LTC6991IS6-TRPBF 查看數據表（PDF） - Analog Devices
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LTC6991IS6-TRPBF Datasheet PDF : 24 Pages
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LTC6991
APPLICATIONS INFORMATION
RPW
2.26k
CPW
470pF
RST
OUT
LTC6991
GND
V+
RSET
715k
SET
DIV
OUT
2.25V TO 5.5V
R1
0.1µF
1M
( ) tPULSE
=
–RPW
•
CPW
•
In
1–
VRST(RISING)
V+
tPULSE ≈ –2.26kΩ • 470pF • In(1 – 0.61)
tPULSE ≈ 1µs
1µs PULSE WIDTH
60 SECONDS
R2
392k
6991 F13a
Figure 13a. Self-Resetting Circuit (DIVCODE = 4)
RPW
2.26k
CPW
470pF
RST
OUT
LTC6991
GND
V+
RSET
715k
SET
DIV
OUT
2.25V TO 5.5V
( ) tPULSE = –RPW • CPW • In
VRST(FALLING)
V+
tPULSE ≈ –2.26kΩ • 470pF • In(0.43)
tPULSE ≈ 0.9µs
R1
0.1µF
392k
0.9µs PULSE WIDTH
60 SECONDS
R2
1M
6991 F13b
Figure 13b. Self-Resetting Circuit (DIVCODE = 11)
Figure 13.
Self-Resetting Circuits
Voltage Controlled Frequency
The RST pin has hysteresis to accommodate slow-
changing input voltages. Furthermore, the trip points
are proportional to the supply voltage (see Note 6 and
the RST Threshold Voltage vs Supply Voltage curve in
Typical Performance Characteristics). This allows an RC
time constant at the RST input to generate a delay that is
nearly independent of the supply voltage.
A simple application of this technique allows the LTC6991
output to reset itself, producing a well-controlled pulse
once each cycle. Figure 13a and Figure 13b show circuits
that produce approximately 1µs pulses once a minute.
The only difference is in the POL bit setting, which con-
trols whether the pulse is positive or negative.
With one additional resistor, the LTC6991 output frequency
can be manipulated by an external voltage. As shown in
Figure 14, voltage VCTRL sources/sinks a current through
RVCO to vary the ISET current, which in turn modulates the
output frequency as described in Equation (3).
fOUT
=
1MHz • 50kΩ
1024 • NDIV • RVCO
⎛
• ⎜1+
⎝
R VCO
RSET
−
VCTRL
VSET
⎞
⎟
⎠
(3)
RST
OUT
LTC6991
GND
V+
RVCO
VCTRL
SET
DIV
RSET
V+
C1
0.1µF R1
R2
6991 F14
Figure 14. Voltage-Controlled Oscillator
6991fc
16
For more information www.linear.com/LTC6991
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