LT1249 Linear Technology Corporation, LT1249 Datasheet
LT1249
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LT1249 Summary of contents
Page 1
... By using fixed high frequency PWM current averaging without the need for slope compensation, the LT1249 achieves far lower line current distortion, with a smaller magnetic element than systems that use either peak current detection or zero current switching approach, in both continuous and discontinuous modes of operation ...
Page 2
... Input Voltage ............................................ V SENSE M Input Current.............................................. 5mA OUT Operating Junction Temperature Range LT1249C ................................................ 100 C LT1249I ........................................... – 125 C Thermal Resistance (Junction-to-Ambient) N8 Package ................................................ 100 C/W S8 Package ................................................. 120 C/W Storage Temperature Range ..................– 150 C Lead Temperature (Soldering, 10 sec)................. 300 C ELECTRICAL CHARACTERISTICS range, otherwise specifications are 5V, no load on any outputs, unless otherwise noted ...
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... OUT 12 15 17.5 V – 3.0 CC 0.9 0.5 1 (VA – 1.5) AC OUT Transconductance of Current Amplifier –20 –40 –60 –80 –100 50 –120 0 –140 1k 10k 100k 1M 10M FREQUENCY (Hz) 1249 G02 LT1249 = 3.5V, OUT UNITS 7 – kHz 2.3 V kHz ...
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... LT1249 W U TYPICAL PERFORMANCE CHARACTERISTICS Reference Voltage vs Temperature 7.536 7.524 7.512 7.500 7.488 7.476 7.464 7.452 7.440 7.428 –75 –50 – JUNCTION TEMPERATURE ( C) Supply Current vs Supply Voltage – 125 ...
Page 5
... VA (Pin 5): This is the output of the voltage error OUT amplifier. The output is clamped at 12V. When the output goes below 1.5V, the multiplier output current is zero operation, M OUT LT1249 Transconductance of Current Amplifier Over Temperature 400 350 300 250 200 ...
Page 6
... This is the inverting input to the voltage SENSE amplifier. V (Pin 7): This is the supply of the chip. The LT1249 has CC a very fast gate driver required to fast charge high power MOSFET gate capacitance. High current spikes occur during charging. For good supply bypass, a 0.1 F ceramic ...
Page 7
... OUT power factor. Synchronization The LT1249 can be externally synchronized in a frequency range of 127kHz to 160kHz. Figure 2 shows the synchro- nizing circuit. Synchronizing occurs when CA pulled below 0.5V with an external transistor and a Schottky diode. The Schottky diode and the 10k pull-up resistor are ...
Page 8
... In the lockout state, the LT1249 only draws 250 A, the oscillator is off, the V GTDR pins remain low to keep the power MOSFET off. Start-Up and Supply Voltage The LT1249 draws only 250 A before the chip starts at 16V trickle start, a 90k resistor from the power CC ...
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... For longer life, capacitor with higher ripple current rating or parallel capacitors should be used. Protection Against Abnormal Current Surge Conditions The LT1249 has an upper limit on the allowed voltage across the current sense resistor. The voltage into the M pin connected to this resistor must not exceed – 6V OUT while the chip is running and – ...
Page 10
... In normal operation, the voltage into M exceed 1.1V, but under surge conditions, the voltage could temporarily go higher. To date, no field failures due to surges have been reported for normal LT1249 configu- rations, but if the possibility exists for extremely large current surges, please read the following discussion. ...
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... MIN (0.508) MIN 0.018 0.003 (0.457 0.076) N8 1098 0.189 – 0.197* (4.801 – 5.004 0.150 – 0.157** (3.810 – 3.988 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC SO8 1298 LT1249 11 ...
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... LT1249 U TYPICAL APPLICATION + 90V EMI TO FILTER 6A 270V – 0.047 F 0.47 F 330k VA OUT – SENSE 4.7nF COILTRONICS CTX02-12236 (TYPE 52 CORE) AIR MOVEMENT NEEDED AT POWER LEVEL GREATER THAN 250W. 2. COILTRONICS CTX02-12295 (MAGNETICS Kool M ** THIS SCHOTTKY DIODE IS TO CLAMP GTDR WHEN MOS SWITCH TURNS OFF. ...