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ML4411CS Datasheet(PDF) 11 Page - Micro Linear Corporation |
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ML4411CS Datasheet(HTML) 11 Page - Micro Linear Corporation |
11 / 14 page 11 ML4411/ML4411A +5V D1 TO ML4411 PIN 16 R2 R1 IC1 IC1 IC1 TO ML4411 PIN 18 D2 C2 1/6 1/6 1/6 ML4411 PIN 17 C1 Figure 11. Analog Start-up Circuit TO ML4411 PIN 28 R3 – + A1 – + A1 C3 R4 +12V R5 R6 TO ML4411 PIN 20 SYMBOL VALUE A1 LM358 IC1 74HC14 D1, D2 IN4148 R1 1Mý R2 1Mý R3 100Ký SYMBOL VALUE R4 100Ký R5 50Ký R6 50Ký C1 3.3µF C2 3.3µF C3 0.47µF Figure 12. Analog Speed Control In Condition 2 above, the P-Channel MOSFET is pulled up inside the ML4411 with a 16Ký resistor. If the current through C(CGp) is greater than VTH Þ 16K when the N-FET turns on, the P-FET could turn on simultaneously, causing cross-conduction. Adding R1 as shown in Figure 14 eliminates this. The size of R1 will depend on the fall time of the phase voltage, and the size of the C(DGp). D1 may be needed for high power applications to limit the negative current pulled (through C(DGn)) out of the substrate diode in the ML4411 when P-FET turns off. P N D1 C(DGn) C(DGp) RG(P) RG(N) R1 VCC2 Figure 14. Causes of Cross-conduction Adding a series damping resistor to the N-FET gate (RGn) will slow the fall time. The damping resistor should be low enough to: Avoid turning on the N-Channel gate when the PNP turns on via the same mechanism outlined in condition 2 above Not severely increase the switching losses in the N-FET UNIPOLAR OPERATION Unipolar mode offers the potential advantage of lower motor drive cost by only requiring the use of 3 transistors to drive the motor. The ML4411 will operate in unipolar mode (Figure 15) provided the following precautions are taken: 1. The IC supplies should not exceed 12V + 10%. 2. The phase pins on the IC should not exceed the supply voltage. VCC2 1K P 5 4 INHIBIT N3 Q2 + – A6 ML4411A ONLY P3 16K Figure 13. Alternate cross-conduction prevention for ML4411A 1. When transitioning from mode 0 to mode A (see table 1) P3 goes from on to off at the same time N3 goes from off to on. If the P3 turns off slowly and N3 turns on quickly, cross-conduction may occur. This condition has been prevented inside the IC on the ML4411A through the addition of comparator A6 on the P3 output (Figure 9). This comparator may cause an oscillation when the N3 switches on due to the capacitive coupling effect described below pulling the P3 pin below VCC2-1.4V. To avoid this, use the circuit in Figure 13. 2. When the MOSFET in the same phase switches on gate current flows due to capacitive coupling of current through the MOSFET’s drain to gate capacitance. This could cause the device that was off to be turned on. |
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