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BR650705 17.52
 
 
   

 

The Pololu high-power motor drivers are compact carriers for the VNH3SP30 and VNH2SP30 motor driver integrated circuits from ST. The board incorporates most of the components of the typical application diagram on page 8 of the VNH2SP30 datasheet, including pull-up and current-limiting resistors and a FET for reverse battery protection. (The current sense circuit is populated on both versions of the board, but only the VNH2SP30 supports current sense.) All you need to add is a micro controller or other control circuit to turn the H-Bridge on and off. If you need a full motor control solution, we also have a high-power motor controller with feedback that uses the same chips.

In a typical application, the motor power supply is connected at the bottom of the board, the motor on the right side of the board, and the control connections to the left side of the board. The diagnostic pins can be left disconnected if you do not want to monitor the fault conditions of the motor driver chip. INA and INB control the direction of the motor, and the PWM pin turns the motor on or off. For the VNH2SP30 version, the current sense (CS) pin will output approximately 0.13 volts per amp of output current.

VNH3SP30 and VNH2SP30 Comparison

  VNH3SP30  VNH2SP30
MOSFET on-resistance (per leg) 34 mΩ 19 mΩ
Maximum PWM frequency 10 kHz 20 kHz
Current sense none approximately 0.13 volts per amp
Over-voltage shutoff none (operates up to 30 V) could be as low as 16 V (19 V typical)
Time to overheat at 20 A* 8 seconds 35 seconds
Time to overheat at 15 A* 30 seconds 150 seconds
Current for infinite run time* 9 A 14 A

*Typical results using Pololu motor driver carrier with 100% duty cycle at room temperature.

Real-world power dissipation considerations

The motor drivers have maximum current ratings of 30 A continuous. However, the chips by themselves will overheat at lower currents (see table above for typical values). The actual current you can deliver will depend on how well you can keep the motor driver cool. The carrier printed circuit board is designed to draw heat out of the motor driver chips, but performance will be improved by adding a heat sink. In our tests, we were able to deliver short durations (on the order of milliseconds) of 30 A and several seconds of 20 A without overheating. At 6 A, the chips gets just barely noticeably warm to the touch. For high-current installations, the motor and power supply wires should also be soldered directly instead of going through the supplied terminal blocks, which are rated for up to 15 A.

Many motor controllers or speed controllers can have peak current ratings that are substantially higher than the continuous current rating; this is not the case with these motor drivers, which have a 30 A continuous rating and a over-current protection that can kick in as low as 30 A (45 A typical). Therefore, the stall current of your motor should not be more than 30 A. (Even if you expect to run at a much lower average current, the motor can still draw high currents when it is starting or if you use low duty cycle PWM to keep the average current down.)

Reverse-battery protection

The motor driver boards include an N-channel MOSFET for reverse-battery protection. This component keeps the motor driver from destroying itself if the input power is accidentally connected backwards. However, this component does slightly increase the total resistance between your battery and your motor. For slightly improved performance, the MOSFET can be bypassed by connecting the negative battery terminal to the bypass pin. (This terminal will also need to be connected to your logic supply ground.)

 

 

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Copyright 2003 British Robotics
Last modified: March 16, 2008