1
dc1699af
DEMO MANUAL DC1699A
DESCRIPTION
LT6108-1/LT6108-2
High Side Current Sense Amplifier
with Reference and a Comparator
Demonstration circuit 1699A features the LT
®
6108, a
high side current sense amplifier with a comparator and
a 400mV reference.
The demo board circuit amplifies the voltage across an
onboard current sense resistor, to provide a precision
unipolar voltage output that is proportional to the sensed
current. The board has one onboard comparator and an
integrated 400mV reference that sets the threshold for the
comparator. There are two versions of this demonstration
circuit, A and B, indicating which version of the LT6108
is installed. The DC1699A-A (LT6108-1) has a latching
L
, LT, LTC, LTM, TimerBlox, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
PERFORMANCE SUMMARY
OPERATING PRINCIPLES
comparator, while the DC1699A-B (LT6108-2) has a non
latching comparator. Both current sense gain and cur-
rent fault limits are set by onboard resistors and are the
same for both boards. The gain is set at 25V/V and the
comparator is set to trip at a current threshold of 500mA.
The key performance specifications are listed in the table
below.
Design files for this circuit board are available at
http://www.linear.com/demo
(T
A
= 25°C)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Input Supply Range
2.7
60
V
V
IOUT
Measured Output Signal
I
LOAD
= 100mA
250
mV
I
OUT
Output Load Current Range
Thermal Limit of R
SENSE
4
A
I
QA
V
IN
Quiescent Current DC1699A-A
V
IN
= 12V
800
μA
I
QB
V
IN
Quiescent Current DC1699A-B
V
IN
= 12V
650
μA
V
THR
Comparator Threshold
V
IOUT
= 1.25V
500
mA
The LT6108 operates by amplifying the voltage drop across
a sense resistor that is in series with the load. The voltage
drop at the amplifier inputs is translated, via the internal
variable current source, to a ground referenced signal at
the amplifier output. The circuit gain is set by the ratio of
the output resistor to the input resistor (see Figure 1). The
comparator thresholds are set by the internal reference
and the current trip points are set by dividing the output
resistance into a network of three resistors. The DC1699A
is shipped with a 100mΩ sense resistor, a gain of 25 and
current fault threshold of 500mA.
SENSEHI
LT6108
I
SENSE
R
SENSE
V
+
7
V
–
4
V
+
R
IN
V
BATT
SENSELO
8
1
OUTA 6
dc1699a F01
R
OUT
V
OUT
–
+
Figure 1. Amplifier Operation
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