HT70XX
5V power line monitoring circuit
Generally, a minimum operating voltage of 4.5V is guar-
anteed in a 5V power line system. The HT7044A is rec-
ommended for use as 5V power line monitoring circuit.
·
5V power line monitor with power-on reset
5 V P o w e r lin e
R
D
·
Varying the detectable voltage with a diode
V
IN
V f1
V f2
V
D D
V
O U T
H T 7 0 X X A
V
V
D D
S S
V
S S
C
V
Detectable Voltage = V
f1
+V
f2
+V
DET
O U T
H T 7 0 4 4 A
V
S S
Malfunction analysis
V
S S
The following circuit demonstrates the way a circuit ana-
lyzes malfunctions by monitoring the variation or spike
noise of power supply voltage.
V
V
O U T
D D
·
with 5V voltage regulator
5 V V o lta g e r e g u la to r
V
IN
H T 7 1 5 0
G N D
5 V
H T 7 0 X X A
V
D D
V
S S
V
S S
V
O U T
Charge monitoring circuit
The following circuit shows a charged monitor for pro-
tection against battery deterioration by overcharging.
When the voltage of the battery is higher than the set de-
tectable voltage, the transistor turns on to bypass the
charge current, protecting the battery from overcharg-
ing.
H T 7 0 4 4 A
V
S S
Change of detectable voltage
If the required voltage is not found in the standard prod-
uct selection table, it is possible to change it by using ex-
ternal resistance dividers or diodes.
·
Varying the detectable voltage with a resistance di-
V
S o la r
C e ll
V
T r
O U T
D D
vider
V
IN
B A T T
L o a d
R
A
V
D D
V
V
O U T
S S
H T 7 0 X X A
R
B
H T 7 0 X X A
V
S S
V
S S
R
A
+
R
B
´
V
DET
R
B
R
A
+
R
B
Hysteresis width =
´
V
HYS
R
B
Detectable voltage =
Rev. 1.60
8
January 14, 2003
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
