LTC2954
Pushbutton On/Off
Controller with µP Interrupt
FEATURES
DESCRIPTION
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The LTC®2954 is a pushbutton on/off controller that
manages system power via a pushbutton interface. An
enable output toggles system power while an interrupt
output provides debounced pushbutton status. The interrupt output can be used in menu driven applications to
request a system power-down. A power kill input allows
a microprocessor or system to reset the enable output,
effectively powering down the system. Independently
adjustable on and off timers allow dependable pushbutton
control of the enable output and resistance to accidental
toggling of system power.
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Adjustable Power On/Off Timers
Low Supply Current: 6μA
Wide Operating Voltage Range: 2.7V to 26.4V
Low Leakage EN Output (LTC2954-1) Allows DC/DC
Converter Control
High Voltage EN Output (LTC2954-2) Allows Circuit
Breaker Control
Simple Interface Allows Graceful μP Shutdown
High Input Voltage PB Pin with Internal Pull-Up
Resistor
±10kV ESD HBM on PB Input
Accurate 0.6V Threshold on KILL Comparator Input
8-Pin 3mm × 2mm DFN and ThinSOT™ Packages
APPLICATIONS
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Pushbutton PowerPath™ Control
Portable Instrumentation Meters
Blade Servers
Portable Customer Service PDA
Desktop and Notebook Computers
The LTC2954 operates over a wide 2.7V to 26.4V input voltage range to accommodate a wide variety of input power
supplies. Very low quiescent current (6μA typical) makes
the LTC2954 ideally suited for battery powered applications.
Two versions of the part are available to accommodate
either positive or negative enable polarities.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
TYPICAL APPLICATION
Pushbutton On/Off with Interrupt
VIN
VOUT
TURN-ON PULSE
DC/DC
+
100k
9V
EN
LTC2954-2
GND
STAYS ON
TURNS OFF
INT
INT
INT
KILL
KILL
ONT
TURNS ON
10k
μP/μC
PB
LONG PULSE
PB
100k
EN
VIN
SHORT PULSE
INTERRUPT
INTERRUPT
2954 TA01b
PDT
2954 TA01a
1μF
tPDT = 6.4 SECONDS
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1
LTC2954
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (VIN) .................................. –0.3V to 33V
Input Voltages
PB ............................................................ –6V to 33V
ONT ...................................................... –0.3V to 2.7V
PDT ....................................................... –0.3V to 2.7V
KILL ......................................................... –0.3V to 7V
Output Voltages
INT ......................................................... –0.3V to 10V
EN/EN .................................................... –0.3V to 33V
Operating Temperature Range
LTC2954C-1 ............................................. 0°C to 70°C
LTC2954C-2 ............................................. 0°C to 70°C
LTC2954I-1 ..........................................–40°C to 85°C
LTC2954I-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
PIN CONFIGURATION
TOP VIEW
GND 1
8
INT
ONT 2
7
EN/EN
6
PDT
5
KILL
PB 3
VIN 4
9
TOP VIEW
VIN 1
PB 2
ONT 3
GND 4
8 KILL
7 PDT
6 EN/EN
5 INT
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
DDB PACKAGE
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
LTC2954CDDB-1#PBF
TAPE AND REEL
LTC2954CDDB-1#TRPBF
PART MARKING*
LCJG
PACKAGE DESCRIPTION
8-Lead (3mm × 2mm) Plastic DFN
TEMPERATURE RANGE
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
LTC2954CTS8-2#PBF
LTC2954ITS8-1#PBF
LTC2954ITS8-2#PBF
LEAD BASED FINISH
LTC2954CDDB-1
LTC2954CTS8-1#TRPBF
LTC2954CTS8-2#TRPBF
LTC2954ITS8-1#TRPBF
LTC2954ITS8-2#TRPBF
TAPE AND REEL
LTC2954CDDB-1#TR
LTCJH
LTCNK
LTCJH
LTCNK
PART MARKING*
LCJG
8-Lead Plastic TSOT-23
8-Lead Plastic TSOT-23
8-Lead Plastic TSOT-23
8-Lead Plastic TSOT-23
PACKAGE DESCRIPTION
8-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
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
LTC2954CTS8-2
LTC2954ITS8-1
LTC2954ITS8-2
LTC2954CTS8-1#TR
LTC2954CTS8-2#TR
LTC2954ITS8-1#TR
LTC2954ITS8-2#TR
LTCJH
LTCNK
LTCJH
LTCNK
8-Lead Plastic TSOT-23
8-Lead Plastic TSOT-23
8-Lead Plastic TSOT-23
8-Lead Plastic TSOT-23
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–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/
2
2954fb
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
VIN
Supply Voltage Range
Steady State Operation
l
IIN
VIN Supply Current
System Power-On, VIN = 2.7V to 24V
l
VIN Falling
l
VUVL
VIN Undervoltage Lockout
VUVL(HYST)
VIN Undervoltage Lockout
Hysteresis
MIN
TYP
2.7
6
MAX
UNITS
26.4
V
12
μA
2.2
2.3
2.5
V
50
400
700
mV
26.4
V
Pushbutton, Enable (PB, EN/EN))
VPB(MIN, MAX)
PB Voltage Range
Single-Ended
l
–1
IPB
PB Input Current
2.5V < VPB < 26.4V
VPB = 1V
VPB = 0.6V
l
l
l
–1
–3
–6
–9
±1
–12
–15
μA
μA
μA
l
0.6
0.8
1
V
1
1.6
2
200
256
325
ms
±0.1
±1
μA
μA
0.11
0.4
V
VPB(VTH)
PB Input Threshold
PB Falling
VPB(VOC)
PB Open Circuit Voltage
IPB = –1μA
t EN, LOCKOUT
EN/EN Lockout Time (Note 5)
Enable Released → Enable Asserted
l
IEN(LKG)
EN/EN Leakage Current
VEN/ EN = 1V, Sink Current Off
VEN/ EN = 26.4V, Sink Current Off
l
l
VEN(VOL)
EN/EN Voltage Output Low
IEN/ EN = 500μA
l
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
Time (Note 4)
l
52
64
82
ms
t PDT
Additional Adjustable PB
Power-Down Debounce Time
CPDT = 1500pF
l
9
11.5
13.5
ms
t INT,MIN
Minimum INT Pulse Width
INT Asserted → INT Released
l
26
32
41
ms
Maximum INT Pulse Width
CPDT = 1500pF, INT Asserted → INT Released
l
35
43.5
54.5
ms
±1
μA
0.11
0.4
V
0.63
V
t INT,MAX
μP Handshake Pins (INT, KILL)
IINT(LKG)
INT Leakage Current
VINT = 3V
l
VINT(VOL)
INT Output Voltage Low
IINT = 3mA
l
VKILL(TH)
KILL Input Threshold Voltage
KILL Falling
l
0.57
0.6
l
10
30
VKILL(HYST)
KILL Input Threshold Hysteresis
IKILL(LKG)
KILL Leakage Current
t KILL(PW)
KILL Minimum Pulse Width
t KILL(PD)
KILL Propagation Delay
KILL Falling → Enable Released
l
t KILL,ON BLANK
KILL Turn-On Blanking (Note 3)
KILL = Low, Enable Asserted → Enable Released
l
V KILL = 0.6V
l
l
50
mV
±0.1
μA
30
400
μs
512
30
μs
650
ms
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LTC2954
ELECTRICAL CHARACTERISTICS
thus turning off system power. This time delay does not include t DB,ON
or t ONT.
Note 4: To manually force an immediate release of the EN/EN pin, the
pushbutton input must be held low for at least tPD,MIN (internal default
power-down timer) + t PDT (adjustable by placing external capacitor at
PDT pin).
Note 5: The enable lockout 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. PB is ignored during this lockout
time. This time delay does not include tDB,ON or tONT.
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: The KILL 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 KILL and PB inputs are ignored during this period. If KILL
remains low at the end of this time period, the enable output is released,
TYPICAL PERFORMANCE CHARACTERISTICS
Internal Default Turn-On
Debounce Time (tDB, ON) vs VIN
Supply Current vs Supply Voltage
Supply Current vs Temperature
10
50
15
TA = 25°C
VIN = 26.4V
8
4
2
9
T = –40°C
6
3
–25
0
25
50
TEMPERATURE (°C)
75
0
100
5
20
25
30
35
ONT PULL-UP CURRENT (μA)
2954 G04
5
10
15
VIN (V)
20
25
30
Turn-Off Debounce Time (tDB, OFF)
vs VIN
50
–3.4
1000
0
2954 G03
ONT Pull-Up Current
vs Temperature
TA = 25°C
VIN = 3.3V
100
10
ONT EXTERNAL CAPACITANCE (nF)
15
2954 G02
10000
1
10
VIN (V)
Turn-On Debounce Time (tDB, ON +
tONT) vs ONT External Capacitance
100
20
0
0
2954 G01
1000
30
10
TA = 25°C
40
–3.2
tDB, OFF (ms)
0
–50
tDB, ON + tONT (ms)
tDB, ON (ms)
IVIN (μA)
VIN = 2.7V
10
40
T = 85°C
VIN = 3.3V
6
IVIN (μA)
T = 25°C
12
VIN = 26.4V
–3.0
VIN = 2.7V
–2.8
–2.6
–50
30
20
10
0
–25
0
25
50
TEMPERATURE (°C)
75
100
2954 G05
0
5
10
15
VIN (V)
20
25
30
2954 G06
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LTC2954
TYPICAL PERFORMANCE CHARACTERISTICS
PB Power-Down Debounce Time
(tPD,MIN + tPDT) vs PDT External
Capacitance
Internal Default PB Power-Down
Debounce Time (t PD,MIN) vs VIN
PDT Pull-Up Current
vs Temperature
10000
70
–3.4
TA = 25°C
VIN = 3.3V
60
tPD, MIN + tPDT (ms)
tPD, MIN (ms)
40
30
20
PDT PULL-UP CURRENT (μA)
TA = 25°C
50
1000
100
–3.2
VIN = 26.4V
–3.0
VIN = 2.7V
–2.8
10
0
10
0
10
5
15
VIN (V)
20
25
30
100
10
PDT EXTERNAL CAPACITANCE (nF)
1
300
TA = 25°C
VIN = 3.3V
PB VOLTAGE (mV)
–150
–100
–50
VIN = 3.3V
200
TA = 100°C
150
TA = 25°C
TA = –45°C
100
50
0
–5
0
5
10 15
PB VOLTAGE (V)
20
25
EN/EN VOL vs Current Load
0
5
10
15
20
EXTERNAL PB RESISTANCE TO GROUND (kΩ)
30
2954 G11
EN (LTC2954-2) Voltage vs VIN
EN (LTC2954-1) Voltage vs VIN
1.0
TA = 25°C
VIN = 3.3V
4
TA = 25°C
100k PULL-UP FROM EN TO VIN
0.8
TA = 25°C
100k PULL-UP FROM EN TO VIN
3
400
300
0.6
EN (V)
EN (V)
EN/EN VOLTAGE (mV)
500
100
2954 G09
2954 G10
600
75
250
–200
PB CURRENT (μA)
0
25
50
TEMPERATURE (°C)
–25
PB Voltage vs External PB
Resistance to Ground
PB Current vs PB Voltage
0
–10
–2.6
–50
2954 G08
2954 G07
–250
1000
2
0.4
200
0
0.0
1
0.2
100
0
0.5
1.5
2.0
1.0
EN/EN CURRENT LOAD (mA)
2.5
0
1
2
3
4
VIN (V)
2954 G12
0
0
1
2
3
4
VIN (V)
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.
PB (Pin 2/Pin 3): Pushbutton Input. Connecting PB to
ground through a momentary switch provides on/off
control via the EN/EN and INT outputs. An internal 100k
pull-up resistor connects to an internal 1.9V bias voltage.
The rugged PB input withstands ±10kV ESD HBM and
can be pulled up to 26.4V externally without consuming
extra current.
ONT (Pin 3/Pin 2): Turn-On Time Input. Placing an external
capacitor to ground determines the additional time (6.4
seconds/μF) the PB pin must be held low before the enable
output is asserted. Floating this pin results in a default
turn on debounce time of 32ms.
GND (Pin 4/Pin 1): Device Ground.
INT (Pin 5/Pin 8): Open Drain Interrupt Output. After a
pushbutton turn-off event is detected (tDB,OFF), the LTC2954
interrupts the system (μP) by asserting the INT pin low.
The μP would perform power-down and housekeeping
tasks and then assert the KILL pin low, thus releasing the
enable output. The INT pulse width is a minimum of 32ms
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
are immediately released.
EN (LTC2954-1, Pin 6/Pin 7): Open Drain Enable Output.
This pin is intended to enable system power. EN is asserted
high after a valid PB turn-on event (tDB,ON + tONT). EN is
released low if: a) KILL is not driven high (by μP) within
512ms of the initial valid PB power turn-on event, b) KILL
is driven low during normal operation, c) PB is pressed
and held low (tPD,MIN + tPDT) during normal operation. This
pin can connect directly to a DC/DC converter shutdown
pin that provides an internal pull-up. Otherwise a pull-up
resistor to an external supply is required. The operating
range for this low leakage pin is 0V to 26.4V.
EN (LTC2954-2, Pin 6/Pin 7): Open Drain Enable Bar
Output. This pin is intended to enable system power. EN is
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
512ms of the initial valid PB power turn-on event, b) KILL
is driven low during normal operation, c) PB is pressed
and held low (tPD,MIN + tPDT) during normal operation. This
pin can connect directly to a DC/DC converter shutdown
pin that provides an internal pull-up. Otherwise a pull-up
resistor to an external supply is required. The operating
range of this pin is 0V to 26.4V.
PDT (Pin 7/Pin 6): Power-Down Time Input. A capacitor
to ground determines the additional time (6.4 seconds/μF)
that the pushbutton must be held low before immediately
releasing the EN/EN and INT outputs. Floating this pin
results in a pushbutton power-down time of 64ms.
KILL (Pin 8/Pin 5): Kill Input. Forcing KILL low releases the
enable output. During system turn-on, this pin is blanked by
a 512ms internal timer (tKILL,ON BLANK) to allow the system
to pull KILL high. This pin has an accurate 0.6V threshold
and can be used as a voltage monitor input. If unused,
connect to a low voltage output supply (see Figure 6).
Exposed Pad (Pin 9 DFN Only): Exposed Pad may be left
open or connected to device ground.
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6
LTC2954
BLOCK DIAGRAM
EN (–1)
EN (–2)
HIGH VOLTAGE
1.5k
VIN
REGULATOR
2.7V TO 26.4V
2.4V
2.4V
29V
ZENER
KILL
OSCILLATOR
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
tKILL, ON BLANK
tONT
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
IGNORED
PB
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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8
LTC2954
APPLICATIONS INFORMATION
Description
The LTC2954 is a pushbutton on/off controller that provides
control of system power via a pushbutton interface. An
enable output toggles system power while an interrupt
output provides debounced pushbutton status. The interrupt output can be used in menu driven applications to
request a system power-down. A power kill input allows
a microprocessor or system to release the enable output,
effectively powering down the system. Independently adjustable on and off timers allow dependable pushbutton
control of the enable output and resistance to accidental
toggling of system power.
The length of time the pushbutton input (PB) must be held
low in order to toggle the enable (EN/EN) output on and
off is independently adjustable with external capacitors
at the ONT/PDT pins, respectively. During normal operation, the interrupt output (INT) is asserted 32ms after PB
goes low. INT then tracks PB until either PB or EN/EN is
released. See Timing Diagrams on page 8.
The KILL input is used to immediately release the enable
output. During a normal power-down sequence, INT requests a system power-down. The μP then performs its
housekeeping tasks and then sets KILL low. If the μP fails
to set KILL low, the user can force a system shutdown by
pressing and holding the pushbutton until the PDT timer
expires.
Turn On
When power is first applied to the LTC2954, the part initializes the output pins. Any DC/DC converters connected
to the EN/EN pin will therefore be held off. To assert the
enable output, PB must be held low for a minimum of
32ms (tDB, ON). The LTC2954 provides additional turn-on
debounce time (tONT) via an optional capacitor connected
to the ONT pin. The following equation describes the additional time that PB must be held low before asserting the
enable output. CONT is the ONT external capacitor (μF):
CONT = 1.56 × 10–4 [μF/ms] • (tONT – 1ms)
Once the enable output is asserted, any DC/DC converters
connected to this pin are turned on. The KILL input from
the μP is ignored during a succeeding 512ms blanking
time (t KILL,ON BLANK). This blanking time represents the
maximum time required to power up the DC/DC converter
and the μP. If KILL is not brought high during this 512ms
time window, the enable output is released. The assumption is that 512ms is sufficient time for the system to
power up.
Turn Off
To initiate a power-down sequence, assert the INT output
low by pressing the pushbutton for a minimum of 32ms
(tDB,OFF). The interrupt signal serves as a power-down
request to the μP. The μP would then perform power-down
and housekeeping tasks and assert KILL low when done.
This in turn releases the enable output, thus shutting off
system power.
Adjustable Power-Down Timer
The LTC2954 provides a failsafe feature that allows the
user to turn off system power (via PB) under system fault
conditions. For cases when the μP fails to respond to the
interrupt signal, the user can force an immediate powerdown by pressing and holding down the pushbutton. The
length of time that PB must be held low is given by a fixed
internal 64ms delay (tPD,MIN) plus an adjustable powerdown timer delay (tPDT, see Timing Diagrams on page 8).
The adjustable delay is set by placing an optional external
capacitor on the PDT pin. Use the following equation to
calculate the capacitance for the desired delay. CPDT is the
PDT external capacitor (μF):
CPDT = 1.56 × 10-4 [μF/ms] • (tPDT – 1ms)
Simplified Power On/Off Sequence
Figure 1 shows a simplified LTC2954-1 power-on and
power-off sequence. A high to low transition on PB (t1)
initiates the power on sequence. In order to assert the
enable output, the PB pin must stay low continuously (PB
high resets timers) for a time controlled by the default
32ms and the external ONT capacitor (t2 –t1). Once EN
goes high (t2), an internal 512ms blanking timer is started.
This blanking timer is designed to give sufficient time for
the DC/DC converter to reach its final voltage, and to allow
the μP enough time to perform power-on tasks.
The KILL pin must be pulled high within 512ms of the EN
pin going high. Failure to do so results in the EN pin going
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9
LTC2954
APPLICATIONS INFORMATION
t1
t2
PB
t3
t4
t5
t6
t8
t9
PB IGNORED
PB & KILL IGNORED
t KILL, ON BLANK
tDB, ON
t7
tDB, OFF
ONT
tONT
PDT
tPD, MIN
INT
t < tPDT
KILL
μP DRIVES
KILL LOW
XXX DON'T CARE
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
2954fb
10
LTC2954
APPLICATIONS INFORMATION
low 512ms after it went high. Note that the LTC2954 does
not sample KILL and PB until after the 512ms internal timer
has expired. The reason PB is ignored is to ensure that
the system is not forced off while powering on. Once the
512ms timer expires (t4), the release of the PB pin is then
debounced with an internal 32ms timer. The system has
now properly powered on and the LTC2954 monitors PB
and KILL for a turn-off command while consuming only
6μA of supply current.
A high to low transition on PB (t5) starts the power-off
sequence debounce timer. In order to assert the interrupt
output (INT), PB must stay low continuously (PB high
resets debounce timer) for 32ms (t6–t5). At the completion of the power-down debounce timer (t6), an internal
interrupt timer keeps the interrupt output low for at least
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
adjustable power-down timer is started. The capacitor
placed at the PDT pin will determine the time period of
this timer. If the pushbutton is released prior to 16 cycles
of the PDT pin, the interrupt output will go high (t8). Note
that the enable output is not directly changed by this
interrupt pulse. The function of the interrupt signal is to
initiate a software shutdown. At t9, the μP has performed
its power-down functions and asserted the KILL input
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
to low transition.
Aborted Power-On Sequence
The power-on sequence is aborted when the KILL remains
low at the end of the 512ms blanking time. Figure 2 is a
simplified version of an aborted power-on sequence. At
time tABORT, since KILL 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 KILL low, as
shown in (Figure 3). At time t KILL, KILL is set low by the
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 PB) 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
KILL releases enable, the internal 256ms timer ignores the
PB pin. This is shown as tEN/EN, LOCKOUT in (Figure 4).
tEN/EN, LOCKOUT
PB
tKILL
DC/DC
TURNS OFF
PB
DC/DC
TURNS OFF
PB BLANKING
(INTERNAL
SIGNAL)
256ms
EN
EN
μP SETS
KILL LOW
KILL
PB IGNORED
POWER ON
μP SETS
KILL LOW
KILL
XXX DON’T CARE
XXX DON’T CARE
2954 F04
2954 F03
Figure 3. μP Turns Off Power (LTC2954-1)
Figure 4. DC/DC Turn-Off Blanking (LTC2954-1)
2954fb
11
LTC2954
APPLICATIONS INFORMATION
LTC2954-1, LTC2954-2 Versions
The LTC2954-1 (high true EN) and LTC2954-2 (low true
EN) differ only by the polarity of the high voltage (33V ABS
MAX), enable pin. The LTC2954-1 EN pin is a low leakage
high true open drain output designed to drive the shutdown
pin of DC/DC converters. The LTC2954-2 is a low leakage,
low true open drain enable output designed to drive the
gate of an external PFET. The LTC2954-2 provides a user
manual power path control.
High Voltage Pins
The VIN, PB and EN/EN pins can operate at voltages up to
26.4V. PB can, additionally, operate below ground (–6V)
without latching up the device. PB has an ESD HBM rating
of ±10kV. If the pushbutton switch connected to PB exhibits high leakage current, then an external pull-up resistor
to VIN is recommended. Furthermore, if the pushbutton
switch is physically located far from the LTC2954 PB pin,
parasitic capacitances may couple onto the high impedance PB input. Additionally, parasitic series inductance
may cause unpredictable ringing at the PB pin. Placing
a 5.1k resistor from the PB pin to the pushbutton switch
would mitigate parasitic inductance problems. Placing a
0.1μF capacitor on the PB pin would lessen the impact of
parasitic capacitive coupling.
TYPICAL APPLICATIONS
Voltage Monitoring with KILL Input
The KILL pin can be used as a voltage monitor. Figure 5
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
0.6V and the EN pin is quickly pulled low. Note that the
resistor values should be as large as possible, but small
VIN = 9V
enough to keep leakage currents from tripping the 0.6V
KILL comparator.
The DC/DC converter shown has an internal pull-up current on its SHDN pin. A pull-up resistor on EN is thus not
needed.
Operation Without μP
Figure 6 shows how to connect the KILL pin when there
is no circuitry available to drive it. The minimum pulse
VIN = 9V
VIN
VOUT
3.3V
VIN
LT1767-3.3
R3
806k
1%
3.3V
VOUT
LT1767-3.3
SHDN**
SHDN**
R2
100k
1%
R1
100k
VIN
C4
0.1μF
R1
10k
EN
LTC2954-1
C4
0.1μF
INT
INT
VIN
EN
LTC2954-1
INT
μP
PB
KILL
GND ONT
PDT
KILL
(OPEN DRAIN)
2954 F05
CONT*
0.033μF
CPDT*
1μF
* OPTIONAL
** SHDN INTERNALLY PULLED
UP BY THE LT1767-3.3
Figure 5. Input Voltage Monitoring with KILL Input
PB
KILL
GND ONT
PDT
CONT*
0.033μF
+
CPDT*
1μF
* OPTIONAL
** SHDN INTERNALLY
PULLED UP BY
THE LT1767-3.3
C3*
0.01μF
2954 F06
Figure 6. No μP Application
2954fb
12
LTC2954
TYPICAL APPLICATIONS
PFET through a resistive divider. The KILL pin serves as
a voltage monitor. When VOUT drops below 6V, causing a
KILL voltage below VKILL(TH), the EN pin becomes an open
circuit 30μs later. Since the PDT pin is open-circuited, the
power-down debounce time defaults to 64ms.
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 KILL pin. The optional CPDT external
capacitor extends the length of time (beyond 64ms) that
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 environments. Transients below ground (>–6V) and above VIN
(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).
To protect the LTC2954 from a reverse battery connection, place a 1k resistor in series with the VIN pin (see
Figure 10).
VIN
VIN
LTC2954-1/
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
2954fb
14
LTC2954
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
R = 0.115
TYP
5
R = 0.05
TYP
0.40 ± 0.10
8
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.20 ±0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
2.00 ±0.10
(2 SIDES)
0.56 ± 0.05
(2 SIDES)
0.75 ±0.05
0 – 0.05
4
0.25 ± 0.05
1
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
(DDB8) DFN 0905 REV B
0.50 BSC
2.15 ±0.05
(2 SIDES)
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
MAX
2.90 BSC
(NOTE 4)
0.65
REF
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.22 – 0.36
8 PLCS (NOTE 3)
0.65 BSC
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
(NOTE 3)
1.95 BSC
TS8 TSOT-23 0710 REV A
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
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.
17
LTC2954
TYPICAL APPLICATION
9V
BATTERY
VIN
+
R5
910k
R8
1k
VOUT
LT1761-1.8
SHDN
1.8V
VIN
C4
0.1μF
R1
10k
EN
INT
INT
PB
KILL
KILL
GND ONT
PDT
LTC2954-1
CONT*
0.033μF
μP
CPDT*
1μF
*OPTIONAL
2954 TA02
Figure 10. Reverse Battery Protection
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
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Programmable Quad Supply Monitor
Adjustable RESET, 10-Lead MSOP and 3mm × 3mm DFN Packages
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Pin-Programmable Dual Supply Monitors
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3mm × 2mm DFN Packages
LTC2909
Precision Triple/Dual Input UV, OV and Negative
Voltage Monitor
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Octal Positive/Negative Voltage Monitor
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Quad UV/OV Positive/Negative Voltage Monitor
Adjustable UV and OV Trip Values
LTC2950/LTC2951
Pushbutton On/Off Controllers
High Voltage, Low Power Pushbutton Controller with
Power-Down Fault Detect KILL Timer
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
LT4351
MOSFET Diode-OR Controller
Wide Input Range: 1.2V to 18V
LTC2952
Pushbutton PowerPath™ Controller with
Supervisor
Automatic Low Loss Switchover Between DC Sources
LTC2953
Pushbutton ON/OFF Controller with Voltage
Monitoring
High Voltage Pushbutton Controller with 200ms Voltage Reset Monitor
2954fb
18 Linear Technology Corporation
LT 0211 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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