Datasheet

LTC2954
12
2954fb
LTC2954-1, LTC2954-2 Versions
The LTC2954-1 (high true EN) and LTC2954-2 (low true
EN) differ only by the polarity of the high voltage (33V ABS
MAX), enable pin. The LTC2954-1 EN pin is a low leakage
high true open drain output designed to drive the shutdown
pin of DC/DC converters. The LTC2954-2 is a low leakage,
low true open drain enable output designed to drive the
gate of an external PFET. The LTC2954-2 provides a user
manual power path control.
High Voltage Pins
The V
IN
, PB and EN/EN pins can operate at voltages up to
26.4V. PB can, additionally, operate below ground (–6V)
without latching up the device. PB has an ESD HBM rating
of ±10kV. If the pushbutton switch connected to PB exhib-
its high leakage current, then an external pull-up resistor
to V
IN
is recommended. Furthermore, if the pushbutton
switch is physically located far from the LTC2954 PB pin,
parasitic capacitances may couple onto the high imped-
ance PB input. Additionally, parasitic series inductance
may cause unpredictable ringing at the PB pin. Placing
a 5.1k resistor from the PB pin to the pushbutton switch
would mitigate parasitic inductance problems. Placing a
0.1μF capacitor on the PB pin would lessen the impact of
parasitic capacitive coupling.
Figure 5. Input Voltage Monitoring with KILL Input Figure 6. No μP Application
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 func-
tion. It is driven by a low leakage open drain output of the
μP. It is also connected to a resistive divider that monitors
battery voltage (V
IN
). When the battery voltage falls be-
low 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
APPLICATIONS INFORMATION
PB
V
IN
V
OUT
SHDN**
V
IN
= 9V
EN
INT
KILL
INT
KILL
(OPEN DRAIN)
LTC2954-1
GND
ONT PDT
LT1767-3.3
μP
R1
10k
3.3V
2954 F05
C4
0.1μF
R3
806k
1%
R2
100k
1%
* OPTIONAL
** SHDN INTERNALLY PULLED
UP BY THE LT1767-3.3
V
IN
C
ONT
*
0.033μF
C
PDT
*
1μF
V
IN
= 9V
3.3V
R1
100k
C3*
0.01μF
2954 F06
+
C4
0.1μF
PB
EN
INT
KILL
LTC2954-1
GND ONT PDT
V
IN
C
ONT
*
0.033μF
C
PDT
*
1μF
* OPTIONAL
** SHDN INTERNALLY
PULLED UP BY
THE LT1767-3.3
V
IN
V
OUT
SHDN**
LT1767-3.3
TYPICAL APPLICATIONS
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