M51954B RENESAS [Renesas Technology Corp], M51954B Datasheet - Page 7

• Manufacturer Part Number: M51954B
• Description: Voltage Detecting, System Resetting IC Series
• Manufacturer: RENESAS [Renesas Technology Corp]

M51953A,B/M51954A,B
Notice for use
About the Power Supply Line
1. About bypass capacitor
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.
(1) The difference at delay time becomes remarkable.
(2) Difficulty to react to a momentary voltage decrease.
(3) Original delay time is not obtained.
REJ03D0776-0200 Rev.2.00 Aug 20, 2007
Page 7 of 10
Because the ripple and the spike of the high frequency noise and the low frequency are superimposed to the power
supply line, it is necessary to remove these.
Therefore, please install C
and the GND line as shown in following figure 3.
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.
For example, the reaction time t
The momentary voltage-decrease that is longer than such t
delay capacitance is enlarged, t
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.
When the momentary voltage-decrease time ‘t’ is equivalent to t
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)
V
CC
Figure 4 Time Chart at Momentary Voltage-Decrease
Example of ripple
noise measures
1
C
and C
1
+
Figure 3 Example of Ripple Noise Measures
PHL
PHL
2
C
also becomes long. For instance, it becomes about 100 to 200 µs in case of
for the low frequency and for the high frequency between the power supply line
2
is 10 µs when delay capacitor Cd = 0.1 µF.
Output
V
CC
t
PHL
t
PHL
GND
tpd
are occurs, the detection becomes possible. When the
PHL
M51953
M51954
, the discharge becomes insufficient and the
Power-supply
Delay capacitor
Cd
Output