L6258EP_07 STMICROELECTRONICS [STMicroelectronics], L6258EP_07 Datasheet - Page 19

• Manufacturer Part Number: L6258EP_07
• Description: PWM controlled high current DMOS universal motor driver
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

L6258EP
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 6.
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
ib
dB
dB
dB
=
Vsense
⋅
Gs
=
Vsense
⋅
------- -
Rb
1
PWM current control loop
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