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L292
(Rev.:1993)

SWITCH-MODE DRIVER FOR DC MOTORS

STMicroelectronics 

L292

CLOSED-LOOP SYSTEM STEP RESPONSE

a) Small - signals analysis.

The transfer function (3) can be written as follows:

s

IM

VI

(s)

=

0.044

Rs

1+

2ξωo

1+

2 ξs + s2

ωo ω o 2

(7)

where

wo

=

√GmoRs

R4 C RF CF

is the cutoff frequency

ξ

=

√R4C

4 RF CF Gmo Rs

is the dumping factor

By choosing the ξ value, it is possible to determine

the system response to an input step signal.

Examples :

1) ξ = 1 from which

IM

(t)

=

0.044

Rs

[

1

−

e

−

t

2RF

CF

(1

+

4

t

RF

CF)

]

•

Vi

(where Vi is the amplitude of the input step).

2) ξ

=

1

√2

from which

IM (t)

=

0.044

Rs

(1

−

cos

2

t

RF

CF

e

−

2

t

RF

CF

)

Vi

Figure 8. Small Signal Step Response

(normalized amplitude vs.

t / RFCF).

V7 = 200 mV/div.

IM = 100 mA/div.

t = 100 µs/div.

with VI = 1.5 Vp.

8/12

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