L292

10/13

t = 100

It is possible to verify that the L292 works in "closed-loop" conditions during the entire motor current rise-

time: the voltage at pin 7 inverting input of the error amplifier) is locked to the reference voltage VR,

present at the non-inverting input of the same amplifier.

The previous linear analysis is correct for this example.

Descresing the

ξ value, the rise-time of the current decreases. But for a good stability, from relationship

(6), the maximum value of

ξ is:

(phase margin = 45°)

b) Large signal reponse

The large step signal response is limited by slew-rate and inductive load.

In this case, during the rise-time of the motor current, The L292 works is open-loop condition.

CLOSED LOOP SYSTEM BANDWIDTH.

A good choice for x is the value 1 / Ö2. In this case :

(8)

The module of the transfer function is :

(9)

The cutoff frequency is derived by the expression (9) by putting

= 0.707 ·

(-3 dB), from which:

ξmin

1

2

4

2

--------------

=

I

M

V

I

----- s

()

0.044

R

s

---------------

1sR

+

12s R

2s

2

R

F

2

C

F

2

++

----------------------------------------------------------------------

=

I

M

V

I

-----

0.044

R

s

---------------

21

ω

2

R

F

2

C

F

2

+

12

ωR

+

()

2

1

+

[]

12

–

ωR

()

2

1

+

[]

⋅

----------------------------------------------------------------------------------------------------------------------

=

I

M

V

I

-----

0.044

R

s

---------------

ω

T

0.9

R

---------------

f

T

0.9

2

πR

-----------------------

==