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參數(shù)資料
| 型號： | LM2698 |
| 文件頁數(shù)： | 10/17頁 |
| 文件大?。?/td> | 503K |
| 代理商： | LM2698 |
Operation
(Continued)
be connected very close to pin 6 to effectively filter high
frequency noise. When operating at 1.25 MHz switching
frequency, a minimum bypass capacitance of 0.22 μF is
recommended.
Output Capacitor
The output capacitor in a boost converter provides all the
output current when the switch is closed and the inductor is
charging. As a result, it sees very large ripple currents. The
output capacitor should be capable of handling the maxi-
mum RMS current. The RMS current in the output capacitor
is:
where,
and
D = (V
OUT
- V
IN
)/V
OUT
The ESR and ESL of the output capacitor directly control the
output ripple. Use capacitors with low ESR and ESL at the
output for high efficiency and low ripple voltage. Surface
mount tantalums, surface mount polymer electrolytic, and
polymer tantalum, Sanyo OS-CON, or multi-layer ceramic
capacitors are recommended at the output.
Compensation
This section presents a step-by-step procedure to design the
compensation network at pin 1 (V
) of the LM2698. These
design methods will produce a conservative and stable con-
trol loop.
There is a minimum inductance requirement in any current
mode converter. This is a function of V
OUT
, duty cycle, and
switching frequency, among other things. The graphs below
plot the recommended inductance range vs. duty cycle for
V
OUT
= 12V. The two lines represent the upper and lower
bounds of the recommended inductance range. The simpli-
fied compensation procedure that follows assumes that the
inductance never drops below the Q = 5 line. Figure 4 plots
the equation:
(1)
where,
R
DSON
= 0.15,
Se = 0.072
*
f
S
,
and Q = 0.5 and 5
Use Q = 5 to calculate the minimum inductance recom-
mended for a stable design. Choosing an inductor between
the Q = 0.5 and Q = 5 values provides a good tradeoff
between size and stability. Note that as V
drops less than
5V, R
increases, as shown in the Typical Performance
Characteristics section (R
vs.V
curve). The worst
case R
should be used when choosing the induc-
tance. To view plots for different Vout, multiply the Y axis by
a factor of V
/12, or plot Equation (1) for the respective
output voltage.
20012654
20012653
FIGURE 4. Minimum Inductance Requirements for (a) f
S
= 600kHz and (b) f
S
= 1.25MHz
L
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| LM2698EVAL | 功能描述:電源管理IC開發(fā)工具 EVAL BOARDFOR LM2698 RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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| LM2698MM-ADJ/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 1.35A BOOST REG RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2698MM-ADJ/NOPB | 制造商:Texas Instruments 功能描述:DC/DC Converter (DC-DC) / Switching Regu |
| LM2698MMX-ADJ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
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