Datasheet

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LTC2945

2945fa

For more information www.linear.com/LTC2945

Typical applicaTion

FeaTures DescripTion

Wide Range

C Power Monitor

Wide Range Power Monitor with Onboard ADC and I

applicaTions

Rail-to-Rail Input Range: 0V to 80V

Wide Input Supply Range: 2.7V to 80V

Shunt Regulator for Supplies >80V

Δ∑ ADC with less than ±0.75% Total Unadjusted Error

12-Bit Resolution for Current and Voltages

Internal Multiplier Calculates 24-Bit Power Value

Stores Minimum and Maximum Values

Alerts When Limits Exceeded

Additional ADC Input Monitors an External Voltage

Continuous Scan and Snapshot Modes

Shutdown Mode with I

< 80µA

Split SDA for Opto-Isolation

Available in 12-Lead 3mm × 3mm QFN and MSOP

Packages

Telecom Infrastructure

Industrial

Automotive

Consumer

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

Technology Corporation. All other trademarks are the property of their respective owners.

INTERFACE

NINE I

ADDRESSES

SENSE

–

ALERT

SCL

SDAI

SDAO

ADIN

INTV

ADR1

ADR0

GND

LTC2945

MEASURED

VOLTAGE

LOAD

0.1µF

0.02Ω

4V TO 80V

2945 TA01

ADC Differential

Nonlinearity (ADIN)

ADC Integral Nonlinearity

(ADIN)

The LT C

2945 is a rail-to-rail system monitor that mea-

sures current, voltage, and power. It features an operating

range of

2.7V to 80V and includes a shunt regulator for

supplies above 80V to allow flexibility in the selection of

input supply. The current measurement range of 0V to

80V is independent of the input supply. An onboard 0.75%

accurate 12-bit ADC measures load current, input voltage

and an auxiliary external voltage. A 24-bit power value is

generated by digitally multiplying the measured 12-bit load

current and input voltage data. Minimum and maximum

values are stored and an overrange alert with program

mable thresholds minimizes the need for software polling.

Data is reported via a standard I

C interface. Shutdown

mode reduces power consumption to 20µA.

The LTC2945 I

C interface includes separate data input

and output pins for use with standard or opto-isolated I

connections. The LTC2945-1 has an inverted data output

for use with inverting opto-isolator configurations.

CODE

–0.3

ADC DNL (LSB)

0.3

0.0

0.1

0.2

–0.2

–0.1

3072 40961024 2048

2945 TA01a

CODE

–0.3

ADC INL (LSB)

0.3

0.0

0.1

0.2

–0.2

–0.1

3072 40961024 2048

2945 TA01b

Summary of content (34 pages)

PAGE 1
LTC2945 Wide Range I2C Power Monitor Features n n n n n n n n n n n n n Description Rail-to-Rail Input Range: 0V to 80V Wide Input Supply Range: 2.7V to 80V Shunt Regulator for Supplies >80V Δ∑ ADC with less than ±0.
PAGE 2
LTC2945 Absolute Maximum Ratings (Notes 1, 2) VDD Voltage............................................... –0.3V to 100V SENSE+ Voltage............................................–1V to 100V SENSE– Voltage......–1V or SENSE+ – 1V to SENSE+ + 1V INTVCC Voltage (Note 3)............................ –0.3V to 5.9V ADR1, ADR0, ADIN, ALERT, SDAO, SDAO Voltage.......................................................... –0.3V to 7V INTVCC Clamp Current............................................
PAGE 3
LTC2945 Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2945CUD#PBF LTC2945CUD#TRPBF LFWK 12-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC2945IUD#PBF LTC2945IUD#TRPBF LFWK 12-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C LTC2945CUD-1#PBF LTC2945CUD-1#TRPBF LFYX 12-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC2945IUD-1#PBF LTC2945IUD-1#TRPBF LFYX 12-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C LTC2945CMS#PBF LTC2945CMS#TRPBF 2945 12-
PAGE 4
LTC2945 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VDD is from 4V to 80V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RES Resolution (No missing codes) (Note 5) l 12 VFS Full-Scale Voltage ∆SENSE (Note 7) VIN ADIN l l l 101.7 101.7 2.033 LSB LSB Step Size ∆SENSE VIN ADIN TUE Total Unadjusted Error (Note 6) ∆SENSE VIN ADIN l l l ±0.
PAGE 5
LTC2945 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VDD is from 4V to 80V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS I2C INTERFACE TIMING fSCL(MAX) Maximum SCL Clock Frequency 400 kHz tLOW Minimum SCL Low Period 0.65 1.3 µs tHIGH Minimum SCL High Period 50 600 ns tBUF(MIN) Minimum Bus Free Time Between Stop/Start Condition 0.12 1.
PAGE 6
LTC2945 Typical Performance Characteristics 800 VDD Supply Current 70 VDD = 48V, TA = 25°C, unless noted. VDD Supply Current in Shutdown 600 INTVCC Supply Current 700 650 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 60 750 50 40 30 575 550 525 20 600 0 20 40 60 VDD SUPPLY VOLTAGE (V) 10 80 0 20 40 60 VDD SUPPLY VOLTAGE (V) 2945 G01 5.2 22.5 INTVCC Load Regulation 5.5 12.5 2 3 4 5 VCC SUPPLY VOLTAGE (V) 5.0 4.9 4.8 6 0 2 4 6 LOAD CURRENT (mA) 8 0.1 0.
PAGE 7
LTC2945 Typical Performance Characteristics ADC Integral Nonlinearity (∆SENSE) VDD = 48V, TA = 25°C, unless noted. ADC Differential Nonlinearity (∆SENSE) 0.4 ADC Total Unadjusted Error (∆SENSE) 0.50 ADC TOTAL UNADJUSTED ERROR (%) 0.3 0.2 ADC DNL (LSB) ADC INL (LSB) 0.2 0.0 0.1 0.0 –0.1 –0.2 –0.2 –0.4 0 1024 2048 CODE 3072 –0.3 4096 0 1024 3072 2048 CODE 2945 G10 4096 0.25 0.00 –0.25 –0.
PAGE 8
LTC2945 Pin Functions ADIN: ADC Input. The onboard ADC measures voltages between 0V and 2.048V. Tie to ground if unused. ADR1, ADR0: I2C Device Address Inputs. Connecting these pins to INTVCC, GND or leaving the pins open configures one of nine possible addresses. See Table 1 in Applications Information section for details. ALERT: Fault Alert Output. Open drain logic output that is pulled to ground after an ADC conversion resulted in a fault to alert the host controller.
PAGE 9
LTC2945 Block Diagram SENSE+ VDD SENSE– ADR0 ADR1 ALERT DECODER + VSTBY 20X – 5.7V VSTBY GEN INTV CC 2 IC 735k SDAO/SDAO (LTC2945 / LTC2945-1) VREF = 2.048V 735k LOGIC SDAI VSTBY 12 MUX 6.3V 15k 6.4V 12-BIT ADC SCL REGISTERS 15k 6.4V ADIN GND 2945 BD 2945fa For more information www.linear.
PAGE 10
LTC2945 Timing Diagram SDA tSU,DAT tHD,DATO tHD,DATI tSU,STA tSP tHD,STA tSP tBUF tSU,STO 2945 TD SCL tHD,STA REPEATED START CONDITION 10 REPEATED START CONDITION STOP CONDITION START CONDITION 2945fa For more information www.linear.
PAGE 11
LTC2945 Operation The LTC2945 accurately monitors current, voltage, and power of any supply rail from 0V to 80V. An internal linear regulator allows the LTC2945 to operate directly from a 4V to 80V rail, or from an external supply voltage between 2.7V and 5.9V. Quiescent current is less than 0.9mA in normal operation. Enabling shutdown mode via the I2C interface reduces the quiescent current to below 80μA. The LTC2945 includes a shunt regulator for operation from supply voltages above 80V.
PAGE 12
LTC2945 Applications Information out of the six total ADC data registers (∆SENSE MSB/LSB, VIN MSB/LSB, and ADIN MSB/LSB), with the eight MSBs in the first register and the four LSBs in the second (see Table 2). The lowest 4 bits in the LSB registers are set to 0. These data registers are updated immediately following the corresponding ADC conversion, giving an effective refresh rate of 7.5Hz in continuous scan mode.
PAGE 13
LTC2945 Applications Information RSNS VIN 4V TO 80V SENSE+ RSNS VIN >80V R1 VOUT SENSE– R2 INTVCC SENSE+ Q1 LTC2945 VDD ADIN LTC2945 R3 INTVCC C2 SENSE– R4 GND 2945 F03a GND RSHUNT 2945 F02a Figure 3a. LTC2945 Derives Power Through High-Side Shunt Regulator Figure 2a.
PAGE 14
LTC2945 Applications Information GND VDD INTVCC C2 GND LTC2945 SENSE– VNEG –4V TO –80V SENSE+ 2945 F03b RSNS VOUT Figure 3d. LTC2945 Derives Power from the Supply Being Monitored in Low-Side Current Sense Topology power dissipation, a larger resistance is advantageous. The worst-case power dissipated in an RSHUNT of 5.4k is calculated to be 0.8W. So, three 0.5W rated 1.8k resistors in series would suffice for this example.
PAGE 15
LTC2945 Applications Information Storing Minimum and Maximum Values The LTC2945 compares each measurement including the calculated power with the stored values in the respective MIN and MAX registers for each parameter (Table 2). If the new conversion is beyond the stored minimum or maximum values, the MIN or MAX registers are updated with the new values. The MIN and MAX of the registers are refreshed at the end of their respective ADC conversions in both continuous scan mode and snapshot mode.
PAGE 16
LTC2945 Applications Information STATUS MEASURED DATA DIGITAL COMPARATOR LOGIC THRESHOLD DATA FAULT LATCH ENA_ALERT_RESPONSE ALERT RESET 2945 F04 Figure 4. LTC2945 Fault Alert Generation Blocks SDA a6 - a0 SCL b7 - b0 1-7 8 9 1-7 b7 - b0 8 9 1-7 8 9 S P START CONDITION ADDRESS R/W ACK DATA ACK DATA STOP CONDITION ACK 2945 F05 Figure 5.
PAGE 17
LTC2945 Applications Information Stuck-Bus Reset The LTC2945 I2C interface features a stuck bus reset timer to prevent it from holding the bus lines low indefinitely if the SCL signal is interrupted during a transfer. The timer starts when either SCL or SDAI is low, and resets when both SCL and SDAI are pulled high. If either SCL or SDAI are low for over 33ms, the stuck-bus timer will expire and the internal I2C interface and the SDAO pin pulldown logic will be reset to release the bus.
PAGE 18
LTC2945 Applications Information If two or more LTC2945s on the same bus are generating alerts when the ARA is broadcasted, the bus master will repeat the alert response protocol until the ALERT line is released. The device with the highest priority (lowest address) will reply first and the device with the lowest priority (highest address) will reply last. ALERT S RESPONSE R A ADDRESS 0001100 1 0 DEVICE ADDRESS a7:a0 A P 1 2945 F12 Figure 12.
PAGE 19
LTC2945 Applications Information 3.3V 5V R4 10k SDAI R5 0.82k R6 0.51k R7 10k VDD LTC2945 µP 1/2 MOCD207M SDA GND GND SDAO 1/2 MOCD207M 2945 F13 Figure 13. Opto-Isolation of a 10kHz I2C Interface Between LTC2945 and Microcontroller (SCL Omitted for Clarity) GND RSHUNT 3.3V R3 1k R1 10k R2 0.51k R4 10k SDAI INTVCC VDD VDD LTC2945 VEE C1 1µF µP 1/2 MOCD207M SDA GND GND SENSE– VEE SDAO SENSE+ 1/2 MOCD207M 2945 F14 VOUT RSNS 0.02Ω Figure 14.
PAGE 20
LTC2945 Applications Information 3.3V 48V R4 20k R5 7.5k R6 0.51k R7 10k SDAI VDD LTC2945-1 µP 1/2 MOCD207M SDAO GND SDA GND 1/2 MOCD207M 2945 F16 Figure 16. Opto-Isolation of a 1.5kHz I2C Interface Between LTC2945-1 and Microcontroller (SCL Omitted for Clarity) VIN 48V C1 1µF INTVCC VDD C2 1µF 1/2 ACPL-064L* R5 2k 3.3V VCC LTC2945-1 M1 GND SDAO R6 2k BS170 R7 2k VDD VCC µP ISO_SDA SDAI GND GND SDA GND 2945 F17 1/2 ACPL-064L* * CMOS OUTPUT Figure 17.
PAGE 21
LTC2945 Applications Information Table 1.
PAGE 22
LTC2945 Applications Information 17h MAX ∆SENSE LSB R/W** Maximum ∆SENSE LSB Data 00h 18h MIN ∆SENSE MSB R/W** Minimum ∆SENSE MSB Data FFh 19h MIN ∆SENSE LSB R/W** Minimum ∆SENSE LSB Data FOh 1Ah MAX ∆SENSE THRESHOLD MSB R/W Maximum ∆SENSE Threshold MSB to Generate Alert FFh 1Bh MAX ∆SENSE THRESHOLD LSB R/W Maximum ∆SENSE Threshold LSB to Generate Alert FOh 1Ch MIN ∆SENSE THRESHOLD MSB R/W Minimum ∆SENSE Threshold MSB to Generate Alert 00h 1Dh MIN ∆SENSE THRESHOLD LSB R/W Mi
PAGE 23
LTC2945 Applications Information Table 3. CONTROL Register A (00h) - Read/Write BIT NAME OPERATION A7 ADC Snapshot Mode Enable Enables ADC Snapshot Mode; 1 = Snapshot Mode Enabled. Only channel selected by A6 and A5 is measured by the ADC. After the conversion, the BUSY bit is reset and the ADC is halted. 0 = Snapshot Mode Disabled (Continuous Scan Mode.
PAGE 24
LTC2945 Applications Information Table 5.
PAGE 25
LTC2945 Applications Information Table 7. ADC, ADC MIN/MAX, MIN/MAX ADC THRESHOLD Register Data Format: MSB Bytes-Read/Write* BIT (7) BIT (6) BIT (5) BIT (4) BIT (3) BIT (2) BIT (1) BIT (0) Data (11) Data (10) Data (9) Data (8) Data (7) Data (6) Data (5) Data (4) *Set Bit A4 before writing to ADC and MIN/MAX ADC Registers Table 8.
PAGE 26
LTC2945 Typical Applications A Wide Range Supply Monitor RSNS 0.02Ω VIN 0V TO 80V SENSE+ 2.7V TO 5.9V VOUT SENSE– R1 2k R2 2k R3 2k SCL INTVCC SDA ADR1 SDAO INT VADIN ADIN GND 3.3V VOUT SENSE– R1 2k R2 2k R3 2k VDD SCL SCL INTVCC SDAI SDA ADR1 SDAO VDD µP C2 0.1µF ALERT ADR0 SENSE+ VDD SCL LTC2945 RSNS 0.02Ω VIN 4V TO 80V 3.3V SDAI VDD C2 0.
PAGE 27
LTC2945 Typical Applications Power Monitoring in –48V System Using Low Side Sensing (1.5kHz I2C Interface) –48V RTN R1 20k R2 20k 3.3V C2 0.1µF VDD INTVCC ADR1 C1 1µF R4 1k R7 0.51k R3 1k R8 0.51k R9 10k R10 10k R11 10k VDD SCL LTC2945 SCL SDAI µP VEE MOCD207M GND SDA ADIN SDAO ADR0 INT GND ALERT SENSE – VEE –48V INPUT SENSE+ MOCD207M CONTROL REGISTER A2 = 0 VOUT RSNS 0.
PAGE 28
LTC2945 Typical Applications Power Monitoring in –48V System Using External Linear Regulator to Supply Opto-couplers and SCL/SDA Resistive Pull-Ups LT3010-5 –48V RTN IN C3 0.1µF OUT C2 1µF SHDN SENSE GND 5V VEE R7 0.5k VDD R4 1k ADR1 INTVCC R1 1k R2 10k R8 0.51k R9 1k R10 1k R11 10k VDD VCC SCL LTC2945 C1 1µF R3 0.
PAGE 29
LTC2945 Typical Applications Ruggedized 4V to 70V High Side Power Monitor with Surge Protection Up to 200V RSNS 0.02Ω VIN SENSE + VOUT SENSE– INTVCC VDD R12 100Ω R4 1k LTC2945 T1 SMAJ70A DIODES, INC Q1 PZTA42 R1 1k R3 0.51k 3.3V C2 1µF R2 1k R8 0.51k R7 0.51k FGND R9 1k R10 1k R11 10k VDD VCC SCL C1 0.1µF SCL SDAI SDA GND HCPL-063L FGND µP 3.
PAGE 30
LTC2945 Typical Applications Wide Range –4V to –500V Negative Power Monitor (10kHz I2C Interface) RTN M1 BSP135 R5 750k R13 10k R4 1k R3 1k R1 2k R2 2k VDD R6 750k 3.3V C1 0.1µF VEE R7 0.51k R8 0.51k R9 10k R10 10k R11 10k VDD SCL Z1 4.7V LTC2945 SCL SDAI VEE ADIN GND R12 5k SDA ADR1 SDAO INT ADR0 C2 0.1µF SENSE – + SENSE CONTROL REGISTER A2 = 0 RSNS 0.02Ω GND 2945 TA10 ALERT INTVCC VEE 30 µP MOCD207M MOCD207M VOUT 2945fa For more information www.linear.
PAGE 31
LTC2945 Package Description MS Package 12-Lead Plastic MSOP (Reference LTC DWG # 05-08-1668 Rev A) 0.889 ±0.127 (.035 ±.005) 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 4.039 ±0.102 (.159 ±.004) (NOTE 3) 0.65 (.0256) BSC 0.42 ±0.038 (.0165 ±.0015) TYP 12 11 10 9 8 7 RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) DETAIL “A” 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) 0° – 6° TYP 0.406 ±0.076 (.016 ±.003) REF GAUGE PLANE 0.53 ±0.152 (.021 ±.006) DETAIL “A” 0.18 (.
PAGE 32
LTC2945 Package Description UD Package 12-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1855 Rev Ø) 0.70 ±0.05 3.50 ± 0.05 1.65 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 11 12 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 1.65 ± 0.10 (4-SIDES) 2 0.200 REF 0.25 ± 0.05 (UD12) QFN 0709 REV Ø 0.00 – 0.
PAGE 33
LTC2945 Revision History REV DATE DESCRIPTION A 09/13 Added Limits to Full-Scale Voltage PAGE NUMBER 4 Removed Note 5 from I2C Interface Timing 5 Added Note 5 to SCL, SDAI Input Capacitance 5 Added ADIN and Resistive Divider Information with Regards to Figure 3a and Figure 3c 12 Revised Figure 3a and Figure 3c 13 Revised Figure 13 and Figure 17 19, 20 Revised Bottom Figure 26 Top Figure: Replaced SMAJ78A with SMAJ70A and Changed C2 Connection from VEE to FGND 29 Added “Isolated Wide Ran
PAGE 34
LTC2945 Typical Application 3.3V Input Supply Monitor with 12V VDD Input RSNS 0.02Ω VIN 3.3V SENSE+ VDD 12V ADR1 C2 0.1µF R1 2k R2 2k R3 2k IN– VDD SCL SDAI SDA RIN1 1k GND ADIN SENSE+ INT VADIN IN+ VDD GND 2945 TA12 2.7V TO 5.9V INTVCC RIN2 1k RSNS 0.02Ω VIN 0V TO 44V µP SDAO ALERT ADR0 VOUT V– SCL LTC2945 INTVCC LT6105 V+ 3.