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  • Z-scale controller driver circuit using MC33880

  • Created: Mar 19, 2015

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The schematic diagram as shown is a Z-scale train controller driver circuit using Freescale MC33880. The circuit is designed to operate between 5.5V to 24.5V. The typical output voltage clamp is +45V for low side drive and -20V for high side drive. The circuit is designed to drive small coils and hence, there is no need to add protection diodes. It features an internal reverse battery protection on Vpwr. However, it depends upon the designer if he wants to add those for additional protection.

The MC33880 device is an 8-output hardware configurable high side/ low side switch with 8-bit serial input control using the Serial Peripheral Interface (SPI). Two of the outputs can be controlled directly via microcontroller for Pulse-Width Modulation (PWM) applications. The MC33880 controls various inductive or incandescent loads by directly interfacing with a microcontroller. The circuit's innovative monitoring and protection features include very low standby currents, "cascadable" fault reporting, internal 40V output clamping for low side configurations, internal -20V output clamping for high side configurations, output specific diagnostics, and independent shutdown of outputs.

An SPI protocol specifies 4 signal wires: Master Out Slave In (MOSI) signal is generated by Master, recipient is the slave, Master In Slave Out (MISO) wherein slaves generate MISO signals and recipient is the master. Serial Clock (SCLK or SCK) signal is generated by the master to synchronize data transfers between the master and the slave, Slave Select (SS) from master to Chip Select (CS) of slave signal is generated by master to select individual slave/peripheral devices. The SS/CS is an active low signal. Splitting the 32 outputs in four banks of 8 (i.e., 4 high side bank power supplies are connected to 4 low side 8-pin connectors connected in parallel) allows one to drive one output by applying power to the correct bank power supply and setting the corresponding low-side connector to ground while others remain in high impedance state. In this case, the circuit becomes simple yet effective.



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