M51957A,B/M51958A,B
Setting of Delay Capacity
Please use capacitor Cd for the delay within the range of 10 µF or less.
When a value that is bigger than this is set, the problem such as following (1), (2), and (3) becomes remarkable.
t
VCC
tpd
Output
tPHL
Figure 9 Time Chart at Momentary Voltage-Decrease
(1) The difference at delay time becomes remarkable.
A long delay setting of tens of seconds is fundamentally possible. However, when set delay time is lengthened, the
range of the difference relatively grows, too. When a set value is assumed to be ‘tpd’, the difference occurs in the
range from 0.47 × tpd to 2.05 × tpd. For instance, 34 seconds can be calculated at 100 µF. However, it is likely to
vary within the ranges of 16-70 seconds.
(2) Difficulty to react to a momentary voltage decrease.
For example, the reaction time tPHL is 10 µs when delay capacitor Cd = 0.1 µF.
The momentary voltage-decrease that is longer than such tPHL are occurs, the detection becomes possible. When the
delay capacitance is enlarged, tPHL also becomes long. For instance, it becomes about 100 to 200 µs in case of
circuit constant C1 = 100 µF.
(Characteristic graph 1 is used and extrapolation in case of Cd = 100 µF.)
Therefore, it doesn't react to momentary voltage-decrease that is shorter than this.
(3) Original delay time is not obtained.
When the momentary voltage-decrease time ‘t’ is equivalent to tPHL, the discharge becomes insufficient and the
charge starts at that state. This phenomenon occurs at large capacitance. And, original delay time tpd is not
obtained.
Please refer to characteristic graph 2. (Delay time versus input pulse width)
Characteristic Graph 1
Reaction Time vs. Delay Capacitance
(Example data)
Characteristic Graph 2
Delay Time vs. Momentary Voltage Decrease Pulse Width
(Example data)
1000
10000
Delay Capacitance
0.01µF
0.033µF
0.1µF
0.33µF
1µF
2.2µF
3.3µF
200
100
1000
100
10
10
1
1
0.01
0.1
1
10
100
1
10
100
Pulse Width (µs)
1000
10000
Delay Capacitance Cd (µF)
Figure 10 Characteristic Graph
REJ03D0778-0200 Rev.2.00 Aug 20, 2007
Page 10 of 13
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