L6711TR STMicroelectronics, L6711TR Datasheet - Page 42

• Manufacturer Part Number: L6711TR
• Description: IC CTRLR 3PHASE VID/DACS 48-TQFP
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6711TR

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 1.55 V
• Current - Output: 2A
• Frequency - Switching: 150kHz
• Voltage - Input: 12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 48-TQFP Exposed Pad, 48-eTQFP, 48-HTQFP, 48-VQFP
• Power - Output: 2.5W
• Output Voltage: 0.8 V to 1.581 V
• Output Current: 95 A
• Input Voltage: 13.8 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: 0 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-5363-2; L6711TR

System control loop compensation
42/50
Removing the dependence from the Error Amplifier gain, so assuming this gain high
enough, the control loop gain results:
With further simplifications, it results:
Considering now that in the application of interest it can be assumed that Ro>>R
ESR<<Ro and R
The ACM control loop gain is designed to obtain a high DC gain to minimize static error and
cross the 0dB axes with a constant -20dB/dec slope with the desired crossover frequency
Both the poles are fixed once the output filter is designed and the zero is fixed by ESR and
the Droop resistance.
To obtain the desired shape an R
implementation. A zero at
integrator minimizes the static error while placing the zero in correspondence with the L-C
resonance a simple -20dB/dec shape of the gain is assured).
In fact, considering the usual value for the output filter, the LC resonance results to be at
frequency lower than the above reported zero.
Compensation network can be simply designed placing
over frequency
G
G
G
R
T
F
LOOP
LOOP
LOOP
. Neglecting the effect of Z
=
amplitude and has a typical value of 3V
PWM
R
--------------------------------- -
C
FB
s
s
s
F
=
V
=
=
=
=
I N
------------------- -
V
–
–
–
4
-- -
5
4
-- -
5
4
-- -
5
4
-- -
5
Co
OSC
R
F
---------------
------------------
------------------
------------------
DROO
T
V
V
V
V
V
L
-- -
3
V
V
V
IN
as desired obtaining:
osc
5
-- -
4
OSC
OSC
OSC
I N
I N
I N
P<<Ro, it results:
is the PWM transfer function where V
T
----------------------------------- -
Z
Z
--------------
Z
--------------
R
R
P
F
F
------------------------------------------------------ -
3
FB
FB
s
s
s
F
Z
F
=1/R
R
F
(s), the transfer function has one zero and two poles.
+
DROOP
Ro
------------------------------------ -
---------------------------------------------------------------------------------------------------------------------------------
s
s
Z
2
L
F
Ro
-C
F
+
Co
L
s
C
R
F
F
+
DROOP
+
series network is considered for the Z
⎛
is then introduced together with an integrator. This
R
------ -
L
-- -
3
Rs
------- -
Rg
3
ESR
1
L
+
+
s
+
s Co
---------------------------------------------------------------------------------------------------------------------------------
s
Z
-------------- -
R
2
P
---------------
3 Ro
FB
Co
s
L
⎞
⎠
R
1
+
L
-- -
3
D ROOP
+
Co ESR
+
s Co
s
Z
=
---------------
3 Ro
+
L
ESR
LC
OSC
R
+
DROOP
Co
and imposing the cross-
+
is the oscillator ramp
Co ESR
R
------ -
3
//Ro
L
+
1
+
+
ESR
F
(s)
Co
L
R
------ -
;
3
L
L6711
+
1