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参数资料
| 型号： | LT1374IR-5#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 8.5 A SWITCHING REGULATOR, 560 kHz SWITCHING FREQ-MAX, PSSO7 |
| 封装： | PLASTIC, D2PAK-7 |
| 文件页数： | 16/32页 |
| 文件大小： | 698K |
| 代理商： | LT1374IR-5#TRPBF |
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23
LT1374
1374fd
APPLICATIONS INFORMATION
WU
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What About a Resistor in the Compensation Network?
It is common practice in switching regulator design to
add a “zero” to the error amplifier compensation to
increase loop phase margin. This zero is created in the
external network in the form of a resistor (RC) in series
with the compensation capacitor. Increasing the size of
this resistor generally creates better and better loop
stability, but there are two limitations on its value. First,
the combination of output capacitor ESR and a large
value for RC may cause loop gain to stop rolling off
altogether, creating a gain margin problem. An approxi-
mate formula for RC where gain margin falls to zero is:
GMP = Transconductance of power stage = 5.3A/V
GMA = Error amplifier transconductance = 2(10–3)
ESR = Output capacitor ESR
2.42 = Reference voltage
With VOUT = 5V and ESR = 0.03, a value of 6.5k for RC
would yield zero gain margin, so this represents an upper
limit. There is a second limitation however which has
nothing to do with theoretical small signal dynamics.
This resistor sets high frequency gain of the error ampli-
fier, including the gain at the switching frequency. If
switching frequency gain is high enough, output ripple
voltage will appear at the VC pin with enough amplitude
to muck up proper operation of the regulator. In the
marginal case,
subharmonic switching occurs, as evi-
denced by alternating pulse widths seen at the switch
node. In more severe cases, the regulator squeals or
hisses audibly even though the output voltage is still
roughly correct. None of this will show on a theoretical
Bode plot because Bode is an amplitude insensitive
analysis.
Tests have shown that if ripple voltage on the VC
is held to less than 100mVP-P, the LT1374 will be well
behaved. The formula below will give an estimate of VC
ripple voltage when RC is added to the loop, assuming
that RC is large compared to the reactance of CC at
500kHz.
GMA = Error amplifier transconductance (2000Mho)
If a computer simulation of the LT1374 showed that a
series compensation resistor of 3k gave best overall loop
response, with adequate gain margin, the resulting VC pin
ripple voltage with VIN = 10V, VOUT = 5V, ESR = 0.1,
L = 10H, would be:
This ripple voltage is high enough to possibly create
subharmonic switching. In most situations a compromise
value (< 2k in this case) for the resistor gives acceptable
phase margin and no subharmonic problems. In other
cases, the resistor may have to be larger to get acceptable
phase response, and some means must be used to control
ripple voltage at the VC pin. The suggested way to do this
is to add a capacitor (CF) in parallel with the RC/CC network
on the VC pin. Pole frequency for this capacitor is typically
set at one-fifth of switching frequency so that it provides
significant attenuation of switching ripple, but does not
add unacceptable phase shift at loop unity-gain frequency.
With RC = 3k,
How Do I Test Loop Stability?
The “standard” compensation for LT1374 is a 1.5nF
capacitor for CC, with RC = 0. While this compensation will
work for most applications, the “optimum” value for loop
compensation components depends, to various extent, on
parameters which are not well controlled. These include
inductor value (±30% due to production tolerance, load
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1374IRPBF | 制造商:Linear Technology 功能描述:DC-DC Converter Step-Down 5-25V DDPAK8 |
| LT1374IR-SYNC | 功能描述:IC REG BUCK ADJ 4.5A D2PAK RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT1374IR-SYNC#PBF | 功能描述:IC REG BUCK ADJ 4.5A D2PAK RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT1374IS8 | 功能描述:IC REG BUCK ADJ 4.5A 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT1374IS8#PBF | 功能描述:IC REG BUCK ADJ 4.5A 8SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
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