L6258 STMicroelectronics, L6258 Datasheet - Page 19

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L6258

Manufacturer Part Number
L6258
Description
Manufacturer
STMicroelectronics
Datasheet

Specifications of L6258

Operating Current
15mA
Motor Controller Type
PWM Motor Controller
Package Type
PowerSO
Operating Supply Voltage (min)
12V
Operating Supply Voltage (typ)
34V
Operating Supply Voltage (max)
5.25V
Lead Free Status / Rohs Status
Not Compliant
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L6258
3.4
Before analysing the error amplifier block and the sense transconductance block, we have to
do this consideration:
Aloop
Ax|
and
Bx|
this means that Ax|dB is the sum of the power amplifier and load blocks;
Ax|
The BODE analysis of the transfer function of Ax is:
Figure 7.
The Bode plot of the Ax|dB function shows a DC gain of -1.9dB and a pole at 163Hz.
It is clear now that (because of the negative gain of the Ax function), Bx function must have
an high DC gain in order to increment the total open loop gain increasing the bandwidth too.
Error amplifier and sense amplifier
As explained before the gain of these two blocks is:
Bx
Being the voltage across the sense resistor the input of the Bx block and the error amplifier
voltage the output of the same, the voltage gain is given by:
dB
dB
dB
dB
= ACerr
dB
= ACpw|
= ACerr|
= (29,5) + (-31.4) = -1.9dB
= Ax
Ax bode plot
dB
dB
dB
dB
+ Bx
+ ACsense
+ ACsense|
+ ACload|
dB
dB
dB
ib
dB
=
Vsense Gs
=
Vsense
------- -
Rb
1
PWM current control loop
19/32

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