LTC2951-1/LTC2951-2
Pushbutton On/Off
Controller
FEATURES
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DESCRIPTION
Adjustable Pushbutton Debounce and Delay Timers
Low Supply Current: 6µA
Wide Operating Voltage Range: 2.7V to 26.4V
EN Output (LTC2951-1) Allows DC/DC Converter
Control
EN Output (LTC2951-2) 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 ThinSOTTM Packages
APPLICATIONS
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Portable Instrumentation Meters
Blade Servers
Portable Customer Service PDA
Desktop and Notebook Computers
The LTC®2951 is a micropower, wide input voltage range
pushbutton ON/OFF controller. The part contains a pushbutton input which controls the toggling of an open-drain
enable output. The pushbutton turn OFF debounce time
is externally programmable, while the turn ON debounce
time is fixed at 128ms. A simple microprocessor interface
allows for proper system housekeeping prior to powerdown. Under system fault conditions, an adjustable KILL
timeout delay ensures proper power-down.
The LTC2951 operates over a 2.7V to 26.4V input voltage
range to accommodate a variety of input power supplies.
Very low quiescent current (6µA typical) makes the
LTC2951 ideally suited for battery powered applications.
Two versions of the part are available to accommodate
either positive or negative enable polarities. The parts
are available in 8-pin 3mm × 2mm DFN and ThinSOT
packages.
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.
TYPICAL APPLICATION
VIN
2.7V TO 26.4V
VIN
Turn-On Debounce
VOUT
DC/DC
BUCK
SHDN**
VIN
LTC2951-1
PB
GND
2V/DIV
INT
INT
KILL
KILL
µP/µC
PB
128ms
OFFT
KILLT
CKILLT*
0.033µF
2951 TA01
EN
R1
10k
EN
COFFT*
0.033µF
*OPTIONAL
25ms/DIV
2951 TA01b
**SHDN INTERNALLY PULLED UP BY DC/DC
295112fb
1
LTC2951-1/LTC2951-2
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage (VIN)................................... –0.3V to 33V
Input Voltages
PB.............................................................. –6V to 33V
KILLT..................................................... –0.3V to 2.7V
OFFT...................................................... –0.3V to 2.7V
KILL .........................................................–0.3V to 7V
Output Voltages
INT.......................................................... –0.3V to 10V
EN/EN..................................................... –0.3V to 10V
Operating Temperature Range
LTC2951C-1.............................................. 0°C to 70°C
LTC2951C-2.............................................. 0°C to 70°C
LTC2951I-1............................................–40°C to 85°C
LTC2951I-2...........................................–40°C to 85°C
Storage Temperature Range
DFN Package...................................... –65°C to 125°C
TSOT-23..............................................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................... 300°C
PIN CONFIGURATION
TOP VIEW
GND 1
KILLT 2
PB 3
VIN 4
9
8
INT
7
EN/EN
6
OFFT
5
KILL
TOP VIEW
VIN 1
PB 2
KILLT 3
GND 4
8 KILL
7 OFFT
6 EN/EN
5 INT
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
DDB PACKAGE
8-LEAD (3mm × 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
LTC2951CDDB-1#PBF
LTC2951CDDB-1#TRPBF
LBTB
8-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2951CDDB-2#PBF
LTC2951CDDB-2#TRPBF
LBTD
8-Lead (3mm × 2mm) Plastic DFN
0°C to 70°C
LTC2951IDDB-1#PBF
LTC2951IDDB-1#TRPBF
LBTB
8-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2951IDDB-2#PBF
LTC2951IDDB-2#TRPBF
LBTD
8-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
LTC2951CTS8-1#PBF
LTC2951CTS8-1#TRPBF
LTBTC
8-Lead Plastic TSOT
0°C to 70°C
LTC2951CTS8-2#PBF
LTC2951CTS8-2#TRPBF
LTBTF
8-Lead Plastic TSOT
0°C to 70°C
LTC2951ITS8-1#PBF
LTC2951ITS8-1#TRPBF
LTBTC
8-Lead Plastic TSOT
–40°C to 85°C
LTC2951ITS8-2#PBF
LTC2951ITS8-2#TRPBF
LTBTF
8-Lead Plastic TSOT
–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/
295112fb
2
LTC2951-1/LTC2951-2
The
l denotes the specifications which apply over the full operating
ELECTRICAL
CHARACTERISTICS
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
MIN
IIN
VIN Supply Current
System Power-On, VIN = 2.7V to 24V
l
VUVL
VIN Undervoltage Lockout
VIN Falling
l
VUVL(HYST)
VIN Undervoltage Lockout Hysteresis
TYP
2.7
MAX
UNITS
26.4
V
6
12
µA
2.2
2.3
2.4
V
l
50
300
600
mV
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
VPB = 1V
VPB = 0.6V
l
l
l
–1
–3
–6
–9
±1
–12
–15
µA
µA
µA
VPB(VTH)
PB Input Threshold
PB Falling
l
0.6
0.8
1
V
tEN/EN, Lockout
EN/EN Lockout Time (Note 5)
Enable Released → Enable Asserted
l
200
256
325
ms
IEN/EN(LKG)
EN/EN Leakage Current
VEN/EN = 1V, Sink Current Off
l
±0.1
µA
VEN/EN(VOL)
EN/EN Voltage Output Low
IEN/EN = 3mA
l
0.11
0.4
V
VPB(VOC)
PB Open-Circuit Voltage
IPB = –1µA
l
1
1.6
2
V
Timing Pins (KILLT, OFFT)
IKILLT, OFFT(PU)
KILLT/OFFT Pull-Up Current
VKILLT, OFFT = 0V
l
–2.4
–3
–3.6
µA
IKILLT, OFFT(PD)
KILLT/OFFT Pull-Down Current
VKILLT, OFFT = 1.3V
l
2.4
3
3.6
µA
tDB, ON
Turn-On Debounce Time
PB Falling → Enable Asserted
l
100
128
163
ms
tDB, OFF
Internal Turn-Off Debounce Time
OFFT Pin Float, PB Falling → INT Falling
l
26
32
41
ms
tOFFT
Additional Adjustable Turn-Off Time
COFFT = 1500pF
l
9
11.5
13.5
ms
±1
µA
µP Handshake Pins (INT, KILL)
IINT(LKG)
INT Leakage Current
VINT = 3V
l
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
I KILL(LKG)
KILL Leakage Current
±0.1
µA
t KILL(PW)
KILL Minimum Pulse Width
t KILL(PD)
KILL Propagation Delay
VKILL = 0.6V
l
l
30
µs
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
t KILL, OFF DELAY Internal KILL Turn-Off Delay (Note 4)
KILLT Pin Float, KILL = High, INT Asserted →
Enable Released
l
100
128
163
ms
l
9
11.5
13.5
ms
t KILL,OFF DELAY, Additional Adjustable KILL Turn-Off Delay CKILLT = 1500pF
(Note 4)
ADDITIONAL
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,
thus turning off system power. This time delay does not include tDB,ON.
Note 4: The internal KILL turn-off delay (tKILL, OFF DELAY) is the default
delay from the initiation of a power-off sequence (INT falling, KILL = high),
to the release of the enable output. The additional, adjustable KILL turn-off
delay (tKILL, OFF DELAY, ADDITIONAL) uses an optional external capacitor
(CKILLT) to provide extra delay from INT falling to the release of the enable
output. If the KILL input switches low at any time during KILL turn-off
delay, enable is released, thus turning off system power.
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.
295112fb
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LTC2951-1/LTC2951-2
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
Supply Current vs Supply Voltage
10
10
8
IVIN (µA)
VIN = 3.3V
6
VIN = 2.7V
4
6
4
2
2
–25
0
25
50
TEMPERATURE (°C)
75
0
100
0
5
10
15
20
25
10000
TA = 25°C
tDB, OFF + tOFFT (ms)
tDB, OFF (ms)
30
20
10
15
VIN (V)
20
1000
100
25
10
30
1
100
10
OFFT EXTERNAL CAPACITOR (nF)
tKILL, OFF DELAY (ms)
160
120
80
40
0
0
5
10
15
VIN (V)
20
25
2951 G07
20
25
VIN = 26.4V
–3.0
VIN = 2.7V
–2.8
–25
0
25
50
TEMPERATURE (°C)
75
100
2951 G06
KILLT Pull-Down Current
vs Temperature
10000
–3.4
1000
100
10
30
–3.2
–2.6
–50
1000
KILLT PULL-DOWN CURRENT (µA)
TA = 25°C
15
VIN (V)
OFFT Pull-Down Current
vs Temperature
KILL Turn-Off Delay
vs KILLT External Capacitor
tKILL, OFF DELAY + tKILL, OFF DELAY, ADDITIONAL (ms)
Internal Default KILL Turn-Off
Delay (tKILL, OFF DELAY) vs VIN
10
2951 G05
2951 G04
200
5
–3.4
TA = 25°C
VIN = 3.3V
10
5
0
2951 G03
Turn-Off Debounce Time (tDB, OFF
+ tOFFT) vs OFFT External Capacitor
40
0
0
30
2951 G02
Internal Default Turn-Off
Debounce Time (tDB, OFF) vs VIN
0
80
VIN (V)
2951 G01
50
120
40
OFFT PULL-DOWN CURRENT (µA)
0
–50
TA = 25°C
160
tDB, ON (ms)
8
IVIN (µA)
200
TA = 25°C
VIN = 26.4V
Turn-On Debounce Time
(tDB, ON) vs VIN
1
100
10
KILLT EXTERNAL CAPACITOR (nF)
1000
2951 G08
–3.2
VIN = 26.4V
–3.0
VIN = 2.7V
–2.8
–2.6
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
2951 G09
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LTC2951-1/LTC2951-2
TYPICAL PERFORMANCE CHARACTERISTICS
PB Voltage vs External
PB Resistance to Ground
PB Current vs PB Voltage
–250
300
TA = 25°C
VIN = 3.3V
250
PB VOLTAGE (mV)
PB CURRENT (µA)
–200
–150
–100
200
TA = 100°C
150
TA = 25°C
TA = –45°C
100
–50
0
–10
VIN = 3.3V
50
–5
0
5
10 15
PB VOLTAGE (V)
20
25
0
30
0
5
10
15
20
EXTERNAL PB RESISTANCE TO GROUND (kΩ)
2951 G11
2951 G10
EN/EN VOL vs Current Load
0.8
300
0.6
200
0.4
100
0.2
0
2
6
8
4
EN/ EN CURRENT LOAD (mA)
10
0
4
TA = 25°C
100k PULL-UP FROM EN TO VIN
2
1
0
1
2
3
4
VIN (V)
2951 G12
TTAA == 25°C
25°C
100k
100k PULL-UP
PULL-UP FROM
FROM EN
EN TO
TO VVIN
IN
3
EN (V)
TA = 25°C
VIN = 3.3V
400
0
EN (LTC2951-2) Voltage vs VIN
EN (LTC2951-1) Voltage vs VIN
1.0
EN (V)
EN/EN VOLTAGE (mV)
500
0
0
1
2
3
4
VIN (V)
2951 G13
2951 G14
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5
LTC2951-1/LTC2951-2
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 pin. An internal 100k pull-up resistor connects to an internal 1.9V bias voltage. The rugged
PB input can be pulled up to 26.4V externally without
consuming extra current.
KILLT (Pin 3/Pin 2): Additional, Adjustable KILL Turn-Off
Delay Input (tKILL, OFF DELAY, ADDITIONAL). A capacitor to
ground provides additional delay time (beyond the internal
default 128ms, tKILL, OFF DELAY) from INT falling to the
automatic release of the enable output. The KILL turn-off
delay feature ensures the release of the enable pin under
system fault conditions, such as the µP not responding
to the LTC2951 interrupt signal (INT low).
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 + tOFFT),
the LTC2951 interrupts the system (µP) by bringing the
INT pin low. Once the system finishes its power-down and
housekeeping tasks, it sets KILL low, which in turn releases
the enable output. If at the end of the power-down timer
period (tKILL, OFF DELAY + tKILL, OFF DELAY, ADDITIONAL) KILL
is still high, the enable output is released immediately.
INT may optionally be tied to KILL to release the enable
output immediately after the turn-off event has been
detected (INT low).
EN (LTC2951-1, Pin 6/Pin 7): Open-Drain Enable Output.
This pin is intended to enable system power. EN goes high
after a valid PB turn-on event (tDB, ON). EN goes low if:
a) KILL is not driven high within 512ms of the initial valid
PB power turn-on event, b) KILL is driven low during
normal operation, or c) a second valid PB event (power
turn-off) is detected. 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 pin is 0V to 10V.
EN (LTC2951-2, Pin 6/Pin 7): Open-Drain Enable Output.
This pin is intended to enable system power. EN is asserted
low after a valid PB turn-on event (tDB, ON). EN releases
high if: a) KILL is not driven high within 512ms of the initial
valid PB power turn-on event, b) KILL is driven low during
normal operation, or c) a second valid PB event (power
turn-off) is detected. 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 10V.
OFFT (Pin 7/Pin 6): Additional Adjustable Turn-Off Time
Input (tOFFT). A capacitor to ground determines the additional time (beyond the internal default 32ms, tDB, OFF)
that the PB pin must be held low before initiating a powerdown sequence (INT falling). Floating this pin results in a
default turn-off debounce time of 32ms.
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): Exposed Pad may be left open or
connected to device ground.
295112fb
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LTC2951-1/LTC2951-2
BLOCK DIAGRAM
EN/EN
VIN
2.7V TO 26.4V
REGULATOR
2.4V
2.4V
OSCILLATOR
100k
KILL
PB
LOGIC
10µs
FILTER
DEBOUNCE
0.6V
0.8V
INT
OSCILLATOR
GND
2951 BD
KILLT
OFFT
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LTC2951-1/LTC2951-2
TIMING DIAGRAMS
tKILL(PW)
KILL
tKILL(PD)
EN/EN
2951 TD01
PB
PB & KILL IGNORED
tDB, ON
tKILL, ON BLANK
EN
(LTC2951-1)
EN
(LTC2951-2)
2951 TD02
Power-On Timing
295112fb
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LTC2951-1/LTC2951-2
TIMING DIAGRAMS
PB
PB IGNORED
tDB, OFF
t OFFT
OFFT
16 CYCLES
INT
t KILL, OFF DELAY
t KILL, OFF DELAY, ADDITIONAL
KILLT
16 CYCLES
EN
(LTC2951-1)
EN
(LTC2951-2)
2951 TD03
Power-Off Timing, KILL > 0.6V
295112fb
9
LTC2951-1/LTC2951-2
APPLICATIONS INFORMATION
Description
Turn-Off
The LTC2951 is a low power (6µA), wide input voltage range
(2.7V to 26.4V), pushbutton On/Off controller that can interface to a µP and a power supply. The part incorporates
all the flexible timing needed to debounce the pushbutton
input (PB). The LTC2951 also provides a simple interface
(INT output, KILL input) to allow a system to power on and
power off in a controlled manner. The wide input voltage
range allows a system designer to operate from single cell
to multi-cell battery stacks. Very low quiescent current
makes the LTC2951 ideal for continuously monitoring the
on/off pushbutton of a handheld device.
To initiate a power-off sequence, PB must be held low for a
minimum of 32ms (tDB, OFF). Additional turn-off debounce
time may be added via an optional capacitor connected
to the OFFT pin (tOFFT). The following equation describes
the additional time that PB must be held low to initiate a
power-off sequence. COFFT is the OFFT external capacitor:
Turn-On
KILL Turn-Off Delay
When power is first applied to the LTC2951, the part initializes the output pins. Any DC/DC converters connected to
the EN/EN pin will, therefore, be off. To assert the enable
output, PB must be held low for a minimum of 128ms
(tDB, ON).
The LTC2951 provides a failsafe feature that allows the
user to turn off system power (via PB) under system fault
conditions. During a normal power-down sequence, the
LTC2951 first interrupts the µP by setting INT low. The
µP then performs power-down and housekeeping tasks
and drives KILL low when done. The LTC2951 releases the
enable output, thus turning off system power. The KILL
turn-off timer starts when INT is driven low. If the µP fails
to respond during this timeout period, the enable output
will automatically release. The default power-down timeout
period is 128ms (t KILL, OFF DELAY), which can be extended
by placing an optional capacitor on the KILLT pin (t KILL,
OFF DELAY, ADDITIONAL). The following equation describes
the additional power-down timeout period. CKILLT is the
KILLT external capacitor:
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 the 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.
COFFT = 1.56E-4 [µF/ms] • (tOFFT – 1ms)
Once PB has been validly pressed, INT is switched low.
This alerts the µP to perform its power-down and housekeeping tasks.
CKILLT = 1.56e-4 [µF/ms] • (t KILL, OFF DELAY, ADDITIONAL – 1ms)
Note that KILL can be driven low (thereby releasing the
enable output) at any time after t KILL, ON BLANK period.
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LTC2951-1/LTC2951-2
APPLICATIONS INFORMATION
Simplified Power-On/-Off Sequence
Figure 1 shows a simplified LTC2951-1 power-on and
power-off sequence. A high to low transition on PB (t1)
initiates the power-on sequence. This diagram does not
show any bounce on PB . In order to assert the enable
output, the PB pin must stay low continuously (PB high
resets timers) for 128ms (t2–t1). Once EN goes high (t2),
an internal 512ms blanking timer is started. This blanking timer is designed to give sufficient time for the DC/
DC converter to reach its final voltage, and to allow the
µP enough time to perform power-on tasks.
The KILL pin must be pulled high within 512ms of the
EN pin going high. Failure to do so results in the EN
t1
t2
PB
t3
t4
pin going low 512ms after it went high. (EN = low, see
Figure 2). Note that the LTC2951 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 LTC2951 monitors PB
and KILL (for a turnoff command) while consuming only
6µA of supply current.
A high to low transition on PB (t5) initiates the power-off
sequence. PB must stay low continuously (PB high resets
debounce timer) for a period controlled by the default 32ms
t5
t6
PB & KILL IGNORED
t DB, ON
t KILL, ON BLANK
t7
PB IGNORED
< t KILL,
OFF DELAY
t DB, OFF
t OFFT
OFFT
INT
KILL
EN
2951 F01
Figure 1. Simplified Power-On/-Off Sequence for LTC2951-1
295112fb
11
LTC2951-1/LTC2951-2
APPLICATIONS INFORMATION
and the external OFFT capacitor (t6–t5). At the completion
of the OFFT timing (t6), an interrupt (INT) is set, signifying that EN will be switched low after the KILL turn-off
(t KILL, OFF DELAY + t KILL, OFF DELAY, ADDITIONAL) timeout
period. Once a system has finished performing its powerdown operations, it can set KILL low (t7) and thus immediately set EN low, terminating the KILL turn-off timer. The
release of the PB pin is then debounced with an internal
32ms timer.
The system is now in its reset state: where the LTC2951
is in low power mode (6µA). PB is monitored for a high
to low transition.
Aborted Power-On Sequence
The power-on sequence is aborted when the KILL remains
low after the end of the 512ms blanking time. Figure 2 is
a simplified version of an aborted power-on sequence.
At time tABORT, since 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.
tABORT
PB
t KILL
tDB, ON
PB
512ms
INTERNAL
TIMER
PB & KILL IGNORED
DC/DC
TURNS OFF
EN
POWER-ON
TIMING
POWER
TURNED OFF
EN
µP SETS
KILL LOW
KILL
XXX DON’T CARE
2951 F03
µP FAILED TO SET
KILL HIGH
KILL
Figure 3. µP Turns Off Power (LTC2951-1)
2951 F02
Figure 2. Aborted Power-On Sequence for LTC2951-1
295112fb
12
LTC2951-1/LTC2951-2
APPLICATIONS INFORMATION
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, PB is ignored during the internal 256ms
timer period. This is shown as tEN/EN, LOCKOUT in Figure 4.
LTC2951-1, LTC2951-2 Versions
The LTC2951-1 (high true EN) and LTC2951-2 (low true
EN) differ only by the polarity of the EN/EN pin. Both versions allow the user to extend the amount of time that the
PB must be held low in order to begin a valid power-off
sequence. An external capacitor placed on the OFFT pin
adds additional time to the turn-off debounce time. If
no capacitor is placed on the OFFT pin, then the turn-off
debounce time is given by an internally fixed 32ms timer.
Both versions of the LTC2951 provide extendable KILL
turn-off timer, t KILL, OFF DELAY, ADDITIONAL, by connecting
an optional external capacitor on the KILLT pin. The default
KILL turn-off delay time is 128ms, t KILL, OFF DELAY.
High Voltage Pins
The VIN and PB 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 LTC2951 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 5k 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.
t EN/EN, LOCKOUT
PB
POWER ON
PB & KILL IGNORED
DC/DC
TURNS OFF
PB BLANKING
PB IGNORED
256ms
EN
µP SETS
KILL LOW
KILL
XXX DON’T CARE
2951 F04
Figure 4. DC/DC Turn-Off Blanking (LTC2951-1)
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13
LTC2951-1/LTC2951-2
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 resistor 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 enough to keep leakage currents from tripping
the 0.6V KILL comparator.
VIN
9V
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
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.
VIN
3.3V
VOUT
LT1767-3.3
SHDN**
5.4V THRESHOLD
C4
0.1µF
VIN
EN
LTC2951-1
R2
100k
1%
R1
10k
INT
INT
µP
KILL
(OPEN DRAIN)
KILL
PB
GND
R3
806k
1%
OFFT
KILLT
CKILLT*
0.033µF
COFFT*
0.033µF
*OPTIONAL
**SHDN INTERNALLY PULLED UP BY THE LT1767-3.3
2951 F05
Figure 5. Input Voltage Monitoring with KILL Input
VIN
9V
3.3V
VOUT
VIN
LT1767-3.3
SHDN**
C4
0.1µF
VIN
LTC2951-1
C3*
PB
0.01µF
GND KILLT
INT
+
KILL
C3*
0.01µF
OFFT
CKILLT*
0.033µF
2951 F06
R1
100k
EN
COFFT*
0.033µF
*OPTIONAL
**SHDN INTERNALLY PULLED UP BY THE LT1767-3.3
Figure 6. No µP Application
295112fb
14
LTC2951-1/LTC2951-2
TYPICAL APPLICATIONS
PowerPathTM Switching
PB Pin in a Noisy Environment
The EN open-drain output of the LTC2951-2 is designed
to switch on/off an external power PFET. This allows a
user to connect/disconnect a power supply (or battery)
to its load by toggling the PB pin. Figure 7 shows the
LTC2951-2 controlling a two cell Li-Ion battery application.
The INT and KILL pins are connected to the output of the
PFET through a resistor divider. The KILL pin serves as a
voltage monitor. When VOUT drops below 6V, the EN pin
is open-circuited 30µs later.
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).
Reverse-Battery Protection
To protect the LTC2951 from a reverse-battery connection, place a 1k resistor (R8) in series with the VIN pin
(see Figure 10).
LTC2951-1/LTC2951-2
VIN
VIN
2.4V
R7
10k
PB
100k
EXTERNAL BOARD
LEAKAGE CURRENT
>2µA
GND
PINS OMITTED
FOR CLARITY
IF EXTERNAL PARASITIC BOARD
LEAKAGE >2µA, USE EXTERNAL
PULL-UP RESISTOR
2951 F09
Figure 9. External Pull-Up Resistor on PB Pin
295112fb
16
LTC2951-1/LTC2951-2
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)
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
R = 0.115
TYP
5
R = 0.05
TYP
0.40 ± 0.10
8
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
295112fb
17
LTC2951-1/LTC2951-2
PACKAGE DESCRIPTION
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
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
295112fb
18
LTC2951-1/LTC2951-2
REVISION HISTORY
(Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
01/11
Revised Features and Typical Application
1
Updated Pin Configuration
2
Revised Electrical Characteristics section
3
Revised Pin Functions section
6
Revised Block Diagram
7
Minor edit to Figure 1
11
Added C3 to Figure 6
14
Updated Figure 8
15
Updated Related Parts
20
295112fb
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.
19
LTC2951-1/LTC2951-2
TYPICAL APPLICATION
9V
BATTERY
+
VIN
R5
910k
R8
1k
VOUT
LT1761-1.8
SHDN
1.8V
C4
0.1µF
VIN
R1
10k
EN
LTC2951-1
INT
INT
PB
KILL
KILL
GND KILLT
OFFT
CKILLT*
0.033µF
COFFT*
0.033µF
*OPTIONAL
µP
2951 F10
Figure 10. Reverse-Battery Protection Using R8
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC2900
Programmable Quad Supply Monitor
Adjustable RESET, 10-Lead MSOP and 3mm × 3mm DFN Packages
LTC2904/LTC905
Pin-Programmable Dual Supply Monitors
Adjustable RESET and Tolerance, 8-Lead SOT-23 and 3mm × 2mm DFN Packages
LTC2950
Micropower Pushbutton On/Off Controller
High Voltage Pushbutton Controller with µP Interface and Adjustable On-Time
LTC2953
Pushbutton On/Off Controller with Voltage
Monitoring
High Voltage Pushbutton Controller with 200ms Voltage Reset Monitor
LTC2954
Pushbutton On/Off Controller with MP Interrupt Allows Controlled Software System Shutdown
LTC2952
Pushbutton PowerPath Controller with
Supervisor
Automatic Low Loss Switchover Between DC Sources
LTC4411
2.6A Low Loss Ideal Diode in ThinSOT
No External MOSFET, Automatic Switching Between DC Sources
LTC4412HV
PowerPath 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
295112fb
20 Linear Technology Corporation
LT 0111 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
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