Datasheet

LTC2955
16
2955f
mitigate the effect of the board leakage, a 10k resistor to
V
IN
is recommended (see Figure 12).
APPLICATIONS INFORMATION
Enhancing V
IN
Ruggedness
Placing a 1k resistor and a 10nF capacitor at the V
IN
pin
can be used to enhance ruggedness in some applications.
A 1k resistor in series with the V
IN
pin allows the LTC2955
to withstand reverse-input voltages. The LTC2955’s V
IN
pin
is internally clamped to one diode voltage below ground.
In battery operated applications where a battery could be
inserted improperly, this resistor will limit the current and
allow internal clamping to protect the pin.
Figure 12. External Pull-Up Resistor on PB Pin
Figure 13. Enhancing V
IN
Ruggedness
Figure 14. Using a Slide Switch to Prevent Accidental
Turn-On/Off
Figure 15. Using a Slide or Toggle Switch to Turn-On/Off
Adding a 10nF capacitor in addition to the 1k resistor can
protect against high voltage input transients that would
exceed the 40V Absolute Maximum Voltage rating of the
V
IN
pin. These could occur during hot-plugging into a
battery or AC adapter. This can also protect against tran-
sients that may appear on the PCB ground during large
ESD strikes at the PB pin.
The maximum operating current of the LTC2955 is less
than 3µA, creating an insignificant voltage drop across
the resistor. Using a capacitor value of 10nF provides
sufficient filtering for most applications and larger values
can actually diminish its effectiveness.
Applications with Slide Switch
In some applications, to prevent accidental toggling of the
system power, a slide switch is preferred over a pushbut-
ton. Figure 14 shows a slide switch added in series with
the pushbutton. The user can slide the switch open to
activate the HOLD/LOCK function, where the pushbutton
is disabled. Figure 15 shows a slide switch connected to
the LTC2955 ON pin resistive divider. If the user slides
the switch to the ON position, the LTC2955 ON pin is high
*OPTIONAL
PB
INT
KILL
ON
V
IN
LTC2955TS8-1
GND TMR
C
ONT*
0.033µF
EN
C4
10nF
R8
1k
9V
BATTERY
2955 F13
µP
R1
10k
KILL
INT
V
IN
V
OUT
LT3060
SHDN
+
PINS OMITTED
FOR CLARITY
EXTERNAL BOARD
LEAKAGE CURRENT
R7
10k
IF EXTERNAL PARASITIC BOARD
LEAKAGE >2µA USE EXTERNAL
PULL-UP RESISTOR
PB
V
IN
V
IN
900k
V
LDO
LTC2955-1/
LTC2955-2
GND
0.8V
>2µA
2955 F12
NORMAL
HOLD/LOCK
PB
V
IN
V
IN
ON
SEL
LTC2955DDB-1
GND
EN
2955 F14
PB
V
IN
V
IN
SEL
ON
LTC2955DDB-1
GND
OFF
ON
EN
2955 F15