LTC6994CS6-2#PBF Linear Technology, LTC6994CS6-2#PBF Datasheet - Page 17

• Manufacturer Part Number: LTC6994CS6-2#PBF
• Manufacturer: Linear Technology

Specifications of LTC6994CS6-2#PBF

• Lead Free Status / Rohs Status: Compliant

applicaTions inForMaTion
Voltage-Controlled Delay
With one additional resistor, the LTC6994 output delay
can be manipulated by an external voltage. As shown in
Figure 10, voltage V
R
the delay as described in Equation (3):
MOD
t
DELAY
to vary the I
V
CTRL
=
N
Figure 10. Voltage-Controlled Delay
R
DIV
MOD
50kΩ
•R
R
SET
CTRL
SET
MOD
current, which in turn modulates
IN
GND
SET
sources/sinks a current through
•
LTC6994
µP
1+
R
OUT
R
DIV
V
MOD
SET
+
1µs
D
CLK
CS/LD
0.1µF
IN
–
V
C1
0.1µF
V
V
LTC1659
CTRL
V
CC
SET
+
V
Figure 11. Digitally Controlled Delay
+
GND
R1
R2
699412 F10
REF
V
0.1µF
OUT
LTC6078
V
(3)
+
1/2
+
–
R
MOD
Digital Delay Control
The control voltage can be generated by a DAC (digital-to-
analog converter), resulting in a digitally-controlled delay.
Many DACs allow for the use of an external reference. If
such a DAC is used to provide the V
dependency can be eliminated by buffering V
it as the DAC’s reference voltage, as shown in Figure 11.
The DAC’s output voltage now tracks any V
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 delay.
I
When operating with I
1.25µA to 20µA range, the master oscillator operates
outside of the 62.5kHz to 1MHz range in which it is most
accurate.
The oscillator will still function with reduced accuracy for
I
stop. Under this condition, the delay timing can still be
initiated, but will not terminate until I
the master oscillator starts again.
At the other extreme, it is not recommended to operate
the master oscillator beyond 2MHz because the accuracy
of the DIV pin ADC will suffer.
SET
SET
< 1.25µA. At approximately 500nA, the oscillator will
Extremes (Master Oscillator Frequency Extremes)
R
SET
t
D
DELAY
IN
GND
SET
IN
= 0 TO 4095
LTC6994
LTC6994-1/LTC6994-2
=
N
DIV
50k
OUT
DIV
• R
V
+
MOD
•
SET
1+
R
R
C1
0.1µF
699412 F11
MOD
SET
outside of the recommended
1µs
–
4096
V
D
+
IN
R1
R2
CTRL
SET
voltage, the V
increases and
SET
SET
and using
variation
17
699412fa
SET