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参数资料
| 型号： | LM2735XMFEVAL/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 14/58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 |
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SNVS485F – JUNE 2007 – REVISED APRIL 2013
80
60
40
20
gm-Pole
RC-Pole
D = 0.625
Vi = 5V
Vo = 12V
Io = 500 mA
Co = 10 mF
Lo = 5 mH
180
90
Cf = 220 pF
0
Fz-cf = 8 kHz
gm-zero
0
RHP-Zero = 107 kHz
-20
Fp-cf = 77 kHz
Fp-rc = 660 Hz
-40
-60
Ext (Cf)
-Zero
Ext (Cf)-Pole
RHP-Zero
-90
-80
10
-180
100 1k 10k 100k 1M
FREQUENCY
Figure 24. LM2735 With External Compensation
The simplest method to determine the compensation component value is as follows.
Set the output voltage with the following equation.
R 2 = ¨ ¨
where
§ V OUT
? V REF
·
- 1 ? ? x R 1
1
?
R1 is the bottom resistor and R2 is the resistor tied to the output voltage.
(10)
The next step is to calculate the value of C3. The internal compensation has been designed so that when a zero
is added between 5 kHz & 10 kHz the converter will have good transient response with plenty of phase margin
for all input & output voltage combinations.
F ZERO - CF =
1
2 S ( R 2 x C f )
= 5 kHz o 10 kHz
(11)
Lower output voltages will have the zero set closer to 10 kHz, and higher output voltages will usually have the
zero set closer to 5 kHz. It is always recommended to obtain a Gain/Phase plot for your actual application. One
could refer to the Typical applications section to obtain examples of working applications and the associated
component values.
Pole @ origin due to internal gm amplifier:
F P-ORIGIN
Pole due to output load and capacitor:
(12)
F P- RC =
1
2 S (R Load C OUT )
(13)
This equation only determines the frequency of the pole for perfect current mode control (CMC). I.e, it doesn’t
take into account the additional internal artificial ramp that is added to the current signal for stability reasons. By
adding artificial ramp, you begin to move away from CMC to voltage mode control (VMC). The artifact is that the
pole due to the output load and output capacitor will actually be slightly higher in frequency than calculated. In
this example it is calculated at 650 Hz, but in reality it is around 1 kHz.
The zero created with capacitor C3 & resistor R2:
14
Product Folder Links: LM2735
Copyright ? 2007–2013, Texas Instruments Incorporated
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