参数资料
型号: LM2735XMFEVAL
厂商: National Semiconductor
文件页数: 13/58页
文件大小: 0K
描述: BOARD DEMO FOR LM2735 SOT23-5
标准包装: 1
主要目的: DC/DC,步升
输出及类型: 1,非隔离
输出电压: 12V
电流 - 输出: 500mA
输入电压: 3 ~ 5.5 V
稳压器拓扑结构: 升压
频率 - 开关: 1.6MHz
板类型: 完全填充
已供物品: 板,文档
已用 IC / 零件: LM2735
V FB
R 2
V O
C 3
R LOAD
SNVS485F – JUNE 2007 – REVISED APRIL 2013
R 1
Figure 22. Setting Vout
A good value for R1 is 10k ? .
R 2 = ¨ ¨
§ V OUT
? V REF
·
- 1 ? ? x R 1
1
(9)
COMPENSATION
The LM2735 uses constant frequency peak current mode control. This mode of control allows for a simple
external compensation scheme that can be optimized for each application. A complicated mathematical analysis
can be completed to fully explain the LM2735’s internal & external compensation, but for simplicity, a graphical
approach with simple equations will be used. Below is a Gain & Phase plot of a LM2735 that produces a 12V
output from a 5V input voltage. The Bode plot shows the total loop Gain & Phase without external compensation.
80
gm-Pole
180
60
RC-Pole
40
20
Vi = 5V
Vo = 12V
90
0
-20
-40
Io = 500 mA
Co = 10 P F
Lo = 5 P H
gm-Zero
0
-90
RHP-Zero
-60
-80
-180
10
100
1k
10k
100k
1M
FREQUENCY
Figure 23. LM2735 Without External Compensation
One can see that the Crossover frequency is fine, but the phase margin at 0dB is very low (22°). A zero can be
placed just above the crossover frequency so that the phase margin will be bumped up to a minimum of 45°.
Below is the same application with a zero added at 8 kHz.
Copyright ? 2007–2013, Texas Instruments Incorporated
Product Folder Links: LM2735
13
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