LTC2954

Pushbutton On/Off
Controller with µP Interrupt
FEATURES DESCRIPTION
n Adjustable Power On/Off Timers The LTC®2954 is a pushbutton on/off controller that
n Low Supply Current: 6μA manages system power via a pushbutton interface. An
n Wide Operating Voltage Range: 2.7V to 26.4V enable output toggles system power while an interrupt
n Low Leakage EN Output (LTC2954-1) Allows DC/DC output provides debounced pushbutton status. The inter-
Converter Control rupt output can be used in menu driven applications to
n High Voltage EN Output (LTC2954-2) Allows Circuit request a system power-down. A power kill input allows
Breaker Control a microprocessor or system to reset the enable output,
n Simple Interface Allows Graceful μP Shutdown effectively powering down the system. Independently
n High Input Voltage PB Pin with Internal Pull-Up adjustable on and off timers allow dependable pushbutton
Resistor control of the enable output and resistance to accidental
n ±10kV ESD HBM on PB Input toggling of system power.
n Accurate 0.6V Threshold on KILL Comparator Input
n
The LTC2954 operates over a wide 2.7V to 26.4V input volt-
8-Pin 3mm × 2mm DFN and ThinSOT™ Packages
age range to accommodate a wide variety of input power
supplies. Very low quiescent current (6μA typical) makes
APPLICATIONS the LTC2954 ideally suited for battery powered applications.
n
Two versions of the part are available to accommodate
Pushbutton PowerPath™ Control
n
either positive or negative enable polarities.
Portable Instrumentation Meters
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
n Blade Servers PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks
n are the property of their respective owners.
Portable Customer Service PDA
n Desktop and Notebook Computers

TYPICAL APPLICATION
Pushbutton On/Off with Interrupt

VIN VOUT
TURN-ON PULSE SHORT PULSE LONG PULSE
DC/DC
+ PB
100k 100k
9V

EN TURNS ON STAYS ON TURNS OFF

VIN EN 10k

LTC2954-2 INT INT INT

μP/μC
INTERRUPT INTERRUPT
PB KILL KILL
2954 TA01b
GND ONT PDT
2954 TA01a

1μF

tPDT = 6.4 SECONDS

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LTC2954
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (VIN) .................................. –0.3V to 33V Operating Temperature Range
Input Voltages LTC2954C-1 ............................................. 0°C to 70°C
PB ............................................................ –6V to 33V LTC2954C-2 ............................................. 0°C to 70°C
ONT ...................................................... –0.3V to 2.7V LTC2954I-1 ..........................................–40°C to 85°C
PDT ....................................................... –0.3V to 2.7V LTC2954I-2 ..........................................–40°C to 85°C
KILL ......................................................... –0.3V to 7V Storage Temperature Range
Output Voltages DFN Package ..................................... –65°C to 125°C
INT ......................................................... –0.3V to 10V TSOT-23 ............................................. –65°C to 150°C
EN/EN .................................................... –0.3V to 33V Lead Temperature (Soldering, 10 sec)................... 300°C

PIN CONFIGURATION
TOP VIEW

TOP VIEW
GND 1 8 INT
VIN 1 8 KILL
ONT 2 7 EN/EN
9 PB 2 7 PDT
PB 3 6 PDT ONT 3 6 EN/EN
VIN 4 5 KILL GND 4 5 INT

TS8 PACKAGE
DDB PACKAGE 8-LEAD PLASTIC TSOT-23
8-LEAD (3mm s 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 140°C/W
TJMAX = 125°C, θJA = 165°C/W
EXPOSED PAD (PIN 9) PCB GND CONNECTION OPTIONAL

ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2954CDDB-1#PBF LTC2954CDDB-1#TRPBF LCJG 8-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C
LTC2954CDDB-2#PBF LTC2954CDDB-2#TRPBF LCNJ 8-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C
LTC2954IDDB-1#PBF LTC2954IDDB-1#TRPBF LCJG 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C
LTC2954IDDB-2#PBF LTC2954IDDB-2#TRPBF LCNJ 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C
LTC2954CTS8-1#PBF LTC2954CTS8-1#TRPBF LTCJH 8-Lead Plastic TSOT-23 0°C to 70°C
LTC2954CTS8-2#PBF LTC2954CTS8-2#TRPBF LTCNK 8-Lead Plastic TSOT-23 0°C to 70°C
LTC2954ITS8-1#PBF LTC2954ITS8-1#TRPBF LTCJH 8-Lead Plastic TSOT-23 –40°C to 85°C
LTC2954ITS8-2#PBF LTC2954ITS8-2#TRPBF LTCNK 8-Lead Plastic TSOT-23 –40°C to 85°C
LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2954CDDB-1 LTC2954CDDB-1#TR LCJG 8-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C
LTC2954CDDB-2 LTC2954CDDB-2#TR LCNJ 8-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C
LTC2954IDDB-1 LTC2954IDDB-1#TR LCJG 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C
LTC2954IDDB-2 LTC2954IDDB-2#TR LCNJ 8-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C
LTC2954CTS8-1 LTC2954CTS8-1#TR LTCJH 8-Lead Plastic TSOT-23 0°C to 70°C
LTC2954CTS8-2 LTC2954CTS8-2#TR LTCNK 8-Lead Plastic TSOT-23 0°C to 70°C
LTC2954ITS8-1 LTC2954ITS8-1#TR LTCJH 8-Lead Plastic TSOT-23 –40°C to 85°C
LTC2954ITS8-2 LTC2954ITS8-2#TR LTCNK 8-Lead Plastic TSOT-23 –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
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 LTC2954
ELECTRICAL CHARACTERISTICS The l 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)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Supply Voltage Range Steady State Operation l 2.7 26.4 V
IIN VIN Supply Current System Power-On, VIN = 2.7V to 24V l 6 12 μA
VUVL VIN Undervoltage Lockout VIN Falling l 2.2 2.3 2.5 V
VUVL(HYST) VIN Undervoltage Lockout 50 400 700 mV
Hysteresis
Pushbutton, Enable (PB, EN/EN))
VPB(MIN, MAX) PB Voltage Range Single-Ended l –1 26.4 V
IPB PB Input Current 2.5V < VPB < 26.4V l ±1 μA
VPB = 1V l –1 –6 –12 μA
VPB = 0.6V l –3 –9 –15 μA
VPB(VTH) PB Input Threshold PB Falling l 0.6 0.8 1 V
VPB(VOC) PB Open Circuit Voltage IPB = –1μA 1 1.6 2 V
t EN, LOCKOUT EN/EN Lockout Time (Note 5) Enable Released → Enable Asserted l 200 256 325 ms
IEN(LKG) EN/EN Leakage Current VEN/ EN = 1V, Sink Current Off l ±0.1 μA
VEN/ EN = 26.4V, Sink Current Off l ±1 μA
VEN(VOL) EN/EN Voltage Output Low IEN/ EN = 500μA l 0.11 0.4 V
Power-On Timing Pin (ONT)
IONT(PU) ONT Pull-Up Current VONT = 0V l –2.4 –3 –3.6 μA
IONT(PD) ONT Pull-Down Current VONT = 1.3V l 2.4 3 3.6 μA
tDB, ON Internal Turn-On Debounce Time ONT Pin Float, PB Falling → Enable Asserted l 26 32 41 ms
tONT Additional Adjustable Turn-On Time CONT = 1500pF l 9 11.5 13.5 ms
Power-Down Timing Pin (PDT)
IPDT(PU) PDT Pull-Up Current VPDT = 0V l –2.4 –3 –3.6 μA
IPDT(PD) PDT Pull-Down Current VPDT = 1.3V l 2.4 3 3.6 μA
t DB, OFF Turn-Off Interrupt Debounce Time PB Falling → INT Falling l 26 32 41 ms
t PD,MIN Internal PB Power-Down Debounce PDT Pin Float, PB Falling → Enable Released l 52 64 82 ms
Time (Note 4)
t PDT Additional Adjustable PB CPDT = 1500pF l 9 11.5 13.5 ms
Power-Down Debounce Time
t INT,MIN Minimum INT Pulse Width INT Asserted → INT Released l 26 32 41 ms
t INT,MAX Maximum INT Pulse Width CPDT = 1500pF, INT Asserted → INT Released l 35 43.5 54.5 ms
μP Handshake Pins (INT, KILL)
IINT(LKG) INT Leakage Current VINT = 3V l ±1 μA
VINT(VOL) INT Output Voltage Low IINT = 3mA l 0.11 0.4 V
VKILL(TH) KILL Input Threshold Voltage KILL Falling l 0.57 0.6 0.63 V
VKILL(HYST) KILL Input Threshold Hysteresis l 10 30 50 mV
IKILL(LKG) KILL Leakage Current V KILL = 0.6V l ±0.1 μA
t KILL(PW) KILL Minimum Pulse Width l 30 μs
t KILL(PD) KILL Propagation Delay KILL Falling → Enable Released l 30 μs
t KILL,ON BLANK KILL Turn-On Blanking (Note 3) KILL = Low, Enable Asserted → Enable Released l 400 512 650 ms

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LTC2954
ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings thus turning off system power. This time delay does not include t DB,ON
may cause permanent damage to the device. Exposure to any Absolute or t ONT.
Maximum Rating condition for extended periods may affect device Note 4: To manually force an immediate release of the EN/EN pin, the
reliability and lifetime. pushbutton input must be held low for at least tPD,MIN (internal default
Note 2: All currents into pins are positive; all voltages are referenced to power-down timer) + t PDT (adjustable by placing external capacitor at
GND unless otherwise noted. PDT pin).
Note 3: The KILL turn-on blanking timer period is the waiting period Note 5: The enable lockout time is designed to allow an application to
immediately after the enable output is asserted. This blanking time allows properly power-down such that the next power-up sequence starts from a
sufficient time for the DC/DC converter and the μP to perform power-up consistent powered-down configuration. PB is ignored during this lockout
tasks. The KILL and PB inputs are ignored during this period. If KILL time. This time delay does not include tDB,ON or tONT.
remains low at the end of this time period, the enable output is released,

TYPICAL PERFORMANCE CHARACTERISTICS

Internal Default Turn-On

Supply Current vs Temperature Supply Current vs Supply Voltage Debounce Time (tDB, ON) vs VIN
10 15 50
VIN = 26.4V TA = 25°C

8 12 T = 25°C 40
T = 85°C
VIN = 3.3V
6 9 tDB, ON (ms) 30
IVIN (μA)

IVIN (μA)

VIN = 2.7V T = –40°C

4 6 20

2 3 10

0 0 0
–50 –25 0 25 50 75 100 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30
TEMPERATURE (°C) VIN (V) VIN (V)
2954 G01 2954 G02 2954 G03

Turn-On Debounce Time (tDB, ON + ONT Pull-Up Current Turn-Off Debounce Time (tDB, OFF)
tONT) vs ONT External Capacitance vs Temperature vs VIN
10000 –3.4 50
TA = 25°C TA = 25°C
VIN = 3.3V
40
ONT PULL-UP CURRENT (μA)

–3.2
tDB, ON + tONT (ms)

1000
tDB, OFF (ms)

VIN = 26.4V 30
–3.0
VIN = 2.7V 20
100
–2.8
10

10 –2.6 0
1 10 100 1000 –50 –25 0 25 50 75 100 0 5 10 15 20 25 30
ONT EXTERNAL CAPACITANCE (nF) TEMPERATURE (°C) VIN (V)
2954 G04 2954 G05 2954 G06

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 LTC2954
TYPICAL PERFORMANCE CHARACTERISTICS
PB Power-Down Debounce Time
Internal Default PB Power-Down (tPD,MIN + tPDT) vs PDT External PDT Pull-Up Current
Debounce Time (t PD,MIN) vs VIN Capacitance vs Temperature
70 10000 –3.4
TA = 25°C
VIN = 3.3V
60
TA = 25°C

PDT PULL-UP CURRENT (μA)

–3.2
50

tPD, MIN + tPDT (ms)

1000
tPD, MIN (ms)

VIN = 26.4V
40
–3.0
30 VIN = 2.7V
100
20
–2.8

10

0 10 –2.6
0 5 10 15 20 25 30 1 10 100 1000 –50 –25 0 25 50 75 100
VIN (V) PDT EXTERNAL CAPACITANCE (nF) TEMPERATURE (°C)
2954 G07 2954 G08 2954 G09

PB Voltage vs External PB
PB Current vs PB Voltage Resistance to Ground
–250 300
TA = 25°C VIN = 3.3V
VIN = 3.3V
250
–200
PB VOLTAGE (mV)
PB CURRENT (μA)

200
TA = 100°C
–150
150 TA = 25°C
–100
TA = –45°C
100

–50
50

0 0
–10 –5 0 5 10 15 20 25 30 0 5 10 15 20
PB VOLTAGE (V) EXTERNAL PB RESISTANCE TO GROUND (kΩ)
2954 G10 2954 G11

EN/EN VOL vs Current Load EN (LTC2954-1) Voltage vs VIN EN (LTC2954-2) Voltage vs VIN
600 1.0 4
TA = 25°C TA = 25°C TA = 25°C
VIN = 3.3V 100k PULL-UP FROM EN TO VIN 100k PULL-UP FROM EN TO VIN
500
0.8
3
EN/EN VOLTAGE (mV)

400
0.6
EN (V)

EN (V)

300 2
0.4
200
1
0.2
100

0 0 0
0.0 0.5 1.0 1.5 2.0 2.5 0 1 2 3 4 0 1 2 3 4
EN/EN CURRENT LOAD (mA) VIN (V) VIN (V)
2954 G12 2954 G13 2954 G14

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LTC2954
PIN FUNCTIONS (TSOT-23/DFN)
VIN (Pin 1/Pin 4): Power Supply Input: 2.7V to 26.4V. and held low (tPD,MIN + tPDT) during normal operation. This
pin can connect directly to a DC/DC converter shutdown
PB (Pin 2/Pin 3): Pushbutton Input. Connecting PB to
pin that provides an internal pull-up. Otherwise a pull-up
ground through a momentary switch provides on/off
resistor to an external supply is required. The operating
control via the EN/EN and INT outputs. An internal 100k
range for this low leakage pin is 0V to 26.4V.
pull-up resistor connects to an internal 1.9V bias voltage.
The rugged PB input withstands ±10kV ESD HBM and EN (LTC2954-2, Pin 6/Pin 7): Open Drain Enable Bar
can be pulled up to 26.4V externally without consuming Output. This pin is intended to enable system power. EN is
extra current. asserted low after a valid PB turn-on event (t DB,ON + t ONT).
EN releases high if: a) KILL is not driven high (by μP) within
ONT (Pin 3/Pin 2): Turn-On Time Input. Placing an external
512ms of the initial valid PB power turn-on event, b) KILL
capacitor to ground determines the additional time (6.4
is driven low during normal operation, c) PB is pressed
seconds/μF) the PB pin must be held low before the enable
and held low (tPD,MIN + tPDT) during normal operation. This
output is asserted. Floating this pin results in a default
pin can connect directly to a DC/DC converter shutdown
turn on debounce time of 32ms.
pin that provides an internal pull-up. Otherwise a pull-up
GND (Pin 4/Pin 1): Device Ground. resistor to an external supply is required. The operating
INT (Pin 5/Pin 8): Open Drain Interrupt Output. After a range of this pin is 0V to 26.4V.
pushbutton turn-off event is detected (tDB,OFF), the LTC2954 PDT (Pin 7/Pin 6): Power-Down Time Input. A capacitor
interrupts the system (μP) by asserting the INT pin low. to ground determines the additional time (6.4 seconds/μF)
The μP would perform power-down and housekeeping that the pushbutton must be held low before immediately
tasks and then assert the KILL pin low, thus releasing the releasing the EN/EN and INT outputs. Floating this pin
enable output. The INT pulse width is a minimum of 32ms results in a pushbutton power-down time of 64ms.
and stays low as long as PB is asserted. If PB is asserted
for longer than tPD,MIN + tPDT, the INT and EN/EN outputs KILL (Pin 8/Pin 5): Kill Input. Forcing KILL low releases the
are immediately released. enable output. During system turn-on, this pin is blanked by
a 512ms internal timer (tKILL,ON BLANK) to allow the system
EN (LTC2954-1, Pin 6/Pin 7): Open Drain Enable Output. to pull KILL high. This pin has an accurate 0.6V threshold
This pin is intended to enable system power. EN is asserted and can be used as a voltage monitor input. If unused,
high after a valid PB turn-on event (tDB,ON + tONT). EN is connect to a low voltage output supply (see Figure 6).
released low if: a) KILL is not driven high (by μP) within
512ms of the initial valid PB power turn-on event, b) KILL Exposed Pad (Pin 9 DFN Only): Exposed Pad may be left
is driven low during normal operation, c) PB is pressed open or connected to device ground.

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 LTC2954
BLOCK DIAGRAM

EN (–1)
EN (–2)
HIGH VOLTAGE
VIN 1.5k
REGULATOR 2.4V
2.7V TO 26.4V
29V
2.4V ZENER

OSCILLATOR KILL
100k
PB
LOGIC
10μS
FILTER DEBOUNCE 0.6V

0.8V
INT
OSCILLATOR

GND

ONT PDT
2954 BD

TIMING DIAGRAMS

tKILL(PW)

KILL

tKILL(PD)

EN/EN

2954 TD01

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LTC2954
TIMING DIAGRAMS
PB PB & KILL IGNORED

tDB, ON tONT tKILL, ON BLANK

ONT

16 CYCLES

EN
(LTC2954-1)

2954 TD02

Power-On Timing

PB PB IGNORED

tDB, OFF t < tPDT

PDT

tPD,MIN

INT

tINT,MIN
2954 TD03

Off Interrupt Timing, PB Pressed and Released, Enable Remains Active

PB
PB IGNORED

tDB, OFF
16 CYCLES

PDT

tPD,MIN tPDT

INT

tINT,MAX

EN
(LTC2954-1)

2954 TD04

Forced Off, Power-Down Timing, PB Pressed and Held Low for t > (tPD,MIN + tPDT)
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 LTC2954
APPLICATIONS INFORMATION
Description maximum time required to power up the DC/DC converter
and the μP. If KILL is not brought high during this 512ms
The LTC2954 is a pushbutton on/off controller that provides
time window, the enable output is released. The assump-
control of system power via a pushbutton interface. An
tion is that 512ms is sufficient time for the system to
enable output toggles system power while an interrupt
power up.
output provides debounced pushbutton status. The inter-
rupt output can be used in menu driven applications to Turn Off
request a system power-down. A power kill input allows
a microprocessor or system to release the enable output, To initiate a power-down sequence, assert the INT output
effectively powering down the system. Independently ad- low by pressing the pushbutton for a minimum of 32ms
justable on and off timers allow dependable pushbutton (tDB,OFF). The interrupt signal serves as a power-down
control of the enable output and resistance to accidental request to the μP. The μP would then perform power-down
toggling of system power. and housekeeping tasks and assert KILL low when done.
This in turn releases the enable output, thus shutting off
The length of time the pushbutton input (PB) must be held system power.
low in order to toggle the enable (EN/EN) output on and
off is independently adjustable with external capacitors Adjustable Power-Down Timer
at the ONT/PDT pins, respectively. During normal opera-
tion, the interrupt output (INT) is asserted 32ms after PB The LTC2954 provides a failsafe feature that allows the
goes low. INT then tracks PB until either PB or EN/EN is user to turn off system power (via PB) under system fault
released. See Timing Diagrams on page 8. conditions. For cases when the μP fails to respond to the
interrupt signal, the user can force an immediate power-
The KILL input is used to immediately release the enable down by pressing and holding down the pushbutton. The
output. During a normal power-down sequence, INT re- length of time that PB must be held low is given by a fixed
quests a system power-down. The μP then performs its internal 64ms delay (tPD,MIN) plus an adjustable power-
housekeeping tasks and then sets KILL low. If the μP fails down timer delay (tPDT, see Timing Diagrams on page 8).
to set KILL low, the user can force a system shutdown by The adjustable delay is set by placing an optional external
pressing and holding the pushbutton until the PDT timer capacitor on the PDT pin. Use the following equation to
expires. calculate the capacitance for the desired delay. CPDT is the
PDT external capacitor (μF):
Turn On
CPDT = 1.56 × 10-4 [μF/ms] • (tPDT – 1ms)
When power is first applied to the LTC2954, the part ini-
tializes the output pins. Any DC/DC converters connected Simplified Power On/Off Sequence
to the EN/EN pin will therefore be held off. To assert the
enable output, PB must be held low for a minimum of Figure 1 shows a simplified LTC2954-1 power-on and
32ms (tDB, ON). The LTC2954 provides additional turn-on power-off sequence. A high to low transition on PB (t1)
debounce time (tONT) via an optional capacitor connected initiates the power on sequence. In order to assert the
to the ONT pin. The following equation describes the ad- enable output, the PB pin must stay low continuously (PB
ditional time that PB must be held low before asserting the high resets timers) for a time controlled by the default
enable output. CONT is the ONT external capacitor (μF): 32ms and the external ONT capacitor (t2 –t1). Once EN
goes high (t2), an internal 512ms blanking timer is started.
CONT = 1.56 × 10–4 [μF/ms] • (tONT – 1ms) This blanking timer is designed to give sufficient time for
Once the enable output is asserted, any DC/DC converters the DC/DC converter to reach its final voltage, and to allow
connected to this pin are turned on. The KILL input from the μP enough time to perform power-on tasks.
the μP is ignored during a succeeding 512ms blanking The KILL pin must be pulled high within 512ms of the EN
time (t KILL,ON BLANK). This blanking time represents the pin going high. Failure to do so results in the EN pin going
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LTC2954
APPLICATIONS INFORMATION
t1 t2 t3 t4 t5 t6 t7 t8 t9

PB PB & KILL IGNORED PB IGNORED

tDB, ON t KILL, ON BLANK tDB, OFF

ONT

tONT

PDT

tPD, MIN

INT

t < tPDT

KILL XXX DON'T CARE μP DRIVES

KILL LOW

EN

2954 F01

Figure 1. Simplified Power On/Off Sequence for LTC2954-1. μP Asserts KILL After an Interrupt

tABORT

PB

tDB,ON + tONT 512ms

INTERNAL
TIMER

POWER-ON
TIMING

POWER
TURNED OFF

EN

μP FAILED TO SET
KILL HIGH

KILL

2954 F02

Figure 2. KILL Remaining Low Aborts Power-On Sequence for LTC2954-1

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 LTC2954
APPLICATIONS INFORMATION
low 512ms after it went high. Note that the LTC2954 does Aborted Power-On Sequence
not sample KILL and PB until after the 512ms internal timer The power-on sequence is aborted when the KILL remains
has expired. The reason PB is ignored is to ensure that low at the end of the 512ms blanking time. Figure 2 is a
the system is not forced off while powering on. Once the simplified version of an aborted power-on sequence. At
512ms timer expires (t4), the release of the PB pin is then time tABORT, since KILL is still low, EN pulls low (thus
debounced with an internal 32ms timer. The system has turning off the DC/DC converter).
now properly powered on and the LTC2954 monitors PB
and KILL for a turn-off command while consuming only μP Turns Off Power During Normal Operation
6μA of supply current.
Once the system has powered on and is operating nor-
A high to low transition on PB (t5) starts the power-off mally, the μP can turn off power by setting KILL low, as
sequence debounce timer. In order to assert the interrupt shown in (Figure 3). At time t KILL, KILL is set low by the
output (INT), PB must stay low continuously (PB high μP. This immediately pulls EN low, thus turning off the
resets debounce timer) for 32ms (t6–t5). At the comple- DC/DC converter.
tion of the power-down debounce timer (t6), an internal
interrupt timer keeps the interrupt output low for at least DC/DC Turn Off Blanking
32ms, even if PB is released between t6 and t7. If PB is
low at the end of this 32ms internal timer (t7), the external When the DC/DC converter is turned off, it can take a sig-
adjustable power-down timer is started. The capacitor nificant amount of time for its output to decay to ground. It
placed at the PDT pin will determine the time period of is desirable to wait until the output of the DC/DC converter
this timer. If the pushbutton is released prior to 16 cycles is near ground before allowing the user (via PB) to restart
of the PDT pin, the interrupt output will go high (t8). Note the converter. This condition guarantees that the μP has
that the enable output is not directly changed by this always powered down completely before it is restarted.
interrupt pulse. The function of the interrupt signal is to Figure 4 shows the μP turning power off. After a low on
initiate a software shutdown. At t9, the μP has performed KILL releases enable, the internal 256ms timer ignores the
its power-down functions and asserted the KILL input PB pin. This is shown as tEN/EN, LOCKOUT in (Figure 4).
low. This releases the enable output, which in turn shuts
down system power. Note that if the pushbutton is held
long enough to count 16 cycles at the PDT pin, the enable
pin would be released immediately after the 16th cycle.
The system is now in its reset state where the LTC2954 is
in low power mode (6μA) and PB is monitored for a high tEN/EN, LOCKOUT

to low transition. PB POWER ON PB IGNORED

tKILL
DC/DC
TURNS OFF
PB 256ms
PB BLANKING
(INTERNAL
DC/DC SIGNAL)
TURNS OFF

EN
EN

μP SETS
KILL LOW μP SETS
KILL LOW

KILL XXX DON’T CARE KILL XXX DON’T CARE

2954 F03 2954 F04

Figure 3. μP Turns Off Power (LTC2954-1) Figure 4. DC/DC Turn-Off Blanking (LTC2954-1)
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LTC2954
APPLICATIONS INFORMATION
LTC2954-1, LTC2954-2 Versions without latching up the device. PB has an ESD HBM rating
The LTC2954-1 (high true EN) and LTC2954-2 (low true of ±10kV. If the pushbutton switch connected to PB exhib-
EN) differ only by the polarity of the high voltage (33V ABS its high leakage current, then an external pull-up resistor
MAX), enable pin. The LTC2954-1 EN pin is a low leakage to VIN is recommended. Furthermore, if the pushbutton
switch is physically located far from the LTC2954 PB pin,
high true open drain output designed to drive the shutdown
parasitic capacitances may couple onto the high imped-
pin of DC/DC converters. The LTC2954-2 is a low leakage,
ance PB input. Additionally, parasitic series inductance
low true open drain enable output designed to drive the
may cause unpredictable ringing at the PB pin. Placing
gate of an external PFET. The LTC2954-2 provides a user
a 5.1k resistor from the PB pin to the pushbutton switch
manual power path control.
would mitigate parasitic inductance problems. Placing a
High Voltage Pins 0.1μF capacitor on the PB pin would lessen the impact of
parasitic capacitive coupling.
The VIN, PB and EN/EN pins can operate at voltages up to
26.4V. PB can, additionally, operate below ground (–6V)

TYPICAL APPLICATIONS
Voltage Monitoring with KILL Input enough to keep leakage currents from tripping the 0.6V
KILL comparator.
The KILL pin can be used as a voltage monitor. Figure 5
shows an application where the KILL pin has a dual func- The DC/DC converter shown has an internal pull-up cur-
tion. It is driven by a low leakage open drain output of the rent on its SHDN pin. A pull-up resistor on EN is thus not
μP. It is also connected to a resistive divider that monitors needed.
battery voltage (VIN). When the battery voltage falls be-
low the set value, the voltage at the KILL pin falls below Operation Without μP
0.6V and the EN pin is quickly pulled low. Note that the Figure 6 shows how to connect the KILL pin when there
resistor values should be as large as possible, but small is no circuitry available to drive it. The minimum pulse
VIN = 9V VIN = 9V

VIN VOUT 3.3V VIN VOUT 3.3V

LT1767-3.3 LT1767-3.3
R3
806k SHDN** SHDN**
1%
R2
100k
1%
R1
100k
R1
VIN EN VIN EN
C4 10k C4
LTC2954-1 LTC2954-1
0.1μF 0.1μF
INT INT INT
μP
PB KILL KILL PB KILL
(OPEN DRAIN)
GND ONT PDT GND ONT PDT + C3*
2954 F05
CONT* CPDT* 0.01μF
CONT* CPDT* * OPTIONAL 0.033μF 1μF * OPTIONAL
0.033μF 1μF ** SHDN INTERNALLY PULLED ** SHDN INTERNALLY 2954 F06

UP BY THE LT1767-3.3 PULLED UP BY

THE LT1767-3.3

Figure 5. Input Voltage Monitoring with KILL Input Figure 6. No μP Application

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12
 LTC2954
TYPICAL APPLICATIONS
width detected is 30μs. If there are glitches on the resis- PFET through a resistive divider. The KILL pin serves as
tor pull-up voltage that are wider than 30μs and transition a voltage monitor. When VOUT drops below 6V, causing a
below 0.6V, then an appropriate bypass capacitor should KILL voltage below VKILL(TH), the EN pin becomes an open
be connected to the KILL pin. The optional CPDT external circuit 30μs later. Since the PDT pin is open-circuited, the
capacitor extends the length of time (beyond 64ms) that power-down debounce time defaults to 64ms.
the PB input must be held low before releasing the enable
output. PB Pin in a Noisy Environment
The rugged PB pin is designed to operate in noisy environ-
High Voltage PowerPath Switching
ments. Transients below ground (>–6V) and above VIN
The high voltage EN open drain output of the LTC2954-2 (<33V) will not damage the rugged PB pin. Additionally,
is designed to switch on/off an external power PFET. This the PB pin can withstand ESD HBM strikes up to ±10kV.
allows a user to connect/disconnect a power supply (or In order to keep external noise from coupling inside the
battery) to its load by toggling the PB pin. Figure 7 shows LTC2954, place an R-C network close to the PB pin. A 5.1k
the LTC2954-2 controlling a two cell Li-Ion battery ap- resistor and a 0.1μF capacitor should suffice for most noisy
plication. The KILL pin is connected to the output of the applications (see Figure 8).

VOUT
R5 M1
100k VOUT,TRIP POINT = 6V
R9
100k R1
4.2V + 909k
SINGLE CELL
Li-Ion BATTERY 1%

C4 VIN EN
0.1μF
CERAMIC LTC2954-2 INT
OPTIONAL GLITCH
4.2V + PB KILL FILTER CAPACITOR
SINGLE CELL VTH = 0.6V INPUT
Li-Ion BATTERY GND ONT PDT
R4
100k C3*
CONT* 1% 0.1μF
0.033μF
*OPTIONAL 2954 F07

Figure 7. PowerPath Control with 6V Undervoltage Detect

VIN
PARASITICS
TRACE
R6 VIN EN
CAPACITANCE
5.1k
PB LTC2954-1 INT
NOISE

TRACE C5 KILL
INDUCTANCE 0.1μF GND ONT PDT

DETAILS OMITTED
FOR CLARITY

2954 F08

Figure 8. Noisy PB Trace

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13
LTC2954
TYPICAL APPLICATIONS
External Pull-Up Resistor On PB Reverse Battery Protection
An internal pull-up resistor on the PB pin makes an ex- To protect the LTC2954 from a reverse battery connec-
ternal pull-up resistor unnecessary. Leakage current on tion, place a 1k resistor in series with the VIN pin (see
the PB board trace, however, will affect the open circuit Figure 10).
voltage on the PB pin. If the leakage is too large (>2μA),
the PB 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).

LTC2954-1/
VIN VIN LTC2954-2
2.4V

R7
10k
100k
PB
EXTERNAL BOARD
LEAKAGE CURRENT
>2μA GND
PINS OMITTED
FOR CLARITY
2954 F09
IF EXTERNAL PARASITIC BOARD
LEAKAGE >2μA, USE EXTERNAL
PULL-UP RESISTOR

Figure 9. External Pull-Up Resistor On PB Pin

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14
 LTC2954
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)

0.61 ±0.05 R = 0.115 0.40 ± 0.10

3.00 ±0.10
(2 SIDES) R = 0.05 TYP
(2 SIDES)
TYP 5 8
0.70 ±0.05
2.55 ±0.05
2.00 ±0.10
1.15 ±0.05 PIN 1 BAR PIN 1
(2 SIDES)
TOP MARK R = 0.20 OR
(SEE NOTE 6) 0.25 × 45°
PACKAGE 0.56 ± 0.05
OUTLINE (2 SIDES) CHAMFER
4 1 (DDB8) DFN 0905 REV B
0.25 ± 0.05 0.200 REF 0.75 ±0.05 0.25 ± 0.05
0.50 BSC 0.50 BSC
2.20 ±0.05 2.15 ±0.05
(2 SIDES) (2 SIDES)
0 – 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS BOTTOM VIEW—EXPOSED PAD

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

2954fb

15
LTC2954
PACKAGE DESCRIPTION
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637 Rev A)

0.40 0.65 2.90 BSC

MAX REF (NOTE 4)

1.22 REF

2.80 BSC 1.50 – 1.75

3.85 MAX 2.62 REF 1.4 MIN (NOTE 4)

PIN ONE ID

RECOMMENDED SOLDER PAD LAYOUT 0.22 – 0.36

0.65 BSC
PER IPC CALCULATOR 8 PLCS (NOTE 3)

0.80 – 0.90

0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’

0.30 – 0.50 REF

0.09 – 0.20 1.95 BSC TS8 TSOT-23 0710 REV A

(NOTE 3)
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

2954fb

16
 LTC2954
REVISION HISTORY (Revision history begins at Rev B)

REV DATE DESCRIPTION PAGE NUMBER

B 2/11 Revised Pin Descriptions for EN and EN pins 6
Revised notes for Figures 5 and 6 in Typical Applications 12

2954fb

17
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.
LTC2954
TYPICAL APPLICATION
VIN VOUT
9V +
R8 R5
BATTERY LT1761-1.8
1k 910k
SHDN

1.8V
R1
VIN EN
C4 10k
0.1μF
LTC2954-1 INT INT
μP
PB KILL KILL
GND ONT PDT

CONT* CPDT*
0.033μF 1μF
*OPTIONAL 2954 TA02

Figure 10. Reverse Battery Protection

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2954fb

LT 0211 REV B • PRINTED IN USA

18 Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417
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