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SMA7029M Scheda tecnica(PDF) 4 Page - Sanken electric |
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SMA7029M Scheda tecnica(HTML) 4 Page - Sanken electric |
4 / 7 page 8 SLA7022MU/SLA7029M/SMA7022MU/SMA7029M SLA7022MU/SLA7029M/SMA7022MU/SMA7029M 2-Phase Stepper Motor Unipolar Driver ICs (2-Phase Excitation) sDetermining the Output Current Fig. 1 shows the waveform of the output current (motor coil cur- rent). The method of determining the peak value of the output current (IO) based on this waveform is shown below. (Parameters for determining the output current IO) Vb: Reference supply voltage r1,r2: Voltage-divider resistors for the reference supply voltage RS: Current sense resistor (1) Normal rotation mode IO is determined as follows when current flows at the maximum level during motor rotation. (See Fig.2.) (2) Power down mode The circuit in Fig.3 (rx and Tr) is added in order to decrease the coil current. IO is then determined as follows. Equation (2) can be modified to obtain equation to determine rx. Fig. 4 and 5 show the graphs of equations (1) and (2) respec- tively. (NOTE) Ringing noise is produced in the current sense resistor RS when the MOSFET is switched ON and OFF by chopping. This noise is also generated in feedback signals from RS which may there- fore cause the comparator to malfunction. To prevent chopping malfunctions, r5(r6) and C3(C4) are added to act as a noise filter. RS C3 r2 r1 r6 r5 Vb(5V) 7,(9) 3,(13) Fig. 2 Normal mode 0 Phase A Phase A IO Fig. 1 Waveform of coil current (Phase A excitation ON) RS C3 r2 r1 r6 r5 Vb(5V) 7,(9) 3,(13) rx Tr Power down signal Fig. 3 Power down mode 4 3 2 1 0 01234 Current sense resistor RS ( Ω) IO= r1+r2 RS r1=510 Ω r2=100 Ω rx= ∞ Vb=5V r2 · Vb Fig. 4 Output current IO vs. Current sense resistor RS Fig. 5 Output current IOPD vs. Variable current sense resistor rx 2.0 1.5 1.0 0.5 00 200 400 600 800 Variable current sense resistor rX ( Ω) 1000 1200 RS =0.5 Ω RS =0.8 Ω RS =1 Ω IOPD= 1+ RS r1=510 Ω r2=100 Ω Vb=5V 1 · Vb r1(r2+rX) r2 · rX Application Notes However, when the values of these constants are increased, the response from RS to the comparator becomes slow. Hence the value of the output current IO is somewhat higher than the calculated value. rX= 1 Vb Rs • IOPD 1 r1 −1 − 1 r2 ................................................................ (1) IO ≅ • r2 r1+r2 Vb RS ......................................................... (2) IOPD ≅ • 1 r1(r2+rX) r2 • rX Vb RS 1+ |
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