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参数资料
| 型号： | L6918D |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 1200 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | SO-28 |
| 文件页数： | 16/35页 |
| 文件大小： | 431K |
| 代理商： | L6918D |
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L6918 L6918A
AVERAGE CURRENT MODE (ACM) CONTROL LOOP
The average current mode control loop is reported in figure 15. The current information IFB sourced by the FB
pin flows into RFB implementing the dependence of the output voltage from the read current.
The ACM control loop gain results (obtained opening the loop after the COMP pin):
where:
–
is the equivalent output resistance determined by the droop function;
–ZP(s) is the impedance resulting by the parallel of the output capacitor (and its ESR) and the applied
load Ro;
–ZF(s) is the compensation network impedance;
–ZL(s) is the parallel of the two inductor impedance;
– A(s) is the error amplifier gain;
–
is the ACM PWM transfer function where
Vosc is the oscillator ramp amplitude
and has a typical value of 2V
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>>RL; ESR<<Ro and
RDROOP<<Ro, it results:
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
ωT. Neglecting the effect of ZF(s), the
transfer function has one zero and two poles. 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 RF-CF series network is considered for the ZF(s) implementation.
A zero at
ωf=1/RFCF is then introduced together with an integrator. This integrator minimizes the static error
G
LOOP s
()
PW M Z
F s
() R
DROOP
Z
P s
()
+
()
Z
P s
() Z
L s
()
+
()
Z
F s
()
As
()
---------------
1
As
()
------------
+
R
FB
+
--------------------------------------------------------------------------------------------------------------------
–
=
R
DROOP
Rsense
Rg
---------------------- R
FB
=
PW M
4
5
---
V
IN
V
OS C
-------------------
=
G
LOOP s
()
4
5
---
V
IN
V
OS C
-------------------
Z
F s
()
Z
P s
() Z
L s
()
+
------------------------------------
Rs
Rg
--------
Z
P s
()
R
FB
---------------
+
–
=
G
LOOP s
()
4
5
---
V
IN
V
OSC
-------------------
Z
F s
()
R
FB
---------------
Ro
R
DROOP
+
Ro
R
L
2
-------
+
-------------------------------------
1s C o
R
DROOP //Ro
E SR
+
()
+
s
2
Co
L
2
---
s
L
2Ro
---------------
Co ESR
Co
R
L
2
-------
+
+
1
+
+
----------------------------------------------------------------------------------------------------------------------------------
–
=
G
LOOP s
()
4
5
---
V
IN
V
OSC
-------------------
Z
F s
()
R
FB
---------------
1s Co
R
DROOP
ESR
+
()
+
s
2
Co
L
2
---
s
L
2Ro
---------------
C o ESR
Co
R
L
2
-------
+
+
1
+
+
----------------------------------------------------------------------------------------------------------------------------------
–
=
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相关代理商/技术参数 |
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|---|---|
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| L6919CD | 功能描述:DC/DC 开关控制器 Prog Dual-Phase Cont RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| L6919CDTR | 功能描述:DC/DC 开关控制器 Prog Dual-Phase Cont RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
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