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LTC693 データシート(PDF) 13 Page - Linear Technology

部品番号 LTC693
部品情報  Microprocessor Supervisory Circuits
PDF  20 Pages
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メーカー  LINER [Linear Technology]
ホームページ  http://www.linear.com
Logo LINER - Linear Technology

LTC693 データシート(HTML) 13 Page - Linear Technology

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LTC692/LTC693
13
0692fb
APPLICATIONS INFORMATION
10μF
100μF
VIN
VOUT
ADJ
692_3 • F08
VCC
0.1μF
TO μP
PFO
GND
LT1086-5
VIN ≥ 7.5V
R4
10k
PFI
LTC692
LTC693
R1
51k
R2
10k
R3
300k
5V
+
+
10μF
10μF
VIN VOUT
ADJ
692_3 • F09
0.1μF
TO μP
LT1086-5
VIN ≥ 6.5V
R4
10k
R1
27k
R3
2.7M
R2
8.2k
5V
R5
3.3k
VCC
GND
PFO
PFI
LTC692
LTC693
+
+
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
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 VIN is 100mV/ms and the total time to execute
a shutdown procedure is 8ms. Also, the noise of VIN is
200mV. With these assumptions in mind, we can reason-
ably set VL = 7.25V which is 1.25V greater than the sum of
maximum reset voltage threshold and the dropout voltage
of LT
®1086-5 (4.5V + 1.5V) and VHYSTERESIS = 850mV.
V5V
R1
R3
850mV
R3 5.88 R1
HYSTERESIS ==
≈
Choose R3 = 300k and R1 = 51k. Also select R4 = 10k
which is much smaller than R3.
7.25V = 1. 3V 1+
R2
–
(5V – 1.3V)51
51
1 3 310
kk
Vk
.(
)
⎛
⎝⎜
⎞⎞
⎠⎟
R2 = 10.1k, Choose nearest 5% resistor 10k and recal-
culate VL,
V1.3V 1
10 k
–
(5V – 1.3V)51
1.3V(310 k
L =+
⎛
⎝⎜
⎞
⎠
51k
k
) ⎟⎟
=
=+
+
⎛
⎝⎜
⎞
⎠⎟
=
732
.V
V1.3V 1
51k
10k
51k
300k
8.151
H
V
V
(7.32V – 6.25V)
100mV/ms
10.7ms
=
VHYSTERESIS = 8.151V – 7.32V = 831mV
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 VIN.



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