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MC33395 Datasheet(PDF) 10 Page - Motorola, Inc |
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MC33395 Datasheet(HTML) 10 Page - Motorola, Inc |
10 / 16 page 33395 MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA 10 SYSTEM /APPLICATION INFORMATION INTRODUCTION The 33395 and 33395T devices are designed to provide the necessary drive and control signal buffering and amplification to enable a DSP or MCU to control a three-phase array of power MOSFETs such as would be required to energize the windings of powerful brushless DC (BLDC) motors. It contains built-in charge pump circuitry so that the MOSFET array may consist entirely of N-Channel MOSFETs. It also contains feedback sensing circuitry and control circuitry to provide a robust overall motor control design. FUNCTIONAL DESCRIPTION Gate Drive Circuits The gate drive outputs (GDH1, GDH2, etc.) supply the peak currents required to turn ON and hold ON the MOSFETs, as well as turn OFF and hold OFF the MOSFETs. Charge Pump The current capability of the charge pump is sufficient to supply the gate drive circuit’s demands when PWM’ing at up to 28 kHz. Two external charge pump capacitors and a reservoir capacitor are required to complete the charge pump’s circuitry. Charge reservoir capacitance is a function of the total MOSFET gate charge (QG) gate drive voltage level relative to the source (VGS) and the allowable sag of the drive level during the turn-on interval (VSAG). CRES can be expressed by the following formula: For example, for QG = 60 nC, VGS = 14 V, VSAG = 0.2 V: Proper charge pump capacitance is required to maintain, and provide for, adequate gate drive during high demand turn- ON intervals. Use the following formula to determine values for CP1 and CP2: For example, for the above determination of CRES = 0.15 µF: By averaging these two values, the proper CPn value can be determined: CP1 and CP2 =(0.0075 µF + 0.015 µF) ÷ 2 = 0.01 µF Thermal Shutdown Function The device has internal temperature sensing circuitry which activates a protective shutdown function should the die reach excessively elevated temperatures. This function effectively limits power dissipation and thus protects the device. Overvoltage Shutdown Function When the supply voltage (VIGN) exceeds the specified over- voltage shutdown level, the part will automatically shut down to protect both internal circuits as well as the load. Operation will resume upon return of VIGN to normal operating levels. Low Voltage Reset Function When the logic supply voltage (VDD) drops below the minimum voltage level or when the part is initially powered up, this function will turn OFF and hold OFF the external MOSFETs until the voltage increases above the minimum voltage level required for normal operation. Control Logic The control logic block controls when the low-side and high- side drivers are enabled. The logic implements the Truth Table found in the specification and monitors the M0, M1, PWM, CL, OT, OV, LSE, and HSE terminals. Note that the drivers are enabled 3 µs after the PWM edge. During complimentary chop mode the high-side and low-side drives are alternatively enabled and disabled during the PWM cycle. To prevent shoot- through current, the high-side drive turn-on is delayed by tD1, and the low-side drive turn on is delayed by tD2 (see Figure 2, page 9). CRES = QG x VGS 2 x VGS x VSAG - VSAG2 CRES = (60 nC) x (14 V) 2 x (14 V) x (0.2 V) - (0.2)2 = 0.15 µF CRES 20 < CP1 = CP2 < 10 CRES 0.15 µF 20 = 0.075 µF, lower limit; and 10 0.15 µF = .015 µF, upper limit Freescale Semiconductor, Inc. For More Information On This Product, Go to: www.freescale.com |
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