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L6235Q Arkusz danych(PDF) 11 Page - STMicroelectronics |
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L6235Q Arkusz danych(HTML) 11 Page - STMicroelectronics |
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11 / 33 page  L6235Q Circuit description Doc ID 018997 Rev 2 11/33 4.3 PWM current control The L6235Q includes a constant OFF time PWM current controller. The current control circuit senses the bridge current by sensing the voltage drop across an external sense resistor connected between the source of the three lower power MOSFET transistors and ground, as shown in Figure 9. As the current in the motor increases, the voltage across the sense resistor increases proportionally. When the voltage drop across the sense resistor becomes greater than the voltage at the reference input pin VREF, the sense comparator triggers the monostable switching the bridge off. The power MOSFET remains off for the time set by the monostable and the motor current recirculates around the upper half of the bridge in slow decay mode, as described in Section 4.4. When the monostable times out, the bridge again turns on. Since the internal dead time, used to prevent cross conduction in the bridge, delays the turn-on of the power MOSFET, the effective OFF time tOFF is the sum of the monostable time plus the dead time. Figure 10 shows the typical operating waveforms of the output current, the voltage drop across the sensing resistor, the pin RC voltage and the status of the bridge. More details regarding the synchronous rectification and the output stage configuration are included in Section 4.4. Immediately after the power MOSFET turns on, a high peak current flows through the sense resistor due to the reverse recovery of the freewheeling diodes. The L6235 provides a 1µs blanking time tBLANK that inhibits the comparator output so that the current spike cannot prematurely re-trigger the monostable. Figure 9. PWM current controller simplified schematic DRIVERS + DEAD TIME S Q R DRIVERS + DEAD TIME DRIVERS + DEAD TIME OUT3 OUT2 SENSEB SENSEA RSENSE RCOFF ROFF COFF VREF OUT1 + + - - 1 μs 5mA BLANKER SENSE COMPARATOR MONOSTABLE SET 2.5V 5V FROM THE LOW-SIDE GATE DRIVERS BLANKING TIME MONOSTABLE VSB VS VSA TO GATE LOGIC (0) (1) |
Podobny numer części - L6235Q |
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Podobny opis - L6235Q |
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