ltc6993-1 Linear Technology Corporation, ltc6993-1 Datasheet - Page 16

• Manufacturer Part Number: ltc6993-1
• Description: Electrical Specifications Subject To Change
• Manufacturer: Linear Technology Corporation

applicaTions inForMaTion
LTC6993-1/LTC6993-2
LTC6993-3/LTC6993-4
Basic Operation
The simplest and most accurate method to program the
LTC6993 is to use a single resistor, R
SET and GND pins. The design procedure is a four step
process.
Step 1: Select the POL Bit Setting.
The LTC6993 can generate positive or negative output
pulses, depending on the setting of the POL bit. The POL
bit is the DIVCODE MSB, so any DIVCODE ≥ 8 has POL = 1
and produces active-low pulses.
Step 2: Select LTC6993 Version.
Two input-related choices dictate the proper LTC6993 for
a given application:
Use Table 2 to select a particular variety of LTC6993.
Step 3: Select the N
As explained earlier, the voltage on the DIV pin sets the
DIVCODE which determines both the POL bit and the N
value. For a given output pulse width (t
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

• Is TRIG a rising or falling-edge input?
• Should retriggering be allowed?
16
t
DIV
OUT
µs
/V
≤
+
N
ratio to apply to the DIV pin.
DIV
≤
t
1
OUT
µs
DIV
OUT
Frequency Divider Value.
.
OUT
SET
DIV
, between the
), N
will provide
DIV
DIV
should
value.
DIV
(1)
DIV
Step 4: 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.
Example: Design a one-shot circuit that satisfies the fol-
lowing requirements:
Step 1: Select the POL Bit Setting.
For inverted (negative) output pulse, choose POL = 1.
Step 2: Select the LTC6993 Version.
A rising-edge retriggerable input requires the LTC6993-2.
Step 3: 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 4: Select R
Calculate the correct value for R
• t
• Negative Output Pulse
• Rising-Edge Trigger Input
• Retriggereable Input
• Minimum power consumption
6.25 ≤ N
R
R
SET
SET
OUT
=
=
= 100µs
50
50
1
1
DIV
µs
µs
SET
k
k
DIV
≤ 100
•
•
N
SET
100
t
resistor. POL = 1 and N
OUT
value that meets the requirements of
DIV
8
.
DIV
OUT
µs
DIV
=
Frequency Divider Value.
= 100µs:
625
include 8 and 64. N
k
SET
SET
.
using Equation (2):
DIV
= 8 requires
DIV
69931234p
= 8 is
SET
(2)