LTC6994CDCB-1#PBF Linear Technology, LTC6994CDCB-1#PBF Datasheet - Page 16

• Manufacturer Part Number: LTC6994CDCB-1#PBF
• Manufacturer: Linear Technology

Specifications of LTC6994CDCB-1#PBF

• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Pin Count: 6
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

LTC6994-1/LTC6994-2
applicaTions inForMaTion
Basic Operation
The simplest and most accurate method to program the
LTC6994 is to use a single resistor, R
SET and GND pins. The design procedure is a 3-step
process.
Step 1: Select the LTC6994 Version and POL Bit Setting.
Choose LTC6994-1 to delay one (rising or falling) input
transition. The POL bit then defines which edge is to be
delayed. POL = 0 delays rising edges. POL = 1 delays
falling edges.
Choose LTC6994-2 to delay rising and falling edges. Set
POL = 0 for normal operation, or POL = 1 to invert the
output.
Step 2: Select the N
As explained earlier, the voltage on the DIV pin sets the
DIVCODE which determines both the POL bit and the
N
be selected to be within the following range:
To minimize supply current, choose the lowest N
However, in some cases a higher value for N
better accuracy (see Electrical Characteristics).
Table 1 can also be used to select the appropriate N
values for the desired t
With POL already chosen, this completes the selection of
DIVCODE. Use Table 1 to select the proper resistor divider
or V
Step 3: Calculate and Select R
The final step is to calculate the correct value for R
using the following equation:
Select the standard resistor value closest to the calculated
value.

DIV
R
t
DELAY
16
DIV
SET
value. For a given delay time (t
µs
/V
=
+
≤
50
ratio to apply to the DIV pin.
1
µs
N
k
DIV
•
t
DELAY
≤
N
DIV
t
DIV
DELAY
1
µs
DELAY
Frequency Divider Value.
.
SET
.
DELAY
SET
DIV
), N
, between the
will provide
DIV
DIV
should
value.
SET
(1)
DIV
(2)
Example: Design a one-shot circuit to delay falling edges
by t
Step 1: Select the LTC6994 Version and POL Bit Setting.
To delay negative transitions, choose the LTC6994-1 with
POL = 1.
Step 2: Select the N
Choose an N
Equation (1), using t
Potential settings for N
the best choice, as it minimizes supply current by us-
ing a large R
DIVCODE = 14. Using Table 1, choose R1 = 102k and R2
= 976k values to program DIVCODE = 14.
Step 3: Select R
Calculate the correct value for R
Since 625k is not available as a standard 1% resistor,
substitute 619k if a –0.97% shift in t
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 9.
6.25 ≤ N
R
DELAY
SET
=
= 100µs with minimum power consumption.
50
1
DIV
µs
Figure 9. 100µs Negative-Edge Delay
SET
k
DIV
R
625k
≤ 100
SET
•
SET
100
resistor. POL = 1 and N
value that meets the requirements of
IN
GND
SET
8
.
LTC6994-1
DIV
DELAY
µs
DIV
=
Frequency Divider Value.
OUT
625
DIV
V
= 100µs:
include 8 and 64. N
+
k
SET
2.25V TO 5.5V
using Equation (2).
DELAY
R1
102k
DIVCODE = 14
R2
976k
699412 F09
DIV
is acceptable.
= 8 requires
DIV
= 8 is
699412p