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LTC2952

2952f

APPLICATIONS INFORMATION

The timing diagram in Figure 8 shows the

⎯P⎯B 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 commmand is a

result of a push-button on event and the turn-off command

is a result of a push-button off event.

Note that a complete push-button consists of a push event

and a release event. The push event (falling edge) on and

off debounce durations on the

⎯P⎯B 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

⎯P⎯B pin must satisfy before it is recognized as

a valid push-button on or off.

tONT = CONT • (9.3MΩ)

tOFFT = COFFT • (9.3MΩ)

CONT and COFFT are the ONT and OFFT external program-

ming capacitors respectively.

Note that during the push event of the push-button off,

the

⎯I⎯N⎯T pin is asserted low after the initial 26ms debounce

duration. The

⎯I⎯N⎯T pin asserts low when the ⎯P⎯B pin is held

low during the OFFT debounce duration and during the

shutdown sequence. If the

⎯P⎯B pin pulls high before the

OFFT time ends, the

⎯I⎯N⎯Tpinimmediatelyturnshighimped-

ance. On the other hand, if the

⎯P⎯B pin is still held low at

the end of the OFFT time, the

⎯I⎯N⎯T pin continues to assert

low throughout the ensuing shutdown sequence.

On a release event (rising edge) of the push-button switch

following a valid push event, the

⎯P⎯B pin must be continu-

ously held above its rising threshold (0.8V) for a ﬁxed

26ms internal debounce time.

In a typical application, the

⎯P⎯B pin is connected to a

push-button 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 push-button switch is

physically located far from the LTC2952’s

⎯P⎯B pin, signals

may couple onto the high impedance

⎯P⎯B input. Placing

a 0.1µF capacitor from the

⎯P⎯B pin to ground reduces the

impact of signal coupling. Additionally, parasitic series

inductance may cause undesirable ringing at the

⎯P⎯B pin.

This can be minimized by placing a 5k

Ω resistor in series

and located next to the switch.

Accurate Comparator Input Pins

VM, PFI,

⎯K⎯I⎯L⎯L, M1 and M2

VM, PFI,

⎯K⎯I⎯L⎯L, M1 and M2 are high impedance input pins

to accurate comparators with a falling threshold of 0.500V.

Figure 8. Push-Button Debounce Timing Diagram

Figure 9. Setting the Comparator Trip Point

0.5V

VTRIP

2952 F09

–

2952 F08

ONT CAP

OFFT CAP

INTERNAL

ON/OFF SIGNAL

tOFFT

tONT

<tONT

tONT

tDB,OFF

26ms

<tOFFT

tDB,OFF

26ms

tDB,ON

26ms

tDB,ON

26ms

tDB,ON

26ms

tDB,OFF

26ms

<tDB,ON

26ms

<tDB,OFF

26ms

<tDB,OFF

26ms

tDB

26ms

tDB

26ms

tDB

26ms

<tDB

26ms

INVALID PB

PUSH EVENT

INVALID PB

‘TURN-OFF’ EVENT

VALID PB

‘TURN-ON’ EVENT

INVALID PB

PUSH EVENT

INVALID PB

RELEASE EVENT

INT

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