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LT2940

2940f

TYPICAL APPLICATION

DESCRIPTION

Power and Current Monitor

The LT

2940 measures a high side current and a differ-

ential voltage, multiplies them and outputs a current

proportional to instantaneous power. Bidirectional high

side currents and bipolar voltage differences are correctly

handled by the four-quadrant multiplier and push-pull

output stage, which allows the LT2940 to indicate forward

and reverse power ﬂ ow.

An integrated comparator with inverting and noninvert-

ing open-collector outputs makes the LT2940 a complete

power level monitor. In addition, an output current pro-

portional to the sensed high side current allows current

monitoring. The current mode outputs make scaling,

ﬁ ltering and time integration as simple as selecting ex-

ternal resistors and/or capacitors.

Load Monitor Alarms Above 60W

FEATURES

APPLICATIONS

Four-Quadrant Power Measurement

±5% Power Measurement Accuracy

4V to 80V High Side Sense, 100V Max

Current Mode Power and Current Outputs

Output Bandwidth Exceeds 500kHz

±3% Current Measurement Accuracy

6V to 80V Supply Range, 100V Max

Inverting and Noninverting Open-Collector

Comparator Outputs

Available in 12-Pin DFN (3mm × 3mm) and 12-Lead

MSOP Packages

Board Level Power and Current Monitoring

Line Card and Server Power Monitoring

Power Sense Circuit Breaker

Power Control Loops

Power/Energy Meters

Battery Charger Metering

CMP

PMON IMON

CMPOUT

LATCH

–

2940 TA01a

110k

–

10.0k

0A TO 10A

LED ON WHEN

LOAD

> 60W

LOAD

= V

LOAD

• I

LOAD

6V TO 80V

LOAD

LT2940

GND

20m

IMON

= I

LOAD

• 100

PMON

= P

LOAD

• 20.75

24.9K 4.99k

LOAD

= 20m

LOAD

(A)

LOAD

(W)

PMON

(V)

2.0

1.5

1.0

10 12 14

0.5

2.5

120

80V

30V

15V

10V

2940 TA01b

LED ON

LED OFF

LOAD

=6V

60W ALARM

Monitor Output Level and Load Power

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.

Summary of content (24 pages)

PAGE 1
LT2940 Power and Current Monitor FEATURES n n n n n n n n n DESCRIPTION Four-Quadrant Power Measurement ±5% Power Measurement Accuracy 4V to 80V High Side Sense, 100V Max Current Mode Power and Current Outputs Output Bandwidth Exceeds 500kHz ±3% Current Measurement Accuracy 6V to 80V Supply Range, 100V Max Inverting and Noninverting Open-Collector Comparator Outputs Available in 12-Pin DFN (3mm × 3mm) and 12-Lead MSOP Packages The LT®2940 measures a high side current and a differential voltage, multiplie
PAGE 2
LT2940 ABSOLUTE MAXIMUM RATINGS (Notes 1, 2) VCC , I+, I– , LATCH .................................... –0.3V to 100V V+, V– , CMP+ ............................................. –0.3V to 36V Voltage Sense (V+ – V– ) .........................................±36V Current Sense (I+ – I– ) ............................................±36V PMON, IMON (Note 3) ...... –0.3V to VCC + 1V, Up to 16V CMPOUT, CMPOUT .................................... –0.3V to 36V CMPOUT, CMPOUT DC Output Current ..................
PAGE 3
LT2940 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. All speciﬁcations apply at 6V ≤ VCC ≤ 80V, unless otherwise speciﬁed.
PAGE 4
LT2940 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. All speciﬁcations apply at 6V ≤ VCC ≤ 80V, unless otherwise speciﬁed. SYMBOL VPMON EPMON PARAMETER Power Monitor Output Compliance Voltage Power Monitor Output Total Error (Note 4) CONDITIONS MIN TYP MAX UNITS VCC ≤ 12V, IPMON ≥ 0μA l 0 VCC – 4.5 V 12V < VCC < 30V, IPMON ≥ 0μA l 0 7.
PAGE 5
LT2940 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. All speciﬁcations apply at 6V ≤ VCC ≤ 80V, unless otherwise speciﬁed. SYMBOL PARAMETER CONDITIONS ICMPOUT(LK) CMPOUT Leakage Current CMP+ Low, V CC = 36V, 0.4V ≤ VCMPOUT ≤ 36V l MIN TYP MAX ICMPOUT(OL) CMPOUT Output Low Voltage CMP+ Low, ICMPOUT = 3mA ICMPOUT(LK) CMPOUT Leakage Current CMP+ High, VCC = 36V, 0.
PAGE 6
LT2940 TYPICAL PERFORMANCE CHARACTERISTICS 1500 PMON and IMON Voltage Compliance 300 VCC ≥ 15V VV = 40 • VI 500 IPMON (μA) TA = 25°C I = 200μA 200 OUTPUT CURRENT (μA) 1000 VPMON = 0V 0 VPMON = 0.5V VPMON = 4V –500 –1000 Supply Current vs Supply Voltage 3.6 100 VCC = 30V VCC = 6V 0 VCC = 12V I = –200μA –300 –2 0 VV • VI (V2) 2 4 –5 0 5 10 15 OUTPUT VOLTAGE (V) 2940 G04 2.6 VCC = 30V IPMON = –200μA IIMON = –200μA 2.
PAGE 7
LT2940 TYPICAL PERFORMANCE CHARACTERISTICS PMON Input Feedthrough vs Frequency Power Supply Rejection Ratio vs Frequency 0 PMON OUTPUT SIGNAL (dBVPK) REJECTION RATIO (dBV) 80 60 IMON PMON 40 20 V = 12V CC RPMON = 5k ON 2VDC BIAS RIMON = 5k ON 2VDC BIAS TA = 25°C 0 100 1k 10k 100k FREQUENCY (Hz) 1M RELATIVE TO ±1VPK RPMON = 5k ON 2VDC BIAS –10 TA = 25°C –20 –30 VV = ±2VPK VI = 0mV, dV = 0 –40 VI = ±200mVPK VV = 0V, dI = 0 –50 –60 100 10k 100k 1M 10M FREQUENCY (Hz) 2940 G14 SEE TEST CIRCUITS FO
PAGE 8
LT2940 PIN FUNCTIONS CMPOUT (Pin 1): Inverting Open-Collector Comparator Output. When the LATCH pin’s state does not override the comparator, CMPOUT pulls low when CMP+ > 1.24V. The pull-down shuts off when CMP+ < 1.21V, or VCC < 2.5V or when the LATCH pin is low. CMPOUT may be pulled up to 36V maximum. Do not sink more than 22mA DC. V+, V – (Pins 8, 7): Voltage Sense Inputs. The voltage difference between these pins is the voltage input factor to the power calculation multiplier.
PAGE 9
LT2940 FUNCTIONAL BLOCK DIAGRAM 11 10 I+ I– 12 6 GIMON = 1000 VCC μA V + GND IMON 5 – μA KPMON = 500 2 V 8 7 V+ + PMON 4 V– – 4-QUADRANT MULTIPLIER 3 CMP+ 1.24V VCC 9 LATCH BGAP REF AND UVLC UVLC + – CMPOUT D CLR 1 Q CMPOUT LE 2 LATCHLO THREE-STATE LATCHHI DECODE 2940 BD TEST CIRCUITS Resistor on DC Bias I-to-V Ampliﬁer 12V PMON OR IMON VOUT RL PMON OR IMON RFB 4.
PAGE 10
LT2940 APPLICATIONS INFORMATION Introduction Multiplier Operation The LT2940 power and current monitor brings together circuits necessary to measure, monitor and control power. In circuits where voltage is constant, power is directly proportional to current. The LT2940 enables power monitoring and control in applications where both the current and the voltage may be variable due to supply voltage uncertainty, component parametric changes, transient conditions, time-varying signals, and so forth.
PAGE 11
LT2940 APPLICATIONS INFORMATION Table 1.
PAGE 12
LT2940 APPLICATIONS INFORMATION IIN PIN = VIN • IIN VIN RSENSE LOAD 11 10 I+ I– LT2940 + IMON – R2 8 R1 7 V+ V– IIMON 5 VIMON RIMON VV = VIN • R1 R1 m kV = R1 + R2 R1 + R2 VI = IIN • RSENSE m k I = RSENSE + PMON IPMON 4 – VPMON RPMON 2940 F03 Figure 3. Basic Power Sensing Application Showing Derivation of kV and kI the full-scale output current of ±200μA, the achievable full-scale power is: 0 .
PAGE 13
LT2940 APPLICATIONS INFORMATION Multiplier Operating Regions The operating regions of the four-quadrant multiplier are illustrated in Figure 4. Note that while Figure 2’s axes employed logarithmic (octave) scales to allow constant-power trajectories to be straight lines, Figure 4’s axes are linear to better accommodate negative inputs. Constant-power trajectories are thus arcs.
PAGE 14
LT2940 APPLICATIONS INFORMATION below full-scale also affords scaling ﬂexibility. Line (D) along IPMON = 100μA covers a 4:1 range like (A), but the maximum VI is 100mV, which reduces voltage drop and dissipation in the sense resistor. Variable power applications comprise power measuring, whether battery charging, energy metering or motor monitoring, variable load-boxes, and other circuits where the signiﬁcant metric is not a single value, and voltage and current may be independent of each other.
PAGE 15
LT2940 APPLICATIONS INFORMATION When the LATCH pin voltage exceeds 2.5V, the next high result from the comparator also enables the comparator latch. The CMPOUT pin goes open (high), and the CMPOUT pin sinks current (low) regardless of the changes to the CMP+ level until the latch is cleared. Latch activation is level sensitive, not edge sensitive, so if CMP+ > 1.24V when LATCH is brought above 2.5V, the comparator result is high, and the latch is set immediately.
PAGE 16
LT2940 TYPICAL APPLICATIONS 120W Supply Monitor Includes ICC of LT2940 SUPPLY 30V TO 80V 100V (MAX) RS 0A TO 4A LOAD 50mΩ 1W VLOGIC I+ R14 3.9k R12 3.9k 1/8W 5mA MAX I– VCC R2 140k LATCH OVP CMPOUT OVERPOWER (OVP) GOES HIGH WHEN SUPPLY POWER > 120W V+ LT2940 R1 10.0k CMPOUT CMP+ V– PMON R3 6.19k IMON GND 2940 TA02 R4 13.7k VPMON SCALE = 30 W V kV = 120W FULL-SCALE 1 15 kI = 50mΩ 12.5W PWM Heat Source RS 200mΩ 3 INPUT 9.5V TO 14.
PAGE 17
LT2940 TYPICAL APPLICATIONS 30W Linear Heat Source RS 200mΩ 3 10V TO 40V + C1 100μF 50V R3 10k VCC I+ R2 102k LT2940 C2 22nF D2 27V I– V+ V R1 25.5k – V+ R PMON GND IMON LM334 V– R4 680Ω R5 6.8k D1 1N457 HEATSINK Q = 30W R6 51Ω Q1 VN2222 R8 1k R7 3.3k C3 470pF kV = 1 15 kI = 200mΩ 3 Q2 TIP129 R9 10k Q3 D44VH11 R10 100Ω 10A/V R11 100mΩ 2940 TA04 Wide Input Range 10W PWM Heat Source RS 200mΩ 3 22.
PAGE 18
LT2940 TYPICAL APPLICATIONS 8V to 32V, 8W Load 12V RS 200mΩ 8V TO 32V R3 2k 12V VCC I– I+ R2 30k LT2940 C1 100nF V+ V+ R1 10k LM334 V– R7 6.8Ω 10W R V– R4 680Ω R5 6.8k IMON GND PMON kV = D1 1N457 1 4 200μA/A CURRENT MONITOR OUTPUT kI = 200mΩ R6 10Ω Q1 FDB3632 C4 100nF 2940 TA06 Adjustable 0W to 10W Load Box with UVLO and Thermal Shutdown 10V TO 40V INPUT R2 120k V – V+ 12V VCC LATCH 12V R15 10k R16 10k C13 10nF R13 10k I+ I– PMON CMPOUT CMPOUT IMON GND CMP+ R4 4.
PAGE 19
LT2940 TYPICAL APPLICATIONS 1-Cell Monitor with Bottom-Side Sense 12V C1 100nF R12 1k 5% RS1 215Ω 1W/V R4 ±2.5W MAX 12.4k RS2 215Ω I+ VCC R2 30k 1% R1 121k LT2940 V– IMON D1 5.1V CHARGER+ V+ PMON R5 4.99k LOAD+ I– CYCLON 2V, 4.5AH DT CELL* LT1635 1A/V ±1A MAX + REF – 200mV Q1 2N3904 12V + OA – GND Q2 2N3904 2940 TA08 R6 1k 1% kV = 121 = 0.8 151 R7 200Ω 1% R9 200Ω 1% R8 1k 1% RS3 200mΩ kI = 200mΩ LOAD– CHARGER– *www.hawkerpowersource.
PAGE 20
LT2940 TYPICAL APPLICATIONS 28V Power to Frequency Converter RS 200mΩ 28V INPUT 10V TO 40V LOAD R2 120k kV = 1 5 kI = 200mΩ I+ VCC V+ V– PMAX = 10W fOUT = LATCH 10W 1000Hz LT2940 R1B 30k Q2 R5, 100k CMPOUT PMON C7 10nF R1A 30k I– VCC D3 D4 R6, 100k CMPOUT VCC IMON GND CMP+ Q3 IN + C5 1μF WIMA IN – D2 D1 10V LTC1440 + – V+ C6 VCC 100nF OUT HYST REF = 1N4148 OPTO-ISOLATOR Q1 R4B 10k R4A 240k CENTRAL SEMI CCLM2700 R9 1M V– = 2N7000 GND C4 2.
PAGE 21
LT2940 TYPICAL APPLICATIONS AC Power and Current Monitor T1 12.6VAC SECONDARY + RS 200mΩ 3 C1A 220μF 25V D1 1N4001 R3 10Ω VCC + LOAD I+ I– V+ C1B 220μF 25V V– D3 5.1V D2 1N4001 kV = 1 5 kI = 200mΩ 3 R1 30k LT2940 R2 120k R6 1k GND PMON 2940 TA12 IMON R4 15k 10W/V ±30WPK R5 15k 1A/V ±3APK Fully Isolated AC Power and Current Monitor 7A 1 • 117V “L” • T1 500 RS1 RS2 4.99Ω 4.99Ω VCC VCC 15V C1 47μF 25V R12 1k R4 4.22k 1kW/ V ±853 WPK R5 4.99k C12 100nF D1 5.
PAGE 22
LT2940 PACKAGE DESCRIPTION DD Package 12-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1725 Rev A) 0.70 ±0.05 3.50 ±0.05 2.10 ±0.05 2.38 ±0.05 1.65 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 2.25 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ±0.10 (4 SIDES) R = 0.115 TYP 7 0.40 ± 0.10 12 2.38 ±0.10 1.65 ± 0.10 PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) 6 0.200 REF 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 2.
PAGE 23
LT2940 PACKAGE DESCRIPTION MS Package 12-Lead Plastic MSOP (Reference LTC DWG # 05-08-1668 Rev Ø) 0.889 p 0.127 (.035 p .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 4.039 p 0.102 (.159 p .004) (NOTE 3) 0.65 (.0256) BSC 0.42 p 0.038 (.0165 p .0015) TYP 0.406 p 0.076 (.016 p .003) REF 12 11 10 9 8 7 RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) DETAIL “A” 3.00 p 0.102 (.118 p .004) (NOTE 4) 4.90 p 0.152 (.193 p .006) 0o – 6o TYP GAUGE PLANE 0.53 p 0.152 (.021 p .006) 1 2 3 4 5 6 1.10 (.
PAGE 24
LT2940 TYPICAL APPLICATION Integrating Watt-Hour Meter 6V TO 80V 0A TO 2A LOAD (80W MAX) 5V IN 5V OUT SHDN C16 LT3014 1μF ADJ GND R17 309k C17 0.47μF VCC I+ C19 0.1μF C20 0.1μF V+ S1B S2B S3B S4B I– R2 215k CB+ CB – LTC6943 R16 100k V+ R15 24.9k kV = RS 100mΩ V+ V– – + R14 20.0k CMP+ LT2940 LTC6702 1 20 V– SHA R18 49.9k GND Q1 2N7002 12V Q RESET VSS IMON kI = 100mΩ CT 2.2μF C18 0.1μF VDD F CMPOUT PMON R1 11.3k CA– 5V LATCH GND C1 1μF CA+ CMPOUT – + R13 4.