Datasheet

LTC1696
8
BLOCK DIAGRA
W
–
+
+
1.185V
0.865V
1696 BD
TIMER/
RESET
10µA +
FUNCTION
OF FB1 AND FB2
OVERDRIVE
INTERNAL 5V SUPPLY
BANDGAP
REFERENCE
0.88V
–
+
–
+
–
+
6
OUT
4
FB2
FB1
5
1
GND
LOGIC
GLITCH
FILTER
2V
UVLO
R1
+
–
+
–
2
V
CC
3
R2
INTERNAL 5V SUPPLY
V
REF
R3R4
APPLICATIO S I FOR ATIO
WUUU
Feedback Inputs
The LTC1696 has two feedback inputs that allow monitor-
ing of two output voltages. The trip point of the internal
comparator is set by an internal reference of 0.88V with
±2% accuracy. The output voltage, V
S
, is sensed through
an external resistor divider network (Figure 1). The resis-
tors R1 and R2 values are calculated with the typical trip
point of 0.88V.
R
RR
V
S
1
12
088
+
=•.
R
VR
S
2
088 1
088
=
()
–. •
.
As an example, let’s calculate values for R1 and R2 for a
3.3V supply in which an overvoltage indication is required
V
REF
= 0.88V
FB1
R2
V
S
R1
LTC1696
+
–
–
+
Figure 1
at +10% (3.63V). First, a value for R1 is chosen based on
the allowable resistor divider string current. This is deter-
mined by power dissipation requirements and possible
sensitivity to noise coupling into the resistor divider. In
this exercise, assume the resistor divider current is 20µA.
R1 is calculated from: