L292(1993) 查看數據表（PDF） - STMicroelectronics

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L292
(Rev.:1993)

SWITCH-MODE DRIVER FOR DC MOTORS

STMicroelectronics 

L292

Neglecting the VCEsat of the bridge transistors and the VBE of the diodes:

Gmo = 1 2 Vs

RM VR

where : VS = supply voltage

(1)

VR = 8 V (reference voltage)

DC TRANSFER FUNCTION

In order to be sure that the current loop is stable the following condition is imposed :

1 + sRC = 1 + s LM

RM

(pole cancellation)

(2)

from which RC = LM

RM

(Note that in practice R must greater than 5.6 KΩ)

The transfer function is then,

IM (s) =

VI

R2 R4

R1 R3

Gmo

1 + s RF CF

Gmo Rs + s R4 C + s2 RF CF R4 C

(3)

In DC condition, this is reduced to

IM

VI

(o)

=

R2

R1

R4

R3

•

1

Rs

=

0.044

Rs

[ A]

V

(4)

OPEN-LOOP GAIN AND STABILITY CRITERION

For RC = LM / RM, the open loop gain is:

Aβ

=

1

sR subF C

•

Gmo

Rs

R4

RF

1 + s RF CF

=

Gmo Rs C

R4

s

1

(1 + s RF CF)

(5)

In order to achieve good stability, the phase margin must be greater than 45° when | Aβ | = 1.

That means that, at fF = 1

must be | Aβ | < 1 (see fig. 7), that is :

2 π RF CF

|

A

β

|

f

=

2

π

1

RF

CF

=

Gmo Rs

R4 C

RF CF

√2

<1

(6)

Figure 7. Open Loop Frequency Response

7/12

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