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LTC2950-1/LTC2950-2 Push Button On/Off Controller FEATURES

DESCRIPTION
The LTC(R)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 microprocessor 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 (6A typical) makes the LTC2950 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 either 8-lead 3mm x 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.

Adjustable Push Button On/Off Timers Low Supply Current: 6A Wide Operating Voltage Range: 2.7V to 26V EN Output (LTC2950-1) Allows DC/DC Converter Control EN Output (LTC2950-2) Allows Circuit Breaker Control Simple Interface Allows Graceful P Shut Down 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 x 2mm DFN and ThinSOTTM Packages
APPLICATIONS

Portable Instrumentation Meters Blade Servers Portable Customer Service PDA Desktop and Notebook Computers
TYPICAL APPLICATION
VIN 3V - 26V
Turn On Debounce
VIN VOUT DC/DC BUCK SHDN EN R1 10k INT P/C KILL
2950 TA01
VIN LTC2950-1 PB GND ONT CONT* 0.033F
EN INT KILL OFFT COFFT* 0.033F
2V/DIV PB
10ms/DIV *OPTIONAL
2950 TA01b
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LTC2950-1/LTC2950-2 ABSOLUTE MAXIMUM RATINGS
(Note 1)
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 .............................................. 0C to 70C LTC2950-C2 .............................................. 0C to 70C LTC2950-I1 .......................................... - 40C to 85C LTC2950-I2 .......................................... - 40C to 85C Storage Temperature Range DFN Package..................................... - 65C to 125C TSOT-23 ............................................ - 65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C
PIN CONFIGURATION
TOP VIEW GND 1 ONT 2 PB 3 VIN 4 9 8 7 6 5 INT EN/EN OFFT KILL VIN 1 PB 2 ONT 3 GND 4 TOP VIEW 8 KILL 7 OFFT 6 EN/EN 5 INT
DDB8 PACKAGE 8-LEAD (3mm 2mm) PLASTIC DFN TJMAX = 125C, JA = 165C/W EXPOSED PAD (PIN 9) UNCONNECTED
TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125C, JA = 140C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE 0C to 70C 0C to 70C -40C to 85C -40C to 85C 0C to 70C 0C to 70C -40C to 85C -40C to 85C LTC2950CDDB-1#TRMPBF LTC2950CDDB-1#TRPBF LBKP 8-Lead Plastic DFN LTC2950CDDB-2#TRMPBF LTC2950CDDB-2#TRPBF LBNG 8-Lead Plastic DFN LTC295ICDDB-1#TRMPBF LTC295ICDDB-1#TRPBF LBKP 8-Lead Plastic DFN LTC295ICDDB-2#TRMPBF LTC295ICDDB-2#TRPBF LBNG 8-Lead Plastic DFN LTC2950CTS8-1#TRMPBF LTC2950CTS8-1#TRPBF LTBKN 8-Lead Plastic TSOT-23 LTC2950CTS8-2#TRMPBF LTC2950CTS8-2#TRPBF LTBNF 8-Lead Plastic TSOT-23 LTC2950ITS8-1#TRMPBF LTC2950ITS8-1#TRPBF LTBKN 8-Lead Plastic TSOT-23 LTC2950ITS8-2#TRMPBF LTC2950ITS8-2#TRPBF LTBNF 8-Lead Plastic TSOT-23 TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on lead based finish parts. 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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LTC2950-1/LTC2950-2 ELECTRICAL CHARACTERISTICS
SYMBOL VIN IIN VUVL VUVL(HYST) PARAMETER Supply Voltage Range VIN Supply Current VIN Undervoltage Lockout
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 2.7V to 26.4V, unless otherwise noted. (Note 2)
CONDITIONS Steady State Operation System Power On, VIN = 2.7V to 24V VIN Falling

MIN 2.7
TYP 6
MAX 26.4 12 2.4 600
UNITS V A V mV
2.2 50
2.3 300
VIN Undervoltage Lockout Hysteresis Push Button Pin (PB) VPB(MIN, MAX) IPB PB Voltage Range PB Input Current Single-Ended 2.5V < VPB < 26.4V VPB = 1V VPB = 0.6V PB Falling IPB = -1A VONT, OFFT = 0V VONT, OFFT = 1.3V ONT Pin Float, PB Falling Enable Asserted OFFT Pin Float, PB Falling INT Falling

-1 -1 -3 0.6 1 -2.4 2.4 26 9 26 9 -6 -9 0.8 1.6 -3 3 32 11.5 32 11.5
26.4 1 -12 -15 1 2 -3.6 3.6 41 13.5 41 13.5 1 0.11 0.4 0.63 50 0.1
V A A A V V A A ms ms ms ms A V V mV A s s ms ms ms A V
VPB(VTH) VPB(VOC) IONT, OFFT(PU) IONT, OFFT(PD) tDB, On tONT tDB, Off tOFFT IINT(LKG) VINT(VOL) VKILL(TH) VKILL(HYST) IKILL(LKG) tKILL(PW) tKILL(PD) tKILL, On Blank tKILL, Off Delay tEN/EN, Lock Out IEN/EN(LKG) VEN/EN(VOL)
PB Input Threshold PB Open Circuit Voltage ONT/OFFT Pull Up Current ONT/OFFT Pull Down Current Internal Turn On Debounce Time Internal Turn Off Debounce Time
Debounce Timing Pins (ONT, OFFT)
Additional Adjustable Turn On Time CONT = 1500pF Additional Adjustable Turn Off Time COFFT = 1500pF INT Leakage Current INT Output Voltage Low KILL Input Threshold Voltage KILL Input Threshold Hysteresis KILL Leakage Current KILL Minimum Pulse Width KILL Propagation Delay KILL Turn On Blanking (Note 3) KILL Turn Off Delay (Note 4) EN/EN Lock Out Time (Note 5) EN/EN Leakage Current EN/EN Voltage Output Low KILL Falling Enable Released KILL = Low, Enable Asserted Enable Released KILL = High, INT Asserted Enable Released Enable Released Enable Asserted VEN/ EN = 1V, Sink Current Off IEN/ EN = 3mA VKILL = 0.6V VINT = 3V IINT = 3mA KILL Falling
P Handshake Pins (INT, KILL)

0.57 10
0.6 30

30 30 400 800 200 512 1024 256 0.11 650 1300 325 0.1 0.4
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 P 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 fixed 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 configuration. PB is ignored during this lock out time. This time delay does not include tDB, ON or tONT.
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LTC2950-1/LTC2950-2 TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
10 VIN = 26.4V 8 VIN = 3.3V VIN = 2.7V 4 IVIN (A) 8 10
Supply Current vs Supply Voltage
TA = 25C 50
Internal Default Turn On Debounce Time (tDB, ON) vs VIN
TA = 25C 40 tDB, ON (ms)
IVIN (A)
6
6
30
4
20
2
2
10
0 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2950 G01
0
0
5
10
15 VIN (V)
20
25
30
2950 G02
0
0
5
10
15 VIN (V)
20
25
30
2950 G03
Turn On Debounce Time (tDB, ON + tONT) vs ONT External Capacitor
10000 ONT PULL-DOWN CURRENT (A) TA = 25C VIN = 3.3V -3.4
ONT Pull-Down Current vs Temperature
50
Internal Default Turn Off Debounce Time (tDB, OFF) vs VIN
TA = 25C 40
-3.2 VIN = 26.4V -3.0 VIN = 2.7V -2.8 tDB, OFF (ms) 75 100
2950 G05
tDB, ON + tONT (ms)
1000
30
20
100
10
10
1
100 10 ONT EXTERNAL CAPACITOR (nF)
1000
2950 G04
-2.6 -50
-25
0 25 50 TEMPERATURE (C)
0
0
5
10
15 VIN (V)
20
25
30
2950 G06
Turn Off Debounce Time (tDB, OFF + tOFFT) vs OFFT External Capacitor
10000 OFFT PULL-DOWN CURRENT (A) TA = 25C VIN = 3.3V tDB, OFF + tOFFT (ms) -3.4
OFFT Pull-Down Current vs Temperature
-250
PB Current vs PB Voltage
TA = 25C VIN = 3.3V
-3.2 VIN = 26.4V -3.0 VIN = 2.7V -2.8 PB CURRENT (A) 75 100
2950 G08
-200
1000
-150
-100
100
-50
10
1
100 10 OFFT EXTERNAL CAPACITOR (nF)
1000
2950 G07
-2.6 -50
-25
0 25 50 TEMPERATURE (C)
0 -10
-5
0
5 10 15 PB VOLTAGE (V)
20
25
30
2950 G09
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LTC2950-1/LTC2950-2 TYPICAL PERFORMANCE CHARACTERISTICS
PB Voltage vs External PB Resistance to Ground
300 VIN = 3.3V 250 200 150 100 50 0 0 5 10 15 20 EXTERNAL PB RESISTANCE TO GROUND (k)
2950 G10
EN/EN VOL vs Current Load
500 TA = 25C VIN = 3.3V 400 EN/EN VOLTAGE (mV)
PB VOLTAGE (mV)
TA = 100C TA = 25C TA = -45C
300
200
100
0 0 2 6 8 4 EN/EN CURRENT LOAD (mA) 10
2950 G11
EN (LTC2950-1) Voltage vs VIN
1.0 TA = 25C 100k PULL-UP FROM EN TO VIN 4
EN (LTC2950-2) Voltage vs VIN
TA = 25C 100k PULL-UP FROM EN TO VIN 3
0.8
EN (V)
EN (V) 0 2 VIN (V)
2950 G12
0.6
2
0.4 1
0.2
0
1
3
4
0
0
1
2 VIN (V)
3
4
2950 G13
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LTC2950-1/LTC2950-2 PIN FUNCTIONS
(TSOT-23/DFN) EN (LTC2950-2, 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. EN releases high if: a) KILL is not driven high (by P) 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. 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 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. 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 (P) 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 (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 asserted high after a valid PB turn on event. EN is released low if: a) KILL is not driven high (by P) 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.
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LTC2950-1/LTC2950-2 BLOCK DIAGRAMS
EN/EN VIN 2.7V TO 26.4V 2.4V REGULATOR 2.4V
OSCILLATOR 100k PB DEBOUNCE 0.8V OSCILLATOR INT LOGIC 0.6V KILL
GND
2950 BD
ONT
OFFT
TIMING DIAGRAMS
tKILL(PW) KILL
tKILL(PD) EN/EN
2950 TD01
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LTC2950-1/LTC2950-2 TIMING DIAGRAMS
PB tDB, ON tONT PB & KILL IGNORED tKILL, ON BLANK
16 CYCLES
EN (LTC2950-1)
EN (LTC2950-2)
2950 TD02
Power On Timing
PB tDB, OFF tOFFT
PB IGNORED
OFFT 16 CYCLES
INT tKILL, OFF DELAY EN (LTC2950-1)
EN (LTC2950-2)
2950 TD03
Power Off Timing, KILL > 0.6V
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LTC2950-1/LTC2950-2 APPLICATIONS INFORMATION
Description The LTC2950 is a low power (6A), wide input voltage range (2.7V to 26.4V), push button on/off controller that can interface to a P 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 first applied to the LTC2950, 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 LTC2950 provides additional turn on debounce time via an optional capacitor connected to the ONT pin (tONT). The following equation describes the additional time that PB must be held low before asserting the enable output. CONT is the ONT external capacitor: CONT = 1.56E-4 [F/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 P 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 P . 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 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: COFFT = 1.56E-4 [F/ms] * (tOFFT - 1ms) Once PB has been validly pressed, INT is switched low. This alerts the P to perform its power down and housekeeping tasks. The power down time given to the P is 1024ms. Note that the KILL input can be pulled low (thereby releasing the enable output) at any time after tKILL, ON BLANK period. Simplified Power On/Off Sequence Figure 1 shows a simplified 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 sufficient time for the DC/DC converter to reach its final voltage, and to allow the P 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 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 LTC2950 monitors PB and KILL (for a turnoff command) while consuming only 6A 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 finished 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 (6A). PB is monitored for a high to low transition.
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LTC2950-1/LTC2950-2 APPLICATIONS INFORMATION
t1 PB tDB, ON ONT tONT t2 t3 PB & KILL IGNORED tKILL, ON BLANK tDB, OFF t4 t5 t6 PB IGNORED < tKILL, OFF DELAY t7
tOFFT OFFT
INT
EN
2950 F01
Figure 1. Simplified Power On/Off Sequence for LTC2950-1
tABORT PB tDB, ON + tONT 512ms INTERNAL TIMER
POWER ON TIMING POWER TURNED OFF EN P FAILED TO SET KILL HIGH KILL
2950 F02
Figure 2. Aborted Power On Sequence for LTC2950-1
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LTC2950-1/LTC2950-2 APPLICATIONS INFORMATION
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). P Turns Off Power During Normal Operation Once the system has powered on and is operating normally, the P can turn off power by setting KILL low, as shown in Figure 3. At time tKILL, KILL is set low by the P 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 P has always powered down completely before it is restarted. Figure 4 shows the P 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 versions 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 fixed 32ms timer. The LTC2950 fixes 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 P or C would set KILL low prior to the 1024ms timer period (t7 in Figure 1).
tEN/EN, LOCKOUT PB POWER ON PB IGNORED
tKILL PB DC/DC TURNS OFF EN P SETS KILL LOW KILL XXX DON'T CARE
2950 F03
DC/DC TURNS OFF PB BLANKING
256ms
EN
P SETS KILL LOW KILL XXX DON'T CARE
2950 F04
Figure 3. P Turns Off Power (LTC2950-1)
Figure 4. DC/DC Turn Off Blanking (LTC2950-1)
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LTC2950-1/LTC2950-2 APPLICATIONS INFORMATION
The following equations describe the turn on and turn off times. CONT and COFFT are the external programming capacitors: tBD,ON + tONT = 32ms + 1ms + (6.7x106) * CONT tBD,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 0.1F 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 P 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
VIN 9V VIN VOUT 3.3V
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 P Figure 6 shows how to connect the KILL pin when there is no circuitry available to drive it. The minimum pulse width detected is 30s. If there are glitches on the resistor
VIN 9V VIN VOUT 3.3V
LT1767-3.3 SHDN 5.4V THRESHOLD R3 806k 1% EN LTC2950-1 INT PB GND ONT KILL OFFT CONT* 0.033F COFFT* 0.033F *OPTIONAL R2 100k 1% R1 10k INT P KILL (OPEN DRAIN)
2950 F05
LT1767-3.3 SHDN
R1 100k C4 0.1F VIN LTC2950-1 INT PB GND ONT KILL OFFT CONT* 0.033F COFFT* 0.033F *OPTIONAL
2950 F06
C4 0.1F
VIN
EN
+
C3* 0.01F
Figure 5. Input Voltage Monitoring with KILL Input
Figure 6. No P Application
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LTC2950-1/LTC2950-2 TYPICAL APPLICATIONS
pull-up voltage that are wider than 30s 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 30s later. PB Pin in a Noisy Environment The rugged PB pin is designed to operate in noisy environments. 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 0.1F capacitor should suffice for most noisy applications (see Figure 8). External Pull-Up Resistor on PB An internal pull-up resistor on the PB pin makes an external pull-up resistor unnecessary. Leakage current on
VOUT R5 100K 4.2V SINGLE CELL Li-Ion BATTERY M1 VOUT,TRIP POINT = 6V R1 909k 1% VIN LTC2950-2 PB GND ONT EN INT KILL OFFT CONT* 0.033F OPEN DRAIN OUTPUT OPTIONAL GLITCH FILTER CAPACITOR VTH = 0.6V INPUT R4 100k 1% C3* 0.1F
+
C4 0.1F CERAMIC
4.2V SINGLE CELL Li-Ion BATTERY
+
COFFT* 0.033F *OPTIONAL
2950 F07
Figure 7. Power Path Control with 6V Under Voltage Detect
VIN PARASITICS TRACE CAPACITANCE NOISE TRACE INDUCTANCE C5 0.1F R6 5k VIN PB LTC2950-1 EN INT KILL GND ONT OFFT
DETAILS OMITTED FOR CLARITY
2950 F08
Figure 8. Noisy PB Trace
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LTC2950-1/LTC2950-2 TYPICAL APPLICATIONS
the PB board trace, however, will affect the open circuit voltage on the PB pin. If the leakage is too large (>2A), 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 LTC2950 from a reverse battery connection, place a 1k resistor in series with the VIN pin (see Figure 10).
VIN R7 10k
VIN
LTC2950-1/ LTC2950-2 2.4V
100k PB EXTERNAL BOARD LEAKAGE CURRENT >2A GND PINS OMITTED FOR CLARITY
2950 F09
IF EXTERNAL PARASITIC BOARD LEAKAGE >2A, USE EXTERNAL PULL-UP RESISTOR
Figure 9. External Pull-Up Resistor on PB Pin
PACKAGE DESCRIPTION
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702)
0.61 0.05 (2 SIDES) 0.70 2.55 0.05 1.15 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.20 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 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 0.05 PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 0.10 (2 SIDES) 0.56 0.05 (2 SIDES) 0.75 0.05 0.25 PIN 1 R = 0.20 OR 0.25 45 CHAMFER
(DDB8) DFN 0905 REV B
3.00 0.10 (2 SIDES)
R = 0.05 TYP
R = 0.115 TYP 5
0.40 8
0.10
0.200 REF
4 0.05 2.15 0.05 (2 SIDES)
1 0.50 BSC
0 - 0.05
BOTTOM VIEW--EXPOSED PAD
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LTC2950-1/LTC2950-2 PACKAGE DESCRIPTION
TS8 Package 8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637)
0.52 MAX 0.65 REF 2.90 BSC (NOTE 4)
1.22 REF
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC
1.50 - 1.75 (NOTE 4) PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.65 BSC
0.22 - 0.36 8 PLCS (NOTE 3)
0.80 - 0.90 0.20 BSC 1.00 MAX DATUM `A' 0.01 - 0.10
0.30 - 0.50 REF
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
0.09 - 0.20 (NOTE 3)
1.95 BSC
TS8 TSOT-23 0802
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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.
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LTC2950-1/LTC2950-2 TYPICAL APPLICATION
VIN 9V BATTERY VOUT
+
R8 1k
R5 910k
LT1761-1.8 SHDN 1.8V
C4 0.1F
VIN LTC2950-1 PB GND ONT
EN INT KILL OFFT CONT* 0.033F COFFT* 0.033F
R1 10k INT P KILL
*OPTIONAL
2950 F10
Figure 10. Reverse Battery Protection
RELATED PARTS
PART NUMBER LTC2900 LTC2904/2905 LTC4411 LTC4412HV LTC4055 DESCRIPTION Programmable Quad Supply Monitor Pin-Programmable Dual Supply Monitors 2.6A Low Loss Ideal Diode in ThinSOT Power Path Controller in ThinSOT USB Power Controller and Li-Ion Charger COMMENTS Adjustable RESET, 10-Lead MSOP and 3mm x 3mm DFN Packages Adjustable RESET and Tolerance, 8-Lead SOT-23 and 3mm x 2mm DFN Packages No External MOSFET, Automatic Switching Between DC Sources Efficient Diode-ORing, Automatic Switching Between DC Sources, 3V to 36V Automatic Switchover, Charges 1-Cell Li-Ion Batteries
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Linear Technology Corporation
(408) 432-1900
LT 0208 REV B * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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