RNA51957A_10 Datasheet, PDF (11/14 Pages) Renesas Technology Corp – Voltage Detecting, System Resetting IC Series

RNA51957A, B
Preliminary
Setting of Delay Capacity
Please use capacitor Cd for the delay within the range of 10 F or less.
When a value that is bigger than this is set, the problem such as following (1), (2), and (3) becomes remarkable.
t
V_CC
tpd
Output
t_PHL
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 F. 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 t_PHL is 10 s when delay capacitor Cd = 0.1 F.
The momentary voltage-decrease that is longer than such t_PHL are occurs, the detection becomes possible. When the
delay capacitance is enlarged, t_PHL also becomes long. For instance, it becomes about 100 to 200 s in case of
circuit constant C1 = 100 F.
(Characteristic graph 1 is used and extrapolation in case of Cd = 100 F.)
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 t_PHL, 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)
1000
200
100
Characteristic Graph 1
Reaction Time vs. Delay Capacitance
(Example data)
10
Characteristic Graph 2
Delay Time vs. Momentary Voltage Decrease Pulse Width
(Example data)
10000
1000
100
Delay Capacitance
0.01 μF
0.033 μF
0.1 μF
0.33 μF
1 μF
2.2 μF
3.3 μF
10
1
0.01
0.1
1
10
100
Delay Capacitance Cd (μF)
1
1
10
100
1000
10000
Pulse Width (μs)
Figure 10 Characteristic Graph
REJ03D0912-0402 Rev.4.02
Apr 01, 2010
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