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
www.st.com
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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Demonstration board description AN2757
Table 2. EVAL6228QR electrical specification (recommended values)
Parameter Value
Supply voltage range (VS) 8 V to 52 V DC
RMS output current rating (OUT x) up to 1.4 A
Switching frequency up to 100 kHz
Voltage reference range (REFA, REFB) 0 to +5 V
Input and enable voltage range 0 to +5 V
o
Operating temperature range -25
L6228Q thermal resistance junction to ambient 42
C to +125 oC
o
C/W
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AN2757 Demonstration board description
Figure 3. EVAL6228QR reference design schematic
VS
PGND
C3C3
OUT1A
OUT2A
OUT1B
OUT2B
8
31
NC2NC3NC4NC5NC6NC7NC
OUT1A
OUT2A23OUT2B
VSB
20
VSA
3
D1
C4C4
Bat46SWD1Bat46SW
22
VCP
24
VBOOT
17
12
C1C1
9
OUT1B
32
19
NC10NC18NC
SENSEB
SENSEA
RCB
RCA
R10R10
12
R9R9
29
C7C7
11
R7R7
C6C6
30
R6R6
L6228Q
VREFB
13
C2C2
GND
21
GND
1
CLOCK
CONTROL
CW/CCW
HALF/FULL14RESET
27
15
28
R1R1
VREF A
26
EN
16
U1 L6228Q VFQFPN5x5U1 L6228Q VFQFPN5x5
25
C5C5
R5R5
R4R4
R3R3
R8R8
R2R2
C8C8
R12R12
R11R11
C9C9
R14R14
R13R13
CLOCK
CW/CCW
CONTROL
HALF/FULL
EN
RESET
DIAG
SGND
REFA
REFB
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Demonstration board description AN2757
Table 3. EVAL6228QR part list
Part reference Part value Part description
C1 220 nF / 25 V Capacitor
C2 220 nF / 63 V Capacitor
C3 100 µF / 63 V Capacitor
C4 10 nF / 25 V Capacitor
C5 5.6 nF Capacitor
C6, C7 820 pF Capacitor
C8, C9 220 nF Capacitor
D1 BAT46SW Diode
R1, R2, R3, R4, R5, R8 100 kΩ 5% 0.25 W Resistor
R6, R7 100 kΩ 1% 0.25 W Resistor
R9, R10 0.4 Ω 1 W Resistor
R11, R13 20 kΩ 1% 0.25 W Resistor
R12, R14 2 kΩ 1% 0.25 W Resistor
U1 L6228Q Stepper motor driver in VFQFPN5x5
The input lines CW/CCW, CONTROL, HALF / FULL, EN and RESET are connected to
ground through a pull-down resistor which sets the low logic level as default. An external
signal can be applied to change each input status.
D1, C1 and C4 constitute a charge pump circuit, which generates the supply voltage for the
high-side integrated MOSFETs. Due to voltage and current switching at relatively high
frequency, these components are connected through short paths in order to minimize
induced noise on other circuitries.
R1 and C5 are used by the overcurrent protection integrated circuitry (disable time t
is about 200 µs and delay time t
R6, C6 and R7, C7 are used to set the off-time t
about 1 µs using the values in Table 3.).
DELAY
of the two PWM channels to about
OFF
DISABLE
50 µs. The off-time should be adjusted according to the motor electrical characteristics and
supply voltage by changing the R6, C6 and R7, C7 values.
R11, R12, C8 and R13, R14, C9 are low-pass filters which provide an external reference
voltage through a PWM output of a microcontroller.
Figure 4, Figure 5 and Figure 6 show the placement of the components and the layout of the
two layers of the EVAL6228QR reference design board. A GND area has been used to
improve the IC power dissipation.
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AN2757 Demonstration board description
Figure 4. EVAL6228QR component placement
32 mm
27 mm
Figure 5. EVAL6228QR top layer layout
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Demonstration board description AN2757
Figure 6. EVAL6228QR bottom layer layout
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AN2757 Revision history
2 Revision history
Table 4. Document revision history
Date Revision Changes
06-Oct-2008 1 Initial release
28-Jan-2009 2
Updated value in Table 2: EVAL6228QR electrical specification
(recommended values) on page 4
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AN2757
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