LTC6993-1/LTC6993-2
LTC6993-3/LTC6993-4
16
69931234fc
For more information www.linear.com/LTC6993-1
applicaTions inForMaTion
Basic Operation
The simplest and most accurate method to program
the LTC6993 is to use a single resistor, R
SET
, between
the SET and GND pins. The design procedure is a four
step process. Alternatively, Linear Technology offers the
easy-to-use TimerBlox Designer tool to quickly design
any LTC6993 based circuit. Download the free TimerBlox
Designer software at www.linear.com/timerblox.
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:
• Is TRIG a rising or falling-edge input?
• Should retriggering be allowed?
Use Table 2 to select a particular variety of LTC6993.
Step 3: Select the N
DIV
Frequency Divider Value.
As explained earlier, the voltage on the DIV pin sets the
DIVCODE which determines both the POL bit and the N
DIV
value. For a given output pulse width (t
OUT
), N
DIV
should
be selected to be within the following range:
OUT
16µs
≤ N
DIV
≤
OUT
1µs
(1)
To minimize supply current, choose the lowest N
DIV
value.
However, in some cases a higher value for N
DIV
will provide
better accuracy (see Electrical Characteristics).
Table 1 can also be used to select the appropriate N
DIV
values for the desired t
OUT
.
With POL already chosen, this completes the selection of
DIVCODE. Use Table 1 to select the proper resistor divider
or V
DIV
/V
+
ratio to apply to the DIV pin.
Step 4: Calculate and Select R
SET
.
The final step is to calculate the correct value for R
SET
using the following equation:
R
SET
=
1µs
•
OUT
N
DIV
(2)
Select the standard resistor value closest to the calculated
value.
Example: Design a one-shot circuit that satisfies the fol-
lowing requirements:
• t
OUT
= 100µs
• Negative Output Pulse
• Rising-Edge Trigger Input
• Retriggerable Input
• Minimum power consumption
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
DIV
Frequency Divider Value.
Choose an N
DIV
value that meets the requirements of
Equation (1), using t
OUT
= 100µs:
6.25 ≤ N
DIV
≤ 100
Potential settings for N
DIV
include 8 and 64. N
DIV
= 8 is
the best choice, as it minimizes supply current by us-
ing a large R
SET
resistor. POL = 1 and N
DIV
= 8 requires
DIVCODE = 14. Using T
able 1, choose R1 = 102k and
R2 = 976k values to program DIVCODE = 14.
Step 4: Select R
SET
.
Calculate the correct value for R
SET
using Equation (2):
R
SET
=
1µs
•
8
= 625k
