DC-1495A
1
DESCRIPTION
Demonstration circuit 1495A showcases the
LT2940 Power Monitor, configured to measure up
to 30W over a range of 8V to 40V and 0A to 3A.
LEDs indicate when the load power exceeds
12.5W. Power is indicated at PMON with a scaling
factor of 10W/V; IMON indicates current at 1A/V.
All scaling factors and the voltage and current
measurement ranges may be reconfigured by
changing a few resistors. The LT2940’s compara-
tor can monitor either the power output, PMON, or
the current output, IMON.
Design files for this circuit board are available.
Call the LTC factory.
L
, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are
registered trademarks of Linear Technology Corporation. Adaptive Power, C-Load,
DirectSense, Easy Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower
SwitcherCAD, Multimode Dimming, No Latency
∆Σ
, No Latency Delta-Sigma, No
R
SENSE
, Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart,
SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, UltraFast and VLDO are trade-
marks of Linear Technology Corporation. Other product names may be trademarks
of the companies that manufacture the products.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Input Supply Range
8
40
V
V
CC
V
CC
Supply Range
(When Separately Powered)
12
80
V
PMON
Load Power for Full Scale Output
PMON
= 3V
27
30
33
W
IMON
Load Current for Full Scale Output
IMON
= 3V
2.85
3
3.15
A
P
TRIP
Overpower Threshold
Red LED Turns On
11
12.5
14
W
OVERVIEW
The LT2940 is a four-quadrant multiplier designed
to measure current and voltage, multiply them, and
produce an output proportional to power. A sec-
ond output is proportional to the measured cur-
rent. All inputs and outputs are bipolar; the LT2940
measures positive or negative power, voltage and
current. The power and current outputs operate in
current mode, with a full scale of ±200µA. To fa-
cilitate use in a practical application, the current
sense pins (I+ and I–) are designed to operate over
a 4V to 80V common mode range, independent of
the supply pin, V
CC
. This permits the LT2940 to
measure, for example, a 48V supply while operat-
ing on a 12V supply. The LT2940 includes an aux-
iliary comparator with a fixed 1.25V reference and
complementary outputs.
A distinction must be drawn between the features
and performance of the LT2940, and the features
and performance of DC-1495A. The LT2940 has
the following important features:
●
Four quadrant power measurement with bidi-
rectional power and current outputs
●
V
CC
-independent, high-side current sense in-
put
●
4V to 80V current sense input operating
range
●
6V to 80V V
CC
operating range
●
100V absolute maximum rating
DEMO CIRCUIT 1495A
QUICK START GUIDE
LT2940
Power Monitor
