LTC2951

LTC2951 Push Button On/Off Controller FEATURES ■ ■ ■ ■ DESCRIPTIO ■ ■ ■ ■ ■ ■ Adjustable Push Button Debounce and Delay Timers Low Supply Current: 6µA Wide Operating Voltage Range: 2.7V to 26V EN Output (LTC2951-1) Allows DC/DC Converter Control ⎯E⎯N Output (LTC2951-2) Allows Circuit Breaker Control Simple Interface Allows Graceful µP Shut Down High Input Voltage ⎯P⎯B Pin with Internal Pull Up Resistor ±10kV ESD HBM on ⎯P⎯B Input Accurate 0.6V Threshold on ⎯K⎯I⎯L⎯L Comparator Input 8-Pin 3mm × 2mm DFN and ThinSOTTM Packages The LTC®2951 is a micropower, wide input voltage range push button ON/OFF controller. The part contains a push button input which controls the toggling of an open drain enable output. The push button turn OFF debounce time is externally programmable, while the turn ON debounce time is fixed at 128ms. A simple microprocessor interface allows for proper system housekeeping prior to power down. Under system fault conditions, an adjustable ⎯K⎯I⎯L⎯L timeout delay ensures proper power down. The LTC2951 operates over a 2.7V to 26V input voltage range to accommodate a variety of input power supplies. Very low quiescent current (6µA typical) makes the LTC2951 ideally suited for battery powered applications. Two versions of the part are available to accommodate either positive or negative enable polarities. The parts are available in 8-pin 3mm × 2mm DFN and ThinSOT packages. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. APPLICATIO S ■ ■ ■ ■ Portable Instrumentation Meters Blade Servers Portable Customer Service PDA Desktop and Notebook Computers TYPICAL APPLICATIO VIN 3V – 26V VIN VOUT DC/DC BUCK SHDN EN VIN LTC2951-1 PB GND KILLT CKILLT* 0.033µF EN INT KILL OFFT 2951 TA01 R1 10k INT KILL µP/µC 2V/DIV 128ms PB COFFT* 0.033µF *OPTIONAL U Turn On Debounce 25ms/DIV 2951 TA01b U U 2951f 1 LTC2951 ABSOLUTE (Note 1) AXI U RATI GS Operating Temperature Range LTC2951C-1 .............................................. 0°C to 70°C LTC2951C-2 .............................................. 0°C to 70°C LTC2951I-1 .......................................... – 40°C to 85°C LTC2951I-2 .......................................... – 40°C to 85°C Storage Temperature Range DFN Package..................................... – 65°C to 125°C TSOT-23............................................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C Supply Voltage (VIN) ..................................– 0.3V to 33V Input Voltages ⎯P⎯B ............................................................– 6V to 33V KILLT ....................................................– 0.3V to 2.7V OFFT .....................................................– 0.3V to 2.7V ⎯K⎯I⎯L⎯L .........................................................– 0.3V to 7V Output Voltages ⎯I⎯N⎯T .........................................................– 0.3V to 10V EN/⎯E⎯N ....................................................– 0.3V to 10V PACKAGE/ORDER I FOR ATIO TOP VIEW GND 1 KILLT 2 PB 3 VIN 4 9 8 7 6 5 INT EN/EN OFFT KILL DDB8 PACKAGE 8-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 165°C/W EXPOSED PAD (PIN 9) UNCONNECTED ORDER PART NUMBER LTC2951CDDB-1 LTC2951CDDB-2 LTC2951IDDB-1 LTC2951IDDB-2 DDB PART* MARKING LBTB LBTD LBTB LBTD Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. ELECTRICAL CHARACTERISTICS SYMBOL VIN IIN VUVL VUVL(HYST) PARAMETER Supply Voltage Range VIN Supply Current VIN Undervoltage Lockout VIN Undervoltage Lockout Hysteresis The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 2.7V to 26.4V, unless otherwise noted. (Note 2) CONDITIONS Steady State Operation System Power On VIN Falling ● ● ● ● 2 U U W WW U W TOP VIEW VIN 1 PB 2 KILLT 3 GND 4 8 KILL 7 OFFT 6 EN/EN 5 INT TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125°C, θJA = 140°C/W ORDER PART NUMBER LTC2951CTS8-1 LTC2951CTS8-2 LTC2951ITS8-1 LTC2951ITS8-2 TS8 PART* MARKING LTBTC LTBTF LTBTC LTBTF MIN 2.7 2.2 50 TYP 6 2.3 300 MAX 26.4 12 2.4 600 UNITS V µA V mV 2951f LTC2951 ELECTRICAL CHARACTERISTICS SYMBOL Push Button Pin (⎯P⎯B) V⎯P⎯B(MIN, MAX) I⎯P⎯B ⎯P⎯B Voltage Range ⎯P⎯B Input Current Single-Ended 2.5V < V⎯P⎯B < 26.4V V⎯P⎯B = 1V V⎯P⎯B = 0.6V ⎯P⎯B Falling I⎯P⎯B = – 1µA VKILLT, OFFT = 0V VKILLT, OFFT = 1.3V ⎯P⎯B Falling → Enable Asserted OFFT Pin Float, ⎯P⎯B Falling → ⎯I⎯N⎯T Falling ● ● ● ● ● ● The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 2.7V to 26.4V, unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN –1 –1 –3 0.6 1 –2.4 2.4 100 26 9 –6 –9 0.8 1.6 –3 3 128 32 11.5 TYP MAX 26.4 ±1 –12 –15 1 2 –3.6 3.6 163 41 13.5 ±1 0.11 0.57 10 30 30 400 100 9 200 512 128 11.5 256 0.11 650 163 13.5 325 ±0.1 0.4 0.6 30 0.4 0.63 50 ±0.1 UNITS V µA µA µA V V µA µA ms ms ms µA V V mV µA µs µs ms ms ms ms µA V V⎯P⎯B(VTH) V⎯P⎯B(VOC) IKILLT, OFFT(PU) IKILLT, OFFT(PD) tDB, ON tDB, OFF tOFFT I⎯I⎯N⎯T(LKG) V⎯I⎯N⎯T(VOL) V⎯K⎯I⎯L⎯L(TH) V⎯K⎯I⎯L⎯L(HYST) I⎯K⎯I⎯L⎯L(LKG) t ⎯K⎯I⎯L⎯L(PW) t ⎯K⎯I⎯L⎯L(PD) t ⎯K⎯I⎯L⎯L, ON BLANK t ⎯K⎯I⎯L⎯L, OFF DELAY t ⎯K⎯I⎯L⎯L, OFF DELAY, ADDITIONAL ⎯P⎯B Input Threshold ⎯P⎯B Open Circuit Voltage KILLT/OFFT Pull Up Current KILLT/OFFT Pull Down Current Turn On Debounce Time Internal Turn Off Debounce Time Timing Pins (KILLT, OFFT) ● ● ● ● ● Additional Adjustable Turn Off Time COFFT = 1500pF ⎯I⎯N⎯T Leakage Current ⎯I⎯N⎯T Output Voltage Low ⎯K⎯I⎯L⎯L Input Threshold Voltage ⎯K⎯I⎯L⎯L Input Threshold Hysteresis ⎯K⎯I⎯L⎯L Leakage Current ⎯K⎯I⎯L⎯L Minimum Pulse Width ⎯K⎯I⎯L⎯L Propagation Delay ⎯K⎯I⎯L⎯L Turn On Blanking (Note 3) Internal ⎯K⎯I⎯L⎯L Turn Off Delay (Note 4) ⎯K⎯I⎯L⎯L Falling → Enable Released ⎯K⎯I⎯L⎯L = Low, Enable Asserted → Enable Released KILLT Pin Float, ⎯K⎯I⎯L⎯L = High, ⎯I⎯N⎯T Asserted → Enable Released V ⎯K⎯I⎯L⎯L = 0.6V V⎯ I⎯N⎯T = 3V I⎯ I⎯N⎯T = 3mA ⎯K⎯I⎯L⎯L Falling µP Handshake Pins (⎯I⎯N⎯T, ⎯K⎯I⎯L⎯L) ● ● ● ● ● ● ● ● ● ● ● ● ● Additional Adjustable ⎯K⎯I⎯L⎯L Turn Off CKILLT = 1500pF Delay (Note 4) EN/⎯E⎯N Lock Out Time (Note 5) EN/⎯E⎯N Leakage Current EN/⎯E⎯N Voltage Output Low Enable Released → Enable Asserted VEN/ ⎯E⎯N = 1V, Sink Current Off IEN/ ⎯E⎯N = 3mA tEN/⎯E⎯N, Lock Out IEN/⎯E⎯N(LKG) VEN/⎯E⎯N(VOL) Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All currents into pins are positive; all voltages are referenced to GND unless otherwise noted. Note 3: The ⎯K⎯I⎯L⎯L turn on blanking timer period is the waiting period immediately after the enable output is asserted. This blanking time allows sufficient time for the DC/DC converter and the µP to perform power up tasks. The ⎯K⎯I⎯L⎯L and ⎯P⎯B inputs are ignored during this period. If ⎯K⎯I⎯L⎯L remains low at the end of this time period, the enable output is released, thus turning off system power. This time delay does not include tDB, ON. Note 4: The internal ⎯K⎯I⎯L⎯L turn off delay (t⎯K⎯I⎯L⎯L, OFF DELAY) is the default delay from the initiation of a power off sequence (⎯I⎯N⎯T falling, ⎯K⎯I⎯L⎯L = high), to the release of the enable output. The additional, adjustable ⎯K⎯I⎯L⎯L turn off delay (t⎯K⎯I⎯L⎯L, OFF DELAY, ADDITIONAL) uses an optional external capacitor (CKILLT) to provide extra delay from ⎯I⎯N⎯T falling to the release of the enable output. If the ⎯K⎯I⎯L⎯L input switches low at any time during ⎯K⎯I⎯L⎯L turn off delay, enable is released, thus turning off system power. Note 5: The enable lock out time is designed to allow an application to properly power down such that the next power up sequence starts from a consistent powered down configuration. ⎯P⎯B is ignored during this lock out time. This time delay does not include tDB, ON. 2951f 3 LTC2951 TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Temperature 10 VIN = 26.4V 8 VIN = 3.3V VIN = 2.7V 4 IVIN (µA) 8 10 IVIN (µA) 6 6 tDB, ON (ms) 2 0 –50 –25 0 25 50 TEMPERATURE (°C) 50 Internal Default Turn Off Debounce Time (tDB, OFF) vs VIN TA = 25°C 10000 40 tDB, OFF + tOFFT (ms) tDB, OFF (ms) 1000 OFFT PULL-DOWN CURRENT (µA) 30 20 10 0 0 5 10 15 VIN (V) 20 25 30 2951 G06 tKILL, OFF DELAY + tKILL, OFF DELAY, ADDITIONAL (ms) Internal Default ⎯K⎯I⎯L⎯L Turn Off Delay (t⎯K⎯I⎯L⎯L, OFF DELAY) vs VIN 200 TA = 25°C 160 tKILL, OFF DELAY (ms) KILLT PULL-DOWN CURRENT (µA) 120 80 40 0 0 5 10 15 VIN (V) 20 4 UW 75 100 2951 G01 Supply Current vs Supply Voltage TA = 25°C 200 Turn On Debounce Time (tDB, ON) vs VIN TA = 25°C 160 120 4 80 2 40 0 0 5 10 15 VIN (V) 20 25 30 2951 G02 0 0 5 10 15 VIN (V) 20 25 30 2951 G14 Turn Off Debounce Time (tDB, OFF + tOFFT) vs OFFT External Capacitor TA = 25°C VIN = 3.3V –3.4 OFFT Pull-Down Current vs Temperature –3.2 VIN = 26.4V –3.0 VIN = 2.7V –2.8 100 10 1 100 10 OFFT EXTERNAL CAPACITOR (nF) 1000 2951 G07 –2.6 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 2951 G08 ⎯K⎯I⎯L⎯L Turn Off Delay vs KILLT External Capacitor 10000 –3.4 KILLT Pull-Down Current vs Temperature –3.2 VIN = 26.4V –3.0 VIN = 2.7V –2.8 1000 100 25 30 2951 G03 10 1 100 10 KILLT EXTERNAL CAPACITOR (nF) 1000 2951 G04 –2.6 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 2951 G05 2951f LTC2951 TYPICAL PERFOR A CE CHARACTERISTICS ⎯PB Current vs ⎯P⎯B Voltage ⎯ –250 TA = 25°C VIN = 3.3V 300 VIN = 3.3V 250 PB VOLTAGE (mV) 200 150 100 50 0 –5 0 5 10 15 PB VOLTAGE (V) 20 25 30 0 5 10 15 20 EXTERNAL PB RESISTANCE TO GROUND (kΩ) 2951 G10 –200 PB CURRENT (µA) –150 –100 –50 0 –10 500 ⎯ EN/E⎯N VOL vs Current Load TA = 25°C VIN = 3.3V 400 EN/EN VOLTAGE (mV) EN (V) EN (V) 300 200 100 0 0 2 6 8 4 EN/EN CURRENT LOAD (mA) 10 2951 G11 UW ⎯P⎯B Voltage vs External ⎯P⎯B Resistance to Ground TA = 100°C TA = 25°C TA = –45°C 2951 G09 1.0 EN (LTC2951-1) Voltage vs VIN TA = 25°C 100k PULL-UP FROM EN TO VIN 4 ⎯E⎯N (LTC2951-2) Voltage vs VIN TA = 25°C 100k PULL-UP FROM EN TO VIN 0.8 3 0.6 2 0.4 1 0.2 0 0 0 1 2 VIN (V) 2951 G12 3 4 0 1 2 VIN (V) 3 4 2951 G13 2951f 5 LTC2951 PI FU CTIO S VIN (Pin 1/Pin 4): Power Supply Input: 2.7V to 26.4V. ⎯P⎯B (Pin 2/Pin 3): Push Button Input. Connecting PB to ⎯⎯ ground through a momentary switch provides on/off control via the EN/⎯E⎯N pin. An internal 100k pull-up resistor connects to an internal 1.9V bias voltage. The rugged ⎯P⎯B input can be pulled up to 26.4V externally without consuming extra current. KILLT (Pin 3/Pin 2): Additional, Adjustable ⎯K⎯I⎯L⎯L Turn Off Delay Input (t⎯K⎯I⎯L⎯L, OFF DELAY, ADDITIONAL). A capacitor to ground provides additional delay time (beyond the internal default 128ms, t⎯K⎯I⎯L⎯L, OFF DELAY) from ⎯I⎯N⎯T falling to the automatic release of the enable output. The ⎯K⎯I⎯L⎯L turn off delay feature ensures the release of the enable pin under system fault conditions, such as the µP not responding to the LTC2951 interrupt signal (⎯I⎯N⎯T low). GND (Pin 4/Pin 1): Device Ground. ⎯I⎯N⎯T (Pin 5/Pin 8): Open Drain Interrupt Output. After a push button turn-off event is detected (tDB, OFF + tOFFT), the LTC2951 interrupts the system (µP) by bringing the ⎯I⎯N⎯T pin low. Once the system finishes its power down and housekeeping tasks, it sets ⎯K⎯I⎯L⎯L low, which in turn releases the enable output. If at the end of the power down timer period (t⎯K⎯I⎯L⎯L, OFF DELAY + t⎯K⎯I⎯L⎯L, OFF DELAY, ADDITIONAL) ⎯K⎯I⎯L⎯L is still high, the enable output is released immediately. ⎯I⎯N⎯T may optionally be tied to ⎯K⎯I⎯L⎯L to release the enable output immediately after the turn-off event has been detected (⎯I⎯N⎯T low). EN (LTC2951-1, Pin 6/Pin 7): Open Drain Enable Output. This pin is intended to enable system power. EN goes high 6 U U U (TSOT-23/DFN) after a valid ⎯P⎯B turn on event (tDB, ON). EN goes low if: a) ⎯KI⎯L⎯L is not driven high within 512ms of the initial valid ⎯P⎯B ⎯ power turn-on event, b) ⎯K⎯I⎯L⎯L is driven low during normal operation, or c) a second valid ⎯P⎯B event (power turn-off) is detected. The operating range for this pin is 0V to 10V. A 100k pull-up is recommended if not available in the DC/DC converter. ⎯E⎯N (LTC2951-2, Pin 6/Pin 7): Open Drain Enable Output. This pin is intended to enable system power. ⎯E⎯N is asserted low after a valid ⎯P⎯B turn-on event (tDB, ON). ⎯E⎯N releases high if: a) ⎯K⎯I⎯L⎯L is not driven high within 512ms of the initial valid ⎯P⎯B power turn-on event, b) ⎯K⎯I⎯L⎯L is driven low during normal operation, or c) a second valid ⎯P⎯B event (power turn-off) is detected. The operating range of this pin is 0V to 10V. A 100k pull-up is recommended if not available in the DC/DC converter. OFFT (Pin 7/Pin 6): Additional Adjustable Turn Off Time Input (tOFFT). A capacitor to ground determines the additional time (beyond the internal default 32ms, tDB, OFF) that the ⎯P⎯B pin must be held low before initiating a power down sequence (⎯I⎯N⎯T falling). Floating this pin results in a default turn off debounce time of 32ms. ⎯KI⎯L⎯L (Pin 8/Pin 5): ⎯K⎯I⎯L⎯L Input. Forcing ⎯K⎯I⎯L⎯L low releases ⎯ the enable output. During system turn on, this pin is blanked by a 512ms internal timer (t⎯K⎯I⎯L⎯L, ON BLANK) to allow the system to pull ⎯K⎯I⎯L⎯L high. This pin has an accurate 0.6V threshold and can be used as a voltage monitor input. Exposed Pad (Pin 9): Exposed Pad may be left open or connected to device ground. 2951f LTC2951 BLOCK DIAGRA W EN/EN VIN 2.7V TO 26.4V 2.4V REGULATOR 2.4V OSCILLATOR 100k PB DEBOUNCE 0.8V OSCILLATOR INT LOGIC 0.6V KILL 2951 BD GND KILLT OFFT TI I G DIAGRA S tKILL(PW) KILL W UW tKILL(PD) EN/EN 2951 TD01 2951f 7 LTC2951 TI I G DIAGRA S PB tDB, ON PB & KILL IGNORED tKILL, ON BLANK EN (LTC2951-1) EN (LTC2951-2) 2951 TD03 8 W UW EN (LTC2951-1) EN (LTC2951-2) 2951 TD02 Power On Timing PB tDB, OFF tOFFT PB IGNORED OFFT 16 CYCLES INT tKILL, OFF DELAY tKILL, OFF DELAY, ADDITIONAL KILLT 16 CYCLES Power Off Timing, ⎯K⎯I⎯L⎯L > 0.6V 2951f LTC2951 APPLICATIO S I FOR ATIO Description The LTC2951 is a low power (6µA), wide input voltage range (2.7V to 26.4V), push button On/Off controller that can interface to a µP and a power supply. The part incorporates all the flexible timing needed to debounce the push button input (⎯P⎯B). The LTC2951 also provides a simple interface (⎯I⎯N⎯T output, ⎯K⎯I⎯L⎯L input) to allow a system to power on and power off in a controlled manner. The wide input voltage range allows a system designer to operate from single cell to multi-cell battery stacks. Very low quiescent current makes the LTC2951 ideal for continuously monitoring the On/Off push button of a handheld device. Turn On When power is first applied to the LTC2951, the part initializes the output pins. Any DC/DC converters connected to the EN/⎯E⎯N pin will therefore be off. To assert the enable output, ⎯P⎯B must be held low for a minimum of 128ms (tDB, ON). Once the enable output is asserted, any DC/DC converters connected to this pin are turned on. The ⎯K⎯I⎯L⎯L input from the µP is ignored during the succeeding 512ms blanking time (t ⎯K⎯I⎯L⎯L, ON BLANK). This blanking time represents the maximum time required to power up the DC/DC converter and the µP. If ⎯K⎯I⎯L⎯L 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, ⎯P⎯B 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 ⎯P⎯B 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 ⎯P⎯B has been validly pressed, ⎯I⎯N⎯T is switched low. This alerts the µP to perform its power down and housekeeping tasks. U ⎯KI⎯L⎯L Turn Off Delay ⎯ The LTC2951 provides a failsafe feature that allows the user to turn off system power (via ⎯P⎯B) under system fault conditions. During a normal power down sequence, the LTC2951 first interrupts the µP by setting ⎯I⎯N⎯T low. The µP then performs power down and housekeeping tasks and drives ⎯K⎯I⎯L⎯L low when done. The LTC2951 releases the enable output, thus turning off system power. The ⎯K⎯I⎯L⎯L turn off timer starts when ⎯I⎯N⎯T is driven low. If the µP fails to respond during this timeout period, the enable output will automatically release. The default power down timeout period is 128ms (t⎯K⎯I⎯L⎯L, OFF DELAY), which can be extended by placing an optional capacitor on the KILLT pin (t⎯K⎯I⎯L⎯L, OFF DELAY, ADDITIONAL). The following equation describes the additional power down timeout period. CKILLT is the KILLT external capacitor: CKILLT = 1.56e-4 [µF/ms] • (tKI⎯ LL, OFF DELAY, ADDITIONAL – 1ms) ⎯ ⎯⎯ Note that ⎯K⎯I⎯L⎯L can be driven low (thereby releasing the enable output) at any time after t⎯K⎯I⎯L⎯L, ON BLANK period. Simplified Power On/Off Sequence Figure 1 shows a simplified LTC2951-1 power on and power off sequence. A high to low transition on ⎯P⎯B (t1) initiates the power on sequence. This diagram does not show any bounce on ⎯P⎯B. In order to assert the enable output, the ⎯P⎯B pin must stay low continuously (⎯P⎯B high resets timers) for 128ms (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 ⎯K⎯I⎯L⎯L 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 LTC2951 does not sample ⎯K⎯I⎯L⎯L and ⎯P⎯B until after the 512ms internal timer has expired. The reason ⎯P⎯B 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 ⎯P⎯B pin is then debounced with an internal 32ms timer. The system has now properly powered on and the LTC2951 monitors ⎯P⎯B 2951f W U U 9 LTC2951 APPLICATIO S I FOR ATIO t1 PB tDB, ON t2 t3 PB & KILL IGNORED tKILL, ON BLANK tDB, OFF OFFT INT KILL EN 2951 F01 Figure 1. Simplified Power On/Off Sequence for LTC2951-1 PB tDB, ON 512ms INTERNAL TIMER POWER ON TIMING POWER TURNED OFF EN µP FAILED TO SET KILL HIGH KILL 2951 F02 Figure 2. Aborted Power On Sequence for LTC2951-1 2951f 10 U t4 t5 t6 PB IGNORED < tKILL, OFF DELAY t7 tOFFT tABORT W U U LTC2951 APPLICATIO S I FOR ATIO and ⎯K⎯I⎯L⎯L (for a turnoff command) while consuming only 6µA of supply current. A high to low transition on ⎯P⎯B (t5) initiates the power off sequence. ⎯P⎯B must stay low continuously (⎯P⎯B 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 (⎯I⎯N⎯T) is set, signifying that EN will be switched low after the ⎯K⎯I⎯L⎯L turn off (t ⎯K⎯I⎯L⎯L, OFF DELAY + t ⎯K⎯I⎯L⎯L, OFF DELAY, ADDITIONAL) timeout period. Once a system has finished performing its power down operations, it can set ⎯K⎯I⎯L⎯L low (t7) and thus immediately set EN low, terminating the ⎯K⎯I⎯L⎯L turn off timer. The release of the ⎯P⎯B pin is then debounced with an internal 32ms timer. The system is now in its reset state: where the LTC2951 is in low power mode (6µA). ⎯P⎯B is monitored for a high to low transition. Aborted Power On Sequence The power on sequence is aborted when the ⎯K⎯I⎯L⎯L remains low after the end of the 512ms blanking time. Figure 2 is a simplified version of an aborted power on sequence. At time tABORT, since ⎯K⎯I⎯L⎯L is still low, EN pulls low (thus turning off the DC/DC converter). µP Turns Off Power During Normal Operation Once the system has powered on and is operating normally, the µP can turn off power by setting ⎯K⎯I⎯L⎯L low, as shown in Figure 3. At time t ⎯K⎯I⎯L⎯L, ⎯K⎯I⎯L⎯L is set low by the tKILL PB PB & KILL IGNORED DC/DC TURNS OFF EN µP SETS KILL LOW KILL XXX DON’T CARE 2951 F03 Figure 3. µP Turns Off Power (LTC2951-1) U µP. This immediately pulls EN low, thus turning off the DC/DC converter. DC/DC Turn Off Blanking When the DC/DC converter is turned off, it can take a significant amount of time for its output to decay to ground. It is desirable to wait until the output of the DC/DC converter is near ground before allowing the user (via ⎯P⎯B) to restart the converter. This condition guarantees that the µP has always powered down completely before it is restarted. Figure 4 shows the µP turning power off. After a low on ⎯K⎯I⎯L⎯L releases enable, ⎯P⎯B is ignored during the internal 256ms timer period. This is shown as tEN/⎯E⎯N, LOCKOUT in Figure 4. LTC2951-1, LTC2951-2 Versions The LTC2951-1 (high true EN) and LTC2951-2 (low true ⎯E⎯N) differ only by the polarity of the EN/⎯E⎯N pin. Both versions allow the user to extend the amount of time that the ⎯P⎯B must be held low in order to begin a valid power off sequence. An external capacitor placed on the OFFT pin adds additional time to the turn off debounce time. If no capacitor is placed on the OFFT pin, then the turn off debounce time is given by an internally fixed 32ms timer. Both versions of the LTC2951 provide extendable ⎯K⎯I⎯L⎯L turn off timer, t ⎯K⎯I⎯L⎯L, OFF DELAY, ADDITIONAL, by connecting an optional external capacitor on the KILLT pin. The default ⎯K⎯I⎯L⎯L turn off delay time is 128ms, t ⎯K⎯I⎯L⎯L, OFF DELAY. tEN/EN, LOCKOUT PB POWER ON PB & KILL IGNORED PB IGNORED DC/DC TURNS OFF PB BLANKING 256ms EN µP SETS KILL LOW KILL XXX DON’T CARE 2951 F04 W U U Figure 4. DC/DC Turn Off Blanking (LTC2951-1) 2951f 11 LTC2951 APPLICATIO S I FOR ATIO High Voltage Pins The VIN and ⎯P⎯B pins can operate at voltages up to 26.4V. ⎯P⎯B can, additionally, operate below ground (–6V) without ⎯⎯ latching up the device. PB has an ESD HBM rating of ±10kV. If the push button switch connected to ⎯P⎯B exhibits high leakage current, then an external pull-up resistor to VIN is recommended. Furthermore, if the push button switch is physically located far from the LTC2951 ⎯P⎯B pin, parasitic capacitances may couple onto the high impedance ⎯P⎯B input. Additionally, parasitic series inductance may cause unpredictable ringing at the ⎯P⎯B pin. Placing a 5k resistor from the ⎯P⎯B pin to the push button switch would mitigate parasitic inductance problems. Placing a 0.1µF capacitor on the ⎯P⎯B pin would lessen the impact of parasitic capacitive coupling. TYPICAL APPLICATIO S Voltage Monitoring with ⎯K⎯I⎯L⎯L Input The ⎯K⎯I⎯L⎯L pin can be used as a voltage monitor. Figure 5 shows an application where the ⎯K⎯I⎯L⎯L pin has a dual function. It is driven by a low leakage open drain output of the µP. It is also connected to a resistor divider that monitors battery voltage (VIN). When the battery voltage falls below the set value, the voltage at the ⎯K⎯I⎯L⎯L pin falls below 0.6V and the EN pin is quickly pulled low. Note that the resistor values should be as large as possible, but small enough to keep leakage currents from tripping the 0.6V ⎯K⎯I⎯L⎯L comparator. VIN 9V VIN VOUT 3.3V LT1767-3.3 SHDN 5.4V THRESHOLD R3 806k 1% EN LTC2951-1 INT PB GND KILLT KILL OFFT CKILLT* 0.033µF COFFT* 0.033µF *OPTIONAL R2 100k 1% R1 10k INT µP PB GND KILLT KILL OFFT CKILLT* 0.033µF COFFT* 0.033µF VIN LTC2951-1 INT EN C4 0.1µF VIN KILL (OPEN DRAIN) 2951 F05 Figure 5. Input Voltage Monitoring with ⎯K⎯I⎯L⎯L Input 12 U The DC/DC converter shown has an internal pull-up current on its ⎯S⎯H⎯D⎯N pin. A pull-up resistor on EN is thus not needed. Operation Without µP Figure 6 shows how to connect the ⎯K⎯I⎯L⎯L pin when there is no circuitry available to drive it. The minimum pulse width detected is 30µs. If there are glitches on the resistor pull-up voltage that are wider than 30µs and transition below 0.6V, then an appropriate bypass capacitor should be connected to the ⎯K⎯I⎯L⎯L pin. VIN 9V VIN VOUT 3.3V LT1767-3.3 SHDN R1 100k C4 0.1µF W U U U + C3* 0.01µF *OPTIONAL 2951 F06 Figure 6. No µP Application 2951f LTC2951 TYPICAL APPLICATIO S Power Path Switching The ⎯E⎯N open drain output of the LTC2951-2 is designed to switch on/off an external power PFET. This allows a user to connect/disconnect a power supply (or battery) to its load by toggling the ⎯P⎯B pin. Figure 7 shows the LTC2951-2 controlling a two cell Li-Ion battery application. The ⎯I⎯N⎯T and ⎯K⎯I⎯L⎯L pins are connected to the output of the PFET through a resistor divider. The ⎯K⎯I⎯L⎯L pin serves as a voltage monitor. When VOUT drops below 6V, the ⎯E⎯N pin is open circuited 30µs later. ⎯PB Pin in a Noisy Environment ⎯ The rugged ⎯P⎯B pin is designed to operate in noisy environments. Transients below ground (>–6V) and above VIN ⎯ (2µA), the ⎯P⎯B voltage may fall close to the threshold window. To mitigate the effect of the board leakage, a 10k resistor to VIN is recommended (see Figure 9). Reverse Battery Protection To protect the LTC2951 from a reverse battery connection, place a 1k resistor (R8) in series with the VIN pin (see Figure 10). 14 U VIN R7 10k VIN LTC2951-1/ LTC2951-2 2.4V 100k PB EXTERNAL BOARD LEAKAGE CURRENT >2µA GND PINS OMITTED FOR CLARITY 2951 F09 IF EXTERNAL PARASITIC BOARD LEAKAGE >2µA, USE EXTERNAL PULL-UP RESISTOR Figure 9. External Pull-Up Resistor on ⎯P⎯B Pin 2951f LTC2951 PACKAGE DESCRIPTIO U DDB Package 8-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1702) 0.61 ± 0.05 (2 SIDES) 0.675 ± 0.05 2.50 ± 0.05 1.15 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.20 ± 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 ± 0.10 (2 SIDES) 3.00 ± 0.10 (2 SIDES) R = 0.115 TYP 5 0.56 ± 0.05 (2 SIDES) 0.38 ± 0.10 8 0.200 REF 0.75 ± 0.05 4 0.25 ± 0.05 2.15 ± 0.05 (2 SIDES) BOTTOM VIEW—EXPOSED PAD 1 PIN 1 CHAMFER OF EXPOSED PAD (DDB8) DFN 1103 0.50 BSC 0 – 0.05 TS8 Package 8-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1637) 0.52 MAX 0.65 REF 2.90 BSC (NOTE 4) 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.65 BSC 0.22 – 0.36 8 PLCS (NOTE 3) 0.80 – 0.90 0.20 BSC 1.00 MAX DATUM ‘A’ 0.01 – 0.10 0.30 – 0.50 REF NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 0.09 – 0.20 (NOTE 3) 1.95 BSC TS8 TSOT-23 0802 2951f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC2951 TYPICAL APPLICATIO U VIN 9V BATTERY VOUT + R8 1k R5 910k LT1761-1.8 SHDN 1.8V C4 0.1µF VIN LTC2951-1 PB GND KILLT EN INT KILL OFFT CKILLT* 0.033µF COFFT* 0.033µF R1 10k INT µP KILL *OPTIONAL 2951 F10 Figure 10. Reverse Battery Protection Using R8 RELATED PARTS PART NUMBER LTC2900 LTC2904/2905 LTC2950 LTC4411 LTC4412HV LTC4055 DESCRIPTION Programmable Quad Supply Monitor Pin-Programmable Dual Supply Monitors Micropower Push Button On/Off Controller 2.6A Low Loss Ideal Diode in ThinSOT Power Path Controller in ThinSOT USB Power Controller and Li-Ion Charger COMMENTS Adjustable ⎯R⎯E⎯S⎯E⎯T, 10-Lead MSOP and 3mm x 3mm DFN Packages Adjustable ⎯R⎯E⎯S⎯E⎯T and Tolerance, 8-Lead SOT-23 and 3mm × 2mm DFN Packages High Voltage Push Button Controller with µP Interface and Adjustable ON Time No External MOSFET, Automatic Switching Between DC Sources Efficient Diode-ORing, Automatic Switching Between DC Sources, 3V to 36V Automatic Switchover, Charges 1-Cell Li-Ion Batteries 2951f 16 Linear Technology Corporation (408) 432-1900 ● LT/TP 0405 500 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005