upc1555 Renesas Electronics Corporation., upc1555 Datasheet - Page 8

• Manufacturer Part Number: upc1555
• Description: Timer Circuit
• Manufacturer: Renesas Electronics Corporation.

(2) Astable multivibrator example
shown in Fig. d, the circuit is triggered by itself to
operate as an astable multivibrator, because pin 2
(trigger pin) and pin 6 (threshold pin) are connected to
each other. When the output voltage is high, capacitor
C
up to a voltage two-thirds as high as V
pin is turned on, and the output pin becomes low. At
this point C
discharges, and the voltage across C
voltage one-third as high as V
on, and the output voltage becomes high, causing the
charge current to flow into C
This operation is shown in Fig. e. Because C
charging and discharging between one-third as high as
V
frequency is not affected by the supply voltage.
following expressions.
frequency, determine R
required. Moreover, R
8
CC
1
Control voltage
When the PC1555 is used in a circuit configuration
When the output voltage is high, the charge time is
When the output voltage is low, the discharge time is : t
Adding expressions (1) and (2) determines period T
Therefore, the oscillation frequency is
(see Fig. f for reference)
The duty cycle is determined by the equation (5)
The values obtained this way are approximate values, however. If it is necessary to obtain an accurate oscillation
Note 10. If the load is connected across the output and GND pins, a “staircase” occurs in the output waveform.
is charged through R
Oscillation is represented theoretically using the
Note 10
and two-thirds as high as V
0.01 F
Fig. d Astable Multivibrator Example
R
V
L
CC
= 5 to 15 V
1
OUTPUT
starts discharging through R
3
5
1
1
1
and R
, R
and R
1
4
PC1555
2
1
, and C
CC
through R
2
, the trigger pin is turned
2
2
8
. When C
should be 300
CC
7
6
1
1
through actual measurement and confirmation; a trimmer should be used as
CC
, the oscillation
decreases to a
1
, the threshold
and R
2
1
. When C
is charged
1
repeats
2
R
R
again.
C
1
2
1
or higher.
1
: t
: T = t
: f =
: D =
Fig. e Astable Multivibrator Response Waveform
1
2
= 0.693 (R
= 0.693
1
T
0.001
1
R
0.01
100
Fig. f Interrelationships among Oscillation
+ t
1.0
0.1
=
1
10
(R
R
+ 2R
2
0.1
2
1
(R
•
= 0.693 (R
(R
= R
Capacitor (C
R
Output voltage: 5 V/DIV
"H"
1
1
1
Frequency, R1, R2, and C1
(approximate value obtained by
calculation)
2
2
+ 2R
(Free running frequency)
+ 2R
+ R
1.0
2
Oscillation frequency f (Hz)
•
1.44
= 4.8 k , C1 = 0.1 F, R
........................................................
C
"L"
1
2
2
)
) C
2
10
) C
................................................. (2)
t = 0.5 ms/DIV
1
1
1
+ 2R
1
) voltage: 1.7 V/DIV
"H"
100 1.0 k 10 k 100 k
.......................................... (1)
......................................
2
) C
"L"
1
.......................... (3)
"H"
L
= 1 k )
PC1555
(4)
(5)