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, 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 flow.
An integrated comparator with inverting and noninverting open-collector outputs makes the LT2940 a complete
power level monitor. In addition, an output current proportional to the sensed high side current allows current
monitoring. The current mode outputs make scaling,
filtering and time integration as simple as selecting external resistors and/or capacitors.
APPLICATIONS
n
n
n
n
n
n
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
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.
TYPICAL APPLICATION
Load Monitor Alarms Above 60W
ILOAD
Monitor Output Level and Load Power
2.5
0A TO 10A
6V TO 80V
20mΩ
2W
VCC
110k
CMPOUT
LED ON WHEN
PLOAD > 60W
I–
LATCH
V+
LT2940
CMPOUT
1.5
72
LED OFF 48
1.0
60W ALARM
0.5
V–
GND
VLOAD = 6V
LED ON
10.0k
CMP+
PMON
96
10V
PLOAD (W)
1k
I+
15V
2.0
VPMON (V)
5V
30V
+
VLOAD
–
LOAD
120
80V
24
IMON
VPMON = PLOAD • 20.75 mV
W
VIMON = ILOAD • 100
24.9K
mV
A
4.99k
0
0
0
2
4
6
8
ILOAD (A)
10
12
14
2940 TA01b
kV = 1
12
kI = 20mΩ
PLOAD = VLOAD • ILOAD
2940 TA01a
2940f
1
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 ..................22mA
Operating Temperature Range
LT2940C................................................... 0°C to 70°C
LT2940I ................................................–40°C to 85°C
Storage Temperature Range...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MSOP Package ................................................. 300°C
PIN CONFIGURATION
TOP VIEW
CMPOUT
TOP VIEW
12 VCC
1
CMPOUT
2
11
CMP+
3
10 I –
PMON
4
9 LATCH
IMON
5
8 V+
GND
6
7 V–
13
CMPOUT
CMPOUT
CMP+
PMON
IMON
GND
I+
1
2
3
4
5
6
12
11
10
9
8
7
VCC
I+
I–
LATCH
V+
V–
MS PACKAGE
12-LEAD PLASTIC MSOP
DD PACKAGE
12-LEAD (3mm s 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 135°C/W
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 13) PCB GND CONNECTION OPTIONAL
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT2940CDD#PBF
LT2940CDD#TRPBF
LDPP
12-Lead Plastic DFN
0°C to 70°C
LT2940IDD#PBF
LT2940IDD#TRPBF
LDPP
12-Lead Plastic DFN
–40°C to 85°C
LT2940CMS#PBF
LT2940CMS#TRPBF
2940
12-Lead Plastic MSOP
0°C to 70°C
LT2940IMS#PBF
LT2940IMS#TRPBF
2940
12-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.
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/
2940f
2
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
MIN
TYP
MAX
UNITS
Supply
l
6
IPMON = +200μA, IIMON = +200μA
(Note 2)
l
2
Supply Undervoltage Latch Clear
VCC Falling
l
Supply Undervoltage Hysteresis
VCC Rising
Voltage Sense Pin Operating Range
VCC
Supply Voltage Operating Range
80
V
ICC
Supply Current
3.5
5
mA
VCC(UVLC)
2.3
2.5
2.7
V
ΔVCC(HYST)
l
20
75
100
mV
VCC ≤ 12V
l
–0.1
VCC – 3
V
12V < VCC < 30V
l
–0.1
9
V
VCC ≥ 30V
l
–0.1
18
V
Voltage Sense Differential Input Voltage Range VCC < 11V
(Note 5)
l
±(VCC – 3)
V
Voltage Sense
VVSEN(OR)
V+ Pin and V – Pin
VV
VV = V V+ – V V –
VCC ≥ 11V
l
±8
V
VV(CL)
Voltage Sense Differential Clipping Limit
(Note 5)
VCC ≥ 12V
l
±9
V
IVSEN
Voltage Sense Input Bias Current
V+ Pin and V – Pin
l
–300
ΔIVSEN
Voltage Sense Input Offset Current
ΔIVSEN = IV+ – IV –
V V+ = V V –
l
–100
100
nA
±50
±150
nA
80
V
Current Sense
VISEN(OR)
Current Sense Pin Operating Range
I+ Pin and I – Pin
l
4
VI
Current Sense Differential Input Voltage
Range (Note 6)
VI = V I + – V I –
l
±200
mV
VI(CL)
Current Sense Differential Clipping Limit
(Note 6)
l
±225
mV
IISEN
Current Sense Input Bias Current
I+ Pin and I – Pin
l
75
ΔIISEN
Current Sense Input Offset Current
ΔIISEN = II+ – I I –
V I+ = V I –
l
100
125
μA
±200
±800
nA
Power Monitor (Note 2)
IPMON(OR)
Power Monitor Output Current Operating
Range
IPMON(CAPA)
Power Monitor Output Current Capability
l
±200
VCC ≥ 12V, VPMON ≥ 0V, and
V V = –9V, V I = –225mV, or
V V = 9V, V I = 225mV
l
900
1200
μA
VCC ≥ 12V, VPMON ≥ 0.5V, and
V V = –9V, V I = 225mV, or
V V = 9V, V I = –225mV
l
–240
–1200
μA
VCC ≥ 12V, VPMON ≥ 4V, and
V V = –9V, V I = 225mV, or
V V = 9V, V I = –225mV
l
–800
–1200
μA
μA
2940f
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.
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
7.5
V
VCC ≥ 30V, IPMON ≥ 0μA
l
0
12
V
VCC ≤ 12V, IPMON < 0μA
l
0.5
VCC – 4.5
V
12V < VCC < 30V, IPMON < 0μA
l
0.5
7.5
V
VCC ≥ 30V, IPMON < 0μA
l
0.5
|V V • V I | ≤ 0.4V2
|V V • V I | ≤ 0.4V2, 25°C < TA ≤ 85°C
12
V
±2
±5
%FS
±2.5
±7
%FS
|V V • V I
| ≤ 0.4V2, LT2940C
l
±2.5
±9
%FS
|V V • V I
| ≤ 0.4V2, LT2940I
l
±3.5
±12
%FS
Quadrants I and III of Shaded Region
in Figure 4
l
±5
±15
%FS
500
515
μA /V2
KPMON
Power Monitor Scaling Coefficient
IPMON = KPMON • V V • V I
|V V • V I | = 0.4V2
l
VV(OSP)
Power Monitor Voltage Sense Input-Referred
Offset Voltage
V V = 0V
l
±40
±100
mV
VI(OSP)
Power Monitor Current Sense Input-Referred
Offset Voltage
V I = 0mV
l
±2
±6
mV
IPMON(OS)
Power Monitor Output Offset Current
V V – = 0V, V I = 0mV
l
±6
±15
μA
BWPMON
Power Monitor Output Bandwidth
RPMON = 2k
485
0.5
MHz
Current Monitor (Note 2)
IIMON(FS)
Current Monitor Output Current Operating
Range
VIMON
Current Monitor Output Compliance Voltage
EIMON
Current Monitor Output Total Error (Note 4)
l
±200
VCC ≤ 12V, IIMON ≥ 0μA
l
0
VCC – 4.5
V
12V < VCC < 30V, IIMON ≥ 0μA
l
0
7.5
V
VCC ≥ 30V, IIMON ≥ 0μA
l
0
12
V
VCC ≤ 12V, IIMON < 0μA
l
0.5
VCC – 4.5
V
12V < VCC < 30V, IPMON < 0μA
l
0.5
7.5
V
VCC ≥ 30V, IPMON < 0μA
l
0.5
12
V
±1.5
±3
%FS
|V I | ≤ 200mV, 25°C ≤ TA ≤ 85°C
μA
|V I | ≤ 200mV, LT2940C
l
±2
±3.5
%FS
|V I | ≤ 200mV, LT2940I
l
±2
±4
%FS
200mV < |V I | ≤ 225mV
l
V I = ±200mV
l
975
±2.5
±5
%FS
1000
1025
μA /V
±2.5
±7
GIMON
Current Monitor Scaling, IIMON = GIMON • VI
VI(OSI)
Current Monitor Current Sense Input-Referred
Offset Voltage
BWIMON
Current Monitor Output Bandwidth
RIMON = 2k
Comparator Threshold Voltage
CMP+ Rising
l
1.222
ΔVCMP(HYST)
Comparator Threshold Hysteresis
CMP+ Falling
l
–15
–35
–60
mV
ICMP(BIAS)
Comparator Input Bias Current
1V ≤ VCMP+ ≤ 1.5V
l
±100
±300
nA
CMPOUT Output Low Voltage
CMP+ High, ICMPOUT = 3mA
l
0.2
0.4
V
l
1
mV
MHz
Comparator
VCMP(TH)
ICMPOUT(OL)
1.240
1.258
V
2940f
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
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,
0.4V ≤ VCMPOUT ≤ 36V
tDLY
Comparator Propagation Delay
Output Pulling Down
l
VLATCH(IL)
LATCH Input Low Voltage
l
0.5
VLATCH(IO)
LATCH Input Open Voltage
l
1.25
VLATCH(IH)
LATCH Input High Voltage
l
2.0
ILATCH(LK)
LATCH Input Allowable Leakage in
Open State
l
ILATCH(BIAS)
LATCH Input Bias Current
UNITS
±0.15
±1
l
0.2
0.4
V
l
±0.15
±1
μA
0.7
2
μs
0.8
1.2
V
1.5
1.95
V
2.2
2.5
V
±10
μA
μA
VLATCH = 0V
l
–11
–17
–23
μA
VLATCH = 80V
l
11
17
23
μA
Note 3: The LT2940 may safely drive its own PMON and IMON output
voltages above the absolute maximum ratings. Do not apply any external
source that drives the voltage above absolute maximum.
Note 4: Full-scale equals ±200μA.
Note 5: V+ and V – pin voltages must each fall within the voltage sense pin
operating range specification.
Note 6: I+ and I – pin voltages must each fall within the current sense pin
operating range specification.
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: All currents into pins are positive, and all voltages are referenced
to GND unless otherwise noted. Current sourced by the PMON pin or the
IMON pin is defined as positive; current sunk as negative.
TYPICAL PERFORMANCE CHARACTERISTICS
800
VV = VV+ – VV –
VI = VI+ – VI –
PMON Total Error
vs Sense Input Voltages
3
VCC ≥ 11V
VPMON = 0.5V
2
600
200 –2V
0
0V
2V
–400
–200
–2V
1
3
–4V
VV = 8V
2V
0
4V
–2
VI (mV)
200
2940 G01
–3
–200
|VV • VI| ≤ 0.4V2
TA = 25°C
–100
1
0
–8V ≤ VV ≤ 8V
–200mV ≤ VI ≤ 200mV
|VV • VI| ≤ 0.4V2
0
100
200
VI (mV)
2940 G02
VCC = 12V
–1
VCC = 12V
–2
VV = 8V
8V
0
VCC = 80V
2
–1
–200
4V
ONE REPRESENTATIVE UNIT
0V
VV = –8V
EPMON (%FS)
IPMON (μA)
400 –4V
PMON Error Band vs Temperature
4
EPMON (%FS)
PMON Output Current
vs Sense Input Voltages
–3
–4
–50
VCC = 80V
–25
50
25
0
75
TEMPERATURE (°C)
100
125
2949 G03
2940f
5
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
2.4
20
0
20
2940 G05
IMON Current vs Current
Sense Voltage
300
IPMON = 0μA
IIMON = 0μA
3.0
2.8
VCC = 6V VCC = 12V
–4
3.2
–100
–200
–1500
IPMON = 200μA
IIMON = 200μA
3.4
ICC (mA)
PMON Current
vs Power Sense Product
IMON Total Error vs Current
Sense Voltage
2
VI = VI+ – VI –
40
60
VCC (V)
ONE REPRESENTATIVE UNIT
2
–200mV ≤ VI ≤ 200mV
VI – = 12V
VCC = 12V
1
1
VCC = 12V
0
VCC = 80V
–100 VIMON = 0.5V
OUTPUT CURRENT IS
APPROXIMATELY FLAT
TO ABSOLUTE MAXIMUM
VOLTAGE LIMITS
–200
–300
–300
–200
–100
0
100
VI (mV)
200
EIMON (%FS)
EIMON (%FS)
IIMON (μA)
100
VIMON = 0V
VCC = 80V
0
–1
VCC = 12V
–1
VCC = 80V
–2
300
100
2940 G06
IMON Error Band vs Temperature
3
200
0
80
–2
–200
0
VI (mV)
2940 G07
200
–3
–50
2940 G08
–25
50
25
0
75
TEMPERATURE (°C)
100
125
2949 G09
PMON Step Response
PMON Step Response
IMON Step Response
RPMON = 2k ON 2VDC BIAS
CL = 8pF
VCC = 12V
TA = 25°C
VV = ±2V
VI = 200mV
RPMON = 2k ON 2VDC BIAS
CL = 8pF
VCC = 12V
TA = 25°C
VI = ±200mV
VV = 2V
RIMON = 2k ON 2VDC BIAS
CL = 8pF
VCC = 12V
TA = 25°C
VI = ±200mV
VIMON
200mV/DIV
VIMON
200mV/DIV
VIMON
200mV/DIV
500ns/DIV
2940 G10
250ns/DIV
2940 G11
250ns/DIV
2940 G12
2940f
6
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 FOR LOADING CONDITIONS
10M
2940 G13
PMON Frequency Response
to Voltage Sense
PMON Frequency Response
to Current Sense
10
RELATIVE TO DC GAIN
0
I-TO-V
AMP
OUTPUT
–10
–20
RL = 2k
VV = ±2VPK
VI = 200mVDC
IPMON = ±200μAPK (NOM)
TA = 25°C
–40
100
RELATIVE PMON VOLTAGE (dBVPK)
RELATIVE PMON VOLTAGE (dBVPK)
10
–30
RELATIVE TO DC GAIN
0
–20
–30
I-TO-V
AMP
OUTPUT
–10
RL =
2k
–30 V = ±200mV
I
PK
IIMON = ±200μAPK (NOM)
RL = 5k
TA = 25°C
–40
100
1k
10k
100k
1M
10M
FREQUENCY (Hz)
2940 G17
SEE TEST CIRCUITS FOR LOADING CONDITIONS
25
OPEN COLLECTOR CURRENT (mA)
RELATIVE IMON VOLTAGE (dBVPK)
RL = 5k
1k
Open Collector Current
vs Open Collector Voltage
10
–20
VV = 2VDC
VI = ±200mVPK
IPMON = ±200μAPK (NOM)
TA = 25°C
10k
100k
1M
10M
FREQUENCY (Hz)
2940 G16
SEE TEST CIRCUITS FOR LOADING CONDITIONS
IMON Frequency Response
to Current Sense
RELATIVE TO DC GAIN
RL =
2k
–40
100
1k
I-TO-V
AMP
OUTPUT
–10
RL = 5k
10k
100k
1M
10M
FREQUENCY (Hz)
2940 G15
SEE TEST CIRCUITS FOR LOADING CONDITIONS
0
1k
TA = 25°C
OUTPUT PULLING LOW
20
15
VCC = 80V
10
VCC = 6V
5
0
0.1
10
1
OPEN COLLECTOR VOLTAGE (V)
100
2940 G18
2940f
7
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. The difference may be
positive or negative, but both pin voltages must be at or
above GND – 100mV. The input differential voltage range
is ±8V. Do not exceed 36V on either pin.
CMPOUT (Pin 2): Noninverting Open-Collector Comparator
Output. When the LATCH pin’s state does not override the
comparator, CMPOUT pulls low when CMP+ < 1.21V, or
VCC < 2.5V, or when the LATCH pin is low. The pull-down
shuts off when CMP+ > 1.24V. CMPOUT may be pulled up
to 36V maximum. Do not sink more than 22mA DC.
LATCH (Pin 9): Comparator Mode Input. Conditions at this
three-state input pin control the comparator’s behavior.
When LATCH is open, the comparator’s outputs track its
input conditions (with hysteresis). When LATCH is held
above 2.5V, the comparator’s outputs latch when CMP+
exceeds 1.24V (CMPOUT open, CMPOUT pull-down). While
LATCH ≤ 0.5V or VCC < 2.5V, the comparator’s outputs clear
(CMPOUT pull-down, CMPOUT open) regardless of the
CMP+ pin voltage. The LATCH pin high impedance input
state tolerates ±10μA of leakage current. Bypass this pin
to GND to compensate for high dV/dt on adjacent pins.
Do not exceed 100V on this pin.
CMP+ (Pin 3): Positive Comparator Input. The integrated
comparator resolves to high when the pin voltage exceeds
the 1.24V internal reference. The comparator input has
35mV of negative hysteresis, which makes its falling trip
point approximately 1.21V. Do not exceed 36V. Tie CMP+
to GND if unused.
PMON (Pin 4): Proportional-to-Power Monitor Output. This
push-pull output sources or sinks a current proportional
to the product of the voltage sense and current sense
inputs. A resistor from PMON to GND creates a positive
voltage when the power product is positive. The full-scale
output of ±200μA is generated for a sense input product
of ±0.4V2. Do not exceed VCC + 1V, up to 16V maximum.
Tie PMON to GND if unused.
IMON (Pin 5): Proportional-to-Current Monitor Output.
This push-pull output sources or sinks a current proportional to the voltage at the current sense input, which is
typically generated by a sense resistor that measures a
current. A resistor from IMON to GND creates a positive
voltage when the sensed current is positive. The full-scale
output of ±200μA is generated by a current sense input
of ±200mV. Do not exceed VCC + 1V, up to 16V maximum.
Tie IMON to GND if unused.
GND (Pin 6): Device Ground.
I+, I– (Pins 11, 10): Current Sense Inputs. The voltage difference at these pins represents the current input factor to the
power calculation multiplier and to the current scaler. The
difference may be positive or negative, but both pin voltages
must be at least 4V and no more than 80V above GND,
completely independent of the VCC voltage. Both pins sink
approximately 100μA of bias current in addition to having
an effective 5kΩ shunt between them. The input differential
voltage range is ±200mV. Do not exceed ±36V differentially or 100V on either pin.
VCC (Pin 12): Voltage Supply. The voltage supply operating range is 6V to 80V. When operating with VCC > 15V,
package heating can be reduced by adding an external
series dropping resistor. Bypass this pin to GND to improve
supply rejection at frequencies above 10kHz as needed.
Do not exceed 100V on this pin.
Exposed Pad (Pin 13 in DFN Package): The exposed pad
may be left open or connected to device ground. For best
thermal performance, the exposed pad must be soldered
to the PCB.
2940f
8
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
4.99k
RC
499Ω
VOUT
2V
2940 TC01
Q1
2N2369
2V
2940 TC02
2940f
9
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.
The LT2940 power and current monitor contains a fourquadrant multiplier designed to measure the voltage and
current of a generator or load, and output signals proportional to power and current. Figure 1 shows a signal path
block diagram. The operating ranges of the voltage sense
and current sense inputs are included. To simplify the
notation, the differential input voltages are defined as:
The LT2940’s four-quadrant multiplier calculates instantaneous power from its voltage sense and current
sense inputs. Its output driver sources and sinks current proportional to power (magnitude and direction),
which affords flexible voltage scaling, simple filtering
and, into a reference, bipolar signals. Its onboard
comparator is the final piece required for integrated
power monitoring. In addition, the LT2940 provides a
proportional-to-current output that allows for equally
straightforward scaling, filtering and monitoring of the
sensed current.
Please note: although standard convention defines currents as positive going into a pin (as is generally the case
in the Electrical Characteristics table), the opposite is
true of the PMON and IMON pins. Throughout this data
sheet the power and current monitor output currents
are defined positive coming out of PMON and IMON,
respectively. Adopting this convention lets positive voltage
differences at the current and voltage sense pins yield
positive currents sourced from PMON and IMON that
can be scaled to positive ground referenced voltages
with a resistor.
V V = V V+ – V V–
(1a)
V I = V I+ – V I–
(1b)
The full scale output of the multiplier core is ±0.4V2, which
the PMON output driver converts to current through a
scale factor of KPMON.
(2)
IPMON = KPMON • V V • V I
µA
K PMON = 500
V2
(3)
The voltage across the current sense input pins is converted
to a current by the IMON output driver through the scale
factor of GIMON.
IIMON = GIMON • VI
(4)
µA
V
(5)
Both the PMON and IMON outputs reach full-scale at
±200μA.
GIMON = 1000
The headroom and compliance limits for the input and
output pins are summarized in Table 1 for easy reference.
It is important to note that the current sense inputs, I+
and I–, operate over a 4V to 80V range completely independent of the LT2940’s supply pin, VCC. Note also that
the inputs accept signals of either polarity, and that the
VI = VI+ – VI–
±200mV (MAX)
11 10
I+ I–
+
GIMON = 1000
μA
V
IMON
–
VV = VV+ – VV –
±8V (MAX)
8
7
V
+
V–
VV • VI = ±0.4V2 FULL-SCALE
LT2940
+
5
±200μA
FULL-SCALE
4
±200μA
FULL-SCALE
μA
KPMON = 500 2
V
PMON
–
2940 F01
Figure 1. LT2940 Signal Path Diagram
2940f
10
LT2940
APPLICATIONS INFORMATION
Table 1. LT2940 Essential Operating Parameters to Achieve Specified Accuracy (VCC Operating Range = 6V to 80V)
PARAMETER
SENSE
INPUT
PINS
Voltage
V+, V –
PIN VOLTAGE
LIMIT
INPUT
OPERATING
RANGE
SCALING
TO
OUTPUT
MONITOR
OUTPUT
PINS
OUTPUT
OPERATING
RANGE
OUTPUT
VOLTAGE COMPLIANCE
0V to VCC – 3V at VCC ≤ 12V
VV = ±8V
-
-
-
-
0V TO 9V at 12V < VCC < 30V
0V to 18V at VCC ≥ 30V
Current
I+, I –
4V to 80V*
VI = ±200mV
GIMON =
1000μA /V
IMON
IIMON =
±200μA
Sourcing:
0V to VCC – 4.5V at VCC ≤ 7.5V
Power
V+, V –,
I+, I –
See Above Limits
VV • VI = ±0.4V2
KPMON =
500μA / V2
PMON
IPMON =
±200μA
0V to 7.5V at 12V < VCC < 30V
0V to 12V at VCC ≥ 30V
Sinking:
As Above, Except Minimum is 0.5V
* The current sense range is completely independent of the supply voltage.
PMON and IMON outputs are capable of indicating forward
and reverse flow of power and current, provided they are
advantageously biased.
The multiplier core full-scale product of ±0.4V2 may
be reached over a range of voltage and current inputs,
as shown in Figure 2. For example, voltage sense and
current sense combinations of 8V and 50mV, 4V and
100mV, and 2V and 200mV each multiply to 0.4V2, and
thus produce 200μA at PMON. This arrangement allows
the core to operate at full-scale, and therefore at best accuracy, over a 4:1 range of current and voltage, a readily
appreciated feature when monitoring power in variable
supply applications.
Essential Design Equations
A few equations are needed to calculate input scaling factors
and achieve a desired output. Consider the basic application in Figure 3, where the power PIN is to be measured
as the product of voltage VIN and current IIN:
PIN = VIN • IIN
The actual measured quantities VIN and IIN are scaled to be
level-compatible with the LT2940. In this basic application,
a simple resistive voltage divider scales VIN, and a sense
resistor scales IIN.
V V = VIN • kV
kV =
200
IPMON
= 200μA
VI = VI+ – VI– (mV)
100
100μA
25μA
12.5μA
25
1
(7b)
V I = IIN • kI
(8a)
kI = RSENSE
(8b)
IPMON = KPMON • VIN • kV • IIN • kI
(9a)
IPMON = PIN • KPMON • kV • kI
(9b)
or
12.5
0.5
R1
R1 + R2
(7a)
The PMON output current is given by:
50μA
50
(6)
2
VV = VV+ – VV – (V)
4
8
2940 F02
Figure 2. PMON Output Current as a Function
of Sense Input Voltages
The output current may be positive (sourcing) or
negative (sinking) depending on the signs of VIN, kV,
IIN, and kI. Provided that the magnitudes of VV and VI
do not exceed 8V and 200mV as shown in Figure 2, at
2940f
11
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
mk V =
R1 + R2
R1 + R2
VI = IIN • RSENSE mk 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 . 4V 2
PIN(FS) =
k V • kI
(10)
In some applications the PMON output is converted to a
voltage by a load resistor:
VPMON = IPMON • RPMON
(11)
The complete end-to-end scaling is then given by:
VPMON = PIN • KPMON • kV • kI • RPMON
(12)
The current monitor output current at IMON is found by
combining Equations 4 and 8a:
IIMON = IIN • GIMON • kI
(13)
The output current may be positive (sourcing) or negative
(sinking) depending on the signs of IIN and kI. Provided
that the magnitude of VI does not exceed 200mV, at the
full-scale output current of ±200μA the achievable fullscale input current is:
0 . 2V
IIN(FS) =
kI
(14)
If IMON current is converted to a voltage by a load resistor, then:
VIMON = IIMON • RIMON
(15)
Accuracy
The principal accuracies of the power and current monitor
outputs are characterized as absolute percentages of fullscale output currents, using the nominal values of scaling
parameters. The total error of the IPMON output, EPMON, is
typically ±2%, and is defined as:
µA
• ( VV • VI )
IPMON − 500
2
V
• 100 %
EPMON =
200µA
(17)
Contributors to the power output accuracy such as the scaling (KPMON), the output offset (IPMON(OS)), and the voltage
and current sense input offsets (VV(OSP) and VI(OSP)), are
separately specified at key conditions and may be totaled
using the root sum-of-squares (RSS) method.
The total error of the IIMON output, EIMON, is typically
±1.5%, and is defined as:
EIMON =
μA
• VI
V
• 100 %
200μ A
IIMON − 1000
(18)
Contributors to the current output accuracy such as the
scaling (GIMON) and the current sense input offset (VI(OSI))
are separately specified at key conditions. Here again, use
the RSS method of totaling errors.
and the final end-to-end scaling is given by:
VIMON = IIN • GIMON • kI • RIMON
(16)
2940f
12
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.
The heavy line circumscribing the guaranteed accuracy
region is limited both by the product of the sense inputs
(the curved edges) and by each sense input’s differential
range (the straight edges). The maximum product that
realizes the specified accuracy is VV • VI = ±0.4V2, and it
produces nominally full-scale output currents of IPMON =
±200μA. At the same time, the voltage and current sense
inputs must not exceed ±8V and ±200mV, respectively.
In the shaded functional region, multiplying occurs but
the output current accuracy is derated as specified in the
Electrical Characteristics section.
The shaded functional region offers headroom beyond the
guaranteed range in all quadrants, and excellent sourcing
current operation beyond the standard +0.4V2 sense product limit in quadrants I and III. In quadrants II and IV, the
PMON current is limited by compliance range, so accuracy
is not specified. See the Electrical Characteristics and Typical Performance Characteristics sections for operation in
these regions. Inputs beyond those ranges, and out to the
absolute maximum ratings, are clipped internally.
Range and Accuracy Considerations
The LT2940’s performance and operating range may best
be exploited by letting the broad application category steer
design direction.
Constant-power applications comprise power level alarm
circuits, whether tripping a circuit breaker, activating auxiliary circuits, or simply raising an alarm, and single-level
power servo loops. In such applications, accuracy is best
when the full-scale output current of the LT2940 represents
the power level of interest, i.e., the IPMON = 200μA load
line (A) on Figure 5. Spans of voltage or current up to 4:1
naturally fit into the operating range of the LT2940.
Special constant-power applications are the same types of
circuits (level measuring, servos) with additional restrictions. If operating within the guaranteed accuracy region
of Figure 4 is important over voltage or current spans
wider than 4:1, let a PMON current less than full-scale
represent the power level. For example, the load line (B)
of IPMON = 50μA in Figure 5 covers a span of 16:1 (VV = 8V
to 0.5V and VI = 200mV to 12.5mV). Note that operating
along line (C), IPMON = 25μA allows a span of 32:1, but the
channel offsets reduce the value of doing so. Operating
300
II
250
–150
100
–250
100μA
25μA
(C)
IV
12.5
–4
–2
0
VV (V)
2
4
6
8
(D)
25
CURRENT SENSE CLIPPED
–6
(A)
50μA
50
LIMITED
BY PMON
COMPLIANCE
–200
III
–300
–12 –10 –8
IPMON
= 200μA
VI (mV)
VI (mV)
–100
GUARANTEED
ACCURACY
VOLTAGE SENSE CLIPPING
–50
I
200
VOLTAGE SENSE CLIPPED
0
VOLTAGE SENSE CLIPPED
150
50
CURRENT SENSE CLIPPING
LIMITED
BY PMON
COMPLIANCE
200
100
400
I
CURRENT SENSE CLIPPED
10
12
2940 F04
Figure 4. Multiplier Operating Regions vs Sense Input
Voltages. Accuracy Is Derataed in Shaded Areas
(B)
GUARANTEED
ACCURACY
0.5
1
4
2
VV (V)
16
8
2940 F05
Figure 5. Various Constant-Power Curves in Quadrant I
2940f
13
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. Design in
this case requires mapping the LT2940’s sense ranges to
cover the maximum voltage and the maximum current,
while considering whether the power represented is at,
above, or below full-scale IPMON. For example, setting it
at full-scale puts all values in the accurate range, setting
it above puts more accuracy in nominal power levels and
less accuracy in perhaps rarely encountered high levels,
and setting below might afford flexibility to lower dissipation in the current sense resistor.
similar way, a capacitor load on IMON produces a voltage proportional to charge that can be used to create a
coulomb counter.
Comparator Function
The LT2940’s integrated comparator features an internal
fixed reference, complementary open-collector outputs
and configurable latching. A rising voltage at the CMP+
pin is compared to the internal 1.24V threshold. 35mV
(typical) negative hysteresis provides glitch protection and
makes falling inputs trip the comparator at about 1.21V.
The comparator result drives the open-collector CMPOUT
and CMPOUT pins which, when pulling down, sink at
least 3mA down to 0.4V. See the Typical Performance
Characteristics for more information. Complementary
comparator outputs save external components in some
applications. The CMPOUT and CMPOUT pins may be
pulled up externally to 36V maximum.
Comparator Latching
Output Filtering and Integration
Lowpass filtering the output power or current signal is as
simple as adding a capacitor in parallel with the output
voltage scaling resistor at PMON or IMON. For example,
adding 1nF in parallel with the PMON load resistor on the
front page application creates a lowpass corner frequency
of approximately 6.4kHz on the power monitor voltage.
Loaded by only a capacitor, the PMON pin voltage is proportional to the time-integral of power, which is energy.
The integrating watt-hour meter application shown on
the back page takes advantage of this convenience. In a
The LATCH pin controls the behavior of the comparator
outputs. When the LATCH pin is open, the comparator
output latch is transparent. Leakage currents up to ±10μA
will not change the decoded state of the LATCH pin. Internal
circuits weakly drive the pin to about 1.5V. Adding a 10nF
capacitor between LATCH and GND protects against high
dV/dt on adjacent pins and traces. Where more than 30V
and long inductive leads will be connected to LATCH,
damp potentially damaging ringing with a circuit like that
shown in Figure 6.
4V TO 80V
R9B
49.9k
LONG
WIRE
R9A
20k
I+
RESET
I–
LATCH
LT2940
C2
10nF
GND
2940 F06
Figure 6. LATCH Pin Protective Damping
2940f
14
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. The LATCH pin
voltage may be taken safely to 80V regardless of the VCC
pin voltage.
Thermal Considerations
If operating at high supply voltages, do not ignore package
dissipation. At 80V the dissipation could reach 400mW;
more if IMON or PMON current exceeds full-scale. Package thermal resistance is shown in the Pin Configuration
section. Package dissipation can be reduced by simply
adding a dropping resistor in series with the VCC pin, as
shown in Figure 7. The operating range of the current sense
input pins I+ and I– , which extends to 80V independent
of VCC, make this possible. The voltage ranges of the V+,
V– , PMON and IMON pins are, however, limited by VCC.
Consult Table 1 during design. Operating an open-collector output pin with simultaneously large current and
large voltage bias also contributes to package heating and
must be avoided.
The latch is released and the comparator reports a low
when LATCH ≤ 0.5V or when VCC < 2.3V regardless of the
CMP+ pin voltage. In this state, the CMPOUT pin sinks
current (low), while the CMPOUT pin goes open (high).
As with latching, clearing is level-sensitive: comparator
outputs react to the input signal as soon as LATCH ≥ 1.25V
and VCC > 2.7V.
RS
100V MAX
0A TO 1.3A
30V TO 80V
5mA
MAX
36V MAX
R14
20k
OVP
OVERPOWER (OVP) GOES HIGH
WHEN LOAD POWER > 40W
kV =
1
15
kI = 150mΩ
I–
R2
140k
LATCH
V+
LT2940
R1
10.0k
CMPOUT
CMP+
V–
PMON
R3
6.19k
I+
VCC
CMPOUT
LOAD
150mΩ
1/2W
R12
3.9k
10% 1/8W
GND
IMON
2940 F07
R4
13.7k
VPMON
SCALE = 10
W
V
40W FULL-SCALE
Figure 7. Supply Resistor Reduces Package Heating by Reducing VCC Voltage
2940f
15
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 14.5V
+
C1
100μF
25V
R6
10k
Q3
2N3906
I+
VCC
I–
LT2940
R5
10k
LATCH
V+
CMPOUT
CMPOUT
D1
1N5819
Q2
TP0610
V–
R7*
7Ω
HEATSINK
Q = 12.5W
R2
102k
R1
25.5k
CMP+
PMON GND IMON
C4
4.7μF
R4
15.0k
2940 TA03
1
5
kI = 200mΩ
3
tOFF z1.7ms
kV =
Q1
FDS3672
* SEVEN 50Ω, 5W RESISTORS IN PARALLEL.
MULTIPLE UNITS FACILITATE SPREADING HEAT.
2940f
16
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
22.4V TO 72V
+
12V
C1
100μF
100V
R6
10k
Q3
2N3906
R5
10k
I+
VCC
I–
LT2940
LATCH
V+
CMPOUT
CMPOUT
V
CMP+
–
R2
220k
D2
1N4148
12V
R1
13k
Q2
BSS123
R7
50Ω
25W
HEATSINK
Q = 10W
D1
MUR1100E
D3
1N4148
PMON GND IMON
C4
4.7μF
2940 TA05
R4
68k
13
233
kI = 200mΩ
3
tOFF z2ms
kV =
C2
100nF
Q1
FDS3672
2940f
17
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
4.99k
TEMP R10
ADJ
500Ω
D1
1N4003
12V
LT2940
R12
12k
1A/V
CURRENT
MONITOR
OUTPUT
R1
30k
R11
33Ω
C11
10nF
Q2
2N3904*
RS
200mΩ
R14
10Ω
Q3
2N3906
Q1
FDB3632
ICONTROL
= 50mW/μA
R3B
91k
UVLO
R3A
13k
0W TO 10W ADJ
10-TURN
R17
100Ω
–
+
OA
Q4
2N3906
R18
1k
kV =
R19
10k
+
–
200mV
REF
LT1635
1
5
kI = 200mΩ
2940 TA07
*THERMAL SHUTDOWN; COUPLE TO Q1’s HEAT SINK
2940f
18
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.com
(423) 238-5700
Motor Monitor with Circuit Breaker
RS
25mΩ
2
12V
+
I+
VCC
I–
LT2940
R3
10k
RESET
LATCH
V+
CMPOUT
CMPOUT
V–
CMP+
IMON GND PMON
VIMON
6.5A/V
2940 TA09
C5
33nF
R5
12.4k
R4
4.99k
C10
100μF
25V
R2A
10k
1%
R1
10k
1%
MUR120
GE
5BPA34KAA10B
12V, 8A
PM FIELD
R2B
10k
1%
VPMON
100W/V
C4
100nF
1
3
kI = 25mΩ
2
OVERCURRENT TRIP = 8A
kV =
Q1
FDB3632
2940f
19
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
2.2nF
2940 TA10
Secondary-Side AC Circuit Breaker
T1
+
R0
10Ω
C1A
220μF
25V
R2
120k
12.6VAC
SECONDARY
R9
10k
R1
30k
RS
200mΩ
3
Q4
RESISTIVE
LOAD
2X
FDS3732
Q1
D1
1N4001
I+
VCC
VCC
I–
LATCH
R11
10k
V+
R6
1k
D3
5.1V
D2
1N4001
Q2
Q5
R10
1k
Q6
R7
1k
Q7
LT2940
V–
IMON
CMPOUT
CMP+
GND PMON
Q3
R12
10k
CMPOUT
+
C1B
220μF
25V
Q8
R3
15k
1A/V
3APK
1.25A
TRIP
R4
15k
10W/V
30WPK
kV = 30 = 1
150
5
kI = 200mΩ
3
= 2N3906
2940 TA11
2940f
20
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
5.1V
VCC
I+
I–
D2
D4
V+
R1A
68.1Ω
PMON
LT2940
C2
100nF
IMON
R2B
R1B
68.1Ω 200Ω
1%
V–
10A/V
±10APK
GND
D3
D5
R7
10k
2940 TA13
kV =
68 . 1 + 68 . 1
108
1
•
=
200 + 200 + 68 . 1 + 68 . 1 1168 42 . 5 8
LOAD
R2A
200Ω
1%
R6
10k
• •
10.8V
117V
T2
117V
“N”
ISOLATION
BARRIER
= 1N4148
T1 = MINNTRONIX 4810966R
kI =
4 . 99 + 4 . 99
10
=
500
501
T2 = 1168:108 POTENTIAL TRANSFORMER
IN CONSTRUCTING THIS CIRCUIT, THE CUSTOMER AGREES THAT, IN ADDITION TO THE TERMS AND CONDITIONS ON LINEAR TECHNOLOGY CORPORATION’S
(LTC) PURCHASE ORDER DOCUMENTS, LTC AND ANY OF ITS EMPLOYEES, AGENTS, REPRESENTATIVES AND CONTRACTORS SHALL HAVE NO LIABILITY,
UNDER CONTRACT, TORT OR ANY OTHER LEGAL OR EQUITABLE THEORY OF RECOVERY, TO CUSTOMER OR ANY OF ITS EMPLOYEES, AGENTS,
REPRESENTATIVES OR CONTRACTORS, FOR ANY PERSONAL INJURY, PROPERTY DAMAGE, OR ANY OTHER CLAIM (INCLUDING WITHOUT LIMITATION, FOR
CONSEQUENTIAL OR INCIDENTAL DAMAGES) RESULTING FROM ANY USE OF THIS CIRCUIT, UNDER ANY CONDITIONS, FORESEEABLE OR OTHERWISE.
CUSTOMER ALSO SHALL INDEMNIFY LTC AND ANY OF ITS EMPLOYEES, AGENTS, REPRESENTATIVES AND CONTRACTORS AGAINST ANY AND ALL LIABILITY,
DAMAGES, COSTS AND EXPENSES, INCLUDING ATTORNEY’S FEES, ARISING FROM ANY THIRD PARTY CLAIMS FOR PERSONAL INJURY, PROPERTY DAMAGE,
OR ANY OTHER CLAIM (INCLUDING WITHOUT LIMITATION, FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES) RESULTING FROM ANY USE OF THIS CIRCUIT,
UNDER ANY CONDITIONS, FORESEEABLE OR OTHERWISE.
2940f
21
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
2.25 REF
(DD12) DFN 0106 REV A
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD AND TIE BARS SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
2940f
22
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
(.043)
MAX
DETAIL “A”
0.18
(.007)
0.86
(.034)
REF
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.650
(.0256)
BSC
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
0.1016 p 0.0508
(.004 p .002)
MSOP (MS12) 1107 REV Ø
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
2940f
23
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
4.99k
S1A
S2A
S3A
S4A
COSC
1024 COUNTS
= 1 WATT-HOUR
CD4040
RESET
2940 TA14
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1966
Precision Micropower Delta-Sigma RMS-to-DC
Converter
2.7V to 12V Supply Voltage, 170μA Supply Current
LTC1968
Precision Wide Bandwidth RMS-to-DC Converter
4.5V to 6V Supply Voltage, 500kHz 3dB-Error BW
LTC6101/
LTC6101HV
High Voltage, High Side, Precision Current Sense
Amplifiers
4V to 60V/ 5V to 100V, Gain Configurable, SOT-23
LTC6104
Bidirectional High Side, Precision Current Sense
Amplifier
4V to 60V, Gain Configurable, 8-Pin MSOP
LTC6106
Low Cost, High Side Precision Current Sense
Amplifier
2.7V to 36V, Gain Configurable, SOT23
LTC4151
High Voltage I2C Current and Voltage Monitor
Wide Operating Range: 7V to 80V
LTC4215
Positive Hot Swap Controller with ADC and I2C
8-Bit ADC Monitoring Current and Voltages, Supplies from 2.9V to 15V
LT4256-1/
LT4256-2
Positive 48V Hot Swap Controllers with OpenCircuit Detect
Foldback Current Limiting, Open-Circuit and Overcurrent Fault Output,
Up to 80V Supply
LTC4260
Positive High Voltage Hot Swap Controller With
ADC and I2C Monitoring
Wide Operating Range: 8.5V to 80V
LTC4261
Negative Voltage Hot Swap Controller With ADC
and I2C Monitoring
Floating Topology Allows Very High Voltage Operation
2940f
24 Linear Technology Corporation
LT 1109 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2009
工商网监
湘ICP备2023018690号
