ltc693csw-trpbf Linear Technology Corporation, ltc693csw-trpbf Datasheet - Page 13

• Manufacturer Part Number: ltc693csw-trpbf
• Description: Microprocessor Supervisory Circuits
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Example 1: The circuit in Figure 8 demonstrates the use
of the power-fail comparator to monitor the unregulated
power supply input. Assuming the the rate of decay of the
supply input V
a shutdown procedure is 8ms. Also, the noise of V
200mV. With these assumptions in mind, we can reason-
ably set V
maximum reset voltage threshold and the dropout voltage
of LT
Choose R3 = 300k and R1 = 51k. Also select R4 = 10k
which is much smaller than R3.
R3 5.88 R1
7.25V = 1. 3V 1+
V
HYSTERESIS
®
1086-5 (4.5V + 1.5V) and V
≈
L
= 7.25V which is 1.25V greater than the sum of
IN
is 100mV/ms and the total time to execute
=
⎛
⎝ ⎜
5V
R3
R1
51
R2
k
=
–
850mV
(5V – 1.3V)51
1 3 310
V
V
.
IN
IN
+
≥ 6.5V
≥ 7.5V
V
HYSTERESIS
(
R1
51k
R2
10k
Figure 8. Monitoring Unregulated DC Supply with the
LTC692/LT693 Power-Fail Comparator
Figure 9. Monitoring Regulated DC Supply with the
LTC692/LT693 Power-Fail Comparator
10μF
10μF
+
k
V
)
LT1086-5
IN
ADJ
k
⎞ ⎞
⎠ ⎟
V
V
= 850mV.
OUT
IN
LT1086-5
ADJ
V
+
OUT
IN
10μF
+
is
100μF
300k
R1
27k
R2
8.2k
R5
3.3k
R3
R2 = 10.1k, Choose nearest 5% resistor 10k and recal-
culate V
The 10.7ms allows enough time to execute shutdown pro-
cedure for microprocessor and 831mV of hysteresis would
prevent PFO from going low due to the noise of V
2.7M
R3
10k
5V
R4
V
V
V
(7.32V – 6.25V)
HYSTERESIS
H
R4
10k
L
0.1μF
100mV/ms
5V
=
=
0.1μF
TO μP
L
TO μP
1.3V 1
1.3V 1
,
⎛
⎝ ⎜
⎛
⎝ ⎜
PFO
PFI
PFI
PFO
V
= 8.151V – 7.32V = 831mV
V
CC
CC
+
+
LTC692
LTC693
LTC692
LTC693
GND
GND
51k
10 k
10k
51k
=
692_3 • F09
692_3 • F08
10.7ms
–
+
LTC692/LTC693
(5V – 1.3V)51
300k
51k
1.3V(310 k
⎞
⎠ ⎟
=
8.151
) ⎟ ⎟
k
⎞
⎠
V V
=
7 32
.
13
IN
V
.
0692fa