Datasheet

LTC2951-1/LTC2951-2
14
295112fb
TYPICAL APPLICATIONS
Voltage Monitoring with KILL Input
The KILL pin can be used as a voltage monitor. Figure
5 shows an application where the KILL pin has a dual
function. It is driven by a low leakage open-drain output
of the µP. It is also connected to a resistor divider that
monitors battery voltage (V
IN
). When the battery voltage
falls below the set value, the voltage at the KILL pin falls
below 0.6V and the EN pin is quickly pulled low. Note
that the resistor values should be as large as possible,
but small enough to keep leakage currents from tripping
the 0.6V KILL comparator.
The DC/DC converter shown has an internal pull-up cur-
rent on its SHDN pin. A pull-up resistor on EN is thus not
needed.
Operation without µP
Figure 6 shows how to connect the KILL pin when there
is no circuitry available to drive it. The minimum pulse
width detected is 30µs. If there are glitches on the resis-
tor pull-up voltage that are wider than 30µs and transition
below 0.6V, then an appropriate bypass capacitor should
be connected to the KILL pin.
Figure 5. Input Voltage Monitoring with KILL Input
Figure 6. No µP Application
PB
V
IN
SHDN**
V
IN
V
OUT
EN
INT
KILL
INT
KILL
(OPEN DRAIN)
LTC2951-1
GND OFFT
LT1767-3.3
µP
9V
R1
10k
3.3V
2951 F05
C4
0.1µF
R3
806k
1%
R2
100k
1%
5.4V THRESHOLD
*OPTIONAL
**SHDN INTERNALLY PULLED UP BY THE LT1767-3.3
V
IN
C
KILLT
*
0.033µF
C
OFFT
*
0.033µF
KILLT
V
IN
V
IN
V
OUT
LT1767-3.3
9V
3.3V
R1
100k
C3*
0.01µF
2951 F06
+
C4
0.1µF
C3*
0.01µF
PB
EN
INT
KILL
LTC2951-1
GND KILLT OFFT
V
IN
C
KILLT
*
0.033µF
C
OFFT
*
0.033µF
SHDN**
*OPTIONAL
**SHDN INTERNALLY PULLED UP BY THE LT1767-3.3