LTC6993-1 Datasheet, PDF (16/24 Pages) Linear Technology – TimerBlox: Monostable

LTC6993-1/LTC6993-2
LTC6993-3/LTC6993-4
APPLICATIONS INFORMATION
Since 625k is not available as a standard 1% resistor,
substitute 619k if a –0.97% shift in t_OUT is acceptable.
Otherwise, select a parallel or series pair of resistors such
as 309k and 316k to attain a more precise resistance.
The completed design is shown in Figure 7.
TRIG OUT
LTC6993-2
GND
V⁺
SET
DIV
R_SET
625k
2.25V TO 5.5V
0.1µF
R1
102k
DIVCODE = 14
R2
976k
69931234 F07
Figure 7. 100µs Negative Pulse Generator
Voltage-Controlled Pulse Width
With one additional resistor, the LTC6993 output pulse width
can be manipulated by an external voltage. As shown in
Figure 8, voltage V_CTRL sources/sinks a current through
R_MOD to vary the I_SET current, which in turn modulates
the pulse width as described in Equation (3).
t_OUT
=
N_DIV • R_MOD
50kΩ
•
1+
1µs
R_{MOD –}
R_SET
V_CTRL
V_SET
(3)
TRIG OUT
LTC6993
GND
V⁺
R_MOD
V_CTRL
SET
DIV
R_SET
V⁺
C1
0.1µF ^R1
R2
69931234 F08
Figure 8. Voltage-Controlled Pulse Width
Digital Pulse Width Control
The control voltage can be generated by a DAC (digital-to-
analog converter), resulting in a digitally-controlled pulse
width. Many DACs allow for the use of an external refer-
ence. If such a DAC is used to provide the V_CTRL voltage,
the V_SET dependency can be eliminated by buffering V_SET
and using it as the DAC’s reference voltage, as shown in
Figure 9. The DAC’s output voltage now tracks any V_SET
variation and eliminates it as an error source. The SET pin
cannot be tied directly to the reference input of the DAC
because the current drawn by the DAC’s REF input would
affect the pulse width.
V⁺
0.1µF
V⁺
0.1µF
1/2
LTC6078
TRIG OUT
LTC6993
GND
V⁺
SET
DIV
V⁺
C1
0.1µF R1
R2
69931234 F09
D_IN ^VCC
REF
R_MOD
t_OUT
=
N_DIV • R_MOD
50kΩ
1µs
•
1+
R_MOD
R_SET
–
D_IN
4096
D_IN = 0 TO 4095
µP
CLK LTC1659 V_OUT
CS/LD
GND
R_SET
16
Figure 9. Digitally Controlled Pulse Width
69931234f