Datasheet

The circuit is intended to drive abipolar constantcur-
rent throughonemotorwinding. The constantcurrent
is generatedthroughswitch mode regulation.
Thereis a choiceofthreedifferentcurrentlevelswith
the two logic inputs lN0 and lN1. The current can
also be switched off completely.
INPUT LOGIC
If any of the logic inputs is left open, the circuit will
treat it as a high level input.
FUNCTIONAL DESCRIPTION
IN0 IN1 Current Level
H
L
H
L
H
H
L
L
No Current
Low Current
Medium Current
Maximum Current
PHASE- This input determines the direction of cur-
rent flow in the winding, depending on the motor
connections. The signal is fed through a Schmidt-
trigger for noise immunity, and througha time delay
in order to guaranteethat no short-circuit occurs in
the output stage during phase-shift. High level on
the PHASEinputcausesthemotorcurrent flowfrom
Out A through the winding to Out B.
l
H0
and l
H1
- The current level in the motor winding
is selectedwith these inputs. The values of the dif-
ferent current levels are determined by the refer-
encevoltageV
R
togetherwith the value of the sens-
ing resistor R
S
.
CURRENT SENSOR
This part contains a current sensingresistor (R
S
), a
lowpassfilter (R
C
,C
C
) andthreecomparators. Only
one comparator is active at a time. It is activated by
the inputlogic according to the current levelchosen
with signals IN0 and IN1. The motor current flows
through the sensing resistor R
S
. When the current
has increased so that the voltage across R
S
be-
comes higher than the reference voltage on the
other comparatorinput,the comparatoroutputgoes
high, which triggers the pulse generatorand its out-
put goes high during a fixed pulse time (t
off
), thus
switching off the power feed to the motor winding,
and causing the motor current to decrease during
t
off
.
SINGLE-PULSE GENERATOR
The pulse generator is a monostable triggered on
the positive going edge of the comparator output.
The monostableoutputishighduring thepulsetime,
t
off
, which is determined by the timing components
R
t
andC
t
.
t
off
= 0.69 ⋅ R
t
C
t
The single pulse switches off the power feed to the
motor winding, causing the winding current to de-
crease during t
off
.
If a new trigger signal should occur during t
off
,itis
ignored.
OUTPUT STAGE
The output stage contains four Darlington transis-
torsandfour diodes,connectedin an H-bridge. The
twosinking transistors are usedto switch the power
supplied to the motor winding, thus driving a con-
stant current through the winding.
It should be noted however, that it is not permitted
to short circuit the outputs.
V
SS
,V
S
,V
R
The circuit will stand any order of turn-on or turn-off
the supply voltages V
SS
and V
S
. Normal dV/dt val-
ues are then assumed.
Preferably,V
R
shouldbe trackingV
SS
duringpower-
on and power-off if V
S
is established.
ANALOG CONTROL
The current levels can be varied continuouslyif V
R
is varied with a circuit varying the voltage on the
comparator terminal.
POWER LOSSES V
S
OUTPUT CURRENT
TEA3718-TEA3718S
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