LTC2952 Linear Technology, LTC2952 Datasheet - Page 18

• Manufacturer Part Number: LTC2952
• Description: Pushbutton PowerPath Controller
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2952
The timing diagram in Figure 8 shows the PB pin being
debounced and setting an internal ON/OFF signal. Note that
a high at the internal ON/OFF signal indicates that the last
event was a turn-on command and a low at the internal
ON/OFF signal indicates that the last event was a turn-off
command. Here specifically the turn-on command is a
result of a pushbutton on event and the turn-off command
is a result of a pushbutton off event.
Note that a complete pushbutton consists of a push event
and a release event. The push event (falling edge) on and
off debounce durations on the PB pin can be increased
beyond the fixed internal 26ms by placing a capacitor on
the ONT and OFFT pins respectively. The following equa-
tions describe the additional debounce time that a push
event at the PB pin must satisfy before it is recognized as
a valid pushbutton on or off.
C
ming capacitors respectively.
Note that during the push event of the pushbutton off, the
INT pin is asserted low after the initial 26ms debounce
18
ON/OFF SIGNAL
ONT
INTERNAL
OFFT CAP
ONT CAP
t
t
ONT
OFFT
INT
PB
and C
= C
= C
ONT
OFFT
OFFT
t
26ms
DB,ON
• (9.3MΩ)
‘TURN-ON’ EVENT
• (9.3MΩ)
are the ONT and OFFT external program-
VALID PB
t
ONT
26ms
t
DB
t
DB,OFF
26ms
‘TURN-OFF’ EVENT
INVALID PB
Figure 8. Pushbutton Debounce Timing Diagram
t
OFFT
26ms
t
DB
<t
26ms
DB,ON
PUSH EVENT
INVALID PB
t
DB,ON
duration. The INT pin asserts low when the PB pin is
held low during the OFFT debounce duration and during
the shutdown sequence. If the PB pin pulls high before
the OFFT time ends, the INT pin immediately turns high
impedance. On the other hand, if the PB pin is still held
low at the end of the OFFT time, the INT pin continues to
assert low throughout the ensuing shutdown sequence.
On a release event (rising edge) of the pushbutton switch
following a valid push event, the PB pin must be continu-
ously held above its rising threshold (0.8V) for a fixed
26ms internal debounce time.
In a typical application, the PB pin is connected to a
pushbutton switch. If the switch exhibits high leakage
current (>10μA), connecting an external pull-up resistor
to V1, V2 and/or VS (depending on the application) is
recommended. Furthermore, if the pushbutton switch is
physically located far from the LTC2952’s PB pin, signals
may couple onto the high impedance PB input. Placing
a 0.1μF capacitor from the PB pin to ground reduces the
impact of signal coupling. Additionally, parasitic series
inductance may cause undesirable ringing at the PB pin.
This can be minimized by placing a 5k resistor in series
and located next to the switch.
<t
ONT
t
26ms
DB,ON
t
ONT
RELEASE EVENT
INVALID PB
26ms
<t
DB
26ms
t
DB
<t
26ms
DB,OFF
<t
DB,OFF
PUSH EVENT
INVALID PB
t
DB,OFF
26ms
<t
OFFT
t
DB,OFF
26ms
t
OFFT
2952fa
2952 F08