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参数资料
| 型号： | LM2633MTDX/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 275 kHz SWITCHING FREQ-MAX, PDSO48 |
| 封装： | TSSOP-48 |
| 文件页数： | 30/40页 |
| 文件大小： | 1350K |
| 代理商： | LM2633MTDX/NOPB |
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Control Loop Design (Continued)
amplifier, and I
fb2 is the current drawn by the FB2 pin. The
V
fb2 and Ifb2 have a typical value of 1.24V and 18 nA
respectively.
Example: V
out2 = 1.5V, R1 =10 k.
(51)
To calculate the total system tolerance, use the following
equation:
(52)
where
φ is the tolerance of the Channel 2 reference voltage,
and
σ is the tolerance of the resistors.
Example: V
out2
= 3.3V, feedback resistors have a ±1%
tolerance.
(53)
That means the 3.3V output voltage will have a ±2.96%
tolerance over the (LM2633 die) temperature range of 0C to
125C.
Channel 2 output voltage should not go above 6V in
pulse-skip mode. That is because the SENSE2 pin cannot
take a voltage higher than 6V. However, if force-PWM op-
eration is the chosen operating mode, then the SENSE2 pin
can be grounded and there will be no limitation to Channel 2
output voltage.
If the desired Channel 1 voltage is higher than 2V, an
op-amp and a voltage divider can be used to expand the
voltage range, as shown in
It is recommended that the VIDx pins be all tied to ground so
that the DAC is set at 2.00V. That will reduce the total
tolerance. The equations used to calculate Channel 2’s feed-
back resistors and total tolerance still hold, except that the
reference voltage V
fb1 is 2.00V instead of 1.24V. Channel 1
can operate only in force-PWM mode when it is configured
as
Since an op-amp is an active device, pay close attention to
its start up and shut down behavior. Make sure that it does
not create a problem during those times.
Designing a Power Supply without a Load Transient
Specification
Many times the load transient response of a buck regulator is
not a critical issue. In that case, the selection of the power
stage components can start from the inductor ripple current.
Choosing the peak-to-peak ripple current to be 30% of the
maximum load current is often a good starting point. Then
the inductance value can be determined by ripple, switching
frequency and input and output voltages. By rearranging
Equation (13), the inductance value can be calculated as
follows:
(54)
Example: V
in_max = 21V, Vn = 1.6V, Iload_max = 10A.
The output capacitors can be chosen based on the output
voltage ripple requirement. If there is no specific require-
ment, then a ±1% ripple level may be a good starting point.
The equation for determining the impedance of the output
capacitors is:
(55)
If the ESR zero frequency of the capacitor is lower than the
switching frequency, such as the case of aluminum, tantalum
and OSCON capacitors, then the output capacitors are cho-
sen by the ESR value. Otherwise, such as in the case of
ceramic capacitors, the output capacitors are chosen by the
capacitance. The equation is:
(56)
Basically make sure that the product of the impedance of the
capacitors and the ripple current does not exceed the ripple
voltage requirement.
Example: V
n = 1.6V, Irip = 3A.
(57)
If ceramic capacitors are preferred, then the minimum ca-
pacitance is:
(58)
200008B6
FIGURE 18. How to Make V
OUT1 Higher Than 2V
LM2633
www.national.com
36
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| LM2635MX | 功能描述:IC REG SYNCH BUCK 5-BIT 20-SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 电源管理 - 专用 系列:- 应用说明:Ultrasound Imaging Systems Application Note 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:37 系列:- 应用:医疗用超声波成像，声纳 电流 - 电源:- 电源电压:2.37 V ~ 6 V 工作温度:0°C ~ 70°C 安装类型:表面贴装 封装/外壳:56-WFQFN 裸露焊盘 供应商设备封装:56-TQFN-EP（8x8） 包装:管件 |
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