Datasheet

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LTC2955

2955f

LT3008-3.3

OUT

INT

KILL

PGD

SEL

LTC2955DDB-1

2955 TA01a

GNDTMR

3.3V

2.32M

SHDN

0.1µF

8.4V

TRIP

= 5.4V

µP

POWER-FAIL

402k

TYPICAL APPLICATION

FEATURES DESCRIPTION

Pushbutton On/Off

Controller with Automatic

Turn-On

The LTC

2955 is a micropower, pushbutton on/off control-

ler that manages system power by generating a clean enable

output from the supply monitor input and the debounced

pushbutton input. It features an interrupt output that

notifies the system of a pushbutton or low supply event.

When the system is ready, it may use the power kill input

to shut off power. If the pushbutton remains pressed for

more than the configurable turn-off duration, the system

power is forced off.

The supply input covers a wide range from 1.5V to 36V.

The robust pushbutton input handles wide voltage swings

of ±36V and ESD strikes to ±25kV (human body model)

without latchup or damage. A low 1.2µA supply current

maximizes battery run time. Separate versions are avail-

able for positive or negative enable polarities.

Pushbutton On/Off with Interrupt

APPLICATIONS

Automatic Turn-On Via Voltage Monitor Input

Wide Input Supply Range: 1.5V to 36V

Low Supply Current: 1.2μA

±25kV ESD HBM on PB Input

±36V Wide Input Voltage for PB Input

Low Leakage EN Output Allows DC/DC Converter

Control (LTC2955-1)

High Voltage EN Output Drives External P-Channel

MOSFET (LTC2955-2)

Simple Interface Allows Graceful µP Shutdown

Adjustable Turn-Off Timer

10-Lead 3mm × 2mm DFN and 8-Lead ThinSOT™

Packages

Desktop and Notebook Computers

GPS Devices

Portable Instruments

Automotive Electronics

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

ThinSOT and PowerPath are trademarks of Linear Technology Corporation. All other trademarks

are the property of their respective owners.

TURN ON PULSE SHORT PULSE LONG PULSE

TURNS ON STAYS ON

INTERRUPT INTERRUPT

TURNS OFF

2955 TA01b

INT

Automatic Turn-On with Power-Fail Indication

Summary of content (20 pages)

PAGE 1
LTC2955 Pushbutton On/Off Controller with Automatic Turn-On DESCRIPTION FEATURES n n n n n n n n n n Automatic Turn-On Via Voltage Monitor Input Wide Input Supply Range: 1.5V to 36V Low Supply Current: 1.
PAGE 2
LTC2955 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN ............................................................. –0.3V to 40V Input Voltages PB ........................................................... –40V to 40V ON ......................................................... –0.3V to 40V SEL ........................................................ –0.3V to 40V KILL ......................................................... –0.3V to 6V Output Voltages EN/EN ....................................................
PAGE 3
LTC2955 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 7V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Supply VIN Supply Voltage Range l 1.5 IIN VIN Supply Current l 0.5 VUVL VIN Undervoltage Lockout l VIN Undervoltage Lockout Hysteresis l VPB(MIN(MAX)) PB Voltage Range l –36 VPB PB Input Threshold PB Falling l 0.
PAGE 4
LTC2955 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 7V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX tDB(ON) PB, ON Turn-On Debounce Time PB, ON Falling → Enable Asserted tDB(OFF) PB Interrupt Debounce Time tTMR tINT(MIN) UNITS l 19 32 45 ms PB Falling → INT Falling l 19 32 45 ms Additional Turn-Off Debounce Time CTMR = 2200pF l 5.
PAGE 5
LTC2955 TYPICAL PERFORMANCE CHARACTERISTICS ON/KILL Threshold vs Temperature VIN = 7V, TA = 25°C, unless otherwise noted. Turn-On Debounce Time vs Temperature 0.810 Additional Turn-Off Debounce Time vs TMR External Capacitance 36 10000 35 0.805 1000 0.800 tTMR (ms) tDB(ON) (ms) VON/KILL (V) 34 33 100 32 0.795 10 31 0.
PAGE 6
LTC2955 PIN FUNCTIONS EN: Enable Output (LTC2955-1). EN is an active high output to control the turn-on/off of the system power. Connect this pin to the RUN or SHUTDOWN pin of the voltage regulator. The LTC2955 asserts EN high when the pushbutton is pressed or when ON goes high. The output high voltage follows the internal LDO output which provides sufficient margin for most SHUTDOWN pin thresholds. EN: Inverted Enable Output (LTC2955-2).
PAGE 7
LTC2955 BLOCK DIAGRAM VIN 900k EN (2955-2) VLDO EN CONTROL 2μA LTC2955-2 VIN REGULATOR VLDO ≈ 5.2V EN (2955-1) EN CONTROL VLDO LTC2955-1 OSCILLATOR f = 1kHz 900k PB 0.8V EN CONTROL – 2μA DEBOUNCE + OSCILLATOR ON ON VLDO LOGIC PGD* + OFF 0.8V – INT + + 0.8V – – SEL* GND KILL 0.
PAGE 8
LTC2955 OPERATION Overview The LTC2955 is a pushbutton on/off controller that manages system power based on a pushbutton input (PB pin) and a voltage monitor input (ON pin). In a typical application, the enable output (EN/EN) turns on system power when the pushbutton is pressed or the supply monitor detects the presence of a primary or secondary supply such as a wall adaptor or car battery.
PAGE 9
LTC2955 OPERATION A high to low transition on PB (t1) starts the turn-off sequence. In order to assert INT (interrupt output) low, PB must stay low continuously for 32ms (tDB(OFF)). At the end of the 32ms (t2), the INT pin is asserted low and will stay low for at least 32ms (tINT(MIN)), even if the PB pin goes high during this period (t2 to t4). When the μP receives this interrupt signal, it should start to perform its power-down functions and assert KILL low (t3) once it is done.
PAGE 10
LTC2955 OPERATION high). This can be done by holding the pushbutton down for a long period (> tDB(OFF) + tINT(MIN) + tTMR) as shown with the solid lines in Figure 3. If the PB pin remains low at the end of the 32ms minimum INT pulse width (tINT(MIN)), the external timer will start counting (t4). The capacitance at the TMR pin determines the duration of this timer and it will count for 16 cycles (tTMR).
PAGE 11
LTC2955 OPERATION to perform power-down functions. The INT pin will stay low for at least 32ms (tINT(MIN)). When the μP receives this interrupt signal, it should start to perform its powerdown functions and assert the KILL input low (t2) once it is done. The LTC2955-1 will then release the EN and INT outputs, thus turning off the system power, as shown with dotted lines in Figure 5. ON Pin Turn-Off Sequence (DFN Package Only) Figure 5 shows the turn-off sequence of the LTC2955-1 initiated by the ON pin.
PAGE 12
LTC2955 OPERATION PB vs ON Pin With the DFN package, if the turn-on sequence is initiated by the pushbutton, the ON input is ignored until the pushbutton is pressed again to initiate a turn-off sequence. As shown in Figure 6, the PB pin initiates a turn-on sequence at time t1 before the ON pin goes high at time t2. Once EN goes high (t3), the ON input is ignored, so a falling edge at the ON pin (t4) will not initiate a turn-off sequence even if the SEL pin is high.
PAGE 13
LTC2955 OPERATION As shown in Figure 7, if the ON pin is high when power is first applied to the LTC2955-1 at time t1, the EN pin will go high (at t2) after the one second EN lockout time. At time t3, the pushbutton is pressed to activate turn-off while the ON pin remains high. The LTC2955-1 will wait for a rising edge at the ON pin or a low at the PB pin to activate the next turn-on. As shown at time t4, after the one second lockout time, the EN stays low with ON high.
PAGE 14
LTC2955 APPLICATIONS INFORMATION Adjusting the Forced Turn-Off Timing Voltage Monitoring with KILL Input The LTC2955 allows the user to force the system power to turn off if the μP fails to respond during fault conditions. As shown by the solid lines in Figure 3 and Figure 5, when the μP fails to bring the KILL pin low after the interrupt signal is asserted, the user can force a turn-off by holding down the pushbutton.
PAGE 15
LTC2955 APPLICATIONS INFORMATION High Voltage PowerPath™ Switching capacitor at the pin lessens the impact of this coupling. The parasitic series inductance may cause unpredictable ringing at the PB pin; placing a 5.1k resistor from the PB pin to the pushbutton switch reduces this ringing. Figure 11 shows an example of this RC network at the PB pin. The high voltage EN open drain output of the LTC2955-2 is designed to switch on/off an external power P-channel MOSFET.
PAGE 16
LTC2955 APPLICATIONS INFORMATION mitigate the effect of the board leakage, a 10k resistor to VIN is recommended (see Figure 12). LTC2955-1/ LTC2955-2 VIN VIN VLDO R7 10k Adding a 10nF capacitor in addition to the 1k resistor can protect against high voltage input transients that would exceed the 40V Absolute Maximum Voltage rating of the VIN pin. These could occur during hot-plugging into a battery or AC adapter.
PAGE 17
LTC2955 APPLICATIONS INFORMATION and the device turns on. If the user slides the switch to the OFF position, the ON pin voltage drops to 0V and the LTC2955 activates a turn-off since the SEL pin is high (DFN package only). Interface with Switching Regulators The LTC2955-1 EN pin can be connected directly to most switching regulator SHUTDOWN inputs. The EN pin high level output voltage (VEN(VOH)) is typically 4.3V with VIN >5V, and VEN(VOH) = VIN – 0.5V if VIN <5V. With a minimum VIN of 1.
PAGE 18
LTC2955 TYPICAL APPLICATIONS Automatic Power-Up with Pushbutton On/Off Low Voltage Pushbutton Controller Enables Charge Pump LTC3204-3.3 1.8V VOUT VIN LT1763-5 3.3V VIN 12V C+ 2.2μF GND C– 1μF EN PGD VIN LTC2955DDB-1 ON INT EN VIN 1M 5.1k* LTC2955TS8-1 INT PB SHDN 2.2μF SHDN KILL PB 0.1μF* μP VOUT SEL KILL GND 1M μP TMR 2955 TA03 TMR GND ON 2955 TA02 *OPTIONAL RC NETWORK RECOMMENDED TO IMPROVE NOISE IMMUNITY PowerPath Control with Immediate KILL LT3009 VIN 12V VOUT 3.
PAGE 19
LTC2955 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DDB Package 10-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1722 Rev Ø) 0.64 ±0.05 (2 SIDES) 3.00 ±0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 6 0.40 ± 0.10 10 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 2.00 ±0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.25 ± 0.05 0.75 ±0.05 0.200 REF 0.50 BSC 2.39 ±0.05 (2 SIDES) 0.64 ± 0.05 (2 SIDES) 5 0.25 ± 0.
PAGE 20
LTC2955 TYPICAL APPLICATION Pushbutton On/Off Control with Automatic Turn-On When 12V Applied LT3009-3.3 12V P-CHANNEL MOSFET SHDN 4.5V LTC4412 VIN GATE EN GND SENSE VIN CTL SEL STAT LTC2955DDB-1 2.21M 9.