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TDF5242 Datasheet(PDF) 5 Page - NXP Semiconductors |
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TDF5242 Datasheet(HTML) 5 Page - NXP Semiconductors |
5 / 20 page 1997 Sep 12 5 Philips Semiconductors Preliminary specification Brushless DC motor drive circuit TDF5242T FUNCTIONAL DESCRIPTION Introduction Full-wave driving of a three phase motor requires three push-pull output stages. In each of the six possible states two outputs are active, one sourcing (H) and one sinking (L). The third output presents a high impedance (Z) to the motor, which enables measurement of the motor back-EMF (Electro Motive Force) in the corresponding motor coil by the EMF comparator at each output. The commutation logic is responsible for control of the output transistors and selection of the correct EMF comparator. In Table 1, the six possible states of the externally connected output transistors have been depicted and the corresponding output levels on the NA, PA, NB, PB, NC and PC outputs of the TDF5242T. The zero-crossing in the motor EMF (detected by the comparator selected by the commutation logic) is used to calculate the correct moment for the next commutation, that is, the change to the next output state. The delay is calculated (depending on the motor loading) by the adaptive commutation delay block. The output stages are protected by a current limiting circuit and by thermal protection. The detected zero-crossings are used to provide speed information. The information has been made available on the FG output pin. This output provides an output signal with a frequency equal to the commutation frequency. The system will only function when the EMF voltage from the motor is present. Therefore, a start oscillator is provided that will generate commutation pulses when no zero-crossings in the motor voltage are available. A timing function is incorporated into the device for internal timing and for timing of the reverse rotation detection. The TDF5242T also contains an uncommitted transconductance amplifier (OTA) that can be used as a control amplifier. The output is capable of directly driving an external power transistor. The TDF5242T is designed for systems with low current consumption. It uses I2L logic and adaptive base drive for the output transistors (patented). Start-up and commutation control The system has been designed in such a way that the tolerances of the application components are not critical. However, the approximate values of the following components must still be determined: • The start capacitor; this determines the frequency of the start oscillator • The two capacitors in the adaptive commutation delay circuit; these are important in determining the optimum moment for commutation, depending on the type and loading of the motor • The timing capacitor; this provides the system with its timing signals. Table 1 Output states (note 1) Note 1. H = HIGH state; L = LOW state; Z = high-impedance OFF-state. DIR STATE MOT1 OUT-NA OUT-PA MOT2 OUT-NB OUT-PB MOT3 OUT-NC OUT-PC H1 Z L HLH H H L L H2HL L L H H Z L H H3HL L Z LHLH H H4 Z L H H L L LH H H5 LH H H L L Z L H H6 LH H Z LH HL L L 1 Z L H L HHH L L L 2 LH H Z LH HL L L 3 L H H H L LZL H L4 Z L H H LLL H H L 5HL L Z LHLH H L 6HL L L H H Z L H |
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Descripción similar - TDF5242 |
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