Dwarf Boards DB021 : L298 dual motor driver (c) Van Ooijen Technische Informatica version 1.0 PICmicro, In-Circuit Serial Programming and ICSP are registerd trademarks of Microchip Technology Inc. Introduction This document describes the Dwarf Board DB021. This is a peripheral board with an L298 for driving two motors, and two medium-power darlington transistors for driving high-side loads (for instance solenoids). The logic part of the board is powered by the +5 Volt from the Dwarf Bus input connector, but the board is meant to be used with an external power for the motors and the high-side loads. This external power, the motors, and the high side loads connect to screw connectors. The L298 and the darlington transistors are mounted at the edges of the PCB, so they can optionally be fitted to heatsinks. (c) Van Ooijen Technische Informatica page 1 of 5
Circuit The circuit consist of the ML10 Dwarf Bus input connector CON-5, the L298 chip, the two darlington transistors T1 and T2, the output connectors CON-1.. CON-4 and a bunch of kickback-protection diodes D1.. D10. The external power should be connected to CON4, the two motors to CON-2 and CON-3, and the two high-side loads between the connections of CON-1 and the positive rail of the external power. With sufficient cooling the L298 motor driver is rated 2 A per motor, at up to 48 Volt. The DB679A darlingtons are rated at up to 80 Volt. They are switched fully on or off, so no cooling should be required for currents up to 1 A, but the secondary breakdown limits must be observed. The schematic shows 1N4004 diodes, which are probably adequate for most purposes. The kit however contains the faster 1N5819 schottky diodes. (c) Van Ooijen Technische Informatica page 2 of 5
Use The Dwarf Bus pins connect directly to the L298 control inputs and to the DB679A darlington transistors. The table below shows the pin assignments. Refer to the L298 datasheet for more details. Dwarf Bus pin L298 / BD679A pin use 1 +5 Volt Logic power 2 Ground Ground Shared with motor ground 3 D0 L298 input 1 M1 direction / brake 4 D1 L298 input 2 5 D2 L298 enable A M1 enable 6 D3 BD679A nr 1 Open collector output 1 7 D4 L298 input 3 M2 direction / brake 8 D5 L298 input 4 9 D6 L298 enable B M2 enable 10 D7 BD679A nr 2 Open collector output 2 The L298 can drive two motors, M1 and M2. Each motor has 3 control inputs, 2 for direction and 1 for enable. The effect of the logic levels on these pins is shown in the table below. Input 1 (or 3) Input 2 (or 4 ) Enable A (or B) Effect on the motor * * 0 Drivers shut off 0 0 1 Fast brake 0 1 1 Forward 1 0 1 Reverse 1 1 1 Fast brake Component Placement The figure below shows the placement of the components on the PCB. The L298 chip is located at the left edge of the PCB, so it can easily be mounted to a heatsink. The darlington transistors are likewise mounted at the right edge. (c) Van Ooijen Technische Informatica page 3 of 5
DB021 : L298 dual motor driver version 1.0 Assembly The kit contains the PCB and all components as shown in the circuit diagram. Note that for the diodes the kit contains 1N5819 schottky diodes. Assembling the kit is not difficult, no fine-pitched or SMD components are used. Just follow the instructions below carefully. Some soldering experience is recommended. Place the PCB as shown on the pictures and in the previous paragraph. The silkscreen (component side) text should be readable. Place and solder the two 2.2k resistors R1 and R2 (marked red-red-red). Place and solder the 10 diodes 1N5819. The white band on each diode must point up, away from the screw connectors. Place and solder the two 100nF capacitors. Place and solder the ML10 connector Slide the four two-screw connectors together to form one 8-screw connector. Place and solder this connector. Note: the holes where wires can be inserted must face down (to the PCB edge). (c) Van Ooijen Technische Informatica page 4 of 5
Place and solder the two BD679A darlington transistors. The part-metal side of the transistors must face to the right (towards the PCB edge). Place and solder the L298 IC. The text on the chip must face to the right (to the middle of the PCB). The L298 and the darlington transistors are mounted at the edges of the PCB, so they can optionally be fitted to heatsinks (not included in the kit). When you use heatsinks, remember that the metal tab of the L298 is connected to the ground. The datasheet of the BD679A does not state what the metal slab is connected to, so when heatsinks are used the transistors must either have separate heatsinks, or isolation must be used. References The L298 datasheet can be found at http://www.st.com/stonline/books/pdf/docs/1773.pdf Change notes the latest version of this document can be downloaded from http://www.voti.nl/dwarf version date notes 1.0 2004-12-22 first version (c) Van Ooijen Technische Informatica page 5 of 5