STK6712BMK4 Datasheet, PDF (7/10 Pages) Sanyo Semicon Device – Unipolar Fixed-Current Chopper-Type 4-Phase Stepping Motor Driver

STK6712BMK4
Determining Chopping Frequency
The STK6713BMK4 uses constant current for self-excitation.
The I_OH t_OFF time is set to about 14 µs, and the t_ON time can be expressed as:
t_ON ≈
L
R + 0.88
V_CC – (
In (
I_OH
–
e
R
L
tOFF
–
V_CC +
R
0.88
R
(1
–
–
e
L
tOFF
))
(R
+
0.88)
V_CC – (R + 0.88) I_OH
) ............................ (5)
L: Motor winding inductance
R: Motor resistance
V_CC: Motor supply voltage
I_OH: Output current
As a result, the chopping frequency is
1
1
F ≈ _{tON + tOFF} = _{tON + 14 × 10}–6 (Hz) ................................................................................................ (6)
However, note that when the following conditions exist the value for F will change.
14 × 10^–6 ≥
–L
R
In
(
I_OH
V_CC
×R+
+ 0.88
V_CC +
0.88
)
=
t_OFF2
.............................................................................
(7)
t_OFF ≈ t_OFF1 + t_OFF2 = 14 × 10^-6 + t_OFF
1
∴F = _{tON + 14 × 10–6 + tOFF2} (Hz)........................................................................................................ (8)
Because the STK6712BMK4 is self-exciting there will be minor variation in motor inductance during motor revolution.
Final design verification is required in an actual model.
Thermal Radiation Design
The HIC radiator plate size is dependent on the motor output current I_OH (A), motor electrical characteristics, excitation
mode, and excitation input signal clock frequency fclock (Hz).
The thermal resistance for the radiator can be determined from the following expression.
Tc max – Ta
θc – a =
Pd
(°C/W).................................................................................................................. (9)
Tc max = HIC substrate temperature
(°C)
Ta = set internal temperature
(°C)
Pd = HIC internal mean power dissipation (W)
No. 4867-7/10