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LTC2950CTS8-2-TRPBF Datasheet(PDF) 9 Page - Linear Technology |
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LTC2950CTS8-2-TRPBF Datasheet(HTML) 9 Page - Linear Technology |
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9 / 16 page  LTC2950-1/LTC2950-2 9 295012fb APPLICATIONS INFORMATION Description The LTC2950 is a low power (6μA), wide input voltage range (2.7Vto26.4V),pushbuttonon/offcontrollerthatcaninterface toaμPandapowersupply.Theturn-onandturn-offdebounce times are extendable using optional external capacitors. A simple interface (INT output, KILL input) allows a system to power on and power off in a controlled manner. Turn On When power is first applied to the LTC2950, the part ini- tializes the output pins. Any DC/DC converters connected to the EN/EN pin will therefore be held off. To assert the enable output, PB must be held low for a minimum of 32ms (tDB, ON). The LTC2950 provides additional turn on debounce time via an optional capacitor connected to the ONT pin (tONT). The following equation describes the ad- ditional time that PB must be held low before asserting the enable output. CONT is the ONT external capacitor: CONT = 1.56E-4 [μF/ms] • (tONT – 1ms) Once the enable output is asserted, any DC/DC converters connected to this pin are turned on. The KILL input from the μPisignoredduringasucceeding512msblankingtime(tKILL, ON BLANK). This blanking time represents the maximum time required to power up the DC/DC converter and the μP. If KILL is not brought high during this 512ms time window, the enable output is released. The assumption is that 512ms is sufficient time for the system to power up. Turn Off To initiate a power off sequence, PB must be held low for a minimum of 32ms (tDB, OFF). Additional turn off debounce time may be added via an optional capacitor connected to the OFFT pin (tOFFT). The following equation describes the additional time that PB must be held low to initiate a power off sequence. COFFT is the OFFT external capacitor: COFFT = 1.56E-4 [μF/ms] • (tOFFT – 1ms) Once PB has been validly pressed, INT is switched low. This alerts the μP to perform its power down and housekeeping tasks. The power down time given to the μP is 1024ms. NotethattheKILLinputcanbepulledlow(therebyreleasingthe enable output) at any time after tKILL, ON BLANK period. Simplified Power On/Off Sequence Figure 1 shows a simplified LTC2950-1 power on and power off sequence. A high to low transition on PB (t1) initiates the power on sequence. This diagram does not show any bounce on PB. In order to assert the enable output, the PB pin must stay low continuously (PB high resets timers) for a time controlled by the default 32ms and the external ONT capacitor (t2–t1). Once EN goes high (t2), an internal 512ms blanking timer is started. This blanking timer is designed to give sufficient time for the DC/DC converter to reach its final voltage, and to allow the μP enough time to perform power on tasks. The KILL pin must be pulled high within 512ms of the EN pin going high. Failure to do so results in the EN pin going low 512ms after it went high. (EN = low, see Figure 2). Note that the LTC2950 does not sample KILL and PB until after the 512ms internal timer has expired. The rea- son PB is ignored is to ensure that the system is not forced off while powering on. Once the 512ms timer expires (t4), the release of the PB pin is then debounced with an internal 32ms timer. The system has now properly powered on and the LTC2950 monitors PB and KILL (for a turnoff command) while consuming only 6μA of supply current. A high to low transition on PB (t5) initiates the power off sequence. PB must stay low continuously (PB high resets debounce timer) for a period controlled by the default 32ms and the external OFFT capacitor (t6–t5). At the completion of the OFFT timing (t6), an interrupt (INT) is set, signifying that EN will be switched low in 1024ms. Once a system has finished performing its power down operations, it can set KILL low (t7) and thus immediately set EN low), terminating the internal 1024ms timer. The release of the PB pin is then debounced with an internal 32ms timer. The system is now in its reset state: where the LTC2950 is in low power mode (6μA). PB is monitored for a high to low transition. |
Similar Part No. - LTC2950CTS8-2-TRPBF |
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Similar Description - LTC2950CTS8-2-TRPBF |
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