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Pololu Dual MC33926 Motor Driver Carrier
The dual MC33926 motor driver carrier is a breakout board featuring two Freescale MC33926 H-bridge
ICs. It can supply up to almost 3 A continuous current per channel to two brushed DC motors at 5 – 28 V,
and it can tolerate peak currents up to 5 A per channel for a few seconds, making this a great general-
purpose motor driver for medium-sized DC motors and for differential-drive robots that use such motors..
Features
Breakout board for Freescale's MC33926 full H-Bridge
Current feedback, and under-voltage protection
Over-current and over-temperature protection
Delivers 3A continuously to each of it's two motor channels
Reverse voltage protection on motor voltage (Logic voltage
does not have reverse protection)
Key Specifications
Power Requirements: 5 to 28VDC
Communication Interface: 3-5V TTL, PWM(up to 20kHz)
Operating temperature: -40°C to 125°C
Dimensions: 1.10” x 1.8” (Without included hardware)
Application Ideas
Robotics
DC Motor Control
Pictures Courtesy of Pololu
Precautions
This product can get hot enough to burn you long before the chip overheats.
Table of Contents
Features .........................................................1
Key Specifications ...........................................1
Application Ideas ............................................1
Precautions.....................................................1
Packing List ....................................................2
Additional Items Required ...............................2
General Specifications .....................................2
Basic Application Connections ..........................2
Protection .......................................................3
Absolute Maximum Ratings ..............................4
Pin Definitions and Ratings ..............................4
Connection Diagrams ......................................5
Module Dimensions .........................................5
Resources and Downloads ...............................5
Schematic.......................................................6
Copyright © Parallax Inc.
Pololu Dual MC33926 (#28820)
v1.0 11/18/2011 Page 1 of 6
Packing List
(1) MC33926 Dual Carrier Board
25-pin Straight Breakaway male Header
(3) 2-pin 3.5mm Terminal Blocks
Additional Items Required
Soldering Iron and solder
Safety glasses
Heat sink (optional)
General Specifications
Motor Driver:
Motor Channels:
Minimum Operating Voltage:
Maximum Operating Voltage:
Continuous Output Current per Channel:
Current Sense:
Maximum PWM Frequency:
Minimum Logic Voltage:
Maximum Logic Voltage:
Reverse Voltage Protection?:
MC33926
2
5V
28V
2.5A
0.525V/A
20 kHz
2.5V
5.5V
YES
Notes:
1)
2)
3)
4)
5)
Operation from 5-8V reduces maximum current output.
The device is protected from transients up to 40V.
The Continuous output current can be improved with the addition of a heat sink.
SLEW pin should be HIGH for frequencies above 10kHz.
Voltage protection is on Motor Voltage only, Logic Voltage does not have reverse protection.
Basic Application Connections
In a typical application, five I/O lines are used to connect each motor driver channel to a microcontroller:
the two input lines, IN1 and IN2, for direction control, one of the disable lines, D1 or D2, for PWM speed
control, the current sense output, FB, for monitoring motor current draw (connected to an analog-to-digital
converter input) and the status flag, SF, for monitoring motor driver errors. The control lines can be
reduced to two pins per channel if PWM signals are applied directly to the two input pins with both disable
pins held inactive. In each of these cases, the other unused lines must be set to enable proper operation.
Copyright © Parallax Inc.
Pololu Dual MC33926 (#28820)
v1.0 11/18/2011 Page 2 of 6
For example, if D2 is used for the PWM input (as is typically the case), D1 must be held low to prevent it
from disabling the motor driver. The circuit board provides convenient jumper points for overriding the
motor driver defaults without having to connect extra wires to the module.
The current sense and status
flag connections are optional, though monitoring of the status flags can allow detection of latched fault
conditions. The status flags are open-drain output, so the two status flag can be wired together for
applications where I/O pins are scarce and determining which motor driver is experiencing a fault
condition is not necessary. Note that the default state of the enable pin, EN, is LOW, which holds both
motor driver chips in a low-current sleep mode. You will need to hold this pin high (either with an external
connection or via the default-overriding jumper next to the pin) to allow the board to run.
Protection
The MC33926 has under-voltage, over-current, and over-temperature protection. Some protection events
are indicated by the status flag pins (SF).which are active-low pins that can be connected connected to a
single input. If the chip detects an over-current or over-temperature event, the SF is latched LOW and
OUT1 and OUT2 are set to high-impedance. To unlatch the status flag pin toggle the D1, D2 , EN or VIN
lines. The carrier board has a reverse-protection MOSFET for added protection to the motor driver chips.
Real-World Power Dissipation Considerations
The MC33926 motor driver used on this carrier board has a maximum current rating of 5 A continuous.
However, the chip by itself will overheat at lower currents. For example, in our tests at room temperature
with no forced air flow, the chip was able to deliver 5 A for 5 s and 4 A for 18 s before the chip’s thermal
protection started reducing the current. A continuous current of 3 A was right at the over-temperature
threshold; in some tests the thermal protection kicked in after a minute, and in other tests the chip
delivered 3 A for over five minutes without triggering thermal protection. The actual current you can
deliver will depend on how well you can keep the motor driver cool. The carrier’s printed circuit board is
designed to draw heat out of the motor driver chips, but performance can be improved by adding a heat
sink. Our tests were conducted at 100% duty cycle; PWMing the motor will introduce additional heating
proportional to the frequency.
Unlike other H-Bridges, the 33926 has a feature that allows it to gracefully reduce current as the
current exceeds 5 A or as the chip temperature approaches its limit. This means that if you push the chip
close to its limit, you will see less power to the motor, but it might allow you to avoid a complete
shutdown
.
Copyright © Parallax Inc.
Pololu Dual MC33926 (#28820)
v1.0 11/18/2011 Page 3 of 6
Absolute Maximum Ratings
Symbol
Vcc
Quantity
Supply Voltage †
Maximum
28
Units
V
Pin Definitions and Ratings
Pin
VIN
GND
OUT2
OUT1
VDD
IN2
IN1
PWM / D2
Default Function
HIGH
LOW
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
Main 5-28V motor power supply connection
Ground connection for logic and motor power supplies
The motor output pin controlled by IN2
The motor output pin controlled by IN1
3-5 V logic supply connection. This pin is used only for the SF pull-up and default-
overriding jumpers; in the rare case where none of those features is used, VDD
can be left disconnected
The logic input control of OUT2. PWM can be applied to this pin (typically done
with both disable lines inactive)
The logic input control of OUT1. PWM can be applied to this pin (typically done
with both disable pins inactive)
Disable input: when D1 is high, OUT1 and OUT2 are set to high impedance. A D1
PWM duty cycle of 70% gives a motor duty cycle of 30%. Typically, only one of
the two disable pins is used, but the default is for both disable pins to be active.
Disable input: when D1 is high, OUT1 and OUT2 are set to high impedance. A D1
PWM duty cycle of 70% gives a motor duty cycle of 30%. Typically, only one of
the two disable pins is used, but the default is for both disable pins to be active.
Status flag output: an over-current (short circuit) or over-temperature event will
cause SF to be latched LOW. If either of the disable pins (D1 or D2) are disabling
the outputs, SF will also be LOW. Otherwise, this pin is weakly pulled high. This
allows the two SF pins on the board to be tied together and connected to a single
MCU input.
The FB output provides analog current-sense feedback of approximately 525 mV
per amp.
Enable input: when EN is LOW,
both
motor ICs are in a low-current sleep mode.
Output slew rate selection input. A logical LOW results in a slow output rise time
(1.5 μs – 6 μs). A logical HIGH selects a fast output rise time (0.2 μs – 1.45 μs).
This pin should be set HIGH for high-frequency (over 10 kHz) PWM. This pin
determines the slew rate mode for
both
motor driver ICs.
A logical high value inverts the meaning of IN1 and IN2 for
both
motor drivers.
PWM / D1
HIGH
SF
HIGH
FB
EN
SLEW
INV
LOW
LOW
LOW
LOW
Copyright © Parallax Inc.
Pololu Dual MC33926 (#28820)
v1.0 11/18/2011 Page 4 of 6
Connection Diagrams
Module Dimensions
Size: 1.10” x 1.8” (without included hardware)
Weight: 0.25 oz
Resources and Downloads
Check for the latest version of this document, free software from the Pololu Dual MC33926 Motor Driver
Carrier product page. Go to www.parallax.com and search 28820.
Copyright © Parallax Inc.
Pololu Dual MC33926 (#28820)
v1.0 11/18/2011 Page 5 of 6
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