UDN2916A
ELECTRICAL CHARACTERISTICS
(Continued)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
PROTECTION
T
J
Thermal Shutdown Temperature
-
170
-
°C
Figure 1
FUNCTIONAL DESCRIPTION
The circuit is intended to drive both windings of a
bipolar stepper motor.
The peak current control is generated through
switch mode regulation.
There is a choice of three different current levels
with the two logic inputs I
01
- I
11
for winding 1 and
I
02
- I
12
for winding 2.
The current can also be switched off completely
Input Logic (I
0
and I
1
)
The current level in the motor winding is selected
with these inputs. (See fig. 2)
If any of the logic inputs is left open, the circuit will
treat it has a high level input.
I
o
H
L
H
L
I
1
H
H
L
L
Current Level
No Current
Low Current 1/3 I
o
max
Medium Current 2/3 I
o
max
Maximum Current I
o
max
in the windings, depending on the motor connec-
tions. The signal is fed through a Schmidt-trigger
for noise immunity, and through a time delay in
order to guarantee that no short-circuit occurs in
the output stage during phase-shift.
High level on the PHASE input causes the motor
current flow from Out A through the winding to
Out B
Current Sensor
This part contains a current sensing resistor (R
S
),
a low pass filter (R
C
, C
C
) and three comparators.
Only one comparator is active at a time. It is acti-
vated by the input logic according to the current
level chosen with signals I
o
and I
1
.
The motor current flows through the sensing re-
sistor R
S
.
When the current has increased so that the volt-
age across R
S
becomes higher than the refer-
ence voltage on the other comparator input, the
comparator goes high, which triggers the pulse
generator.
The max peak current I
max
can be defined by:
V
ref
I
max
=
Single-pulse Generator
10 R
s
Phase
This input determines the direction of current flow
4/8
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