LTC4251-2 Linear Technology, LTC4251-2 Datasheet
LTC4251-2
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LTC4251-2 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. All parts are available in the 6-Pin SOT-23 package. ...
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... 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 ...
Page 3
... Timer On (Circuit Breaker, Sourcing), V Timer Off (Cooling Cycle, Sinking), V LTC4251/LTC4251-1 Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to V specified. Note 3: UV/ refers for the LTC4251- ...
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... GATE 30 UV/ TIMER = – V SENSE GATE 125 –55 –35 – TEMPERATURE (°C) UV/ refers for the LTC4251-2. vs Undervoltage Lockout Hysteresis LKO V vs Temperature LKH 1.6 1.4 1.2 1 0.8 0.6 0.4 0 105 125 –55 –35 – TEMPERATURE (°C) 425112 G05 ...
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... UV/ 100 TIMER = 0V GATE = HIGH T 1000 –1.5 –1.0 –0.5 0 0.5 1.0 125 (V – (V) SENSE EE LTC4251/LTC4251-1/ LTC4251-2 UV/ refers for the LTC4251-2. UV Threshold vs Temperature 3.375 LTC4251/LTC4251-2 3.275 V 3.175 3.075 2.975 V 2.875 2.775 85 105 125 –55 –35 – TEMPERATURE (°C) 425112 G14 OV Threshold vs Temperature 6 ...
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... TEMPERATURE (° 105 125 65 425112 G25 UV/ refers for the LTC4251-2. I (Circuit Breaking, Sourcing) TMR vs Temperature 280 260 240 220 200 180 85 105 125 –55 –35 – TEMPERATURE (°C) 425112 G23 ...
Page 7
... CTIO S UV/OV refers to the UV pin for the LTC4251-2. The OV comparator in the LTC4251-2 is disabled. All references in the text to overvoltage, OV, V SENSE (Pin 1): Circuit Breaker/Current Limit SENSE Pin. Load current is monitored by sense resistor R between SENSE and V , and controlled in three steps ...
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... U OPERATIO Note that for simplicity, the following assumptions are made in the text. Firstly, UV/OV also means the UV pin of the LTC4251-2. Secondly, all overvoltage conditions and references to OV, V the OV comparator in this part is disabled. Hot Circuit Insertion When circuit boards are inserted into a live backplane, the supply bypass capacitors can draw huge transient currents from the power bus as they charge ...
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 ...
Page 10
... The UV and OV trip point ratio for LTC4251 is designed to match the standard telecom operating range of 43V to and its hysteresis LKH 75V. The LTC4251-2 implements a UV threshold of 43V ) the chip is enabled; LKO only. A divider (R1, R2) is used to scale the supply voltage. Using R1 = 402k and R2 = 32.4k gives a typical operating range of 43 ...
Page 11
... If the SENSE pin detects more than 50mV across R TIMER pin charges C GATE pin pulls low and the LTC4251/LTC4251-1/ LTC4251-2 latch off. The part remains latched off until either the UV/OV pin is momentarily pulsed low dips into UVLO and is then restored. The circuit breaker ...
Page 12
... EE conditions: in UVLO, during the initial timing cycle overvoltage condition, or when the LTC4251/LTC4251-1/ LTC4251-2 are latched off after a short-circuit. When GATE turns on, a 58µA current source charges the MOSFET gate and any associated external capacitance. V gate drive to no more than 14.5V. ...
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... 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 OWING TO CURRENT –48RTN OVERSHOOT 50V/DIV ONSET OF OUTPUT SHORT-CIRCUIT SENSE 200mV/DIV ...
Page 14
... 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
... 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 IN time point 2, the UV/OV divider makes contact and its voltage exceeds V ...
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... LTC4251/LTC4251-1/ LTC4251-2 www.DataSheet4U.com U U 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 6. 1 GND-V EE UV/ TIMER GATE SENSE V OUT Figure 7. System Power-Up Timing (All Waveforms are Referenced to V ...
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... TIMER CLEARS OVLO V TMRH 5.8µA 230µA V TMRL 58µA START-UP CYCLE INITIAL TIMING CYCLE LTC4251/LTC4251-1/ LTC4251-2 , GATE pulls low and latches off. or pulling TIMER below V UVLO . CHECK GATE < V AND SENSE < TMRL GATEL 5.8µA 5.8µ ...
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... LTC4251/LTC4251-1/ LTC4251-2 www.DataSheet4U.com U U 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 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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... 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 ACL ...
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... LTC4251/LTC4251-1/ LTC4251-2 www.DataSheet4U.com TYPICAL APPLICATIO S GND GND (SHORT PIN) 32.4k –48V GND (SHORT PIN –48V SUPPLY RELATED PARTS PART NUMBER DESCRIPTION LT1640AH/LT1640AL Negative High Voltage Hot Swap Controllers in SO-8 LT1641-1/LT1641-2 Positive High Voltage Hot Swap Controllers in SO-8 LTC1642 Fault Protected Hot Swap Controller LTC1921 Dual – ...