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SG2845Y Datasheet(PDF) 11 Page - Microsemi Corporation |
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SG2845Y Datasheet(HTML) 11 Page - Microsemi Corporation |
11 / 12 page C URRENT -M ODE PWM C ONTROLLER SG1844/SG1845 Series PRODUCT DA T ABOOK 1996/1997 11 Copyright © 2000 Rev. 1.4 4/00 P RODUCTION D ATA S HEET TYPICAL APPLICA TION CIRCUITS FIGURE 17. — ISOLATED MOSFET DRIVE FIGURE 16. — BIPOLAR TRANSISTOR DRIVE Current transformers can be used where isolation is required between PWM and Primary ground. A drive transformer is then necessary to interface the PWM output with the MOSFET. The 1844/45 output stage can provide negative base current to remove base charge of power transistor (Q 1) for faster turn off. This is accomplished by adding a capacitor (C 1) in parallel with a resistor (R 1). The resistor (R 1) is to limit the base current during turn on. Pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package. FIGURE 14. — CURRENT SENSE SPIKE SUPPRESSION FIGURE 15. — MOSFET PARASITIC OSCILLATIONS A resistor (R 1) in series with the MOSFET gate reduce overshoot and ringing caused by the MOSFET input capacitance and any inductance in series with the gate drive. (Note: It is very important to have a low inductance ground path to insure correct operation of the I.C. This can be done by making the ground paths as short and as wide as possible.) The RC low-pass filter will eliminate the leading edge current spike caused by parasitics of Power MOSFET. V CC V IN 7 (12) 7 (11) 6 (10) 5 (8) 3 (5) R C R S Q1 I PK I PK(MAX) = 1.0V R S SG1844/45 V CC V IN 7 (12) 7 (11) 6 (10) 5 (8) R S Q1 SG1844/45 3 (5) R 1 SG1844/45 3 (5) 5 (8) 6 (10) 7 (11) R S Q1 V C1 C 1 R 1 R 2 V IN V C I B + V C R 2 » V C1 R 1||R2 » _ V CC V IN 7 (12) 7 (11) 6 (10) 5 (8) 3 (5) SG1844/45 Isolation Boundary C R R S N S N P Q1 V GS Waveforms + _0 + _0 50% DC 25% DC I PK = V (PIN 1) - 1.4 3R S N P N S |
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