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, The LTC2954 operates over a wide 2.7V to 26.4V a push button ON/OFF controller that manages system input voltage range to accommodate a wide variety power via a push button interface. An enable output of input power supplies. Very low quiescent current toggles system power while an interrupt output pro- (6A typical) makes the LTC2954 ideally suited for vides a debounced push button status. The interrupt battery powered applications. Two versions of the output can be used in menu driven applications to re- part are available to accommodate either positive or quest a system power down. A power kill input allows negative enable polarities. The inversion of /EN of a microprocessor or system to reset the enable out- the LTC2954-2 is found in the LTC2954-1 put, effectively powering down the system. Independ- Design files for this circuit board are available. ently adjustable On and Off timers allow dependable Call the LTC factory. push button control of the enable output and resis- tance to accidental toggling of system power. LTC is a trademark of Linear Technology Corporation QUICK START PROCEDURE Demonstration circuit 1090A is easy to set up to evalu- 2. Connect the input power supply of 2.7V to 26.4V ate the performance of the LTC2954-2: across VIN and GND or a 9V battery to the battery connector. 1. Place jumpers in the following positions: 3. Push and hold the push button once to turn on the JP1 CON green LED. CPD JP2 4. Push and hold again on the push button to turn off JP3 UNTIE the green LED. Figure 1. DC1090A Example Setup 1 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 By tying /KILL to /INT through JP3, /KILL is forced low pin to ground which in turn sets the /EN pin low. during the /INT blanking time and thus forces a turn Shorting /PB to ground a second time and holding off. subsequently resets the /EN pin high. The /EN pin is The RC (R and C ) at VIN on the DC1090A provides RPP RPP used to drive the gate of a P-channel MOSFET to con- a reverse polarity protection to the LTC2954-2. If trol the power path to a DC/DC converter. The turn on power is connected in an application such that the po- and off of the circuit is displayed with a green LED larities are ensured to be in the correct configuration, (D2). this RC may be removed from the circuit. The duration that /PB must be shorted to ground in An additional RC (R and C ), located at the /PB pin, F F order to turn on/off the DC/DC converter is independ- acts as a filter and used in an application where the ently programmed by two external capacitors C1 and switch is located far from the LTC2954-2. In such a C2 and selected on the DC1090A with jumper JP1 and case, the RC would be placed next to the switch rather JP2. than the part. If the switch is located near the An internal 500ms timer blanks (ignores) the /KILL LTC2954-2, then the RC may be removed from the signal during system power up. This allows sufficient circuit. time for the DC/DC converter and a P to perform An LDO (U2) is used on the DC1090 to provide a pull- power up tasks. During turn off, a power down timer up voltage of 2.6V which is well below the absolute provides a delay from interrupting the P (/INT=low) maximum on the /INT, /EN, and /KILL pins for the full to turning off the DC/DC converter (/EN=high). This range of input voltage of 2.7V to 26.4V. In an applica- delay gives the P time to perform power down and tion, pull these pins up to a voltage no higher than housekeeping tasks. On the DC1090A, JP1 selects the their rated absolute maximum shown in the data turn on timer, while JP2 is used to adjust the power sheet. (If the interface pins on the DC1090A are pulled down /PB duration. The red LED D1 shows the state up to an external supply higher than 5V, LEDs D1 and of the /INT pin. A P can turn off the converter with D2 should be removed.) no delay by asserting /KILL low. Table 1. DC1090A Typical Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Input Voltage V 2.7V to 26.4V IN V , /PB Turn On V - V OUT IN DS Output Voltage V , /PB Turn On 2.6V 2% 2P6V JP1 on OPEN 32ms /PB Turn On Time JP1 on CAP* 32 + 212ms JP2 on OPEN 32ms /PB Turn Power Down Time JP2 on CAP* 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: -4 C = 1.56 x 10 F/ms (t 1ms) ONT ONT -4 C = 1.56 x 10 F/ms (t 1ms) PDT PDT 2