SA555DT datasheet(13/20 Pages) STMICROELECTRONICS

Part #	SA555DT

Description	General-purpose single bipolar timers

PDF	20 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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13 / 20 page

NE555 - SA555 - SE555

Application information

Doc ID 2182 Rev 6

13/20

Figure 20 shows the waveforms generator by the linear ramp.

The time interval is given by:

Figure 20.

Linear ramp

4.5

50% duty cycle oscillator

For a 50% duty cycle, the resistors RA and RB can be connected as in Figure 21. The time

period for the output high is the same as for astable operation (see Section 4.2 on page 9):

t1 = 0.693 RA C

For the output low it is

Thus the frequency of oscillation is:

T =

(2/3 Vcc RE (R1+R2) C

R1 Vcc - VBE (R1+R2)

---------------------------------------------------------------- VBE = 0.6V

VCC = 5 V

Time:

20 µs/DIV

R1 + 47 kΩ

R2 = 100 kΩ

RE = 2.7 kΩ

C = 0.01 µF

Top trace: input 3 V/DIV

Middle trace: output 5 V/DIV

Bottom trace: output 5 V/DIV

Bottom trace: capacitor voltage 1 V/DIV

[(R. RB)/(RA+RB)].C.Ln

2RA

–

2RB

–

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SA555DT Datasheet(PDF) 13 Page - STMicroelectronics