Datasheet

LTC6991
15
6991fb
APPLICATIONS INFORMATION
LTC6991 as “Wake-Up Timer”
The output latch reset function provided by the RST pin
allows the LTC6991 to enable a larger system at regular
intervals. The on-time can be controlled by the system.
This allows the system to shut itself down immediately
after performing its tasks, reducing power consumption.
Figure 12 shows an example using “black boxes” for a
switching regulator and the system being duty-cycled.
In some cases, an RC filter may be necessary at the RST
LTC6991
THE SYSTEM CAN EXTEND t
ON
AS LONG AS NEEDED (UP TO 50% OF t
OUT
)
V
+
DIV
SET
OUT
GND
RST
R
FILT
100k
R
SET
665k
R2
681k
t
ON
t
ON
t
ON
6991 F12
R1
1M
R
SUPPLY
4.99k
1N4733A
5.1V
3V TO 20V
C
FILT
0.1µF
0.1µF
t
OUT
3570 SECONDS
SWITCHING
REGULATOR
V
IN
V
OUT
V
REG
V
REG
DONE/RST
LTC6991 OUT
SHDN
SYSTEM
V
+
DONE
t
OUT
t
OUT
t
OUT
Figure 12. Powering Up a System Once an Hour
input to filter start-up glitches from the system as it is
powered on.
If the LTC6991 is enabling a switching regulator that can
operate on supplies greater than 5.5V, it will be necessary
to limit the supply voltage provided to the LTC6991. If
the LTC6991 output is not heavily loaded, and if a large
R
SET
resistor is used, the supply current will not be much
larger than 100µA, so a simple regulator circuit can be
constructed using a Zener diode.