LT2940 - True Analog Power and Current Monitoring

True Analog Power and
Current Monitoring
4-Quadrant Multiplication Handles Bidirectional Currents and Bipolar Voltages
The LT®2940 is a power and current monitor for 4V to 80V systems that brings together the necessary circuits to accurately
measure, monitor and control power. Unlike traditional power monitors that rely on data converters and multiplying registers to
calculate power, the LT2940 uses a true 4-quadrant analog multiplier for continuous results with 500kHz bandwidth, ideal for use in
many pulsed, chopped AC and control applications.
Features
4-Quadrant Power Measurement
±5% Power Measurement Accuracy
4V to 80V High-Side Sense, 100V Max
Current Mode Power and Current Outputs
500kHz Bandwidth
±3% Current Measurement Accuracy
6V to 80V Supply Range, 100V Max
Inverting and Noninverting Open-Collector
Comparator Outputs
Available in 12-Pin 3mm × 3mm DFN and
12-Lead MSOP Packages
PMON Output Current
vs Sense Input Voltages
n
800
n
VV = VV+ – VV –
VI = VI+ – VI –
n
n
600
VCC ≥ 11V
VPMON = 0.5V
n
400 –4V
n
n
n
Applications
n
n
n
n
n
n
n
Board Level Power and Current Monitoring
Line Card and Server Power Monitoring
Power Sense Circuit Breaker
MOSFET Power Monitoring
Power/Energy Meters
Battery Charger Metering
Power Control Loops
IPMON (µA)
n
VV = –8V
200 –2V
0
–200
0V
2V
4V
8V
–400
–200
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. Hot Swap is a trademark of
Linear Technology Corporation. All other trademarks are the property of their
respective owners.
0
VI (mV)
200
Application Ideas
RS
25mΩ
2
12V
+
VCC
I
+
LT2940
R3 RESET
10k
LATCH
I
–
10k
1%
V+
CMPOUT
V–
IMON GND PMON
VIMON
6.5A/ V
12.4k
33nF
GE
5BPA34KAA10B
12V, 8A
PM FIELD
10k
1%
CMP+
The LT2940 monitors a 12V, 8A motor, with a
MOSFET serving as a circuit breaker in case the
current exceeds the specified value. If tripped,
a reset command at the latch input pin re-enables
the motor. Motor input power is monitored at the
PMON output.
MUR120
10k
1%
CMPOUT
Motor Monitor with Circuit Breaker
100µF
25V
VPMON
100W/V
100nF
4.99k
FDB3632
50mΩ
10.8V TO 43.2V
34W MAX
Hot Swap Controller with
Power Limiting
100nF
Input power is accurately
limited to 34W over a 4:1 input
voltage range. The LT2940
measures the power, while the
LT4256-1 high voltage
Hot Swap™ controller acts as
the limiting element.
10Ω
10Ω
56Ω
1µF
22k
VCC
100Ω
SENSE
GATE
100nF
LT4256-1
FB
TIMER
13k
2N3904
GND
I+
OVP
CMPOUT
6.19k
3.9k
1/8W
I–
VCC
LT2940
GND
140k
The LT2940 monitors a 30V to 80V supply rail,
including its own supply current. The PMON output
is scaled at 30W/V, the IMON output at 1A/V. The
comparator output trips when power exceeds 120W.
10.0k
CMP+
13.7k
16k
CMP+
V–
V+
CMPOUT
PMON
LT2940
Supply Power and Current Monitor
LATCH
OVERPOWER (OVP) GOES HIGH
WHEN SUPPLY POWER > 120W
100nF
LOAD
50mΩ
1W
VLOGIC
I–
IMON
V+
7.5k
RS
0A TO 4A
I+
VCC
PMON
56k
2N3904
1.5k
3.9k
10nF
100Ω
ON
100nF
OUTPUT
100µF
150Ω
100nF
SUPPLY
30V TO 80V
IRF540
V–
GND
VPMON
30W/V
IMON
20k
VIMON
1A/V
www.linear.com/2940 n 1-800-4-LINEAR
0610A