DEMO MANUAL DC826C-A/DC826C-B LTC2950-2/LTC2951-2 Pushbutton On/Off Controller DESCRIPTION Demonstration circuits 826C-A and 826C-B feature the times. JP3 ties and unties KILL to INT for immediate or LTC 2950-2 and the LTC2951-2 respectively, which are delayed turn off. The INT status is shown with a red LED. low power, wide input voltage range, pushbutton on/off DC826C-A/DC826C-B accepts an input voltage range of controllers. A pushbutton switch shorts the PB pin to 2.7V to 26.4V or a 9V battery for portable demonstration ground which in turn sets the EN pin low (see Note1). and evaluation. Shorting PB to ground a second time subsequently resets Note 1: The inversion of EN of the LTC2950-2/LTC2951-2 the EN pin high. The EN pin is used to connect to a DC/ is found in the LTC2950-1/LTC2951-1. Table 1 provides DC converter shutdown to control the turn on and off of an IC selection guide. the circuit, simulated with a green LED on the DC826C-A/ Design files for this circuit board are available at DC826C-B. DEMO MANUAL DC826C-A/DC826C-B QUICK START PROCEDURE Demonstration circuit 826C-A/826C-B is easy to set up to 2. Connect the input power supply of 2.7V to 26.4V across evaluate the performance of the LTC2950-2/LTC2951-2: V and GND or a 9V battery to the battery connector. IN 1. Place jumpers in the following positions: 3. Push and hold the pushbutton once to turn on the green LED. JP1: 0.033F 4. Push and hold the pushbutton again to turn off the JP2: 0.033F green LED. JP3: UNTIE OPERATING PRINCIPLES The duration that PB must be shorted to ground in order The RC (R and C ) at V on the DC826 provides RPP RPP IN to turn on/off the DC/DC converter is independently pro- reverse polarity protection to the LTC2950-2/LTC2951-2. If grammed (LTC2950-2) by two external capacitors C1 and power is connected in an application such that the polari- C2 and selected on the DC826C-A with jumper JP1 and ties are ensured to be in the correct configuration, this RC JP2. The status of the EN pin, and simulation of the turn may be removed from the circuit. on/off of a DC/DC converter, is displayed with green LED An additional RC (RF and CF), located at the PB pin, acts D2 on the board. as a filter and is used in an application where the switch Figure 1 shows how the EN is connected to the SHDN pin is located far from the LTC2950-2/LTC2951-2. In such a of a DC/DC converter and how INT and KILL interfaces with case, the RC would be placed next to the switch rather a P or C. An internal 500ms timer blanks (ignores) the than the part. If the switch is located near the LTC2950-2/ KILL signal during system power up. This allows sufficient LTC2951-2, then the RC may be removed from the circuit. time for the DC/DC converter and a P to perform power An LDO (U2) is used on the DC826 to provide a pull-up up tasks. During turn off, a power down timer provides voltage of 2.6V which is well below the absolute maximum a delay (LTC2950-2: 1000ms, LTC2951-2: adjustable) on the INT, EN, and KILL pins for the full range of input from interrupting the P (INT = low) to turning off the DC/ voltage of 2.7V to 26.4V. In an application, pull these DC converter (EN = high). This delay gives the P time pins up to a voltage no higher than their rated absolute to perform power down and housekeeping tasks. On the maximum shown in the data sheet. Optional Zener diodes DC826C-B, JP1 selects the power down timer, while JP2 (D3 D5) can be used if the pull-up voltage exceeds the is used to adjust the turn off PB duration. The red LED rated absolute maximum. (If the interface pins on the D1 shows the state of the INT pin. A P can turn off the DC826C-A /DC826C-B will be pulled up to an external converter with no delay by asserting KILL low. By tying supply, LEDs D1 and D2 should be removed.) KILL to INT through JP3, KILL is forced low during the INT blanking time and thus forces a turn off. dc826cf 2