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參數資料
| 型號： | LM5642MTC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩壓器 |
| 英文描述： | High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization |
| 中文描述： | DUAL SWITCHING CONTROLLER, 226 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數： | 21/24頁 |
| 文件大小： | 667K |
| 代理商： | LM5642MTC |
Loop Compensation
(Continued)
As shown in
Figure 11
, the control-output transfer function
consists of one pole (fp), one zero (fz), and a double pole at
fn (half the switching frequency). The following can be done
to create a -20dB /decade roll-off of the loop gain: Place the
first pole at 0Hz, the first zero at fp, the second pole at fz,
and the second zero at fn. The resulting output-control trans-
fer function is shown in
Figure 12
.
The control-output corner frequencies, and thus the desired
compensation corner frequencies, can be determined ap-
proximately by the following equations:
(29)
(30)
Since fp is determined by the output network, it will shift with
loading (Ro). It is best to use a minimum Iout value of
approximately 100mA when determining the maximum Ro
value.
Example: Re=20m
, Co=100uF, Romax=5V/100mA=50
:
(31)
(32)
First determine the minimum frequency (fpmin) of the pole
across the expected load range, then place the first compen-
sation zero at or below that value. Once fpmin is determined,
Rc1 should be calculated using:
(33)
Where B is the desired gain in V/V at fp (fz1), gm is the
transconductance of the error amplifier, and R1 and R2 are
the feedback resistors. A gain value around 10dB (3.3v/v) is
generally a good starting point.
Example: B=3.3v/v, gm=650m, R1=20K
, R2=60.4K
:
(34)
Bandwidth will vary proportional to the value of Rc1. Next,
Cc1 can be determined with the following equation:
(35)
Example: fpmin=695Hz, Rc1=20K
:
(36)
The compensation network (
Figure 13
) will also introduce a
low frequency pole which will be close to 0Hz.
A second pole should also be placed at fz. This pole can be
created with a single capacitor Cc2 and a shorted Rc2 (see
Figure 13
). The minimum value for this capacitor can be
calculated by:
(37)
Cc2 may not be necessary, however it does create a more
stable control loop. This is especially important with high
load currents and in current sharing mode.
Example: fz=80kHz, Rc1= 20K
:
(38)
A second zero can also be added with a resistor in series
with Cc2. If used, this zero should be placed at fn, where the
control to output gain rolls off at -40dB/dec. Generally, fn will
be well below the 0dB level and thus will have little effect on
stability. Rc2 can be calculated with the following equation:
(39)
20060114
FIGURE 11. Control-Output Transfer Function
20060112
FIGURE 12. Output-Control Transfer Function
L
www.national.com
21
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM5642MTC/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642MTCX | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642MTCX/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642XMH | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM5642XMH/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
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