Linear Technology DC 1090A User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1090A

PUSH BUTTON ON/OFF CONTROLLER WITH MICROPROCESSOR INTERRUPT

LTC2954-2

DESCRIPTION

Demonstration Circuit 1090A features the LTC2954-2,

a push button ON/OFF controller that manages system

power via a push button interface. An enable output

toggles system power while an interrupt output pro-

vides a debounced push button status. The interrupt

output can be used in menu driven applications to re-

quest a system power down. A power kill input allows

a microprocessor or system to reset the enable out-

put, effectively powering down the system. Independ-

ently adjustable On and Off timers allow dependable

push button control of the enable output and resis-

tance to accidental toggling of system power.

The LTC2954 operates over a wide 2.7V to 26.4V

input voltage range to accommodate a wide variety

of input power supplies. Very low quiescent current

(6µA typical) makes the LTC2954 ideally suited for

battery powered applications. Two versions of the

part are available to accommodate either positive or

negative enable polarities. The inversion of /EN of

the LTC2954-2 is found in the LTC2954-1

Design files for this circuit board are available.

Call the LTC factory

LTC is a trademark of Linear Technology Corporation

QUICK START PROCEDURE

Demonstration circuit 1090A is easy to set up to evalu-

ate the performance of the LTC2954-2:

Place jumpers in the following positions:

CON

CPD

UNTIE

Connect the input power supply of 2.7V to 26.4V

across VIN and GND or a 9V battery to the battery

connector.

Push and hold the push button once to turn on the

green LED.

Push and hold again on the push button to turn off

the green LED.

Figure 1.

DC1090A Example Setup

JP1

JP2

JP3

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1090A

PUSH BUTTON ON/OFF CONTROLLER WITH MICROPROCESSOR INTERRUPT

OPERATING PRINCIPLES

On the DC1090A, a push button switch shorts the /PB

pin to ground which in turn sets the /EN pin low.

Shorting /PB to ground a second time and holding

subsequently resets the /EN pin high. The /EN pin is

used to drive the gate of a P-channel MOSFET to con-

trol the power path to a DC/DC converter. The turn on

and off of the circuit is displayed with a green LED

(D2).

The duration that /PB must be shorted to ground in

order to turn on/off the DC/DC converter is independ-

ently programmed by two external capacitors C1 and

C2 and selected on the DC1090A with jumper JP1 and

JP2.

An internal 500ms timer blanks (ignores) the /KILL

signal during system power up. This allows sufficient

time for the DC/DC converter and a µP to perform

power up tasks. During turn off, a power down timer

provides a delay from interrupting the µP (/INT=low)

to turning off the DC/DC converter (/EN=high). This

delay gives the µP time to perform power down and

housekeeping tasks. On the DC1090A, JP1 selects the

turn on timer, while JP2 is used to adjust the power

down /PB duration. The red LED D1 shows the state

of the /INT pin. A µP can turn off the converter with

no delay by asserting /KILL low.

By tying /KILL to /INT through JP3, /KILL is forced low

during the /INT blanking time and thus forces a turn

off.

The RC (R

RPP

and C

RPP

) at VIN on the DC1090A provides

a reverse polarity protection to the LTC2954-2. If

power is connected in an application such that the po-

larities are ensured to be in the correct configuration,

this RC may be removed from the circuit.

An additional RC (R

and C

), located at the /PB pin,

acts as a filter and used in an application where the

switch is located far from the LTC2954-2. In such a

case, the RC would be placed next to the switch rather

than the part. If the switch is located near the

LTC2954-2, then the RC may be removed from the

circuit.

An LDO (U2) is used on the DC1090 to provide a pull-

up voltage of 2.6V which is well below the absolute

maximum on the /INT, /EN, and /KILL pins for the full

range of input voltage of 2.7V to 26.4V. In an applica-

tion, pull these pins up to a voltage no higher than

their rated absolute maximum shown in the data

sheet. (If the interface pins on the DC1090A are pulled

up to an external supply higher than 5V, LEDs D1 and

D2 should be removed.)

Table 1.

DC1090A Typical Performance Summary (T

= 25°C)

PARAMETER CONDITION VALUE

Input Voltage V

2.7V to 26.4V

Output Voltage V

OUT

, /PB Turn On

2P6V

, /PB Turn On

- V

2.6V ± 2%

/PB Turn On Time JP1 on OPEN

JP1 on CAP*

32ms

32 + 212ms

/PB Turn Power Down Time JP2 on OPEN

JP2 on CAP*

32ms

32 + 3014ms

*The additional Cap. Adjust time is selected by an external capacitor. The DC1090A adjust times have been pre-selected with 0.033uF at ONT and 0.47uF at CPD to provide

additional 212ms and 3014ms turn on and turn power down time respectively. The additional time is calculated with the following equations as shown in the LTC2954 data

sheet:

ONT

= 1.56 x 10

-4

[µF/ms] • (t

ONT

– 1ms)

PDT

= 1.56 x 10

-4

[µF/ms] • (t

PDT

– 1ms)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1090A

PUSH BUTTON ON/OFF CONTROLLER WITH MICROPROCESSOR INTERRUPT

Figure 2.

Push Button Turn On/Off with ONT and PDT Open (time scale at 10ms/div)

Figure 3.

Push Button Turn On/Off with Capacitors on ONT and PDT

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1090A

PUSH BUTTON ON/OFF CONTROLLER WITH MICROPROCESSOR INTERRUPT

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Authorized Distributor

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DC1090A

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