ELECTRICAL CHARACTERISTICS (continued)

COMPARATOR SECTION PERFORMANCE (Over Operating Temperature Range)

Symbol

Parameter

Test Condtions

Min.

Typ.

Max.

Unit

Input Offset Voltage

±20

mV

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 functionof

the device is to senseand control the current in each

of the load windings.

A commonon-chiposcillator drives thedual chopper

and sets the operatingfrequencyfor 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

responding comparator resets its flip-flop interrupt-

ing the drive current untilthe next oscillatorpulse oc-

curs. The peak current in each winding is pro-

grammed by selecting the value of the sense resis-

each chopper, each of the loads may be pro-

grammed independently allowing the device to be

used to implement microstepping of the motor.

sistor is 1 K

Ω ± 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 deviceand connectingthe R/C pin of the un-

used oscillators to ground.

The equations for the active time of the sync pulse

(T2), the inactivetime of the sync signal (T1)and the

dutycycle can be found by looking at the figure1 and

are :

T2 = 0.69 C1

(1)

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

Input High Voltage

2

V

Input Low Voltage

0.8

V

Output High Voltage

µA

2

3.5

V

Ouptut Low Voltage

0.25

0.4

V

Ouput Source Current - Outputs

1- 4

2.75

mA

OSCILLATOR

Symbol

Parameter

Test Condtions

Min.

Typ.

Max.

Unit

Frequency Range

5

70

KHz

Lower Threshold Voltage

V

Higher Threshold Voltage

V

Internal Discharge Resistor

0.7

1

1.3

k

Ω

L6506 - L6506D

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