LTC2991 in this

state for long durations, or increased conversion latency

will be experienced.

START and STOP Conditions

When the bus is idle, both SCL and SDA must be high. A

bus master signals the beginning of a transmission with

a START condition by transitioning SDA from high to low

while SCL is high. When the bus is in use, it stays busy

if a repeated START (SR) is generated instead of a STOP

condition. The repeated START (SR) conditions are func-

tionally identical to the START (S). When the master has

finished communicating with the slave, it issues a STOP

condition by transitioning SDA from low to high while SCL

is high. The bus is then free for another transmission.

I2C Device Addressing

Eight distinct bus addresses are configurable using the

ADR0, ADR1 and ADR2 pins. Table 1 shows the corre-

spondence between ADR0, ADR1 and ADR2 pin states and

addresses. There is also one global sync address available

at EEh which provides an easy way to synchronize multiple

LTC2991’s on the same I2C bus. This allows write only access

to all LTC2991’s on the bus for simultaneous triggering.

Acknowledge

The acknowledge signal is used for handshaking between

the transmitter and the receiver to indicate that the last byte

of data was received. The transmitter always releases the

SDA line during the acknowledge clock pulse. When the

LTC2991

2991fa

APPLICATIONS INFORMATION

slave is the receiver, it must pull down the SDA line so that

it remains LOW during this pulse to acknowledge receipt

of the data. If the slave fails to acknowledge by leaving

SDA HIGH, then the master can abort the transmission by

generating a STOP condition. After the master has received

the last data bit from the slave, the master must pull down

the SDA line during the next clock pulse to indicate receipt

of the data. After the last byte has been received the master

will leave the SDA line HIGH (not acknowledge) and issue

a STOP condition to terminate the transmission.

Write Protocol

The master begins communication with a START condition

followed by the 7-bit slave address and the RW bit set to

zero. The addressed LTC2991 acknowledges the address

and then the master sends a command byte which indi-

cates which internal register the master wishes to write.

The LTC2991 acknowledges the command byte and then

latches the lower five bits of the command byte into its

internal register address pointer. The master then deliv-

ers the data byte and the LTC2991 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 LTC2991 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 7-bit slave address and the RW bit set to

zero. The addressed LTC2991 acknowledges this and then

the master sends a command byte which indicates which

internal register the master wishes to read. The LTC2991

acknowledges this and then latches the lower five bits

of the command byte into its internal register address

pointer. The master then sends a repeated START condi-

tion followed by the same seven bit address with the RW

bit now set to one. The LTC2991 acknowledges and sends

the contents of the requested register. The transmission

is ended when the master sends a STOP condition. The

byte is read. If the master acknowledges the transmitted

data byte, as in a read word command, the LTC2991 will

send the contents of the next sequential register as the

second data byte. The byte following register 1Fh is register

0h, or the status register.

Control Registers

The control registers (Tables 5 through 8) determine the

selected measurement mode of the device. The LTC2991 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 LTC2991 can be configured

to run particular measurements, or all possible measure-

ments per the configuration specified by the channel enable

control registers is 00h, which translates to a single-ended

voltage measurement of the triggered channels. This mode

prevents the application of remote diode test currents on

pins V1, V3, V5 and V7, and remote diode terminations on

pins V2, V4, V6 and V8 at power-up.

Status Register

The status registers (Tables 3 and 4) report the status of a

particular 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.

Figure 4. Data Transfer Over I2C or SMBus

STOP

2991 F04

START ADDRESS R/W

981-71-71-7

a6-a0 b7-b0 b7-b0

9898

DATA DATAACK ACK ACK

LTC2991

2991fa

APPLICATIONS INFORMATION

Table 1. I2C Base Address

I2C BASE ADDRESS ADR2 ADR1 ADR0

90h 0 0 0

92h 0 0 1

94h 0 1 0

96h 0 1 1

98h 1 0 0

9Ah 1 0 1

9Ch 1 1 0

9Eh 1 1 1

EEh Global Sync Address

S A A DATAW#ADDRESS COMMAND A

0 0 b7:b001001 1a1:a0

FROM MASTER TO SLAVE

XXXXXb3:b0 0

2991 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

S A A DATAW#ADDRESS COMMAND A

0 0 b7:b0

DATA

b7:b001001 1a1:a0 XXXXXb3:b0 0 0

2991 F06

SAASW#ADDRESS COMMAND A

00 10

DATA

b7:b001001 1a1:a0

ADDRESS

1001 1a1:a0XXXXXb3:b0 1

2991 F07

PA#R

SAASW#ADDRESS COMMAND A

00 10

DATA

b7:b001001 1a1:a0

ADDRESS

1001 1a1:a0XXXXXb3:b0 1

2991 F08

PA#DATA

b7:b0

Figure 5. LTC2991 Serial Bus Write Byte Protocol

Figure 6. LTC2991 Serial Bus Repeated Write Byte Protocol

Figure 7. LTC2991 Serial Bus Read Byte Protocol

Figure 8. LTC2991 Serial Bus Repeated Read Byte Protocol

LTC2991

2991fa

APPLICATIONS INFORMATION

Table 2. LTC2991 Register Address and Contents

ADDRESS* †REGISTER NAME READ/WRITE DESCRIPTION

00h STATUS LOW R DATA_VALID Bits (V1 Through V8)

01h CH EN, STAT. HI, TRIGGER** R/W CHANNEL ENABLE , VCC, TINTERNAL Conv. Status, Trigger

02h Reserved N/A Reserved

03h Reserved N/A Reserved

04h Reserved N/A Reserved

05h Reserved N/A Reserved

06h V1, V2 and V3, V4 CONTROL R/W V1, V2, V3 and V4 Control Register

07h V5, V6 and V7, V8 CONTROL R/W V5, V6, V7 and V8 Control Register

08h PWM_Threshold(LSB), VCC, TINTERNAL CONTROL R/W PWM Threshold and TINTERNAL Control Register

09h PWM_Threshold(MSB) R/W PWM Threshold

0Ah V1(MSB) R V1 or TR1 T MSB

0Bh V1(LSB) R V1 or TR1 T LSB

0Ch V2(MSB) R V2, V1 – V2, or TR1 Voltage MSB

0Dh V2(LSB) R V2, V1 – V2, or TR1 Voltage LSB

0Eh V3(MSB) R V3, or TR2 T MSB

0Fh V3(LSB) R V3, or TR2 T LSB

10h V4(MSB) R V4, V3 – V4, or TR2 Voltage MSB

11h V4(LSB) R V4, V3 – V4, or TR2 Voltage LSB

12h V5(MSB) R V5, or TR3 T MSB

13h V5(LSB) R V5, or TR3 T LSB

14h V6(MSB) R V6, V5 – V6, or TR3 Voltage MSB

15h V6(LSB) R V6, V5 – V6, or TR3 Voltage LSB

16h V7(MSB) R V7, or TR4 T MSB

17h V7(LSB) R V7, or TR4 T LSB

18h V8(MSB) R V8, V7 – V8, or TR4 Voltage MSB

19h V8(LSB) R V8, V7 – V8, or TR4 Voltage LSB

1Ah TINTERNAL(MSB) R TINTERNAL MSB

1Bh TINTERNAL(LSB) R TINTERNAL LSB

1Ch VCC(MSB) R VCC MSB

1Dh VCC(LSB) R VCC LSB

* Register address MSBs b7 to b5 are ignored.

** Writing any value triggers a conversion.

† Power-on reset sets all registers to 00h.

LTC2991

2991fa

APPLICATIONS INFORMATION

Table 3. STATUS LOW (00h) Register

BIT NAME OPERATION

b7 V8, T4, V7 – V8 Ready 1 = V8 Register Contains New Data, 0 = V8 Register Data Old

b6 V7, T4, V7 – V8 Ready 1 = V7 Register Contains New Data, 0 = V7 Register Data Old

b5 V6, T3, V5 – V6 Ready 1 = V6 Register Contains New Data, 0 = V6 Register Data Old

b4 V5, T3, V5 – V6 Ready 1 = V5 Register Contains New Data, 0 = V5 Register Data Old

b3 V4, T2, V3 – V4 Ready 1 = V4 Register Contains New Data, 0 = V4 Register Data Old

b2 V3, T2, V3 – V4 Ready 1 = V3 Register Contains New Data, 0 = V3 Register Data Old

b1 V2, T1, V1 – V2 Ready 1 = V2 Register Contains New Data, 0 = V2 Register Data Old

b0 V1, T1, V1 – V2 Ready 1 = V1 Register Contains New Data, 0 = V1 Register Data Old

Table 4. STATUS HIGH, CHANNEL ENABLE (01h) Register (Default 00h)

BIT NAME R/W OPERATION

b7 V7 and V8, V7 – V8, TR4 Enable R/W 1 = V7 and V8, or V7 – V8 or T4 Enabled

0 = V7 and V8, or V7 – V8 or T4 Disabled (Default)

b6 V5 and V6, V5 – V6, TR3 Enable R/W 1 = V5 and V6, or V5 – V6 or T3 Enabled

0 = V5 and V6, or V5 – V6 or T3 Disabled (Default)

b5 V3 and V4, V3 – V4, TR2 Enable R/W 1 = V3 and V4, or V3 – V4 or T2 Enabled

0 = V3 and V4, or V3 – V4 or T2 Disabled (Default)

b4 V1 and V2, V1 – V2, TR1 Enable R/W 1 = V1 and V2, or V1 – V2 or T1 Enabled

0 = V1 and V2, or V1 – V2 or T1 Disabled (Default)

b3 TINTERNAL VCC Enable R/W 1 = TINTERNAL and VCC Enabled

0 = TINTERNAL and VCC Disabled (Default)

b2 BUSY R 1 = A Conversion Is in Process

0 = Sleep Mode (Default)

b1 TINTERNAL R 1 = TINTERNAL Register Contains New Data

0 = TINTERNAL Register Data Old (Default)

b0 VCC R 1 = VCC Register Contains New Data

0 = VCC Register Data Old (Default)

Table 5. V1, V2 and V3, V4 CONTROL (06h) Register (Default 00h)

BIT NAME OPERATION

b7 V3, V4 Filt 1 = Filter Enabled, 0 = Filter Disabled for V3 and V4, V3 – V4 or T2 (Default)

b6 TR2 Kelvin 1 = Kelvin, 0 = Celsius for T2 (Default)

b5 V3, V4 Temperature 1 = Temperature, 0 = Voltage (Per b4 Setting) (Default)

b4 V3, V4 Differential 1 1 = Differential (V3 – V4) and V3 Single-Ended

0 = Single-Ended Voltage (V3 and V4) (Default)

b3 V1, V2 Filt 1 = Filter Enabled, 0 = Filter Disabled for V1 and V2, V1 – V2 or T1 (Default)

b2 TR1 Kelvin 1 = Kelvin, 0 = Celsius for T1 (Default)

b1 V1, V2 Temperature 1 = Temperature, 0 = Voltage (Per b0 Setting) (Default)

b0 V1, V2 Differential 1 = Differential (V1 – V2) and V1 Single-Ended

0 = Single-Ended Voltage (V1 and V2) (Default)

LTC2991

2991fa

APPLICATIONS INFORMATION

Table 6. V5, V6 and V7, V8 CONTROL (07h) Register (Default 00h)

BIT NAME OPERATION

b7 V7, V8 Filt 1 = Filter Enabled, 0 = Filter Disabled for V7 and V8, V7 – V8 or T4 (Default)

b6 TR4 Kelvin 1 = Kelvin, 0 = Celsius for T4 (Default)

b5 V7, V8 Temperature 1 = Temperature, 0 = Voltage (Per b4 Setting) (Default)

b4 V7, V8 Differential 1 = Differential (V7 – V8) and V7 Single-Ended

0 = Single-Ended Voltage (V7 and V8) (Default)

b3 V5, V6 Filt 1= Filter Enabled, 0 = Filter Disabled for V5 and V6, V5 – V6 or T3 (Default)

b2 TR3 Kelvin 1 = Kelvin, 0 = Celsius for T3 (Default)

b1 V5, V6 Temperature 1 = Temperature, 0 = Voltage (Per b0 Setting) (Default)

b0 V5, V6 Differential 1 = Differential (V5 – V6) and V5 Single-Ended

0 = Single-Ended Voltage (V5 and V6) (Default)

Table 7. PWM, VCC and TINTERNAL CONTROL (08h) Register (Default 00h)

BIT NAME OPERATION

b7 PWM[0] PWM Threshold Least Significant Bit (Default = 0)

b6 PWM Invert* 1 = PWM Inverted, 0 = PWM Noninverted (Default)

b5 PWM Enable** 1 = PWM Enabled, 0 = PWM Disabled (Default)

b4 Repeated Acquisition 1 = Repeated Mode

0 = Single Shot (Default)

b3 TINTERNAL Filt 1 = Filter Enabled for TINTERNAL

0 = Filter Disabled TINTERNAL (Default)

b2 TINTERNAL Kelvin 1 = Kelvin, 0 = Celsius for TINTERNAL (Default)

b1 Reserved Reserved

b0 Reserved Reserved

* Noninverted would be an increasing duty cycle for an increasing temperature.

** If disabled and noninverted, the PWM pin will be a logic level 0. If disabled and inverted, the PWM pin will be a logic level 1.

Table 8. PWM Register Format (Default 00h)

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

D8 D7 D6 D5 D4 D3 D2 D1

Note: D0 is located in the MSB of PWM, VCC and TINTERNAL CONTROL (08h) Register

Table 9. Voltage/Current Measurement MSB Data Register Format

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

DV* Sign D13 D12 D11 D10 D9 D8

*Data valid is set when a new result is written into the register. Data valid is cleared

when this register is addressed (read) by the I2C interface.

Table 10. Voltage/Current Measurement LSB Data Register Format

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

D7 D6 D5 D4 D3 D2 D1 D0

LTC2991

2991fa

Table 11. Temperature Measurement MSB Data Register Format

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

DV* X X D12 D11 D10 D9 D8

*Data valid is set when a new result is written into the register. Data valid is cleared

when this register is addressed (read) by the I2C interface.

X Unused

Table 12. Temperature Measurement LSB Data Register Format

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

D7 D6 D5 D4 D3 D2 D1 D0

Table 14. Diode Voltage Measurement LSB Data Register Format

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

D7 D6 D5 D4 D3 D2 D1 D0

Table 13. Diode Voltage Measurement MSB Data Register Format

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

DV* X X D12 D11 D10 D9 D8

*Data valid is set when a new result is written into the register. Data valid is cleared

when this register is addressed (read) by the I2C interface.

X Unused

Table 15. PWM Threshold Register Format

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

D7 D6 D5 D4 D3 D2 D1 D0

D7:D0 = PWM[8:1], bit 0 is located in the PWM, VCC and TINT CONTROL Register (Table 7)

Table 16. Conversion Formats

VOLTAGE FORMATS SIGN BINARY VALUE D[13:0] VOLTAGE

Single-Ended

LSB = 305.18μV = 2.5/213 0 11111111111111 >5

0 10110011001101 3.5000

0 01111111111111 2.5000

0 00000000000000 0.0000

1 11110000101001 –0.3000

Differential

LSB = 19.075μV = 2.5/217 0 11110101101111 0.300

0 10000010001111 0.159

0 00000000000000 0.0000

1 01111101110001 –0.159

1 00001010010001 –0.300

VCC = Result + 2.5V

LSB = 305.18μV = 2.5/213 0 10110011001101 VCC = 6.0

0 10000000000000 VCC = 5.0

0 00001010001111 VCC = 2.7

APPLICATIONS INFORMATION

LTC2991

2991fa

APPLICATIONS INFORMATION

Table 17. Recommended Transistors to Be Used as Temperature Sensors

MANUFACTURER PART NUMBER PACKAGE

Fairchild Semiconductor MMBT3904 SOT-23

Fairchild Semiconductor FMMT3904 SOT-23

Fairchild Semiconductor 2N3904 TO-92

Central Semiconductor CMPT3904 SOT-23

Central Semiconductor CET3904E SOT-883L

Diodes, Inc. MMBT3904 SOT-23

On Semiconductor MMBT3904LT1 SOT-23

NXP MMBT3904 SOT-23

Infineon MMBT3904 SC-70

Rohm UMT3904 SOT-23

Table 16. Conversion Formats

TEMPERATURE FORMATS FORMAT BINARY VALUE D[12:0] TEMPERATURE

Temperature Internal, TR1 Through TR4

LSB = 0.0625 Degrees

Celsius 0011111010000 125.0000

Celsius 0000110010001 25.0625

Celsius 0000110010000 25.0000

Celsius 1110110000000 –40.0000

Kelvin 1100011100010 398.1250

Kelvin 1000100010010 273.1250

Kelvin 0111010010010 233.1250

Kelvin 0010011010000 77.0000

Diode Voltage Formats Sign Binary Value D[13:0] Voltage

Remote Temperature TR1 Through TR4

LSB = 38.15μV

0 00000000000000 0.0000

0 11111111111111 0.31249

0 00000000000000 0.31252

0 11111111111111 0.62501

0 00000000000000 0.62505

0 10011001100100 0.99999

LTC2991

2991fa

High Voltage/Current and Temperature Monitoring

TYPICAL APPLICATIONS

–

–INS 0.1μF

VIN

5V TO 105V

0.1μF

ALL CAPACITORS ±20%

OTHER APPS

VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION:

CONTROL REGISTER: 0x06 0xA0

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

VLOAD REG 0A, 0B: 13.2mV/LSB

V2(ILOAD) REG 0C, 0D: 1.223mA/LSB

TPROCESSOR REG 0E, 0F: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

MMBT3904

RIN

20Ω

ILOAD

0A TO 10A

ROUT

4.99k

200k

4.75k

1% 0.1μF

RSENSE = 1mΩ

–INF

V+

V–

LTC6102HV

OUT

VREG

+IN

VCC V1

LTC2991

2-WIRE I2C

INTERFACE

GND

SDA

SCL

ADR0

ADR1

ADR2

V5 TO V8

2991 TA02

LTC2991

2991fa

TYPICAL APPLICATIONS

Computer Voltage and Temperature Monitoring

Motor Protection/Regulation

MICROPROCESSOR

VCC V1

LTC2991

2-WIRE I2C

INTERFACE

GND

SDA

SCL

ADR0

ADR1

ADR2

2991 TA03

10k

3.3V

30.1k

12V

VOLTAGE AND TEMPERATURE CONFIGURATION

CONTROL REGISTER: 0x06 0x0A

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

V1(+5) REG 0A, 0B: 610μV/LSB

V2(+12) REG 0C, 0D: 1.22mV/LSB

TPROCESSOR REG 0E, 0F: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

0.1μF

OTHER APPS

V5 TO V8

VCC V1

LTC2991

LOADPWR*t7

0.1Ω

MOTOR CONTROL VOLTAGE

0VDC TO 5VDC

0A TO ±2.2A

2-WIRE I2C

INTERFACE

GND

TMOTOR

MMBT3904

SDA

SCL

ADR0

ADR1

ADR2

2991 TA04

MOTOR

TAMBIENT

VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION:

CONTROL REGISTER: 0x06: 0xA1

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

VMOTOR REG 0A, 0B: 305.18μV/LSB

IMOTOR REG 0C, 0D: 194.18μA/LSB

TMOTOR REG 1A, 1B: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

OTHER APPS

V5 TO V8

LTC2991

2991fa

TYPICAL APPLICATIONS

Large Motor Protection/Regulation

Fan/Air Filter/Temperature Alarm

VCC V1

LTC2991

LOADPWR*t7

0.01Ω

1W, 1%

MOTOR CONTROL VOLTAGE

0V TO 40V

0A TO 10A

2-WIRE I2C

INTERFACE

71.5k

10.2k

GND

TMOTOR

MMBT3904

SDA

SCL

ADR0

ADR1

ADR2

2991 TA05

MOTOR

TAMBIENT

VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION:

CONTROL REGISTER 06: 0xA1

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

VMOTOR REG 0A, 0B: 2.44mV/LSB

IMOTOR REG 0C, 0D: 15.54mA/LSB

TMOTOR REG 0E, 0F: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

OTHER APPS

V5 TO V8

VCC V1

LTC2991

2-WIRE I2C

INTERFACE

3.3V

GND

22Ω

0.125W

HEATER

NDS351AN

TEMPERATURE FOR:

HEATER ENABLE

GOOD FAN

BAD FAN

FAN

MMBT3904

SDA

SCL

ADR0

ADR1

2991 TA06

TAMBIENT HEATER ENABLE

2 SECOND PULSE

CONTROL REGISTER 0x06 = 0xAA

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

TFAN1 REG 0A, 0B: 0.0625°C/LSB

TFAN2 REG 0C, 0D: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

3.3V

22Ω

0.125W

FAN

OTHER APPS

V5 TO V8

LTC2991

2991fa

TYPICAL APPLICATIONS

Battery Monitoring

Wet Bulb Psychrometer

REFERENCES

http://en.wikipedia.org/wiki/Hygrometer

http://en.wikipedia.org/wiki/Psychrometrics

VCC V1

LTC2991

μC

GND TDRY TWET

MMBT3904 MMBT3904

SDA

SCL

ADR0

ADR1

ADR2

2991 TA08

470pF

TAMBIENT

DAMP MUSLIN

WATER

RESERVOIR

CONTROL REGISTER 0x06 = 0xAA

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

TWET REG 0A, 0B: 0.0625°C/LSB

TDRY REG 0C, 0D: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

ΔT

NDS351AN

FAN ENABLE

FAN

FAN: SUNON

KDE0504PFB2

OTHER APPS

V5 TO V8

VCC V1

LTC2991

BATTERY I AND V MONITOR

0.1Ω*

CHARGING

CURRENT

2-WIRE I2C

INTERFACE

GND

NiMH

BATTERY

V(t)

100% 100%

ttt

TBATT

MMBT3904

SDA

SCL

ADR0

ADR1

ADR2

2991 TA07

TAMBIENT

*IRC LRF3W01R015F

VOLTAGE AND TEMPERATURE CONFIGURATION:

CONTROL REGISTER: 0xA1

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

VBAT REG 0A, 0B: 305.18μV/LSB

IBAT REG 0C, 0D: 194.2μA/LSB

TBAT REG 0E, 0F: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

+T(t)

100%

I(t)

OTHER APPS

V5 TO V8

LTC2991

2991fa

TYPICAL APPLICATIONS

Wind Direction/Instrumentation

VCC V1

LTC2991

3.3V

μC

GND

MMBT3904 MMBT3904

SDA

SCL

ADR0

ADR1

ADR2

2991 TA10

3.3V

HEATER

75Ω

0.125W

TAMBIENT

CONTROL REGISTER 0x06 0xAA

TAMBIENT REG 1A, 1B 0.0625°C/LSB

TR1 REG 0A, 0B 0.0625°C/LSB

TR2 REG 0E, 0F 0.0625°C/LSB

VCC REG 1C, 1D 2.5V + 305.18μV/LSB

2N7002

HEATER ENABLE

2 SECOND PULSE

OTHER APPS

V5 TO V8

Liquid Level Indicator

VCC

LTC2991

3.3V

μC

GND

SDA

SCL

ADR0

ADR1

ADR2

3.3V

TAMBIENT

CONTROL REGISTER 0x06 = 0xAA

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

TDRY REG 0A, 0B: 0.0625°C/LSB

TWET REG 0C, 0D: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

NDS351AN

2991 TA09

*HEATER: 75Ω 0.125W

*SENSOR MMBT3904, DIODE CONNECTED

SENSOR LO*

ΔT = ~2.0°C pp, SENSOR HI

~0.2°C pp, SENSOR LO

SENSOR HI*

HEATER ENABLE

2 SECOND PULSE

HEATER ENABLE

SENSOR HI

SENSOR LO

OTHER APPS

V5 TO V8

LTC2991

2991fa

Oven Control with Power Monitor

Remote Temperature Sensing with Extended ESD Performance

VCC

2-WIRE

I2C INTERFACE

LTC2991

TAMBIENT

GND

SDA

SCL

ADR0

ADR1

ADR2

OTHER APPLICATIONS

VOLTAGE AND CURRENT (POWER) MONITOR

OVEN

TSET 70°C

TEMPERATURE

SENSOR

HEATER

VCC

PWM

2991 TA11

–

100k

1μF

LT6240

100k

VCC

VOLTAGE, CURRENT, TEMPERATURE AND PWM CONFIGURATION:

CONTROL REGISTER 0x06: 0x01

TAMBIENT REG 1A, 1B 0.0625°C/LSB

VHEATER REG 0A, 0B 305μV/LSB

IHEATER REG 0C, 0D 19.4μV/RHEATERA/LSB

TOVEN REG 16, 17 0.0625°C/LSB

VCC REG 1C, 1D 2.5V + 305.18μV/LSB

0x07: 0xA0

PWM, TINTERNAL, VCC REG:

PWM REGISTER 0x08: 0x50

0x09: 0x1B

VCC

LTC2991

3.3V

GND

SDA

SCL

500Ω

2991 TA13

CONTROL REGISTER 0x06 = 0xAA

REMOTE TEMPERATURE SENSOR REG OB, OB: 0.0625 °C/LSB

MMBT3904

> 8kV ESD

MMBT3904

REMOTE

TEMPERATURE

SENSOR

PROTECTION

DEVICE

TYPICAL APPLICATIONS

LTC2991

2991fa

VCC

LTC2991

3.3V

GND

SDA

SCL

SDA

SCL

1, 4

S0, S1

LTC1393

S2, S3

2, 3

5, 8

6, 7

2991 TA14

LTC2291 REMOTE TEMPERATURE SENSOR REG OB, OB: 0.0625 °C/LSB

LTC2991 CONTROL REGISTER 0x06 0xAA

LTC1393 CONTROL BYTE SENSOR A = 0x0B

LTC1393 CONTROL BYTE SENSOR B = 0x0A

LTC1393 CONTROL BYTE SENSOR C = 0x0C

LTC1393 CONTROL BYTE SENSOR D = 0x0E

LTC1393

WIRED AS A DUAL

CROSS-POINT SWITCH

MMBT3904MMBT3904

WIRE PAIR 1

REMOTE

TEMPERATURE

SENSOR A

REMOTE

TEMPERATURE

SENSOR B

MMBT3904MMBT3904

WIRE PAIR 2

REMOTE

TEMPERATURE

SENSOR C

REMOTE

TEMPERATURE

SENSOR D

QUAD Remote Temperature Sensing with Two Wire Pairs Using One LTC2991 Channel

TYPICAL APPLICATIONS

LTC2991

2991fa

PACKAGE DESCRIPTION

MS Package

16-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1669 Rev Ø)

MSOP (MS16) 1107 REV Ø

0.53 p 0.152

(.021 p .006)

SEATING

PLANE

0.18

(.007)

1.10

(.043)

MAX

0.17 –0.27

(.007 – .011)

TYP

0.86

(.034)

REF

0.50

(.0197)

BSC

16151413121110

12345678

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.

MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

0.254

(.010) 0o – 6o TYP

DETAIL “A”

GAUGE PLANE

5.23

(.206)

MIN

3.20 – 3.45

(.126 – .136)

0.889 p 0.127

(.035 p .005)

RECOMMENDED SOLDER PAD LAYOUT

0.305 p 0.038

(.0120 p .0015)

TYP

0.50

(.0197)

BSC

4.039 p 0.102

(.159 p .004)

(NOTE 3)

0.1016 p 0.0508

(.004 p .002)

3.00 p 0.102

(.118 p .004)

(NOTE 4)

0.280 p 0.076

(.011 p .003)

REF

4.90 p 0.152

(.193 p .006)

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

LTC2991

2991fa

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

A 10/11 Corrected axis label on Figure 9

Inserted new text in I2C Device Addressing section

Inserted new row in Table 1

Revised component values in Typical Application drawing TA05

LTC2991

2991fa

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT 1011 REV A • PRINTED IN USA

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Can Be Used as Linear Temperature Sensor

Parasitic Resistance Voltage and Current Monitoring with Temperature Compensation

VCC V1

2.1k 2.1k

LTC2991

INDUCTOR WITH

RPARASITIC

RPARASITIC ~ 4000ppm/°C

ILOAD

BUCK

REGULATOR

2-WIRE I2C

INTERFACE

GND

THERMAL

COUPLING

CONTROL REGISTER 0x06: 0xA1:

TAMBIENT REG 1A, 1B: 0.0625°C/LSB

VLOAD REG 0A, 0B: 305μV/LSB

ILOAD REG 0C, 0D: 194μA/LSB

TRPARASITIC REG 1A, 1B: 0.0625°C/LSB

VCC REG 1C, 1D: 2.5V + 305.18μV/LSB

QUIET NODE

SWITCHING

WAVEFORM

MMBT3904

VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION

SDA

SCL

ADR0

ADR1

ADR2

2991 TA12

TAMBIENT

1μF

OTHER APPS

V5 TO V8

1μF