ST AN2757 APPLICATION NOTE
AN2757
Application note
EVAL6228QR reference design board
Introduction
This application note describes the evaluation board of the DMOS fully integrated stepper
motor driver L6228Q. The board implements a typical application that can be used as a
reference design to drive two-phase bipolar stepper motors with currents up to 1 A DC.
Thanks to the small footprint of the L6228Q (QFN 5 x 5 mm, 32-lead) the PCB is very
compact (27 x 32 mm).
Figure 1. EVAL6228QR reference design board
January 2009 Rev 2 1/10
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Demonstration board description AN2757
1 Demonstration board description
Table 1. EVAL6228QR pin connections
Name Type Function
VS Power supply Bridge A and bridge B power supply
PGND Ground Power ground terminal
CLOCK Logic input Step clock input
CW/CCW Logic input
CONTROL Logic input
HALF / FULL Logic input
EN Logic input / output
RESET Logic input
DIAG Logic input
SGND Ground Signal ground terminal
REFA Analog input Bridge A current controller reference voltage
REFB Analog input Bridge B current controller reference voltage
OUT1A Power output Bridge A output 1
OUT2A Power output Bridge A output 2
OUT1B Power output Bridge B output 1
Selects the direction of the rotation (high = CW;
low = CCW)
Decay mode selector (high = SLOW decay; low =
FAST decay)
Step mode selector (high = half step; low = full
step)
Chip enable (active high). When low, all power
DMOSs are switched OFF (both bridge A and
bridge B)
Reset pin (active low). When low, the Phase
Sequence Generator is reset to home state (state
1)
Diagnostic pin. When low, an overcurrent or
overtemperature event is signaled
OUT2B Power output Bridge B output 2
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AN2757 Demonstration board description
Figure 2. EVAL6228QR reference design board
CLOCKREFACW/CCW
PGNDRESET
SGND
REFB HALF / FULL CONTROL DIAG
VS
OUT1A
OUT2A
OUT2B
OUT1B
EN
A step-clock input CLOCK is used to apply a clock signal which determines the progress of
the internal state machine. It can be reset to its initial state by pulling down the RESET line.
To perform the PWM current control an analog reference voltage should be provided to each
channel of the driver.
A fixed reference voltage can be easily obtained through a resistive divider from an external
voltage rail and GND (can be the one supplying the microcontroller or the rest of the
application). Otherwise a very simple way to obtain a variable voltage without using a DAC
is to low-pass filter a PWM output of a microcontroller. Table 2 summarizes the electrical
specification of the application, Figure 3 shows the electrical schematic and Table 3 gives
the part list.
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