ltc4251-1 Linear Technology Corporation, ltc4251-1 Datasheet
ltc4251-1
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ltc4251-1 Summary of contents
Page 1
... The LTC4251 UV/OV thresholds are designed to match the standard telecom operating range of – 43V to – 75V. The LTC4251-1 UV/OV thresholds extend the operating range to encompass – 36V to – 72V. The LTC4251-2 implements a UV threshold of – 43V only. ...
Page 2
... Current Out of Sense Pin (20µs Pulse) ............. –200mA Maximum Junction Temperature .......................... 125°C Operating Temperature Range LTC4251C/LTC4251-1C/LTC4251-2C ...... 0°C to 70°C LTC4251I/LTC4251-1I/LTC4251-2I .... – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ELECTRICAL CHARACTERISTICS ...
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... Note 3: UV/ refers for the LTC4251- 1000 T = –40°C A 100 T = 25° 85° 125° 0.1 125 (V) IN LTC4251/LTC4251-1/ LTC4251-2 MIN TYP ● 5.25 5.55 ● 5.61 5.91 0.60 0.26 ● –30 –15 ±0.1 ● 5.8 TMR = 230 TMR = 2V 5.8 TMR 0.7 ...
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... LTC4251/LTC4251-1/ LTC4251 TYPICAL PERFOR A CE CHARACTERISTICS V vs Temperature Z 14 2mA IN 14.0 13.5 13.0 12.5 12.0 –55 –35 – 105 TEMPERATURE (°C) 425112 G04 Circuit Breaker Current Limit Voltage V vs Temperature –55 –35 – 105 125 25 65 TEMPERATURE (° ...
Page 5
... UV/ refers for the LTC4251-2. UV Threshold vs Temperature 3.375 LTC4251/LTC4251-2 3.275 V UVH 3.175 3.075 2.975 V UVL 2.875 2.775 125 –55 –35 – TEMPERATURE (°C) 425112 G14 OV Threshold vs Temperature 6.51 LTC4251-1 6.41 6.31 6.21 6.11 6.01 5.91 5.81 5.71 5.61 –55 –35 – 125 TEMPERATURE (°C) 425112 G17 TIMER Threshold vs Temperature 5.0 4.5 V TMRH 4.0 3 ...
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... TMR vs Temperature 280 260 240 220 200 180 125 –55 –35 – TEMPERATURE (°C) 425112 G23 t and t PLLUG PHLOG vs Temperature 1.3 1.2 1.1 t (LTC4251/LTC4251-1) PHLOG 1.0 0.9 0.8 t PLLUG 0.7 0.6 0.5 –55 –35 – 105 125 TEMPERATURE (°C) 425112 G26 85 105 125 425112 G24 425112fa ...
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... V UVHST comparator is set at V UV/OV < V UV/OV > V LTC4251-1/LTC4251-2 attempt to start-up. The internal UVLO internal fault latch. A high at OV pulls GATE low but does not reset the fault latch. A 1nF to 10nF capacitor at UV/OV eliminates transients and switching noise from affecting at 13V. An internal ...
Page 8
... The flow of current damages the connector pins and glitches the power bus, causing other boards in the system to reset. The LTC4251/ LTC4251-1/LTC4251-2 are designed to turn on a circuit board supply in a controlled manner, allowing insertion or removal without glitches or connector damage. ...
Page 9
... If, owing to an output overload, the voltage drop across R exceeds 50mV, TIMER sources 230µA into C ally charges threshold and the LTC4251/LTC4251-1/ LTC4251-2 latch off. If the overload goes away and SENSE measures less than 50mV this way the circuit breaker function will also respond to low duty cycle overloads, and accounts for fast heating and slow cooling characteristic of the MOSFET ...
Page 10
... LTC4251/LTC4251-1/LTC4251-2 will eventually shut down. Low impedance failures on the load side of the LTC4251/ LTC4251-1/LTC4251-2 coupled with 48V or more driving potential can produce current slew rates well in excess of 50A/µs. Under these conditions, overshoot is inevitable. A fast SENSE comparator with a threshold of 200mV detects overshoot and pulls GATE low much harder and hence much faster than can the weaker current limit loop ...
Page 11
... If more noise immunity is desired, add a 1nF to 10nF filter capacitor from UV/ The UV and OV trip point thresholds for the LTC4251-1 are designed to encompass the standard telecom operating range of –36V to –72V. A divider (R1, R2) is used to scale the supply voltage. Using R1 = 442k and R2 = 34.8k gives a typical operating range of 33 ...
Page 12
... TIMER pull-up. At 100mV, the ACL amplifier servos the MOSFET current, and at 200mV the FCL comparator abruptly pulls GATE low in an attempt to bring the MOSFET current under control. If any of these conditions persists long enough for TIMER to charge C tion (2)), the LTC4251/LTC4251-1/LTC4251-2 latch off and pull GATE low ...
Page 13
... U U APPLICATIO S I FOR ATIO capacitors. If LTC4251, LTC4251-1 or LTC4251-2s are used throughout, they respond by limiting the inrush cur- rent to a value of 100mV capacitors will recharge long before C SUPPLY RING SUPPLY RING OWING OWING TO MOSFET TO CURRENT –48RTN TURN-OFF OVERSHOOT 50V/DIV ...
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... V SENSE pins are strongly recommended. The drawing in Figure 6 illustrates the correct way of making connections between the LTC4251/LTC4251-1/LTC4251-2 and the sense resistor. PCB layout should be balanced and sym- metrical to minimize wiring errors. In addition, the PCB ...
Page 15
... In this example as shown in Figure 8, power is delivered through long connector pins whereas the UV/OV divider makes contact through a short pin. This ensures the power connections are firmly established before the LTC4251/ LTC4251-1/LTC4251-2 are activated. At time point 1, the power pins make contact and V ramps through V IN ...
Page 16
... LTC4251/LTC4251-1/ LTC4251 APPLICATIO S I FOR ATIO If the overvoltage glitch is long enough to deplete the load capacitor, a full start-up cycle may occur as shown be- tween time points 3 through GND-V EE UV/ TIMER GATE SENSE V OUT Figure 7. System Power-Up Timing (All Waveforms are Referenced to V ...
Page 17
... AND TIMER RESTARTS INITIAL TIMING CYCLE. OVLO TIMER CLEARS TMRH 5.8µA 230µA V TMRL 58µA START-UP CYCLE INITIAL TIMING CYCLE LTC4251/LTC4251-1/ LTC4251-2 or pulling TIMER below V UVLO . . CB , CHECK GATE < V AND SENSE < TMRL GATEL CB 5.8µA 5.8µA 58µA ...
Page 18
... LTC4251/LTC4251-1/ LTC4251 APPLICATIO S I FOR ATIO The ramp duration is approximately 200µs. This feature reduces load current dl/dt at start-up. As illustrated in Figure 15, soft-start is initiated by a TIMER transition from 1 V OVHI UV/0V V TMRH TIMER 5.8µA GATE SENSE Figure 11. Overvoltage Timing (All Waveforms are Referenced to V ...
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... SOFT-START REFERENCE ) Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.95 REF 1.22 REF 1.50 – 1.75 2.80 BSC 1.4 MIN (NOTE 4) 0.95 BSC 0.80 – 0.90 1.00 MAX 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) LTC4251/LTC4251-1/ LTC4251-2 END OF INITIAL TIMING CYCLE 5.8µA V TMRH TIMER 230µA V TMRL ~V GS(th) GATE 58µA V ...
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... SENSE Pin Limiting and Push-Reset at TIMER Pin R IN 10k 500mW 1µ UV/OV GATE C1 LTC4251-1 10nF 4 1 TIMER SENSE 220nF Figure 17. Power-Limited Circuit Breaker Application COMMENTS Negative High Voltage Supplies from –10V to –80V Supplies from 9V to 80V, Latched Off/Autoretry 3V to 16.5V, Overvoltage Protection up to 33V ± ...