MC3479FN Datasheet, PDF (7/10 Pages) ON Semiconductor – Stepper Motor Driver

MC3479
Clk
Bias/Set
CW/CCW
Phase A B
L1
L2
L3
L4
Phase A
Output
CDA B
(a) Full Step Mode
CB ADCB
= High Impedance
F/HS
= Logic 0"
OIC
= Don′t Care
AB C D E F G H A B C D
L1
L2
L3
L4
(b) Half Step Mode
CW/CCW
F/HS
= High Impedance
= Logic 0"
= Logic 1", OIC = Logic 0"
L1
L2
L3
L4
Phase A
Output
AB C D E F G H A B C D
(c) Half Step Mode
Figure 7. Output Sequence
CW/CCW ^{= Logic 0"}
F/HS ^{= Logic 1"}
OIC
= Logic 1"
The value of R_B (between this pin and ground) is then
determined by:
RB + ^VM
* 0.7 V
IBS
b) When this pin is opened (raised to V_M) such that I_BS is
< 5.0 mA, the internal logic is set to the Phase A condition, and
the four driver outputs are put into a high impedance state.
The Phase A output (Pin 11) goes active (low), and input
signals at the controls are ignored during this time. Upon
re−establishing I_BS, the driver outputs become active, and
will be in the Phase A position (L1 = L3 = V_OHD, L2 = L4
= V_OLD). The circuit will then respond to the inputs at the
controls.
The Set function (opening this pin) can be used as a
powerup reset while supply voltages are settling. A CMOS
logic gate (powered by V_M) can be used to control this pin as
shown in Figure 12.
c) Whenever the motor is not being stepped, power
dissipation in the IC and in the motor may be lowered by
reducing I_BS, so as to reduce the output (motor) current.
Setting I_BS to 75 mA will reduce the motor current, but will
not reset the internal logic as described above. See Figure 13
for a suggested circuit.
Power Dissipation
The power dissipated by the MC3479 must be such that
the junction temperature (T_J) does not exceed 150°C. The
power dissipated can be expressed as:
P = (V_M  I_M) + (2  I_OD) [(V_M − V_OHD) + V_OLD]
where
V_M = Supply voltage;
I_M = Supply current other than I_OD;
I_OD = Output current to each motor coil;
V_OHD = Driver output high voltage;
V_OLD = Driver output low voltage.
The power supply current (I_M) is obtained from Figure 8.
After the power dissipation is calculated, the junction
temperature can be calculated using:
T_J = (P  R_qJA) + T_A
where R_qJA = Junction−to−ambient thermal resistance
(52°C/W for the DIP, 72°C/W for the FN Package);
T_A = Ambient Temperature.
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