MC3479
http://onsemi.com
7
Figure 7. Output Sequence
Phase A
Output
(a) Full Step Mode
A
CW/CCW
A
A
AA
Bias/Set
Clk
Phase A
Output
Phase A A
(c) Half Step Mode
CD
L3
L4
F
L1
EC
L1
L2
L2
L3
L4
BD
L1
CDBHGDBC EF
(b) Half Step Mode
L2
L3
L4
GH B
BCDBCB
= Logic 0"
= Logic 1"
= Logic 1"
= High Impedance
CW/CCW = Logic 0"
F/HS = Logic 1", OIC = Logic 0"
DBC
= High Impedance
= Logic 0"
= Don′t Care
F/HS
OIC
CW/CCW
F/HS
OIC
The value of R
B
(between this pin and ground) is then
determined by:
R
B
+
V
M
* 0.7 V
I
BS
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.
