LINEAR TECHNOLOGY LT2940 Technical data
True Analog Power and
VI (mV)
–200
400
600
200
0
0 200
–200
–400
800
VV = –8V
–4V
VV = V
V
+ – VV–
VI = V
I
+ – VI–
VCC ≥ 11V
V
PMON
= 0.5V
–2V
0V
2V
8V4V
I
PMON
(µA)
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
n
4-Quadrant Power Measurement
n
±5% Power Measurement Accuracy
n
4V to 80V High-Side Sense, 100V Max
n
Current Mode Power and Current Outputs
n
500kHz Bandwidth
n
±3% Current Measurement Accuracy
n
6V to 80V Supply Range, 100V Max
n
Inverting and Noninverting Open-Collector
Comparator Outputs
n
Available in 12-Pin 3mm × 3mm DFN and
12-Lead MSOP Packages
Applications
n
Board Level Power and Current Monitoring
n
Line Card and Server Power Monitoring
n
Power Sense Circuit Breaker
n
MOSFET Power Monitoring
n
Power/Energy Meters
n
Battery Charger Metering
n
Power Control Loops
PMON Output Current
vs Sense Input Voltages
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.
Hot Swap Controller with
CMP
+
PMON IMON
CMPOUT
CMPOUT
LATCH
V
–
V
+
I
–
I
+
V
CC
140k
LOAD
10.0k
0A TO 4A
V
PMON
30W/V
13.7k6.19k
OVP
SUPPLY
30V TO 80V
OVERPOWER (OVP) GOES HIGH
WHEN SUPPLY POWER > 120W
R
S
LT2940
GND
3.9k
1/8W
50mΩ
1W
V
LOGIC
3.9k
20k
V
IMON
1A/V
CMP
+
PMONIMON
CMPOUT
CMPOUT
RESET
LATCH
V
–
V
+
I
–
I
+
V
CC
10k
1%
MUR120
10k
1%
10k
1%
FDB3632
V
PMON
100W/V
V
IMON
6.5A/V
12V
R
S
LT2940
GND
GE
5BPA34KAA10B
12V, 8A
PM FIELD
25mΩ
2
12.4k
33nF
4.99k
100nF
100µF
25V
R3
10k
+
1µF
100nF
100µF
OUTPUT
100nF
100nF
10Ω
10.8V TO 43.2V
34W MAX
22k
13k
1.5k 7.5k
56k
16k
56Ω
150Ω
50mΩ
IRF540
100nF
100nF
V
CC
I
+
LT2940
V
–
PMON
V
+
IMON
CMP
+
GND
I
–
2N39042N3904
10Ω
100Ω
100Ω
10nF
VCCSENSE
LT4256-1
TIMER
ON
FB
GND
GATE
Power Limiting
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.
Application Ideas
Motor Monitor with Circuit Breaker
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.
www.linear.com/2940 n 1-800-4-LINEAR
Supply Power and Current Monitor
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.
0610A
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