LTC2950-1/LTC2950-2
1
295012fc
EN
2V/DIV
PB
10ms/DIV 2950 TA01b
Push Button On/Off
Controller
The LTC
®
2950 is a micropower, wide input voltage range,
push button ON/OFF controller. The part contains a push
button input with independently programmable ON and OFF
debounce times that control the toggling of an open drain
enable output. The part also contains a simple micropro-
cessor interface to allow for proper system housekeeping
prior to power down. Under system fault conditions, an
internal KILL timer ensures proper power down.
The LTC2950 operates over a wide 2.7V to 26V input
voltage range to accommodate a wide variety of input
power supplies. Very low quiescent current (6μA typical)
makes the LTC2950 ideally suited for battery powered
applications. Two versions of the part are available to ac-
commodate either positive or negative enable polarities.
The parts are available in either 8-lead 3mm × 2mm DFN
or ThinSOT packages.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. ThinSOT is
a trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
n Portable Instrumentation Meters
n Blade Servers
n Portable Customer Service PDA
n Desktop and Notebook Computers
n Adjustable Push Button On/Off Timers
n Low Supply Current: 6μA
n Wide Operating Voltage Range: 2.7V to 26V
n EN Output (LTC2950-1) Allows DC/DC Converter
Control
n EN Output (LTC2950-2) Allows Circuit Breaker
Control
n Simple Interface Allows Graceful μP Shut Down
n High Input Voltage PB Pin with Internal Pull Up
Resistor
n ±10kV ESD HBM on PB Input
n Accurate 0.6V Threshold on KILL Comparator Input
n 8-Pin 3mm × 2mm DFN and ThinSOT™ Packages
VIN
SHDN
VIN
VOUT
EN
INT
KILL
INT
KILL
LTC2950-1
ONT OFFT
DC/DC
BUCK
μP/μC
3V – 26V
*OPTIONAL
R1
10k
2950 TA01
CONT*
0.033μF
COFFT*
0.033μF
PB
GND
VIN
TYPICAL APPLICATION
Turn On Debounce
DESCRIPTION
FEATURES
APPLICATIONS
LTC2950-1/LTC2950-2
2
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Supply Voltage (VIN) ..................................– 0.3V to 33V
Input Voltages
PB .............................................................– 6V to 33V
ONT ......................................................– 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
LTC2950-C1 ............................................. 0°C to 70°C
LTC2950-C2 ............................................. 0°C to 70°C
LTC2950-I1 ......................................... – 40°C to 85°C
LTC2950-I2 ......................................... – 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
TOP VIEW
DDB8 PACKAGE
8-LEAD (3mm s 2mm) PLASTIC DFN
5
6
7
8
9
4
3
2
1GND
ONT
PB
VIN
INT
EN/EN
OFFT
KILL
TJMAX = 125°C, θJA = 165°C/W
EXPOSED PAD (PIN 9) UNCONNECTED
VIN 1
PB 2
ONT 3
GND 4
8KILL
7 OFFT
6 EN/E
N
5INT
TOP VIEW
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 140°C/W
Lead Free Finish
TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2950CDDB-1#TRMPBF LTC2950CDDB-1#TRPBF LBKP 8-Lead Plastic DFN 0°C to 70°C
LTC2950CDDB-2#TRMPBF LTC2950CDDB-2#TRPBF LBNG 8-Lead Plastic DFN 0°C to 70°C
LTC2950IDDB-1#TRMPBF LTC2950IDDB-1#TRPBF LBKP 8-Lead Plastic DFN –40°C to 85°C
LTC2950IDDB-2#TRMPBF LTC2950IDDB-2#TRPBF LBNG 8-Lead Plastic DFN –40°C to 85°C
LTC2950CTS8-1#TRMPBF LTC2950CTS8-1#TRPBF LTBKN 8-Lead Plastic TSOT-23 0°C to 70°C
LTC2950CTS8-2#TRMPBF LTC2950CTS8-2#TRPBF LTBNF 8-Lead Plastic TSOT-23 0°C to 70°C
LTC2950ITS8-1#TRMPBF LTC2950ITS8-1#TRPBF LTBKN 8-Lead Plastic TSOT-23 –40°C to 85°C
LTC2950ITS8-2#TRMPBF LTC2950ITS8-2#TRPBF LTBNF 8-Lead Plastic TSOT-23 –40°C to 85°C
TRM = 500 pieces. *Temperature grades are identifi ed by a label on the shipping container.
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
Consult LTC Marketing for information on lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
PIN CONFIGURATION
ABSOLUTE MAXIMUM RATINGS
(Note 1)
ORDER INFORMATION
LTC2950-1/LTC2950-2
3
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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Supply Voltage Range Steady State Operation l2.7 26.4 V
IIN VIN Supply Current System Power On, VIN = 2.7V to 24V l612 μA
VUVL VIN Undervoltage Lockout VIN Falling l2.2 2.3 2.4 V
VUVL(HYST) VIN Undervoltage Lockout
Hysteresis
50 300 600 mV
Push Button Pin (PB)
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 l0.6 0.8 1 V
VPB(VOC) PB Open Circuit Voltage IPB = –1μA 1 1.6 2 V
Debounce Timing Pins (ONT, OFFT)
IONT, OFFT(PU) ONT/OFFT Pull Up Current VONT, OFFT = 0V l–2.4 –3 –3.6 μA
IONT, OFFT(PD) ONT/OFFT Pull Down Current VONT, OFFT = 1.3V l2.4 3 3.6 μA
tDB, On Internal Turn On Debounce Time ONT Pin Float, PB Falling → Enable Asserted l26 32 41 ms
tONT Additional Adjustable Turn On Time CONT = 1500pF l9 11.5 13.5 ms
tDB, Off Internal Turn Off Debounce Time OFFT Pin Float, PB Falling → INT Falling l26 32 41 ms
tOFFT Additional Adjustable Turn Off Time COFFT = 1500pF l9 11.5 13.5 ms
μP Handshake Pins (INT, KILL)
IINT(LKG) INT Leakage Current VINT = 3V l±1 μA
VINT(VOL) INT Output Voltage Low IINT = 3mA l0.11 0.4 V
VKILL(TH) KILL Input Threshold Voltage KILL Falling l0.57 0.6 0.63 V
VKILL(HYST) KILL Input Threshold Hysteresis 10 30 50 mV
IKILL(LKG) KILL Leakage Current VKILL = 0.6V ±0.1 μA
tKILL(PW) KILL Minimum Pulse Width l30 μs
tKILL(PD) KILL Propagation Delay KILL Falling → Enable Released l30 μs
tKILL, On Blank KILL Turn On Blanking (Note 3) KILL = Low, Enable Asserted → Enable Released l400 512 650 ms
tKILL, Off Delay KILL Turn Off Delay (Note 4) KILL = High, INT Asserted → Enable Released l800 1024 1300 ms
tEN/EN, Lock Out EN/EN Lock Out Time (Note 5) Enable Released → Enable Asserted l200 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 l0.11 0.4 V
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
suffi cient 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 or tONT.
Note 4: The KILL turn off delay is the maximum delay from the initiation
of a shutdown sequence (INT falling), to the release of the enable output.
If the KILL input switches low at any time during this period, enable is
released, thus turning off system power. This time is internally fi xed at
1024ms. This time delay does not include tDB, OFF or tOFFT.
Note 5: The enable lock out time is designed to allow an application to
properly power down such that the next power up sequence starts from
a consistent powered down confi guration. PB is ignored during this lock
out time. This time delay does not include tDB, ON or tONT.
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VIN = 2.7V to 26.4V, unless otherwise noted. (Note 2)
LTC2950-1/LTC2950-2
4
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TEMPERATURE (°C)
–50
IVIN (μA)
10
8
6
4
2
0
–25 02550
2950 G01
75 100
VIN = 26.4V
VIN = 3.3V
VIN = 2.7V
0510 15 20 25 30
VIN (V)
IVIN (μA)
10
8
6
4
2
0
2950 G02
TA = 25°C
2950 G03
VIN (V)
0
0
tDB, ON (ms)
10
20
30
40
50
510 15 20 25 30
TA = 25°C
Supply Current vs Temperature Supply Current vs Supply Voltage
Internal Default Turn On
Debounce Time (tDB, ON) vs VIN
1
tDB, ON + tONT (ms)
100
1000
1000
2950 G04
10 10 100
10000 TA = 25°C
VIN = 3.3V
ONT EXTERNAL CAPACITOR (nF) TEMPERATURE (°C)
–50 –25 0 25 50 75 100
ONT PULL-DOWN CURRENT (μA)
2950 G05
–3.4
–3.2
–3.0
–2.8
–2.6
VIN = 26.4V
VIN = 2.7V
VIN (V)
0
tDB, OFF (ms)
5101520
2950 G06
25 30
50
40
30
20
10
0
TA = 25°C
2950 G07
1
tDB, OFF + tOFFT (ms)
100
1000
1000
10 10 100
10000 TA = 25°C
VIN = 3.3V
OFFT EXTERNAL CAPACITOR (nF)
2950 G08
TEMPERATURE (°C)
–50 –25 0 25 50 75 100
OFFT PULL-DOWN CURRENT (μA)
–3.4
–3.2
–3.0
–2.8
–2.6
VIN = 26.4V
VIN = 2.7V
PB CURRENT (μA)
2950 G09
–10010
20 30–5 5 15 25
–250
–200
–150
–100
–50
0
PB VOLTAGE (V)
TA = 25°C
VIN = 3.3V
Turn On Debounce Time (tDB, ON
+ tONT) vs ONT External Capacitor
ONT Pull-Down Current
vs Temperature
Internal Default Turn Off
Debounce Time (tDB, OFF) vs VIN
Turn Off Debounce Time (tDB, OFF
+ tOFFT) vs OFFT External Capacitor
OFFT Pull-Down Current
vs Temperature PB Current vs PB Voltage
TYPICAL PERFORMANCE CHARACTERISTICS
LTC2950-1/LTC2950-2
5
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2950 G10
0
0
50
100
150
200
250
300
5101520
VIN = 3.3V
TA = 25°C
PB VOLTAGE (mV)
EXTERNAL PB RESISTANCE TO GROUND (kΩ)
TA = –45°C
TA = 100°C
EN/EN CURRENT LOAD (mA)
0
EN/EN VOLTAGE (mV)
500
400
300
200
100
08
2950 G11
24610
TA = 25°C
VIN = 3.3V
VIN (V)
0
EN (V)
4
2950 G12
123
TA = 25°C
100k PULL-UP FROM EN TO VIN
1.0
0.8
0.6
0.4
0.2
0
EN (V)
2950 G13
VIN (V)
04
123
4
3
2
1
0
TA = 25°C
100k PULL-UP FROM EN TO VIN
EN (LTC2950-1) Voltage vs VIN EN (LTC2950-2) Voltage vs VIN
PB Voltage vs External PB
Resistance to Ground EN/EN VOL vs Current Load
TYPICAL PERFORMANCE CHARACTERISTICS
LTC2950-1/LTC2950-2
6
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VIN (Pin 1/Pin 4): Power Supply Input: 2.7V to 26.4V.
PB (Pin 2/Pin 3): Push Button Input. Connecting PB to
ground through a momentary switch provides on/off
control via the EN/EN pin. An internal 100k pull-up resis-
tor connects to an internal 1.9V bias voltage. The rugged
PB input can be pulled up to 26.4V externally without
consuming extra current.
ONT (Pin 3/Pin 2): Additional Adjustable Turn On Time
Input. Placing an external capacitor to ground determines
the additional time (beyond the internal default 32ms)
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 push
button turn-off event is detected, the LTC2950 interrupts the
system (μP) by bringing the INT pin low. Once the system
fi nishes 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 (1024ms) 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 (LTC2950-1, Pin 6/Pin 7): Open Drain Enable Output.
This pin is intended to enable system power. EN is as-
serted high after a valid PB turn on event. 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) a second valid PB event
(power turn-off) is detected. The operating range for this
pin is 0V to 10V.
EN (LTC2950-2, Pin 6/Pin 7): Open Drain Enable Output.
This pin is intended to enable system power. EN is as-
serted low after a valid PB turn-on event. 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) a second valid PB event
(power turn-off) is detected. The operating range of this
pin is 0V to 10V.
OFFT (Pin 7/Pin 6): Additional Adjustable Turn Off Time
Input. A capacitor to ground determines the additional
time (beyond the internal default 32ms) that the PB pin
must be held low before initiating a power down sequence
(INT falling). Floating this pin results in a default turn off
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 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.
Exposed Pad (Pin 9): Exposed Pad may be left open or
connected to device ground.
(TSOT-23/DFN)
PIN FUNCTIONS
LTC2950-1/LTC2950-2
7
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KILL
EN/EN
tKILL(PW)
tKILL(PD)
2950 TD01
LOGIC
OSCILLATOR
OSCILLATOR
DEBOUNCE
2.4V
2.4V
100k
VIN
2.7V TO 26.4V
PB
GND
EN/EN
KILL
INT
ONT OFFT
0.8V
0.6V
2950 BD
REGULATOR
BLOCK DIAGRAM
TIMING DIAGRAMS
LTC2950-1/LTC2950-2
8
295012fc
Power On Timing
Power Off Timing, KILL > 0.6V
tDB, ON tONT
PB
16 CYCLES
PB & KILL IGNORED
EN
(LTC2950-1)
EN
(LTC2950-2)
tKILL, ON BLANK
2950 TD02
tDB, OFF tOFFT
PB
INT
OFFT
PB IGNORED
tKILL, OFF DELAY
2950 TD03
16 CYCLES
EN
(LTC2950-1)
EN
(LTC2950-2)
TIMING DIAGRAMS
LTC2950-1/LTC2950-2
9
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Description
The LTC2950 is a low power (6μA), wide input voltage range
(2.7V to 26.4V), push button on/off controller that can interface
to a μP and a power supply. The turn-on and turn-off debounce
times are extendable using optional external capacitors. A
simple interface (INT output, KILL input) allows a system to
power on and power off in a controlled manner.
Turn On
When power is fi rst applied to the LTC2950, the part ini-
tializes 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 LTC2950 provides additional turn on
debounce time via an optional capacitor connected to the
ONT pin (tONT). The following equation describes the ad-
ditional time that PB must be held low before asserting the
enable output. CONT is the ONT external capacitor:
C
ONT = 1.56E-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 (tKILL,
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 suffi cient time for the system to power up.
Turn Off
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:
C
OFFT = 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. The power down time given to the μP is 1024ms.
Note that the KILL input can be pulled low (thereby releasing the
enable output) at any time after tKILL, ON BLANK period.
Simplifi ed Power On/Off Sequence
Figure 1 shows a simplifi ed LTC2950-1 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 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 suffi cient time for the DC/DC converter
to reach its fi nal 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 low 512ms after it went high. (EN = low, see
Figure 2). Note that the LTC2950 does not sample KILL and
PB until after the 512ms internal timer has expired. The rea-
son 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 LTC2950 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
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 in 1024ms. Once a system has
fi nished performing its power down operations, it can set
KILL low (t7) and thus immediately set EN low), terminating
the internal 1024ms 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 LTC2950
is in low power mode (6μA). PB is monitored for a high
to low transition.
APPLICATIONS INFORMATION
LTC2950-1/LTC2950-2
10
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Figure 1. Simplifi ed Power On/Off Sequence for LTC2950-1
Figure 2. Aborted Power On Sequence for LTC2950-1
tABORT
PB
KILL
POWER ON
TIMING
EN
512ms
INTERNAL
TIMER
tDB, ON + tONT
POWER
TURNED OFF
2950 F02
μP FAILED TO SET
KILL HIGH
t1t2
tDB, ON tONT
t3t4t5t6t7
PB
ONT
OFFT
EN
KILL
INT
PB & KILL IGNORED PB IGNORED
2950 F01
tKILL, ON BLANK tDB, OFF
tOFFT
<tKILL, OFF DELAY
< tKILL,
OFF DELAY
APPLICATIONS INFORMATION
LTC2950-1/LTC2950-2
11
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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.
LTC2950-1, LTC2950-2 VERSIONS
The LTC2950-1 (high true EN) and LTC2950-2 (low true
EN) differ only by the polarity of the EN/EN pin. Both ver-
sions allow the user to extend the amount of time that
the PB must be held low in order to begin a valid power
on/off sequence. An external capacitor placed on the ONT
pin adds additional time to the turn on time. An external
capacitor placed on the OFFT pin adds additional time to
the turn off time. If no capacitor is placed on the ONT
(OFFT) pin, then the turn on (off) duration is given by an
internally fi xed 32ms timer.
The LTC2950 fi xes the KILL turn off delay time (tKILL, OFF
DELAY) at 1024ms. This means that the EN/EN pin will be
switched low/high a maximum of 1024ms after initiating
a valid turn off sequence. Note that in a typical application,
a μP or μC would set KILL low prior to the 1024ms timer
period (t7 in Figure 1).
Figure 3. μP Turns Off Power (LTC2950-1)
tKILL
PB
EN
DC/DC
TURNS OFF
2950 F03
KILL XXX DON’T CARE
μP SETS
KILL LOW
PB PB IGNORED
EN
KILL
PB BLANKING
XXX DON’T CARE
256ms
POWER ON
2950 F04
DC/DC
TURNS OFF
μP SETS
KILL LOW
tEN/EN, LOCKOUT
Figure 4. DC/DC Turn Off Blanking (LTC2950-1)
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 simplifi ed 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 nor-
mally, the μP can turn off power by setting KILL low, as
shown in Figure 3. At time tKILL, 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 sig-
nifi cant 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.
APPLICATIONS INFORMATION
LTC2950-1/LTC2950-2
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The following equations describe the turn on and turn
off times. CONT and COFFT are the external programming
capacitors:
t
BD,ON + tONT = 32ms + 1ms + (6.7x106) • CONT
t
BD,OFF + tOFFT = 32ms + 1ms + (6.7x106) • COFFT
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 push button switch connected to PB exhibits high
leakage current, then an external pull-up resistor to VIN is
recommended. Furthermore, if the push button switch is
physically located far from the LTC2950 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 push button switch would mitigate
parasitic inductance problems. Placing a 0.1μF capacitor
on the PB pin would lessen the impact of parasitic capaci-
tive coupling.
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 func-
tion. 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 be-
low 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.
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
Figure 5. Input Voltage Monitoring with KILL Input Figure 6. No μP Application
PB
VIN
SHDN
VIN
VOUT
EN
INT
KILL
INT
KILL
(OPEN DRAIN)
LTC2950-1
GND ONT OFFT
LT1767-3.3
μP
9V
R1
10k
3.3V
2950 F05
C4
0.1μF
R3
806k
1%
R2
100k
1%
5.4V THRESHOLD
*OPTIONAL
VIN
CONT*
0.033μF
COFFT*
0.033μF
VIN
SHDN
VIN
VOUT
LT1767-3.3
9V 3.3V
R1
100k
C3*
0.01μF
2950 F06
+
C4
0.1μF
*OPTIONAL
PB
EN
INT
KILL
LTC2950-1
GND ONT OFFT
VIN
CONT*
0.033μF
COFFT*
0.033μF
APPLICATIONS INFORMATION
TYPICAL APPLICATIONS
LTC2950-1/LTC2950-2
13
295012fc
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.
Power Path Switching
The EN open drain output of the LTC2950-2 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 LTC2950-2
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.
VOUT
R1
909k
1%
R4
100k
1%
C3*
0.1μF
2950 F07
C4
0.1μF
CERAMIC
*OPTIONAL
OPEN DRAIN OUTPUT
VTH = 0.6V INPUT
R5
100K
M1
+
4.2V
SINGLE CELL
Li-Ion BATTERY
+
4.2V
SINGLE CELL
Li-Ion BATTERY
OPTIONAL GLITCH
FILTER CAPACITOR
VOUT,TRIP POINT = 6V
PB
EN
INT
KILL
LTC2950-2
GND ONT OFFT
VIN
CONT*
0.033μF
COFFT*
0.033μF
PB
VIN
LTC2950-1
GND ONT
R6
5k
2950 F08
TRACE
CAPACITANCE
PARASITICS
C5
0.1μF
DETAILS OMITTED
FOR CLARITY
TRACE
INDUCTANCE
NOISE
EN
INT
KILL
OFFT
VIN
Figure 7. Power Path Control with 6V Under Voltage Detect
Figure 8. Noisy PB Trace
PB Pin in a Noisy Environment
The rugged
PB pin is designed to operate in noisy envi-
ronments. Transients below ground (>–6V) and above VIN
(<30V) will not damage the rugged
PB pin. Additionally,
the PB pin can withstand ESD HBM strikes up to ±10kV.
In order to keep external noise from coupling inside the
LTC2950, place an R-C network close to the
PB pin. A
5k resistor and a 0.1μF capacitor should suffi ce for most
noisy applications (see Figure 8).
External Pull-Up Resistor on PB
An internal pull-up resistor on the
PB pin makes an ex-
ternal pull-up resistor unnecessary. Leakage current on
TYPICAL APPLICATIONS
LTC2950-1/LTC2950-2
14
295012fc
the
PB board trace, however, will affect the open circuit
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).
PB
VIN
LTC2950-1/
LTC2950-2
GND
EXTERNAL BOARD
LEAKAGE CURRENT
100k
2.4V
R7
10k
2950 F09
>2μA
PINS OMITTED
FOR CLARITY
IF EXTERNAL PARASITIC BOARD
LEAKAGE >2μA, USE EXTERNAL
PULL-UP RESISTOR
VIN
Figure 9. External Pull-Up Resistor on PB Pin
Reverse Battery Protection
To protect the LTC2950 from a reverse battery connec-
tion, place a 1k resistor in series with the VIN pin (see
Figure 10).
TYPICAL APPLICATIONS
PACKAGE DESCRIPTION
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
2.00 ±0.10
(2 SIDES)
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
0.40 ± 0.10
BOTTOM VIEW—EXPOSED PAD
0.56 ± 0.05
(2 SIDES)
0.75 ±0.05
R = 0.115
TYP
R = 0.05
TYP
2.15 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
14
85
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0 – 0.05
(DDB8) DFN 0905 REV B
0.25 ± 0.05
2.20 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
0.61 ±0.05
(2 SIDES)
1.15 ±0.05
0.70 ±0.05
2.55 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
0.50 BSC
LTC2950-1/LTC2950-2
15
295012fc
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.
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
PACKAGE DESCRIPTION
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.22 – 0.36
8 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3) TS8 TSOT-23 0802
2.90 BSC
(NOTE 4)
0.65 BSC
1.95 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.52
MAX
0.65
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
LTC2950-1/LTC2950-2
16
295012fc
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
LT 0209 REV C • PRINTED IN USA
VIN
SHDN
VOUT
INT
KILL
LT1761-1.8
R1
10k
R8
1k
R5
910k
2950 F10
C4
0.1μF
+
μP
1.8V
9V
BATTERY
PB
EN
INT
KILL
LTC2950-1
GND ONT OFFT
CONT*
0.033μF
VIN
COFFT*
0.033μF
*OPTIONAL
Figure 10. Reverse Battery Protection
TYPICAL APPLICATION
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
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