LTC6993MP View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC6993MP Datasheet PDF : 26 Pages
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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 tOUT 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
RSET
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 VCTRL sources/sinks a current through
RMOD to vary the ISET current, which in turn modulates
the pulse width as described in Equation (3).
tOUT
=
NDIV • RMOD
50kΩ
•
1+
1µs
RMOD –
RSET
VCTRL
VSET
(3)
TRIG OUT
LTC6993
GND
V+
RMOD
VCTRL
SET
DIV
RSET
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 VCTRL voltage,
the VSET dependency can be eliminated by buffering VSET
and using it as the DAC’s reference voltage, as shown in
Figure 9. The DAC’s output voltage now tracks any VSET
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
DIN VCC
REF
RMOD
tOUT
=
NDIV • RMOD
50kΩ
1µs
•
1+
RMOD
RSET
–
DIN
4096
DIN = 0 TO 4095
µP
CLK LTC1659 VOUT
CS/LD
GND
RSET
Figure 9. Digitally Controlled Pulse Width
69931234fb
17
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