- 您现在的位置：买卖IC网 > PDF目录44717 > LP2975AIMM-12/NOPB (NATIONAL SEMICONDUCTOR CORP) SPECIALTY ANALOG CIRCUIT, PDSO8 PDF资料下载
参数资料
| 型号： | LP2975AIMM-12/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 模拟信号调理 |
| 英文描述： | SPECIALTY ANALOG CIRCUIT, PDSO8 |
| 封装： | MINI, SOP-8 |
| 文件页数： | 7/20页 |
| 文件大小： | 1135K |
| 代理商： | LP2975AIMM-12/NOPB |
Application Hints (Continued)
C
GS =CISS CRSS
G
GD is the Gate-to-Drain capacitance, which is equal to:
C
GD =CRSS
G
m is the transconductance of the FET. The FET data
sheet specifies forward transconductance (G
fs)
at some
value of drain current (defined as I
D). To find Gm at the
desired value of load current (defined as I
L), use the formula:
G
m =Gfs x(IL /ID)
1/2
Where:
R
L is the load resistance.
ESR is the equivalent series resistance of the output
capacitor.
The term R
L / / ESR is defined as:
(R
L xESR)/(RL + ESR)
It can be seen from these equations that C
EFF varies with RL.
To get the worst-case (maximum) value for C
EFF, use the
maximum value of load current, which also means the mini-
mum value of load resistance R
L. It should be noted that in
most cases, the ESR is the dominant term which determines
the value of R
L / / ESR.
Gate Pin Output Impedance
10003420
Gate Capacitance Pole Frequency (f
pg)
The pole frequency resulting from the Gate capacitance
C
EFF is defined as fpg and can be approximated from:
f
pg . 0.16 / (RO xCEFF)
Where:
R
O is the output impedance of the LP2975 Gate pin which
drives the Gate of the FET. It is important to note that R
O is
a function of input supply voltage (see graph GATE PIN
OUTPUT IMPEDANCE).As shown, the minimum value of
R
O is about 550
@ V
IN = 24V, increasing to about 1.55 k
@ V
IN =3V.
Using the equation for f
pg, a family of curves are provided
showing how f
pg varies with CEFF for several values of RO
(see graph f
pg vs. CEFF):
f
pg vs. CEFF
10003421
As can be seen in the graph, values of C
EFF
in the
500 pF–2500 pF range produce values for f
pg between
40 kHz and 700 kHz. To determine what effect f
pg will have
on stability, the bandwidth of the regulator loop must be
calculated (see next section CROSSOVER FREQUENCY
AND PHASE MARGIN).
Crossover Frequency and Phase Margin
The term f
c will be used to define the crossover frequency of
the regulator loop (which is the frequency where the gain
curve crosses the 0 dB axis). The importance of this fre-
quency is that it is the point where the loop gain goes below
unity, which marks the usable bandwidth of the regulator
loop.
It is the phase margin (or lack of it) at f
c that determines
whether the regulator is stable. Phase margin is defined as
the total phase shift subtracted from 180. In general, a
stable loop requires at least 20-30 of phase margin at f
c.
f
c can be approximated by the following equation (all terms
have been previously defined):
10003423
This equation assumes that no C
F is used and fpg/fc > 1.
If the frequency of the Gate capacitance pole f
pg has been
calculated (previous section), the amount of added phase
shift may now be determined. As shown in the graph below
(see graph PHASE SHIFT DUE TO f
pg), the amount of
added phase shift increases as f
pg approaches fc.
The amount of phase shift due to f
pg that can occur before
oscillation takes place depends on how much added phase
shift is present as a result of the C
OUT pole (see previous
section OUTPUT CAPACITOR).
LP2975
www.national.com
15
相关PDF资料 |
PDF描述 |
|---|---|
| LP3470M5X-4.38/NOPB | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO5 |
| LP3470IM5X-3.65/NOPB | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO5 |
| LP3470M5X-3.65/NOPB | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO5 |
| LP3470M5-3.65/NOPB | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO5 |
| LP3906SQ-TKXII | SWITCHING REGULATOR, 2000 kHz SWITCHING FREQ-MAX, QCC24 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LP2975AIMM-3.3 | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| LP2975AIMM-3.3/NOPB | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| LP2975AIMM-5.0 | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| LP2975AIMM-5.0/NOPB | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| LP2975AIMMX-12 | 功能描述:IC REG CTRLR SGL 12V 8MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性晶体管驱动器 系列:- 产品培训模块:More Information on LDOs 标准包装:2,500 系列:- 类型:正，固定式 输出数:2 输出电压:2.8V，3.3V 电流 - 电源:12mA 输入电压:5 V ~ 22 V 工作温度:0°C ~ 70°C 封装/外壳:16-SOIC（0.154"，3.90mm 宽） 供应商设备封装:16-SOIC 包装:带卷 (TR) |
发布紧急采购，3分钟左右您将得到回复。