MC10198 查看數據表（PDF） - Motorola => Freescale
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MC10198 Datasheet PDF : 10 Pages
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MC10198
APPLICATIONS INFORMATION
Circuit Operation:
1.PULSE WIDTH TIMING — The pulse width is deter-
mined by the external resistor and capacitor. The
MC10198 also has an internal resistor (nominally 284
ohms) that can be used in series with RExt. Pin 7, the
external pulse width control, is a constant voltage node
(–3.60 V nominally). A resistance connected in series
from this node to VEE sets a constant timing current IT.
This current determines the discharge rate of the ca-
pacitor:
∆V
IT = CExt ∆T
where
∆T = pulse width
∆V = 1.9 V change in capacitor voltage
Then:
∆T = CExt1.9ITV
If RExt + RInt are in series to VEE:
IT = [(–3.60 V) – (–5.2 V)] ÷ [RExt + 284 Ω]
IT = 1.6 V/(RExt + 284)
The timing equation becomes:
∆T = [(CExt)(1.9 V)] ÷ [1.6 V/(RExt + 284)]
∆T = CExt (RExt + 284) 1.19
where ∆T = Sec
RExt = Ohms
CExt = Farads
FIGURE 1 —
4
CExt
MC10198
7
RInt
284 Ω
–3.60 V External
Pulse Width Control
6
RExt
VEE = –5.2 V
Figure 2 shows typical curves for pulse width
versus CExt and RExt (total resistance includes RInt).
Any low leakage capacitor can be used and RExt can
vary from 0 to 16 k–ohms.
2.TRIGGERING —The Epos and ENeg inputs control the
trigger input. The MC10198 can be programmed to trig-
ger on the positive edge, negative edge, or both. Also,
the trigger input can be totally disabled. The truth table
is shown on the first page of the data sheet.
The device is totally retriggerable. However, as
duty cycle approaches 100%, pulse width jitter can
occur due to the recovery time of the circuit. Recovery
time is basically dependent on capacitance CExt.
Figure 3 shows typical recovery time versus capaci-
tance at IT = 5 mA.
FIGURE 2 – TIMING PULSE WIDTH versus CExt and RExt
100
10
10 kΩ
3 kΩ
1
500 Ω
100
RExt = 0 NOTE: TOTAL RESISTANCE
= RExt + RInt
10
10 pF
100 pF
1000 pF
0.01 µF
CExt – TIMING CAPACITANCE
0.1 µF
FIGURE 3 — RECOVERY TIME versus CExt @ IT = 5 mA
10 µs
1 µs
100 ns
10 ns
1 ns
10 pF
100 pF
1000 pF
0.01 µF
CExt – TIMING CAPACITANCE
0.1 µF
MECL Data
DL122 — Rev 6
3–177
MOTOROLA
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