MB3771
9. Dual (Positive/Negative) Power Supply Voltage Monitoring (VCC = 5 V, VEE = Negative Power
Supply)
Monitors a 5 V and a negative (any given level) power supply. R1, R2, and R3 should be the same value.
Detection Voltage = VSB - VSB × R4/R3
Example if VEE = -5 V, R4 = 91 kΩ
Then the detected voltage = -4.37 V
In cases where VEE may be output when VCC is not output, it is necessary to use a Schottky barrier diode (SBD).
VCC
R5 : 5.1 kΩ
MB3771
8
1
2
RESET
R1 : 20 kΩ
R4
7
VEE
R3 :
20 kΩ
6
5
3
4
0.22 µF
CT
R2 : 20 kΩ
SBD
10. Reference Voltage Generation and Voltage Sagging Detection
(1) 9V Reference Voltage Generation and 5V/9V Monitoring
Detection Voltage = 7.2 V
In the above examples, the output voltage and the detection voltage are determined by the following equations:
Detection Voltage = (R1 + R2) × VSB/R2
15 V
R
5
: 3 kΩ
V
CC : 5 V
MB3771
8
1
2
3
4
RESET
7
6
5
CT
9 V ( 50 mA)
R3 :
7.5 kΩ
R
R
1
: 300 kΩ
: 62 kΩ
0.47 µF
2
R4 :
1.2 kΩ
11
FUJITSU [ FUJITSU ]
