MC3479FN Datasheet, PDF (6/10 Pages) ON Semiconductor – Stepper Motor Driver

MC3479
V_D
This pin allows for provision of a current path for the
motor coil current during switching, in order to suppress
back−EMF voltage spikes. V_D is normally connected to V_M
(Pin 16) through a diode (zener or regular), a resistor, or
directly. The peaks instantaneous voltage at the outputs must
not exceed V_M by more than 6.0 V. The voltage drop across
the internal clamping diodes must be included in this portion
of the design (see Figure 6). Note the parasitic diodes
(Figure 5) across each Q_L of each output provide for a
complete circuit path for the switched current.
3.0
2.0
1.0
0
0
100
200
300
I_D (mA)
Figure 6. Clamp Diode Characteristics
Full/Half Step
When this input is at a Logic “0” (< 0.8 V), the outputs
change a full step with each clock cycle, with the sequence
direction depending on the CW/CCW input. There are four
steps (Phase A, B, C, D) for each complete cycle of the
sequencing logic. Current flows through both motor coils
during each step, as shown in Figure 7.
When taken to a Logic “1” (>2.0 V), the outputs change
a half step with each clock cycle, with the sequence direction
depending on the CW/CCW input. Eight steps (Phase A to
H) result for each complete cycle of the sequencing logic.
Phase A, C, E and G correspond (in polarity) to Phase A, B,
C, and D, respectively, of the full step sequence. Phase B, D,
F and H provide current to one motor coil, while
de−energizing the other coil. The condition of the outputs of
the de−energized coil depends on the OIC input, see Figure 7
timing diagram.
OIC
The output impedance control input determines the output
impedance to the de−energized coil when operating in the
half−step mode. When the outputs are in Phase B, D, F or H
(Figure 7) and this input is at a Logic “0” (<0.8 V), the two
outputs to the de−energized coil are in a high impedance
condition − Q_L and Q_H of both outputs (Figure 5) are off.
When this input is at a Logic “1” (>2.0 V), a low impedance
output is provided to the de−energized coil as both outputs
have Q_H on (Q_L off). To complete the low impedance path
requires connecting V_D to V_M as described elsewhere in this
data sheet.
Bias/Set
This pin can be used for three functions: a) determining
the maximum output sink current; b) setting the internal
logic to a known state; and c) reducing power consumption.
a) The maximum output sink current is determined by the
base drive current supplied to the lower transistors (Q_Ls of
Figure 5) of each output, which in turn, is a function of I_BS.
The appropriate value of I_BS can be approximated using
Figure 11.
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