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LTC2951 Push Button On/Off Controller FEATURES

DESCRIPTIO

Adjustable Push Button Debounce and Delay Timers Low Supply Current: 6A Wide Operating Voltage Range: 2.7V to 26V EN Output (LTC2951-1) Allows DC/DC Converter Control EN Output (LTC2951-2) 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
The LTC(R)2951 is a micropower, wide input voltage range push button ON/OFF controller. The part contains a push button input which controls the toggling of an open drain enable output. The push button 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 power down. Under system fault conditions, an adjustable KILL timeout delay ensures proper power down. The LTC2951 operates over a 2.7V to 26V input voltage range to accommodate a variety of input power supplies. Very low quiescent current (6A 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 x 2mm DFN and ThinSOT packages.
, LTC and LT 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.
APPLICATIO S

Portable Instrumentation Meters Blade Servers Portable Customer Service PDA Desktop and Notebook Computers
TYPICAL APPLICATIO
VIN 3V - 26V
VIN
VOUT DC/DC BUCK
SHDN EN VIN LTC2951-1 PB GND KILLT CKILLT* 0.033F EN INT KILL OFFT
2951 TA01
R1 10k INT KILL P/C
2V/DIV 128ms
PB
COFFT* 0.033F *OPTIONAL
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Turn On Debounce
25ms/DIV
2951 TA01b
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LTC2951 ABSOLUTE
(Note 1)
AXI U RATI GS
Operating Temperature Range LTC2951C-1 .............................................. 0C to 70C LTC2951C-2 .............................................. 0C to 70C LTC2951I-1 .......................................... - 40C to 85C LTC2951I-2 .......................................... - 40C to 85C Storage Temperature Range DFN Package..................................... - 65C to 125C TSOT-23............................................ - 65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C
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
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GND 1 KILLT 2 PB 3 VIN 4 9
8 7 6 5
INT EN/EN OFFT KILL
DDB8 PACKAGE 8-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 165C/W EXPOSED PAD (PIN 9) UNCONNECTED
ORDER PART NUMBER LTC2951CDDB-1 LTC2951CDDB-2 LTC2951IDDB-1 LTC2951IDDB-2
DDB PART* MARKING LBTB LBTD LBTB LBTD
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
ELECTRICAL CHARACTERISTICS
SYMBOL VIN IIN VUVL VUVL(HYST) PARAMETER Supply Voltage Range VIN Supply Current VIN Undervoltage Lockout VIN Undervoltage Lockout Hysteresis
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 Falling

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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 TJMAX = 125C, JA = 140C/W
ORDER PART NUMBER LTC2951CTS8-1 LTC2951CTS8-2 LTC2951ITS8-1 LTC2951ITS8-2
TS8 PART* MARKING LTBTC LTBTF LTBTC LTBTF
MIN 2.7 2.2 50
TYP 6 2.3 300
MAX 26.4 12 2.4 600
UNITS V A V mV
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LTC2951 ELECTRICAL CHARACTERISTICS
SYMBOL 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 VKILLT, OFFT = 0V VKILLT, OFFT = 1.3V PB Falling Enable Asserted OFFT Pin Float, PB Falling INT Falling

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)
PARAMETER CONDITIONS MIN -1 -1 -3 0.6 1 -2.4 2.4 100 26 9 -6 -9 0.8 1.6 -3 3 128 32 11.5 TYP MAX 26.4 1 -12 -15 1 2 -3.6 3.6 163 41 13.5 1 0.11 0.57 10 30 30 400 100 9 200 512 128 11.5 256 0.11 650 163 13.5 325 0.1 0.4 0.6 30 0.4 0.63 50 0.1 UNITS V A A A V V A A ms ms ms A V V mV A s s ms ms ms ms A V
VPB(VTH) VPB(VOC) IKILLT, OFFT(PU) IKILLT, OFFT(PD) tDB, ON tDB, OFF tOFFT IINT(LKG) VINT(VOL) VKILL(TH) VKILL(HYST) IKILL(LKG) t KILL(PW) t KILL(PD) t KILL, ON BLANK t KILL, OFF DELAY t KILL, OFF DELAY,
ADDITIONAL
PB Input Threshold PB Open Circuit Voltage KILLT/OFFT Pull Up Current KILLT/OFFT Pull Down Current Turn On Debounce Time Internal Turn Off Debounce Time
Timing Pins (KILLT, OFFT)

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) Internal KILL Turn Off Delay (Note 4) KILL Falling Enable Released KILL = Low, Enable Asserted Enable Released KILLT Pin Float, KILL = High, INT Asserted Enable Released V KILL = 0.6V V INT = 3V I INT = 3mA KILL Falling
P Handshake Pins (INT, KILL)

Additional Adjustable KILL Turn Off CKILLT = 1500pF Delay (Note 4) EN/EN Lock Out Time (Note 5) EN/EN Leakage Current EN/EN Voltage Output Low Enable Released Enable Asserted VEN/ EN = 1V, Sink Current Off IEN/ EN = 3mA
tEN/EN, Lock Out IEN/EN(LKG) VEN/EN(VOL)
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 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.
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 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.
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LTC2951 TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Temperature
10 VIN = 26.4V 8 VIN = 3.3V VIN = 2.7V 4 IVIN (A) 8 10
IVIN (A)
6
6
tDB, ON (ms)
2
0 -50
-25
0 25 50 TEMPERATURE (C)
50
Internal Default Turn Off Debounce Time (tDB, OFF) vs VIN
10000 TA = 25C
40 tDB, OFF + tOFFT (ms) tDB, OFF (ms) 1000
OFFT PULL-DOWN CURRENT (A)
30
20
10
0 0 5 10 15 VIN (V) 20 25 30
2951 G06
tKILL, OFF DELAY + tKILL, OFF DELAY, ADDITIONAL (ms)
Internal Default KILL Turn Off Delay (tKILL, OFF DELAY) vs VIN
200 TA = 25C 160 tKILL, OFF DELAY (ms)
KILLT PULL-DOWN CURRENT (A)
120
80
40
0
0
5
10
15 VIN (V)
20
4
UW
75 100
2951 G01
Supply Current vs Supply Voltage
TA = 25C 200
Turn On Debounce Time (tDB, ON) vs VIN
TA = 25C 160
120
4
80
2
40
0
0
5
10
15 VIN (V)
20
25
30
2951 G02
0
0
5
10
15 VIN (V)
20
25
30
2951 G14
Turn Off Debounce Time (tDB, OFF + tOFFT) vs OFFT External Capacitor
TA = 25C VIN = 3.3V -3.4
OFFT Pull-Down Current vs Temperature
-3.2 VIN = 26.4V -3.0 VIN = 2.7V -2.8
100
10
1
100 10 OFFT EXTERNAL CAPACITOR (nF)
1000
2951 G07
-2.6 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2951 G08
KILL Turn Off Delay vs KILLT External Capacitor
10000 -3.4
KILLT Pull-Down Current vs Temperature
-3.2 VIN = 26.4V -3.0 VIN = 2.7V -2.8
1000
100
25
30
2951 G03
10
1
100 10 KILLT EXTERNAL CAPACITOR (nF)
1000
2951 G04
-2.6 -50
-25
0 25 50 TEMPERATURE (C)
75
100
2951 G05
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LTC2951 TYPICAL PERFOR A CE CHARACTERISTICS
PB Current vs PB Voltage
-250 TA = 25C VIN = 3.3V -200 PB VOLTAGE (mV) PB CURRENT (A) 300 VIN = 3.3V 250 200 150 100 50 0 -5 0 5 10 15 PB VOLTAGE (V) 20 25 30 0 5 10 15 20 EXTERNAL PB RESISTANCE TO GROUND (k)
2951 G10
-150
-100
-50
0 -10
500
EN/EN VOL vs Current Load
TA = 25C VIN = 3.3V
400 EN/EN VOLTAGE (mV)
EN (V)
EN (V)
300
200
100
0 0 2 6 8 4 EN/EN CURRENT LOAD (mA) 10
2951 G11
UW
PB Voltage vs External PB Resistance to Ground
TA = 100C TA = 25C TA = -45C
2951 G09
1.0
EN (LTC2951-1) Voltage vs VIN
TA = 25C 100k PULL-UP FROM EN TO VIN
4
EN (LTC2951-2) Voltage vs VIN
TA = 25C 100k PULL-UP FROM EN TO VIN
0.8
3
0.6
2
0.4 1 0.2
0
0 0 1 2 VIN (V)
2951 G12
3
4
0
1
2 VIN (V)
3
4
2951 G13
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LTC2951 PI FU CTIO S
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. 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 P 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 push button turn-off event is detected (tDB, OFF + tOFFT), the LTC2951 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 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
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(TSOT-23/DFN) 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. The operating range for this pin is 0V to 10V. A 100k pull-up is recommended if not available in the DC/DC converter. 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. The operating range of this pin is 0V to 10V. A 100k pull-up is recommended if not available in the DC/DC converter. 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 power down 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. Exposed Pad (Pin 9): Exposed Pad may be left open or connected to device ground.
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LTC2951 BLOCK DIAGRA W
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
2951 BD
GND
KILLT
OFFT
TI I G DIAGRA S
tKILL(PW) KILL
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UW
tKILL(PD) EN/EN
2951 TD01
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LTC2951 TI I G DIAGRA S
PB tDB, ON PB & KILL IGNORED tKILL, ON BLANK
EN (LTC2951-1)
EN (LTC2951-2)
2951 TD03
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EN (LTC2951-1)
EN (LTC2951-2)
2951 TD02
Power On Timing
PB tDB, OFF tOFFT
PB IGNORED
OFFT 16 CYCLES
INT tKILL, OFF DELAY tKILL, OFF DELAY, ADDITIONAL KILLT 16 CYCLES
Power Off Timing, KILL > 0.6V
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LTC2951 APPLICATIO S I FOR ATIO
Description The LTC2951 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 part incorporates all the flexible timing needed to debounce the push button 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 push button of a handheld device. Turn On 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). 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 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 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.
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KILL Turn Off Delay 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 P by setting INT low. The P 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 P fails to respond during this timeout period, the enable output will automatically release. The default power down timeout period is 128ms (tKILL, OFF DELAY), which can be extended by placing an optional capacitor on the KILLT pin (tKILL, OFF DELAY, ADDITIONAL). The following equation describes the additional power down timeout period. CKILLT is the KILLT external capacitor: CKILLT = 1.56e-4 [F/ms] * (tKI LL, OFF DELAY, ADDITIONAL - 1ms) Note that KILL can be driven low (thereby releasing the enable output) at any time after tKILL, ON BLANK period. 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 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 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
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LTC2951 APPLICATIO S I FOR ATIO
t1 PB tDB, ON t2 t3 PB & KILL IGNORED tKILL, ON BLANK tDB, OFF
OFFT
INT
KILL
EN
2951 F01
Figure 1. Simplified Power On/Off Sequence for LTC2951-1
PB tDB, ON 512ms INTERNAL TIMER
POWER ON TIMING POWER TURNED OFF EN P FAILED TO SET KILL HIGH KILL
2951 F02
Figure 2. Aborted Power On Sequence for LTC2951-1
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t4 t5 t6 PB IGNORED < tKILL, OFF DELAY t7 tOFFT tABORT
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LTC2951 APPLICATIO S I FOR ATIO
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 after the KILL turn off (t KILL, OFF DELAY + t KILL, OFF DELAY, ADDITIONAL) timeout period. Once a system has finished performing its power down 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 (6A). 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). 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 t KILL, KILL is set low by the
tKILL PB PB & KILL IGNORED DC/DC TURNS OFF EN P SETS KILL LOW KILL XXX DON'T CARE
2951 F03
Figure 3. P Turns Off Power (LTC2951-1)
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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, 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.
tEN/EN, LOCKOUT PB POWER ON PB & KILL IGNORED PB IGNORED DC/DC TURNS OFF PB BLANKING 256ms EN P SETS KILL LOW KILL XXX DON'T CARE
2951 F04
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Figure 4. DC/DC Turn Off Blanking (LTC2951-1)
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LTC2951 APPLICATIO S I FOR ATIO
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 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 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 APPLICATIO S
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 enough to keep leakage currents from tripping the 0.6V KILL comparator.
VIN 9V VIN VOUT 3.3V
LT1767-3.3 SHDN 5.4V THRESHOLD R3 806k 1% EN LTC2951-1 INT PB GND KILLT KILL OFFT CKILLT* 0.033F COFFT* 0.033F *OPTIONAL R2 100k 1% R1 10k INT P PB GND KILLT KILL OFFT CKILLT* 0.033F COFFT* 0.033F VIN LTC2951-1 INT EN
C4 0.1F
VIN
KILL (OPEN DRAIN)
2951 F05
Figure 5. Input Voltage Monitoring with KILL Input
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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 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.
VIN 9V VIN VOUT 3.3V LT1767-3.3 SHDN R1 100k C4 0.1F
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C3* 0.01F
*OPTIONAL
2951 F06
Figure 6. No P Application
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LTC2951 TYPICAL APPLICATIO S
Power Path Switching 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 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 (<33V) will not damage the rugged PB pin. Additionally, PB pin can withstand ESD HBM strikes up to 10kV. the In order to keep external noise from coupling inside the LTC2951, 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).
4.2V SINGLE CELL Li-Ion BATTERY
+
C4 0.1F CERAMIC VIN LTC2951-2 PB GND KILLT EN INT KILL OFFT CKILLT* 0.033F OPEN DRAIN OUTPUT
4.2V SINGLE CELL Li-Ion BATTERY
+
Figure 7. Power Path Control with 6V Under Voltage Detect
PARASITICS TRACE CAPACITANCE NOISE TRACE INDUCTANCE C5 0.1F R6 5k VIN PB LTC2951-1 EN INT KILL GND KILLT OFFT
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VOUT R5 100K M1 VOUT,TRIP POINT = 6V R1 909k 1%
OPTIONAL GLITCH FILTER CAPACITOR VTH = 0.6V INPUT R4 100k 1% C3* 0.1F
COFFT* 0.033F *OPTIONAL
2951 F07
VIN
DETAILS OMITTED FOR CLARITY
2951 F08
Figure 8. Filtering for Noisy PB Traces
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LTC2951 TYPICAL APPLICATIO S
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 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 LTC2951 from a reverse battery connection, place a 1k resistor (R8) in series with the VIN pin (see Figure 10).
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VIN R7 10k
VIN
LTC2951-1/ LTC2951-2 2.4V
100k PB EXTERNAL BOARD LEAKAGE CURRENT >2A GND PINS OMITTED FOR CLARITY
2951 F09
IF EXTERNAL PARASITIC BOARD LEAKAGE >2A, USE EXTERNAL PULL-UP RESISTOR
Figure 9. External Pull-Up Resistor on PB Pin
2951f
LTC2951 PACKAGE DESCRIPTIO U
DDB Package 8-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1702)
0.61 0.05 (2 SIDES) 0.675 0.05 2.50 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 PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 0.10 (2 SIDES) 3.00 0.10 (2 SIDES) R = 0.115 TYP 5 0.56 0.05 (2 SIDES) 0.38 0.10 8 0.200 REF 0.75 0.05 4 0.25 0.05 2.15 0.05 (2 SIDES) BOTTOM VIEW--EXPOSED PAD 1 PIN 1 CHAMFER OF EXPOSED PAD
(DDB8) DFN 1103
0.50 BSC
0 - 0.05
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
2951f
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.
15
LTC2951 TYPICAL APPLICATIO U
VIN 9V BATTERY VOUT
+
R8 1k
R5 910k
LT1761-1.8 SHDN 1.8V
C4 0.1F
VIN LTC2951-1 PB GND KILLT
EN INT KILL OFFT CKILLT* 0.033F COFFT* 0.033F
R1 10k INT P KILL
*OPTIONAL
2951 F10
Figure 10. Reverse Battery Protection Using R8
RELATED PARTS
PART NUMBER LTC2900 LTC2904/2905 LTC2950 LTC4411 LTC4412HV LTC4055 DESCRIPTION Programmable Quad Supply Monitor Pin-Programmable Dual Supply Monitors Micropower Push Button On/Off Controller 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 High Voltage Push Button Controller with P Interface and Adjustable ON Time 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
2951f
16 Linear Technology Corporation
(408) 432-1900
LT/TP 0405 500 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2005

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