参数资料
| 型号： | SC4508AMLTRT |
| 厂商： | Semtech |
| 文件页数： | 16/21页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST INV PWM 12-MLPQ |
| 标准包装： | 1 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1.5MHz |
| 占空比： | 97% |
| 电源电压： | 2.7 V ~ 15 V |
| 降压： | 是 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 是 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 12-VQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC4508AMLDKR |
SC4508A
POWER MANAGEMENT
s p 1 =
s p 2 =
R 2
Application Information (Cont.)
where, the single dominant pole is:
1 + D
R o C o
1
C 2 C 3
C 2 + C 3
The loop transfer function is then
T(s)=G vc (s)G C (s)h
To simplify design, we assume that C 3 <<C 2 , R oesr <<R o,
With these assumptions, the controller zero is placed at
the converter dominant pole, the controller second pole
is placed at the converter ESR zero or RHP zero
depending on whichever is lower. The DC gain is finally
adjusted for desired phase margin. The controller
parameters are determined as following:
Assuming a DC gain ω I ,
C 2 =
g m
ω I
and
R 2 =
1
C 2 ? s p 1
Figure 9. A simple model of buck-boost converter with
current mode control.
C 3 =
1
R 2 ? s z 1
or C 3 =
1
R 2 ? s zRHP
s z 1 =
( 1 ? D ) 2 ? R o
R o =
= 12 ?
h =
= 0 . 04
and the zero due to the output capacitor ESR is:
1
R oesr C o
and the RHP zero associated to the topoly is:
s zRHP =
D ? L
The dominant pole moves as input voltage and output
load varies.
The controller transfer function (from the converter
output (v o ) to the voltage error amplifier output (v c ) is:
For example, if V in =12V, V o =-12V, I o =1A, f s =300kHz,
D=0.51, C o =100uF, R oesr =35m ? , R s =35m ?, one can
calculate that::
V o
I o
0 . 5
V o + 0 . 5
1 +
C 2 =
h ≈ 400 nF
where
G c ( s ) =
s
g m s z 2
s ( C 2 + C 3 ) 1 + s
s p 2
Set ω I = 500, the controller parameters then can be
calculated as:
g m
ω I
and
s z 2 =
1
R 2 C 2
where, g m is the error amplifier transconductance gain
(100 μ ? ? 1 ).
If we use C 2 = 390 nF,
? 2007 Semtech Corp.
16
www.semtech.com
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