Linear LT2940 Quick Start Manual

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-

PERFORMANCE SUMMARY

SYMBOL PARAMETER
V Input Supply Range
IN
V V Supply Range
CC CC
PMON Load Power for Full Scale Output
IMON Load Current for Full Scale Output
P Overpower Threshold
TRIP

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 . This permits the LT2940 to
CC
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.
DEMO CIRCUIT 1495A
QUICK START GUIDE
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 , Operational Filter, PanelProtect, PowerPath, PowerSOT, SmartStart,
SENSE
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.
Specifications are at TA = 25°C
CONDITIONS
(When Separately Powered)
PMON = 3V
IMON = 3V
Red LED Turns On
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-
G
rectional power and current outputs
V -independent, high-side current sense in-
G
CC
put
4V to 80V current sense input operating
G
range
6V to 80V V
G
CC
100V absolute maximum rating
G
DC-1495A
LT2940
Power Monitor
MIN TYP
8
12
27 30
2.85 3
11 12.5
operating range
MAX UNITS
40 V
80 V
33 W
3.15 A
14 W
1