LTC2955CDDB-1#PBF - LINEAR TECHNOLOGY

LTC2955

2955fa

For more information www.linear.com/LTC2955

LT3008-3.3

VOUT

VIN

INT

KILL

PGD

VIN

SEL

LTC2955DDB-1

2955 TA01a

GNDTMR

3.3V

1M R7

2.32M

SHDN

0.1µF

8.4V

VTRIP = 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

n Automatic Turn-On Via Voltage Monitor Input

n Wide Input Supply Range: 1.5V to 36V

n Low Supply Current: 1.2µA

n ±25kV ESD HBM on PB Input

n ±36V Wide Input Voltage for PB Input

n Low Leakage EN Output Allows DC/DC Converter

Control (LTC2955-1)

n High Voltage EN Output Drives External P-Channel

MOSFET (LTC2955-2)

n Simple Interface Allows Graceful µP Shutdown

n Adjustable Turn-Off Timer

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

Packages

n Desktop and Notebook Computers

n GPS Devices

n Portable Instruments

n 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

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pin conFiguraTion

absoluTe MaxiMuM raTings

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 .................................................... –0.3V to 40V

INT ........................................................... –0.3V to 6V

PGD ......................................................... –0.3V to 6V

TMR ...................................................... –0.3V to 2.7V

(Note 1)

TOP VIEW

DDB PACKAGE

10-LEAD (3mm × 2mm) PLASTIC DFN

INT

PGD

*EN/EN

VIN

KILL

TMR

SEL

GND

TJMAX = 125°C, θJA = 55°C/W

EXPOSED PAD (PIN 11) PCB GND CONNECTION OPTIONAL

*PIN 3 IS EN FOR LTC2955-1

AND IS EN FOR L

TC2955-2

TOP VIEW

TS8 PACKAGE

8-LEAD PLASTIC TSOT-23

INT

EN/EN*

VIN

KILL

TMR

GND

TJMAX = 125°C, θJA = 195°C/W

*PIN 7 IS EN FOR LTC2955-1

AND IS EN FOR LTC2955-2

orDer inForMaTion

Operating Temperature Range

LTC2955C ................................................ 0°C to 70°C

LTC2955I .............................................–40°C to 85°C

Storage Temperature Range .................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

TSOT-23 Package .............................................300°C

Lead Free Finish

TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC2955CDDB-1#TRMPBF LTC2955CDDB-1#TRPBF LGBJ 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C

LTC2955CDDB-2#TRMPBF LTC2955CDDB-2#TRPBF LGBM 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C

LTC2955IDDB-1#TRMPBF LTC2955IDDB-1#TRPBF LGBJ 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C

LTC2955IDDB-2#TRMPBF LTC2955IDDB-2#TRPBF LGBM 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C

LTC2955CTS8-1#TRMPBF LTC2955CTS8-1#TRPBF LTGBK 8-Lead Plastic TSOT-23 0°C to 70°C

LTC2955CTS8-2#TRMPBF LTC2955CTS8-2#TRPBF LTGBN 8-Lead Plastic TSOT-23 0°C to 70°C

LTC2955ITS8-1#TRMPBF LTC2955ITS8-1#TRPBF LTGBK 8-Lead Plastic TSOT-23 –40°C to 85°C

LTC2955ITS8-2#TRMPBF LTC2955ITS8-2#TRPBF LTGBN 8-Lead Plastic TSOT-23 –40°C to 85°C

TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.

Consult LTC Marketing for parts specified with wider operating temperature ranges.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through

designated sales channels with #TRMPBF suffix.

(http://www.linear.com/product/LTC2955#orderinfo)

LTC2955

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elecTrical characTerisTics

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Supply

VIN Supply Voltage Range l1.5 36 V

IIN VIN Supply Current l0.5 1.2 3 µA

VUVL VIN Undervoltage Lockout VIN Rising l1.0 1.15 1.3 V

VUVL(HYST) VIN Undervoltage Lockout Hysteresis l30 85 200 mV

Input Pins

VPB(MIN(MAX)) PB Voltage Range l–36 36 V

VPB PB Input Threshold PB Falling l0.6 0.8 1 V

VPB(HYST) PB Input Threshold Hysteresis (Note 3) 40 mV

VPB(VOC) PB Open Circuit Voltage I = –1µA l3.0 4.3 5.5 V

IPB PB Input Leakage Current 6V < PB < 36V

PB = 1V

PB = –36V

–1

–4

±10

–8

–400

µA

VON ON Threshold ON Rising l0.76 0.80 0.84 V

VON(HYST) ON Hysteresis DFN Package Only 40 mV

ION ON Input Leakage Current ON = 1V

ON = 36V

±10

±100

VKILL KILL Input Threshold Voltage KILL Falling l0.76 0.80 0.84 V

VKILL(HYST) KILL Input Threshold Hysteresis (Note 3) 30 mV

IKILL KILL Input Leakage Current KILL = 1V l±50 nA

VSEL SEL Input Threshold l0.4 0.8 1.2 V

ISEL SEL Input Current SEL = 1V

SEL = 36V

±50

±100

Output Pins

VEN/EN(VOL) EN/EN Voltage Output Low I = 1mA l0.175 0.4 V

VEN(VOH) EN Voltage Output High (LTC2955-1) I = 0µA, –0.5µA l1.5 5.5 V

VEN(VOH) EN Voltage Output High (LTC2955-2) I = 0µA, –0.5µA lVIN – 1.5 V

IEN EN Pull-Up Current (LTC2955-1) EN = 0V l–1.2 –2 –2.8 µA

IEN EN Pull-Up Resistance (LTC2955-2) l0.45 0.9 1.35 MΩ

VINT(VOL) INT Voltage Output Low I = 3mA l0.4 V

IINT INT Leakage Current INT = 5V l±50 nA

VPGD(VOH) PGD Voltage Output High I = 0µA, –0.5µA l1.5 5.5 V

VPGD(VOL) PGD Voltage Output Low I = 3mA l0.4 V

IPGD PGD Pull-Up Current PGD = 0V l–1.2 –2 –2.8 µA

ITMR(PU) TMR Pull-Up Current TMR = 0V l–2 –3 –4 µA

ITMR(PD) TMR Pull-Down Current TMR = 1.5V l2 3 4 µA

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)

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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Timing

tDB(ON) PB, ON Turn-On Debounce Time PB Falling or ON Rising → Enable Asserted l19 32 45 ms

tDB(OFF) PB Interrupt Debounce Time PB Falling → INT Falling l19 32 45 ms

tTMR Additional Turn-Off Debounce Time CTMR = 2200pF l5.8 11.5 17.2 ms

tINT(MIN) Minimum INT Pulse Width INT Falling → TMR Rising l19 32 45 ms

tON(PD) ON Interrupt Delay ON Falling → INT Falling, VSEL > 0.8V l200 µs

tPGD(PD) PGD Propagation Delay ON Falling → PGD Falling l200 µs

tKILL(PD) KILL Propagation Delay KILL Falling → Enable Released l60 µs

tKILL(PW) KILL Minimum Pulse Width l60 µs

tKILL(ON BLANK) KILL Turn-On Blanking (Note 4) KILL Low, Enable Asserted → Enable

Released

l304 512 720 ms

tEN(LOCK OUT) EN/EN Lockout Time (Note 5) Enable Released → Enable Asserted l0.6 1 1.4 s

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)

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: All currents into pins are positive; all voltages are referenced to

GND unless otherwise noted.

Note 3: Guaranteed by design, not subject to test.

Note 4: The KILL turn-on blanking time is the waiting period immediately

after the enable output is asserted. This blanking time allows sufficient

time for the regulator and the µP to perform power-up tasks. The KILL, PB,

and ON inputs are ignored during this period.

Note 5: The enable lockout time is the waiting period immediately after the

enable output is released. It allows an application to properly power-down

such that the next power-up sequence starts from a consistent powered

down configuration. PB and ON are ignored during this period.

Typical perForMance characTerisTics

Supply Current vs Temperature Supply Current vs Supply Voltage

Undervoltage Lockout vs

Temperature

VIN = 7V, TA = 25°C, unless otherwise noted.

TEMPERATURE (°C)

–50

UVL

(V)

1.10

1.12

1.14

1.20

1.16

050 75

2955 G03

1.18

–25 25 100

125

TEMPERATURE (°C)

–50

IVIN (µA)

0.8

1.0

1.1

1.2

1.6

1.3

050 75

2955 G01

0.9

1.4

1.5

–25 25 100 125

VIN (V)

IVIN (µA)

0.6

0.8

1.0

1.2

10 20 25

2955 G02

1.4

1.6

515 30 4035

TA = –40°C

TA = 25°C

TA = 85°C

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Typical perForMance characTerisTics

TMR Pull-Up Current

vs Temperature

EN Output High Voltage vs

Temperature

EN Output High Voltage vs Supply

Voltage

EN/EN Output Low Voltage vs

Temperature PB Input Current vs PB Voltage

PB Voltage vs External PB

Resistance to Ground

ON/KILL Threshold vs

Temperature

Turn-On Debounce Time

vs Temperature

Additional Turn-Off Debounce

Time vs TMR External Capacitance

VIN = 7V, TA = 25°C, unless otherwise noted.

TEMPERATURE (°C)

–50

DB(ON)

(ms)

050 75

2955 G05

–25 25 100

125

EXTERNAL PB RESISTANCE TO GROUND (kΩ)

PB VOLTAGE (mV)

100

150

300

200

10 20

2955 G12

250

4030

TA = –40°C

TA = 25°C

TA = 85°C

TEMPERATURE (°C)

–50

ON/KILL

(V)

0.790

0.795

0.810

0.800

050 75

2955 G04

0.805

–25 25 100

125

TEMPERATURE (°C)

–50

EN(VOH)

(V)

3.6

4.0

4.2

4.4

5.0

4.6

050 75

2955 G08

3.8

4.8

–25 25 100

125

TMR EXTERNAL CAPACITANCE (nF)

tTMR (ms)

100

10000

10 100 1000

2955 G06

1000

TEMPERATURE (°C)

–50

ITMR(PU) (µA)

–2.6

–2.8

–2.9

–3.0

–3.4

–3.1

050 75

2955 G07

–2.7

–3.2

–3.3

–25 25 100 125

VIN (V)

VEN(VOH) (V)

0.0

1.0

5.0

2.0

3 5

2955 G09

4.0

3.0

2476

TA = –40°C

TA = 25°C

TA = 85°C

PB VOLTAGE (V)

–40

IPB (µA)

–40

–80

–200

–120

2955 G11

–160

–20 20 40

TEMPERATURE (°C)

–50

VEN/EN(VOL) (mV)

200

150

250

300

450

350

050 75

2955 G10

100

400

–25 25 100 125

VIN = 1.5V

VIN = 7V

I = 1mA

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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). EN is an active

low output to control the turn-on/off of the system power.

It may drive a voltage regulator’s active low enable input,

or it may drive the gate of a P-channel MOSFET. In the

turn-off state, the LTC2955 pulls this pin to VIN through

an internal 900k resistor. The LTC2955 pulls EN to GND

when the pushbutton is pressed or when ON goes high.

Exposed Pad (DFN only): Exposed pad. Leave open or

connect to device ground.

GND: Device Ground.

INT: Open Drain Interrupt Output. Connect this pin to the

interrupt input of the system with a pull-up resistor to the

system supply. The LTC2955 asserts the INT pin low when

it receives the turn-off command from the pushbutton or

the ON pin. The minimum pulse width of the INT signal is

32ms and can be extended through the TMR pin.

KILL: Kill Input. A low at KILL releases the enable output

(EN/EN). This pin can be driven by the microprocessor or it

can be used as a voltage monitor input. Tie to the system

power supply or an external voltage of 1.2V~5V if unused.

ON: Monitor Input. Connect this pin to an external resistive

divider from the monitored voltage. This allows automatic

system turn-on when the monitored voltage transitions

high. For the DFN part, if the SEL pin is tied high, it also

allows automatic system turn-off when the monitored

voltage transitions low. Tie to GND if unused.

PB: Pushbutton Input. This is an active low input with a

900k pull-up to an internal LDO. Connect one terminal of

the pushbutton to this pin and connect the other terminal of

the pushbutton to GND. The pin may be left open if unused.

PGD (DFN only): ON Status Output. A high on this pin

indicates that the voltage at the ON pin is above the input

threshold of 0.8V. This pin can be used as a system input

to inform the system whether the turn-on was triggered by

the ON pin or the pushbutton pin. Leave open if unused.

SEL (DFN only): Mode Select Input. Connect SEL to GND

to block the ON pin falling edge from activating system

turn-off. Connect SEL to VIN to allow both the ON pin rising

and falling edges to activate system turn-on and turn-off

respectively. For the TSOT package, SEL is internally tied

to GND. Do not leave open.

TMR: Timer Pin. A capacitor to ground determines the

additional time (5.2 seconds/μF) beyond the default 64ms

that the pushbutton must be held low before immediately

releasing the EN/EN and INT outputs. The turn-off debounce

time defaults to 64ms if this pin is left open. To disable the

ability to force a system power-down with a pushbutton

press, ground the TMR pin.

VIN: Power Supply Input. For > 20V applications, connect

VIN to the power source through a 1k resistor and bypass

VIN to GND with a 10nF low ESR capacitor.

LTC2955

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block DiagraM

2955 BD

VIN

OFF

*DFN ONLY

TMR

SEL*

GND

VLDO

REGULATOR VLDO ≈ 5.2V

VLDO

2µA

EN CONTROL

900k

0.8V

KILL

INT

PGD*

–

OSCILLATOR

f = 1kHz

OSCILLATOR

DEBOUNCE

LOGIC

2µA

(2955-1)

EN CONTROL

LTC2955-1

VIN

(2955-2)

EN CONTROL

LTC2955-2

900k

VLDO

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Figure 1. Pushbutton Turn-On Timing

operaTion

Overview

The LTC2955 is a pushbutton on/off controller that man-

ages 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.

After the system is powered up, a pushbutton event as-

serts the interrupt output (INT) which can be used in menu

driven applications to request for a system power-down.

A power kill input (KILL) allows a microprocessor or sys-

tem to release the enable output immediately, effectively

powering down the system. System power is also forced

off if the pushbutton remains asserted for more than the

forced turn-off activation time configurable via the TMR pin.

The LTC2955 is also designed with a blanking time after

each system turn on and off event. During this blanking

time, the LTC2955 ignores the KILL, ON and PB pins,

thus ensuring that the system stays on/off for a minimum

amount of time. This provides sufficient time for the voltage

regulator to turn on/off and allows it to charge/discharge

its output to the final voltage. It also allows the µP suf-

ficient time to perform power on/off tasks.

The PGD output indicates the status of the ON pin to allow

the system to differentiate between pushbutton turn-on

or supply plug-in events.

Turn-On Sequence and KILL Blanking Time

The LTC2955-1 asserts the EN output high if the pushbut-

ton is pressed or the ON pin goes high. This is typically

used to turn on a DC/DC converter or linear regulator.

Figure 1 shows the turn-on sequence of the LTC2955-1

initiated by the PB pin. When the button is pressed at time

t1, a high to low transition on the PB pin initiates the turn-

on sequence. The PB pin must stay low continuously for

a period of 32ms (tDB(ON)) before the LTC2955-1 asserts

the EN output high. Once EN goes high (t2), an internal

512ms blanking time (tKILL(OnBlank)) is started. During

this blanking time, the LTC2955-1 ignores the KILL, ON

and PB pins and keeps EN high for at least 512ms. This

provides sufficient time for the voltage regulator to turn

on and charge its output to the final voltage and allows

the µP enough time to perform power on tasks. The µP

must pull the KILL pin high during this 512ms blanking

time, or else EN will go low at the end of this time (t3).

tDB(ON) tKILL(ON BLANK)

PB AND KILL IGNORED

2955 F01

(LTC2955-1)

t1t2t3

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Figure 2.ON Pin Turn-On Timing

Figure 3. Pushbutton Turn-Off Timing

operaTion

At the end of this blanking time, the LTC2955-1 will check

that the PB pin is high. If the PB pin remains low, it will be

ignored until a high is detected on the pin. The next low

on the PB pin will initiate a turn-off sequence.

Figure 2 shows a similar LTC2955-1 turn-on sequence

with the ON pin going high. The timing sequence is very

similar to that initiated by the pushbutton. The PGD output

follows the ON pin.

PB Pin Turn-Off Sequence

Figure 3 shows the turn-off sequence of the LTC2955-1

initiated through the PB pin. A turn-off sequence refers

to the LTC2955-1 releasing the EN output. This turns off

the voltage regulator.

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. The LTC2955-1 will then release INT and pull

EN low, thus turning off the system power, as shown with

dotted lines in Figure 3.

The user can also force the system to power-down if the

µP fails to respond to the interrupt signal (KILL pin remains

16 CYCLES

KILL

TMR

tDB(OFF)

IGNORED

tEN(LOCKOUT)

tTMR

tINT(MIN)

INT

(LTC2955-1)

2955 F03

t1t2t3t4t5t6t7

IGNORED

tDB(ON) tKILL(ON BLANK)

ON AND KILL IGNORED

2955 F02

(LTC2955-1)

PGD

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operaTion

the PB and ON inputs are ignored. This is to allow time for

the voltage regulator to turn off and for its output to decay

to 0V. This ensures that the µP has completely powered

down before it is allowed to restart. After the one second

lockout time, the LTC2955-1 proceeds to the next stage

to wait for a turn-on command and the cycle will repeat

as above. If the PB pin remains low after the EN output

goes low, the LTC2955-1 will delay the start of this lockout

time until the PB pin goes high.

If the PB pin goes high when the external timer is still

counting, as shown in Figure 4, the turn-off sequence will

be aborted. The INT pin is forced high immediately and

the EN pin remains high.

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). If the

PB pin remains low at the end of the 16 cycles (t5), the

LTC2955-1 will force the EN pin low and the INT pin high.

See Applications Information for adjusting tTMR.

After the EN output goes low and the PB pin goes high,

the LTC2955-1 starts the one second lockout time

(tEN(LOCKOUT)). During this lockout time (t6 to t7 in Figure 3)

Figure 4. Pushbutton Turn-Off Aborted

tDB(OFF)

PB IGNORED

t < tTMR

TMR

tINT(MIN)

2955 F04

INT

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ON Pin Turn-Off Sequence (DFN Package Only)

Figure 5 shows the turn-off sequence of the LTC2955-1

initiated by the ON pin. The timing sequence is slightly

different from that by the pushbutton as there is no de-

bounce time (tDB(OFF)) before the INT pin pulls low. The

ON pin falling edge can start the turn-off sequence only

if the following two conditions are met: (1) The preceding

turn-on sequence was initiated by the ON pin rising edge,

and (2) The SEL pin must be tied high (>0.8V). For TS8

package, the ON pin falling edge is ignored.

In Figure 5, a high to low transition at ON (t1) starts the

turn-off sequence. The interrupt output (INT) is asserted

immediately when the ON pin goes low. Unlike the PB

pin turn-off sequence, there is no 32ms debounce time

(tDB(FF)) for the ON pin going low. This allows the system

to initiate a shutdown as soon as the monitored supply is

removed and allows the µP the maximum amount of time

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 power-

down 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.

If the µP fails to respond (KILL pin remains high, as shown

with solid line in Figure 5) and the ON pin remains low 32ms

after INT goes low, the external timer will start counting

for 16 cycles (tTMR, t3 to t4). If the ON pin remains low

at the end of the 16 cycles (t4), the LTC2955-1 will force

the EN pin low and the INT pin high. See Applications

Information for adjusting tTMR.

After the EN output goes low, the LTC2955-1 starts the

one second lockout time (tEN(LOCKOUT)). During this lockout

time (t4 to t5), the PB and ON inputs are ignored.

operaTion

Figure 5. ON Pin Turn-Off Timing (DFN Only, VSEL > 1.2V and the Preceding Turn-On Sequence Was

Initiated by the ON Pin Rising Edge

16 CYCLES

t1t2t5

TMR

tINT(MIN)

tTMR

tEN(LOCKOUT)

INT

PGD

(LTC2955-1)

2955 F05

KILL IGNORED

IGNORED

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operaTion

PB vs ON Pin

With the DFN package, if the turn-on sequence is initi-

ated 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. This allows the system to remain

powered up if it is plugged in and out of a secondary power

source while the system is already turned on.

If the turn-on sequence is initiated by the ON pin, both

the pushbutton and the ON pin falling edge can initiate

the turn-off sequence. For the TS8 package, ON pin falling

edge is always ignored regardless of which pins initiate

the turn-on.

The PB pin has priority over the ON pin, so if the PB pin

goes low and ON pin goes high at the same time, the

LTC2955-1 will monitor the PB pin for the 32ms debounce

time and ignore the ON pin unless the PB pin bounces

during the 32ms.

ON Pin Initial Turn-On

If the LTC2955-1 powers up with the ON pin already high,

the EN pin will go high after a power-up delay of about

one second. Subsequently, if the pushbutton is pressed

to force EN low, the LTC2955-1 will not initiate another

turn-on even if the ON pin remains high. The LTC2955-1

needs a rising edge at the ON pin or a falling edge on the

PB pin to initiate the subsequent turn-on.

Figure 6. Pushbutton Is Pressed Before the ON Pin Goes High

TURN-ON BY PB

PB PIN

PGD PIN

ON PIN

ON GOING LOW IS IGNORED,

SINCE THE EN IS ASSERTED

BY THE PUSHBUTTON

ON PIN IS IGNORED, SINCE

PUSHBUTTON IS PRESSED

FIRST

EN PIN

2955 F06

t1t2t3t4t5

LTC2955

2955fa

For more information www.linear.com/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.

At time t5, only the rising edge of the ON pin or a PB event

will trigger the next turn-on again.

LTC2955-1, LTC2955-2 Versions

The LTC2955-1 and LTC2955-2 differ only by the polarity

of the high voltage (36V absolute maximum) enable pin.

The LTC2955-1 EN pin is a high true output designed to

drive the SHUTDOWN pin of most voltage regulators. In

turn-on mode, this pin is pulled high by a pull-up current of

2µA powered by an internal LDO, which gives a high level

output voltage (VOH) of typically 4.3V. In turn-off mode,

this pin is pulled low by an internal N-channel MOSFET. If

a higher VOH or higher pull-up current is required, connect

the EN pin to an external source through a pull-up resistor.

The LTC2955-2 EN pin is a low true enable output designed

to drive the gate of an external P-channel MOSFET. In

turn-on mode, the EN pin is pulled low by an internal

N-channel MOSFET. In turn-off mode, this pin is pulled

high to VIN through an internal 900k resistor. An external

pull-up resistor can be connected between this pin and

VIN to increase the pull-up current.

Figure 7. Power First Applied to LTC2955-1

TURN-ON BY ON

RISING EDGE

TURN-OFF BY

PUSHBUTTON

ON PIN

PB PIN

VIN A HIGH AT ON PIN IS IGNORED AFTER

THE FIRST TURN-ON/OFF SEQUENCE ON RISING EDGE

POWER FIRST APPLIED TO

LTC2955 VIN PIN

EN PIN

2955 F07

t1t2t3t4t5

TURN-ON BY ON

HIGH LEVEL

tEN(LOCKOUT) tEN(LOCKOUT)

LTC2955

2955fa

For more information www.linear.com/LTC2955

applicaTions inForMaTion

Adjusting the Forced Turn-Off Timing

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. The length of time that PB must be held

low is given by a fixed 64ms delay (tDB(OFF) + tINT(MIN))

plus an adjustable power-down timer delay (tTMR). The

adjustable delay is set by placing an optional external

capacitor on the TMR pin. Use the following equation to

calculate the capacitance for the desired delay. CTMR is

the external capacitor at the TMR pin:

CTMR = 0.19 • tTMR [µF/sec]

As an example, if the required turn-off debounce time is

one second:

tTMR = (1000ms – 64ms)

CTMR = 0.19 • 0.936

Required CTMR is 0.178µF

The ON pin turn-off debounce time is 32ms less than the

PB pin debounce time since there is no tDB(OFF). If the

TMR pin is left open, the turn-off debounce time defaults

to 64ms for the PB pin and 32ms for the ON pin.

Voltage Monitoring with KILL Input

The KILL pin can also be used as a voltage monitor input.

Figure 8 shows an application where the KILL pin has a dual

function. It is driven by a low leakage open drain output

of the µP. It is also connected to a resistive divider that

monitors battery voltage (VIN). When the battery voltage

falls below the set value, the voltage at the KILL pin falls

below 0.8V 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

0.8V KILL comparator.

Operation Without µP

If there is no circuitry available to drive the KILL pin,

this pin can be connected to a voltage regulator output

through a resistive divider or RC network as shown in

Figure 9. The KILL pin acts as a voltage monitor pin that

shuts down the regulator when its output voltage drops

below a certain level.

The minimum pulse width needed to trigger KILL is 30µs.

If there are glitches on the resistor pull-up voltage that

are wider than 30µs and transition below 0.8V, then an

appropriate bypass capacitor should be connected to the

KILL pin.

Figure 8. Input Voltage Monitoring with KILL Input

Figure 9. Application without µP

*OPTIONAL

INT

KILL

VIN

LTC2955TS8-1

GND TMR

CTMR*

1µF

0.1µF

VIN = 9V

2955 F09

10k

VOUT

VIN VOUT

LT3060

SHDN

C3*

0.01µF

*OPTIONAL

INT

KILL

VIN

LTC2955TS8-1

GND TMR

CTMR*

1µF

0.1µF

583k

VIN = 9V

100k

2955 F08

µP

10k

KILL

(OPEN DRAIN)

INT

VOUT

VIN VOUT

LT3060

SHDN

LTC2955

2955fa

For more information www.linear.com/LTC2955

VTH = 0.8V INPUT

*OPTIONAL

2955 F10

INT

KILL

VIN

LTC2955TS8-2

100k

GND TMR

CTMR*

0.033µF

VOUT

VOUT,TRIP POINT = 6V

0.1µF

649k

100k

R5*

100k

C3*

0.1µF

OPTIONAL GLITCH

FILTER CAPACITOR

4.2V

SINGLE CELL

Li-ION BATTERY

4.2V

SINGLE CELL

Li-ION BATTERY

High Voltage PowerPath™ Switching

The high voltage EN open drain output of the LTC2955-2

is designed to switch on/off an external power P-channel

MOSFET. This allows a user to connect/disconnect a power

supply (or battery) to its load by toggling the PB pin. Figure 10

shows the LTC2955-2 controlling a two cell Li-Ion battery

application. The KILL pin is connected to the output of the

external MOSFET through a resistive divider. The KILL pin

serves as a voltage monitor. When VOUT drops below 6V,

the EN pin is pulled high (to VIN) after 15µs later. R9 slows

down the turning on of M1 so as to limit the inrush current

when M1 turns on to charge up the capacitor at VOUT. R5

helps to speed up the turning off of M1 and also to keep

M1 off when the input voltage rise time is fast.

PB Pin in a Noisy Environment

The rugged PB pin is designed to operate in noisy environ-

ments. Transients below ground and above VIN (–36V <

VIN < 36V) will not damage the rugged PB pin. Additionally,

the PB pin can withstand ESD HBM strikes of up to ±25kV.

However, if the pushbutton switch is located physically far

from the LTC2955 PB pin, the parasitic capacitance and

parasitic series inductance of the connecting cable or PCB

trace can create problems. The parasitic capacitance can

couple external noise onto the PB input; placing a 0.1µF

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.

External Pull-Up Resistor on PB Pin

An internal 900k pull-up resistor on the PB pin makes an

external pull-up resistor unnecessary. Leakage current on

the PB board trace, however, will affect the open circuit

voltage on the PB pin. If the leakage is too large (>1µA),

the PB voltage may fall close to the threshold window. To

applicaTions inForMaTion

Figure 10. PowerPath Control with 6V Undervoltage Detect

Figure 11. Noisy PB Trace

DETAILS OMITTED

FOR CLARITY

PB INT

KILL

VIN

LTC2955-1

GND TMR

0.1µF

5.1k

TRACE

CAPACITANCE

PARASITICS

TRACE

INDUCTANCE

NOISE

VIN

2955 F11

LTC2955

2955fa

For more information www.linear.com/LTC2955

mitigate the effect of the board leakage, a 10k resistor to

VIN is recommended (see Figure 12).

applicaTions inForMaTion

Enhancing VIN Ruggedness

Placing a 1k resistor and a 10nF capacitor at the VIN pin

can be used to enhance ruggedness in some applications.

A 1k resistor in series with the VIN pin allows the LTC2955

to withstand reverse-input voltages. The LTC2955’s VIN pin

is internally clamped to one diode voltage below ground.

In battery operated applications where a battery could be

inserted improperly, this resistor will limit the current and

allow internal clamping to protect the pin.

Figure 12. External Pull-Up Resistor on PB Pin

Figure 13. Enhancing VIN Ruggedness

Figure 14. Using a Slide Switch to Prevent Accidental

Turn-On/Off

Figure 15. Using a Slide or Toggle Switch to Turn-On/Off

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. This can also protect against tran-

sients that may appear on the PCB ground during large

ESD strikes at the PB pin.

The maximum operating current of the LTC2955 is less

than 3µA, creating an insignificant voltage drop across

the resistor. Using a capacitor value of 10nF provides

sufficient filtering for most applications and larger values

can actually diminish its effectiveness.

Applications with Slide Switch

In some applications, to prevent accidental toggling of the

system power, a slide switch is preferred over a pushbut-

ton. Figure 14 shows a slide switch added in series with

the pushbutton. The user can slide the switch open to

activate the HOLD/LOCK function, where the pushbutton

is disabled. Figure 15 shows a slide switch connected to

the LTC2955 ON pin resistive divider. If the user slides

the switch to the ON position, the LTC2955 ON pin is high

*OPTIONAL

INT

KILL

VIN

LTC2955TS8-1

GND TMR

CONT*

0.033µF

10nF

BATTERY

2955 F13

µP

10k

KILL

INT

VIN VOUT

LT3060

SHDN

PINS OMITTED

FOR CLARITY

EXTERNAL BOARD

LEAKAGE CURRENT

10k

IF EXTERNAL PARASITIC BOARD

LEAKAGE >2µA USE EXTERNAL

PULL-UP RESISTOR

VIN

900k

VLDO

LTC2955-1/

LTC2955-2

GND

0.8V

>2µA

2955 F12

NORMAL

HOLD/LOCK

VIN

SEL

LTC2955DDB-1

GND

2955 F14

VIN

SEL

LTC2955DDB-1

GND

OFF

2955 F15

LTC2955

2955fa

For more information www.linear.com/LTC2955

applicaTions inForMaTion

If a higher VEN(VOH) is required, an external pull-up resistor

can be connected from the EN pin to any higher voltage

(<36V). The EN pin is designed to be able to sink at least

1mA of current during turn-off, so this external pull-up

resistor value must be selected to source less than 1mA

with EN at 0V.

The LTC2955-1 EN pin can also be connected to switching

regulators with a RUN/SS pin. RUN/SS has a dual func-

tion of a SHUTDOWN threshold and soft-start, with an

internal soft-start pull-up current and an external soft-start

capacitor. The LTC2955 EN pin pull-up current of 2µA will

add to the soft-start pull-up current of the regulator. The

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 1.5V, VEN(VOH) is still higher than most

SHUTDOWN thresholds (usually <1.2V). Figure 16 shows

one such application. The regulator is a boost converter

with a SHUTDOWN high threshold of 0.88V (maximum).

Figure 16. 2-Cell with 3.3V Output

Figure 17. Turn-On/Off a DC/DC Regulator Through the

RUN/SS Pin

Figure 18. Recommended Layout for the VIN Bypass

Capacitor

LTC3528

VOUT

VIN

PGOOD

SHDN

VIN

INT

KILL

VIN TMR

LTC2955TS8-1

2955 F16

499k

GND

VOUT

3.3V

0.4A

287k

GND

4.7µF

1.5V TO 3.2V

22pF

22µF

4.7µH

DC/DC

VOUT

RUN/SS VOUT

GND

CSS

COUT

VIN

INT

VIN

LTC2955TS8-1

2955 F17

µP

GND

TMR

KILL

CIN

soft-start capacitor may need to be increased to maintain

the same soft-start time. The soft-start behavior of the

regulator will remain the same.

Figure 17 shows the LTC2955-1 EN pin connected to a

DC/DC regulator RUN/SS pin.

Layout Considerations

Figure 18 shows example PCB layouts for placing the VIN

pin bypass capacitor. Position the bypass capacitor close

to the LTC2955 on the same side of the PCB and keep the

traces short. For the DFN package, a PCB via should be

placed near the LTC2955 to connect the PB pin (Pin 5)

to the pushbutton. This allows an unbroken trace to be

placed between the VIN pin and the bypass capacitor.

Placing the bypass capacitor close to the LTC2955 gives

the optimum protection against PB pin ESD transients.

2955 F18

GND

CVIN

LTC2955DDB

VIN

LTC2955TS8

GND

CVIN

LTC2955

2955fa

For more information www.linear.com/LTC2955

Typical applicaTions

Low Voltage Pushbutton Controller Enables Charge Pump Automatic Power-Up with Pushbutton On/Off

PowerPath Control with Immediate KILL

LTC3204-3.3

VOUT

C+

C–

VIN

GND

INT

KILL

VIN

LTC2955TS8-1

2955 TA02

µP

GND ONTMR

2.2µF

3.3V

SHDN

2.2µF

1.8V

LT1763-5

VOUT

VIN

INT

KILL

PGD

TMR

VIN

LTC2955DDB-1

2955 TA03

µP

GNDSEL

*OPTIONAL RC NETWORK RECOMMENDED TO IMPROVE NOISE IMMUNITY

SHDN

1µF

12V

0.1µF*

5.1k*

LT3009

VOUT

VIN

KILL

INT

VIN

LTC2955TS8-2

2955 TA04

GND ONTMR

3.3V

100k

SHDN

0.1µF

12V

LTC2955

2955fa

For more information www.linear.com/LTC2955

package DescripTion

Please refer to http://www.linear.com/product/LTC2955#packaging for the most recent package drawings.

2.00 ±0.10

(2 SIDES)

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

0.40 ±0.10

BOTTOM VIEW—EXPOSED PAD

0.64 ±0.05

(2 SIDES)

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

2.39 ±0.05

(2 SIDES)

3.00 ±0.10

(2 SIDES)

106

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

0.200 REF

0 – 0.05

(DDB10) DFN 0905 REV Ø

0.25 ±0.05

0.50 BSC

PIN 1

R = 0.20 OR

0.25 × 45°

CHAMFER

0.25 ±0.05

2.39 ±0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

0.64 ±0.05

(2 SIDES)

1.15 ±0.05

0.70 ±0.05

2.55 ±0.05

PACKAGE

OUTLINE

0.50 BSC

DDB Package

10-Lead Plastic DFN (3mm × 2mm)

(Reference LTC DWG # 05-08-1722 Rev Ø)

LTC2955

2955fa

For more information www.linear.com/LTC2955

Please refer to http://www.linear.com/product/LTC2955#packaging for the most recent package drawings.

1.50 – 1.75

(NOTE 4)

2.80 BSC

0.22 – 0.36

8 PLCS (NOTE 3)

DATUM ‘A’

0.09 – 0.20

(NOTE 3)

TS8 TSOT-23 0710 REV A

2.90 BSC

(NOTE 4)

0.65 BSC

1.95 BSC

0.80 – 0.90

1.00 MAX 0.01 – 0.10

0.20 BSC

0.30 – 0.50 REF

PIN ONE ID

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

3.85 MAX

0.40

MAX

0.65

REF

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

1.4 MIN

2.62 REF

1.22 REF

package DescripTion

LTC2955

2955fa

For more information www.linear.com/LTC2955

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibilit y is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER

A 04/16 Clarified requirements for turn-on 4, 12

LTC2955

2955fa

For more information www.linear.com/LTC2955

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

 LINEAR TECHNOLOGY CORPORATION 2012

LT 0416 REV A • PRINTED IN USA

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC2955

relaTeD parTs

Typical applicaTion

PART NUMBER DESCRIPTION COMMENTS

LTC2900 Programmable Quad Supply Monitor Adjustable RESET, 10-Lead MSOP and 3mm × 3mm DFN Packages

LTC2904/LTC2905 Pin-Programmable Dual Supply Monitors Adjustable RESET and Tolerance, 8-Lead SOT-23 and 3mm × 2mm DFN Packages

LTC2909 Precision Triple/Dual Input UV, OV and

Negative Voltage Monitor

6.5V Shunt Regulator for High Voltage Operation

LTC2910 Octal Positive/Negative Voltage Monitor Eight Adjustable Inputs (0.5V)

LTC2914 Quad UV/OV Positive/Negative Voltage

Monitor

Adjustable UV and OV Trip Values

LTC2950/LTC2951 Pushbutton On/Off Controllers High Voltage, Low Power Pushbutton Controllers with Power-Down Fault Detect KILL

Timer

LTC2952 Pushbutton PowerPath Controller with

Supervisor

Automatic Low Loss Switchover Between DC Sources

LTC2953 Pushbutton Controller with Voltage

Monitoring

Adjustable Supply Monitor with 200ms Reset

LTC2954 Pushbutton On/Off Controller with µP

Interrupt

Adjustable Turn On/Off Timers

LTC4411 2.6A Low Loss Ideal Diode in ThinSOT No External MOSFET, Automatic Switching Between DC Sources

LTC4412HV Power Path Controller in ThinSOT Efficient Diode-ORing, Automatic Switching Between DC Sources, 3V to 36V

LTC4055 USB Power Controller and Li-Ion Charger Automatic Switchover, Charges 1-Cell Li-Ion Batteries

LTC4352 Ideal Diode Controller with Monitoring Controls N-Channel MOSFET, OV to 18V Operation

9.6V THRESHOLD

P-CHANNEL

MOSFET

PGD

INT

KILL

VIN

SEL

TMR

LTC2955DDB-1

2955 TA05

µP

2.21M

200k

33nF

12V

4.5V

GND

SHDN

LT3009-3.3

LTC4412

GATE

SENSE

STAT

VIN

GND

CTL

Pushbutton On/Off Control with Automatic Turn-On

When 12V Applied