The other day I came across this interesting circuit board from a piece of Medical Equipment. I checked the part number out on Newark's site to see if they were still current. I find it more fun to investigate a part if it is still available. In this case an improved version is still being manufactured and is available. Here is the listing from Newark:.
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The chip is a relatively inexpensive way to get solid motor control without any headaches. The above image shows the most common package for the H-bridge — pin TO Before going any further, consider the pinout:. In more extreme cases, the datasheet recommends heat sinking V s — pin 6 — to one square inch of copper on the printed circuit board.
This helps dissipate any potentially destructive wattage due to a hard short circuit between an output and ground where current power through the device can reach upwards of 15A. The direction pin could easily be the most hazardous pin on the chip because it controls the current flow between output 1 and output 2. Thus, it controls which way the motor turns. By effectively shorting the motor terminals the brake pin stops the motor.
Sometimes this is advantageous but some people do not like using the brake pin so in the schematic below it can easily be jumpered to ground and thus tying it low and making it unusable. The direction pin in this case determines which transistors are shorted — sourcing or sinking. Without this input, nothing would happen.
To turn the motor on full speed then set a logic high to the PWM input. Similarly, to turn it off set a logic low. Usually, though, this is not ideal for accurate motor control. Instead, consider the following two most common modes of operation these modes are also explained in the product datasheet. Signed Magnitude PWM: This method most likely achieves more resolution than can be realized by the motor itself, but it also the most intuitive.
The direction pin chooses the direction while the PWM input controls to speed. Changing the PWM affects the speed at which the motor will turn in reverse while toggling the direction pin changes the direction at which the motor turns. The current sensing output can be used to determine what kind of load the motor is under or if the motor is stalling. As can be seen in the motor driver schematic, there is a voltage generating resistor between the current sensing output — pin 8 — and ground.
The resistance you need is directly proportional to the voltage desired usually 5V based on the amount of current being sourced from pin 8 on the LMD According to the datasheet, the current sensing output has a sensitivity of uA per ampere of output current. The user wants to know when the output current spikes and approaches the physical withstanding limit of the LMD, or about 6A, but also wants the flexibility of determining when the motor is consuming 1, 2, and 3 amperes of continuous current.
Since the voltage generating resistor value was calculated with a theoretical voltage maximum of 5V, it is easy to see the corresponding voltages generated with different values of the current output. Using the sample currents above of 1, 2, and 3 amperes and a common 2. When choosing this resistor value, it is a good idea to err on the side of caution and choose a value high enough so that the input voltage to the microcontroller from pin 8 does not exceed that of the analog reference voltage or the maximum allowable voltage of the microcontroller — doing so may cause the individual pin to blow, or even the entire microcontroller to stop working if the voltage is too high for too long.
Pin 9 on the LMD is the thermal flag. As an open collector output the pin needs to be manually pulled high to a maximum 12V and becomes active low when the junction temperature exceeds degrees C. If the junction temperature reaches degrees C, then the IC turns itself off to prevent any further damage.
Could you mail me a list with the components on that board? Especially the values of the capacitors you used?
Great blog site, mate! LMD Motor Driver the path is basically something. This works well with some chips but leads to thermal runaway with others. Do you know if parallel would work? These board designs look amazing! Could you please add the Protel DXP links? Or even straight Gerber files? I have been drowning in data pages for days to find a simple high current stepper driver. I will also check your lcd article. Nice interface board.
Could you please make the DXP available? There seems to be no download link. I tried to verify that my circuit worked, including the thermal flag the subject of my question before I connect it to a motor that can produce any significant load. To test the thermal flag, I connected a ceramic 8 ohm, 20 W resistor to the output pins of the h-bridge and clamped the resistor to the h-bridge so that the heat from the resistor will raise the temperature of the h-bridge.
My method for detecting the thermal warning is to have 5V, an LED and 1 kohm resistor in series to the thermal warning pin pin 09 but the voltage never goes below 3.
Once I get this working, I want to leave the LED and resistor as is for visual indication and add a connection to a PIC microcontroller interrupt that interrupts on a falling edge so that PWM to the h-bridge can be reduced.
Please help. Your email address will not be published. Skip to content. Thursday, April 15, at am. Best Regards Paolo. Thorsten Behrens says:. Monday, December 20, at am. Thank you very much, Thorsten. Thursday, June 02, at am. Jan says:. Monday, July 04, at am. John Piccirillo says:.
Sunday, October 21, at pm. Thanks, John-. ABQuerque says:. Wednesday, August 28, at am. Hi, These board designs look amazing! Jonathan Wright says:. Friday, August 22, at am. It seems a lower value resistor would protect the uC pin better? Andre says:. Sunday, November 02, at am. Thanks Andre. Wednesday, July 15, at pm.
Zack says:. Saturday, September 19, at pm. Leave a Reply Cancel reply Your email address will not be published. Search for:. Proudly powered by WordPress.
LMD18200 Motor Driver
Datasheet Texas Instruments LMD18200