This discrete MOSFET H-bridge motor driver enables bidirectional control of one high-power DC brushed motor. The compact 1.8×1.2-inch board supports a wide 5.5 to 40 V voltage range and is efficient enough to deliver a continuous 23 A without a heat sink. This version outputs an analog voltage proportional to the motor current, and an extra control input allows for coasting in addition to the driving and braking offered by the other Pololu high-power motor drivers.
The Pololu high-power motor driver is a discrete MOSFET H-bridge designed to drive large DC brushed motors. The H-bridge is made up of one N-channel MOSFET per leg, and most of the board’s performance is determined by these MOSFETs (the rest of the board contains the circuitry to take user inputs and control the MOSFETs). The MOSFET datasheet is available under the “Resources” tab. The MOSFETs have an absolute maximum voltage rating of 40 V; higher voltages can permanently destroy the motor driver. Under normal operating conditions, ripple voltage on the supply line can raise the maximum voltage to more than the average or intended voltage, so a safe maximum voltage is approximately 34 V.
Note: Charged battery voltages can be much higher than nominal voltages, so the maximum nominal battery voltage we recommend is 28 V unless appropriate measures are taken to limit the peak voltage.
The versatility of this driver makes it suitable for a large range of currents and voltages: it can deliver up to 23 A of continuous current with a board size of only 1.8" by 1.2" and no required heat sink. With the addition of a heat sink, it can drive a motor with up to about 37 A of continuous current. The module offers a simple interface that requires as few as two I/O lines while allowing for both sign-magnitude and locked-antiphase operation, and an optional third control input unique to this board allows for coasting. This board also features a current-sensing circuit that measures bidirectional motor current with a magnitude up to 30 A and outputs an analog voltage.
Integrated detection of various short-circuit conditions protects against common causes of catastrophic failure; however, please note that the board does not include reverse power protection or any over-current or over-temperature protection. We recommend you use the integrated current sensor to keep the driver from delivering more current than it can safely handle.
The motor and motor power connections are on one side of the board, and the control connections (5V logic) are on the other side. The motor supply should be capable of delivering the high current the motor will require, and a large capacitor should be installed between V+ and ground close to the motor driver to decrease electrical noise. Two axial capacitors are included and one or both can be installed by soldering them into the V+ and GND pins (labeled '+' and '-' on the bottom silkscreen) along the long edges of the board. Such installations are compact but might limit heat sinking options; also, depending on the power supply quality and motor characteristics, a larger capacitor might be required. There are two options for connecting to the high-power signals (V+, OUTA, OUTB, GND): large holes on 0.2" centers, which are compatible with the included terminal blocks, and pairs of 0.1"-spaced holes that can be used with perfboards, breadboards, and 0.1" connectors.
Warning: Take proper safety precautions when using high-power electronics. Make sure you know what you are doing when using high voltages or currents! During normal operation, this product can get hot enough to burn you. Take care when handling this product or other components connected to it.
The logic connections are designed to interface with 5V systems (5.5 V max); the minimum high input signal threshold is 3.5 V, so we do not recommend connecting this device directly to a 3.3 V controller. In a typical configuration, only PWMH and DIR are required, but PWML can be used to enable coasting if both PWML and PWMH are driven low. PWML is pulled high and PWMH is pulled low internally. The two fault flag pins (FF1 and FF2) can be monitored to detect problems (see the Fault Flag Table below for more details). The RESET pin, when held low, puts the driver into a low-power sleep mode and clears any latched fault flags. The V+ pin on the logic side of the board gives you access to monitor the motor’s power supply or pass it on to low-current devices (it should not be used for high current). The board also provides a regulated 5V pin which can provide a few milliamps (this is typically insufficient for a whole control circuit but can be useful as a reference or for very low-power microcontrollers). This pin can be shorted to VCS to power the current sensor, or VCS can be supplied with 5 V externally. If the 5V output pin is used to power VCS, it should not be used for any other purpose as the current sensor will draw close to the limit of the current the 5V pin can supply. When the current sensor is powered by applying 5 V to VCS, the CS pin outputs 66 mV/A for currents between -30 and 30 A centered at 2.5 V (typical error is less than 1.5%).
Motor Control Options
The motor driver can be used in several different modes:
- Sign-magnitude (drive-brake): With PWML disconnected or held high, apply a pulse-width-modulated (PWM) signal to the PWMH pin. The duty cycle of the PWM controls the speed of the motor and the DIR pin controls the direction. During the active (high) portion of the PWM, the motor outputs drive the motor by putting the full V+ voltage across the motor in the direction determined by the DIR pin; during the low portion of the PWM, the motor outputs brake the motor by shorting both motor terminals to ground. This means that the motor alternates between drive and brake at the PWM frequency with the percentage of the driving time determined by the duty cycle.
- Sign-magnitude (drive-coast): Connect the same PWM signal to both the PWMH and PWML pins. The duty cycle of the PWM controls the speed of the motor and the DIR pin controls the direction. During the active (high) portion of the PWM, the motor outputs drive the motor by putting the full V+ voltage across the motor in the direction determined by the DIR pin; during the low portion of the PWM, the motor outputs are disconnected and the motor is allowed to coast. This means that the motor alternates between drive and coast at the PWM frequency with the percentage of the driving time determined by the duty cycle. Drive-coast operation can draw less power than drive-brake operation, but drive-brake operation can produce a more linear relationship between duty cycle and motor speed.
- Variable braking (brake-coast): With PWMH disconnected or held low, apply a PWM signal to the PWML pin (the state of the DIR pin has no effect on this mode). During the active (high) portion of the PWM, the motor outputs brake the motor by shorting both motor terminals to ground; during the low portion of the PWM, the motor outputs are disconnected and the motor is allowed to coast. This means that the motor alternates between brake and coast at the PWM frequency with the percentage of the braking time determined by the duty cycle.
- Locked-antiphase: With PWML disconnected or held high and PWMH held high, apply a PWM signal to the DIR pin. In locked-antiphase operation, a low duty cycle drives the motor in one direction and a high duty cycle drives the motor in the other direction; a 50% duty cycle turns the motor off. A successful locked-antiphase implementation relies on the motor inductance and PWM switching frequency to smooth out the current (e.g. making the current zero in the 50% duty cycle case), so a high PWM frequency might be required.
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