Datasheet

LT6108-1/LT6108-2
18
610812fa
Setting Comparator Threshold
The comparator has an internal 400mV precision reference.
In order to set the trip point of the LT6108 comparator as
configured in Figure 11, the input sense voltage at which
the comparator will trip, V
SENSE(TRIP)
must be calculated:
V
SENSE(TRIP)
= I
SENSE(TRIP)
• R
SENSE
The selection of R
IN
is discussed in the Selection of Exter-
nal Input Gain Resistor R
IN
section. Once R
IN
is selected,
R
OUT
can be calculated:
R
OUT
= R
IN
400mV
V
SENSE(TRIP)
Since the amplifier output is connected directly to the
comparator input, the gain from V
SENSE
to V
OUT
is:
A
V
=
400mV
V
SENSE(TRIP)
APPLICATIONS INFORMATION
As shown in Figure 12, R2 can be used to increase the
gain from V
SENSE
to V
OUT
without changing V
SENSE(TRIP)
.
As before, R1 can be easily calculated:
R1= R
IN
400mV
V
SENSE(TRIP)
The gain is now:
A
V
=
R1+R2
R
IN
This gain equation can be easily solved for R2:
R2 = A
V
• R
IN
– R1
If the configuration of Figure 11 gives too much gain, R2 can
be used to reduce the gain without changing V
SENSE(TRIP)
as shown in Figure 13. A
V
can be easily calculated:
A
V
=
R1
R
IN
OUTA
I
OUTA
–
+
V
+
C1
SENSEHI
INC
6
7
8
5
610812 F11
V
+
V
+
V
–
LT6108-1
SENSELO
EN/RST
OUTC
1
2
3
4
V
RESET
R
C
V
PULLUP
LOAD
V
SUPPLY
V
SENSE
R
SENSE
OVERCURRENT
FLAG
R
IN
+
–
V
–
I
SENSE
=
V
SENSE
R
SENSE
R
OUT
C
L
V
OUT
400mV
REFERENCE
C
LC
–
+
Figure 11. Basic Comparator Configuration