ELECTRICAL CHARACTERISTICS (continued)
COMPARATOR SECTION PERFORMANCE (Over Operating Temperature Range)
Symbol Parameter Test Condtions Min. Typ. Max. Unit
V
IO
Input Offset Voltage V
IN
= 1.4V
±
20
mV
I
IO
Input Offset Curent
±
500
nA
CIRCUIT OPERATION
The L6506 is intended for use with dual bridge driv-
ers, such as the L298, quad darlington arrays, such
as the L7150, quad DMOS array such as L6114-
L6115, or discrete power transistors to drive stepper
motors and other similar loads. The main function of
the device is to sense and control the current in each
of the load windings.
A common on-chip oscillator drives the dual chopper
and sets the operating frequency for the pulse width
modulated drive. The RC network on pin 1 sets the
operating frequency which is given by the equation
:
1
f = for R > 10 K
0.69 RC
The oscillator provides pulses to set the two flip-
flops which in turn cause the outputs to activate the
drive. When the current in the load winding reaches
the programmed peak value, the voltage across the
sense resistor (R
sense
) is equal to V
ref
and the cor-
responding comparator resets its flip-flop interrupt-
ing the drive current until the next oscillator pulse oc-
curs. The peak current in each winding is pro-
grammed by selecting the value of the sense resis-
tor and V
ref
. Since separate inputs are provided for
each chopper, each of the loads may be pro-
grammed independently allowing the device to be
used to implement microstepping of the motor.
Lower threshold of L6506’s oscillator is 1/3 V
CC
. Up-
per threshold is 2/3 V
CC
and internal discharge re-
sistor is 1 KΩ ± 30 %.
Ground noise problems in multiple configurations
can be avoided by synchronizing the oscillators.
This may be done by connecting the sync pins of
each of the devices with the oscillator output of the
master device and connecting the R/C pin of the un-
used oscillators to ground.
The equations for the active time of the sync pulse
(T2), the inactive time of the sync signal (T1) and the
duty cycle can be found by looking at the figure 1 and
are :
R1 R
IN
T2 = 0.69 C1 (1)
R1 + R
IN
T1 = 0.69 R1 C1 (2)
T2
DC = (3)
T1 + T2
LOGIC SECTION (Over Operating Temperature Range - TTL compatible inputs & outputs)
Symbol Parameter Test Condtions Min. Typ. Max. Unit
V
IH
Input High Voltage 2 V
s
V
V
IL
Input Low Voltage 0.8 V
V
OH
Output High Voltage V
CC
= 4.75V
I
OH
= 400
µ
A
2 3.5 V
V
OL
Ouptut Low Voltage V
CC
= 4.75V
I
OH
= 4mA
0.25 0.4 V
I
OH
Ouput Source Current - Outputs
1 - 4
V
CC
= 4.75V 2.75 mA
OSCILLATOR
Symbol Parameter Test Condtions Min. Typ. Max. Unit
f
osc
Frequency Range 5 70 KHz
V
thL
Lower Threshold Voltage 0.33 V
CC
V
V
thH
Higher Threshold Voltage 0.66 V
CC
V
R
i
Internal Discharge Resistor 0.7 1 1.3
k
Ω
L6506 - L6506D
3/8
