SE555-SP Datasheet, PDF (14/18 Pages) Texas Instruments – QML CLASS V PRECISION TIMER

SE555-SP
SGLS401 – FEBRUARY 2010
www.ti.com
Pulse-Position Modulation
As shown in Figure 21, any of these timers can be used as a pulse-position modulator. This application
modulates the threshold voltage and, thereby, the time delay, of a free-running oscillator. Figure 22 shows a
ÎÎÎÎÎ _{triangular-wave modulation signal for such a circuit; however, any wave shape could be used.}
ÎÎÎÎÎ _{VCC (5 V to 15 V)}
ÎÎÎÎÎÎÎÎÎÎ ₄
ÎÎÎÎÎÎÎ _RESET
ÎÎÎÎÎÎÎ ₂
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ^TRIG
8 ^RL
VCC
3
OUT
7
DISCH
RA
Output
R_A = 3 kΩ
R_B = 500 Ω
R_L = 1 kΩ
See Figure 20
Modulation Input Voltage
Modulation ₅
RB
Input
CONT
THRES ⁶
(See Note A)
GND
1
C
NOTE A: The modulating signal can be direct or capacitively coupled to CONT.
For direct coupling, the effects of modulation source voltage and
impedance on the bias of the timer should be considered.
ÎÎÎÎ_CaÎÎÎÎ_paciÎÎÎÎ_{tor V}ÎÎÎÎ_olta^{ÎÎÎÎÎÎÎ}_gOe ^{uÎÎÎÎÎÎÎtputÎÎÎÎVoltÎÎÎÎageÎÎÎÎ}
Time − 0.1 ms/div
Figure 21. Circuit for Pulse-Position Modulation Figure 22. Pulse-Position-Modulation Waveforms
14
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