UPC1555C Просмотр технического описания (PDF) - NEC => Renesas Technology

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производитель

UPC1555C

TIMER CIRCUIT

NEC => Renesas Technology 

µPC1555

(2) Astable multivibrator example

Fig. d Astable Multivibrator Example

VCC = 5 to 15 V

Note 10

RL

R1

48

3

7

OUTPUT

µPC1555

R2

5

6

12

Control voltage

C1

0.01 µ F

Fig. e Astable Multivibrator Response Waveform

t = 0.5 ms/DIV

Output voltage: 5 V/DIV "H"

"H"

"H"

"L"

"L"

Capacitor (C1) voltage: 1.7 V/DIV

(R1 = R2 = 4.8 kΩ, C1 = 0.1 µ F, RL = 1 kΩ)

When the µPC1555 is used in a circuit configuration

Fig. f Interrelationships among Oscillation

shown in Fig. d, the circuit is triggered by itself to

Frequency, R1, R2, and C1

operate as an astable multivibrator, because pin 2

(approximate value obtained by

(trigger pin) and pin 6 (threshold pin) are connected to

calculation)

each other. When the output voltage is high, capacitor

100

C1 is charged through R1 and R2. When C1 is charged

up to a voltage two-thirds as high as VCC, the threshold

10

pin is turned on, and the output pin becomes low. At

this point C1 starts discharging through R2. When C1

1.0

discharges, and the voltage across C1 decreases to a

voltage one-third as high as VCC, the trigger pin is turned

0.1

on, and the output voltage becomes high, causing the

charge current to flow into C1 through R1 and R2 again.

(R1 + 2R2)

0.01

This operation is shown in Fig. e. Because C1 repeats

charging and discharging between one-third as high as

VCC and two-thirds as high as VCC, the oscillation

frequency is not affected by the supply voltage.

Oscillation is represented theoretically using the

0.001

0.1 1.0 10 100 1.0 k 10 k 100 k

Oscillation frequency f (Hz)

(Free running frequency)

following expressions.

When the output voltage is high, the charge time is : t1 = 0.693 (R1 + R2) C1 .......................................... (1)

When the output voltage is low, the discharge time is : t2 = 0.693 • R2 • C1 ................................................. (2)

Adding expressions (1) and (2) determines period T : T = t1 + t2 = 0.693 (R1 + 2R2) C1 .......................... (3)

Therefore, the oscillation frequency is

(see Fig. f for reference)

1

: f= =

1.44

...................................... (4)

T

(R1 + 2R2) C1

The duty cycle is determined by the equation (5)

: D=

R2

........................................................ (5)

R1 + 2R2

The values obtained this way are approximate values, however. If it is necessary to obtain an accurate oscillation

frequency, determine R1, R2, and C1 through actual measurement and confirmation; a trimmer should be used as

required. Moreover, R1 and R2 should be 300 Ω or higher.

Note 10. If the load is connected across the output and GND pins, a “staircase” occurs in the output waveform.

8

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