LTC2954IDDB-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2954IDDB-1' PDF : 18 Pages View PDF
LTC2954
APPLICATIONS INFORMATION
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 VIN, 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 VIN 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.
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 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 (VIN). 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
VIN = 9V
R3
806k
1%
R2
100k
1%
VIN
VOUT
3.3V
LT1767-3.3
SHDN**
C4
0.1μF
VIN
EN
LTC2954-1
INT
PB
KILL
GND ONT
PDT
CONT*
0.033μF
CPDT*
1μF
R1
10k
INT
μP
KILL
(OPEN DRAIN)
2954 F05
* OPTIONAL
** SHDN INTERNALLY PULLED
UP BY THE LT1767-3.3
Figure 5. Input Voltage Monitoring with KILL Input
12
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
VIN = 9V
VIN
VOUT
3.3V
LT1767-3.3
SHDN**
C4
0.1μF
R1
100k
VIN
EN
LTC2954-1
INT
PB
KILL
GND ONT
PDT
+
CONT*
0.033μF
CPDT*
1μF * OPTIONAL
** SHDN INTERNALLY
PULLED UP BY
THE LT1767-3.3
C3*
0.01μF
2954 F06
Figure 6. No μP Application
2954fb
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