Datasheet
LTC6995-1/LTC6995-2
16
699512fa
For more information www.linear.com/LTC6995-1
applicaTions inForMaTion
For shorter power-on reset times (1ms to 73ms) the timer
startup delay becomes a significant part of the total POR
time. To take this delay into account the value for R
SET
can
be modified from the values shown in Table 2. For a POR
time in the range from 1ms to 16ms (DIVCODE = 0), R
SET
should be t
POR
(ms) • 49.5. For a POR time in the range
from 4.5ms to 73ms (DIVCODE = 1), R
SET
is t
POR
(ms) •
10.9. For longer POR times (DIVCODE 2 through 7) the
startup time is insignificant. After power on, the delay fol
-
lowing a reset condition will be in the same range as shown
for t
DELAY
in Table 2 for these two DIVCODE selections.
For short POR times, a more precise estimation of the
startup time can be found from the following:
t
START
(µs)= 256+ 16•(12–DIVCODE)
( )
R
SET
(kΩ)
50
+80
Supply bounce resets the internal timer so the POR circuit
automatically debounces supply noise. POR timing starts
from the time that the V
+
supply has reached approximately
1.4 volts.
Long Timer One Shots and Delay Generators
The POR circuit of Figure 12 is also useful when the reset
inputs are driven. This creates edge triggered timing events
that are active low and can either be re-triggered or can
stop after one programmed interval. The programmed
time interval can range from only 500µs to over 4 hours
with just resistor value changes.
The circuits in Figure 13 show how a POR or active low
interval can be re-started to provide a full system reset time.
The Figure 14 circuit requires an indication from the
system being reset that it is ready before timing out. The
LTC6995-2 can accommodate an active high OK signal.
By forcing a reset condition at power on the LTC6995 can
be used to create a long time delayed rising edge triggered
by either a falling edge signal (LTC6995-1) or a rising edge
signal (LTC6995-2) as show in Figure 15.
Figure 13. System Resets On Command with Full POR Time Interval. Reset Pulse Is Debounced Automatically
LTC6995-1
ACTIVE HIGH RESET
RST
GND
SET
OUT
V
+
DIV
R
SET
100k
R2
R1
0.1µF
V
+
V
+
POR
OUT
POL = 0
RST
t
START
+
1/2 t
OUT
1/2 t
OUT
TIMER
STOPPED
TIMER
STOPPED
RESET
POR POR
V
+
LTC6995-2
ACTIVE LOW RESET
RST
GND
SET
OUT
V
+
DIV
R
SET
100k
R2
R1
0.1µF
V
+
V
+
POR
OUT
POL = 0
RST
699512 F13
t
START
+
1/2 t
OUT
1/2 t
OUT
TIMER
STOPPED
TIMER
STOPPED
RESET
POR POR
V
+