EVAL6228QR

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. January 2009 EVAL6228QR reference design board Rev 2 1/10 www.st.com Demonstration board description 1 Demonstration board description Table 1. EVAL6228QR pin connections Name 2/10 AN2757 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 Selects the direction of the rotation (high = CW; low = CCW) CONTROL Logic input Decay mode selector (high = SLOW decay; low = FAST decay) HALF / FULL Logic input Step mode selector (high = half step; low = full step) EN Logic input / output Chip enable (active high). When low, all power DMOSs are switched OFF (both bridge A and bridge B) RESET Logic input Reset pin (active low). When low, the Phase Sequence Generator is reset to home state (state 1) DIAG Logic input Diagnostic pin. When low, an overcurrent or overtemperature event is signaled 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 OUT2B Power output Bridge B output 2 AN2757 Demonstration board description Figure 2. EVAL6228QR reference design board CW/CCW REFA CLOCK RESET PGND VS OUT1A OUT2A SGND OUT2B OUT1B REFB HALF / FULL CONTROL DIAG 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. 3/10 Demonstration board description Table 2. AN2757 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 Operating temperature range L6228Q thermal resistance junction to ambient 4/10 0 to +5 V -25 oC to +125 oC 42 oC/W REFB REFA SGND DIAG RESET EN HALF/FULL CONTROL CW/CCW R13 R11 R1 R5 CLOCK R12 R3 R4 R8 R2 C5 25 16 14 15 28 27 U1 C9 C8 RESET EN HALF/FULL CONTROL CW/CCW CLOCK 21 GND 1 GND VREF A 26 C2 2 D1 Bat46SW C1 C4 C6 C7 L6228Q RCA 30 R6 VREFB 13 17 VBOOT 3 24 VCP RCB 11 R7 1 22 VSA 29 R9 SENSEA 20 VSB SENSEB 12 R10 10 18 32 9 19 7 8 31 23 2 3 4 5 6 L6228Q VFQFPN5x5 NC NC NC OUT1B OUT2B NC NC OUT1A OUT2A NC NC NC NC NC C3 OUT1B OUT2B OUT1A OUT2A PGND VS Figure 3. R14 AN2757 Demonstration board description EVAL6228QR reference design schematic 5/10 Demonstration board description Table 3. AN2757 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 tDISABLE is about 200 µs and delay time tDELAY about 1 µs using the values in Table 3.). R6, C6 and R7, C7 are used to set the off-time tOFF of the two PWM channels to about 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. 6/10 AN2757 Demonstration board description EVAL6228QR component placement 32 mm Figure 4. 27 mm Figure 5. EVAL6228QR top layer layout 7/10 Demonstration board description Figure 6. 8/10 EVAL6228QR bottom layer layout AN2757 AN2757 2 Revision history 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 9/10 AN2757 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. 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