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参数资料
| 型号： | LT3508IFE#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 4.40 MM, PLASTIC, TSSOP-16 |
| 文件页数： | 6/24页 |
| 文件大小： | 365K |
| 代理商： | LT3508IFE#TR |
LT3508
14
3508f
The minimum operating voltage of an LT3508 application
is limited by the undervoltage lockout (≈3.7V) and by the
maximum duty cycle. The boost circuit also limits the
minimum input voltage for proper start-up. If the input
voltage ramps slowly, or the LT3508 turns on when the
output is already in regulation, the boost capacitor may
not be fully charged. Because the boost capacitor charges
with the energy stored in the inductor, the circuit will rely
on some minimum load current to get the boost circuit
running properly. This minimum load will depend on
input and output voltages, and on the arrangement of the
boost circuit. The minimum load current generally goes
to zero once the circuit has started. Figure 5 shows a plot
of minimum load to start and to run as a function of input
voltage. Even without an output load current, in many
cases the discharged output capacitor will present a load
to the switcher that will allow it to start. The plots show
the worst case, where VIN is ramping very slowly.
Frequency Compensation
The LT3508 uses current mode control to regulate the
output. This simplies loop compensation. In particular, the
LT3508 does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size.
Frequency compensation is provided by the components
tied to the VCpin,asshowninFigure1.Generallyacapacitor
(CC) and a resistor (RC) in series to ground are used. In
addition, there may be a lower value capacitor in parallel.
This capacitor (CF) is not part of the loop compensation
but is used to lter noise at the switching frequency, and
is required only if a phase-lead capacitor is used or if the
output capacitor has high ESR.
Loop compensation determines the stability and transient
performance. Designing the compensation network is a bit
complicated and the best values depend on the application
and in particular the type of output capacitor. A practical
approach is to start with one of the circuits in this data
sheet that is similar to your application and tune the com-
pensation network to optimize the performance. Stability
should then be checked across all operating conditions,
including load current, input voltage and temperature. The
LT1375 data sheet contains a more thorough discussion of
loop compensation and describes how to test the stability
using a transient load.
Figure 6 shows an equivalent circuit for the LT3508 control
loop. The error amplier is a transconductance amplier
with nite output impedance. The power section, consisting
of the modulator, power switch and inductor, is modeled
as a transconductance amplier generating an output
current proportional to the voltage at the VC pin. Note that
the output capacitor integrates this current, and that the
capacitor on the VC pin (CC) integrates the error amplier
output current, resulting in two poles in the loop. In most
cases a zero is required and comes from either the output
capacitor ESR or from a resistor RC in series with CC.
This simple model works well as long as the value of the
inductor is not too high and the loop crossover frequency
APPLICATIONS INFORMATION
Figure 5. The Minimum Input Voltage Depends on Output
Voltage, Load Current and Boost Circuit
LOAD CURRENT (mA)
1
5.0
5.5
6.5
1000
3508 F05a
4.5
4.0
10
100
10000
3.5
3.0
6.0
INPUT
VOLTAGE
(V)
TA = 25°C
VOUT = 3.3V
TO START
TO RUN
LOAD CURRENT (mA)
1
INPUT
VOLTAGE
(V)
6
7
10000
3508 G05b
5
4
10
100
1000
9
8
TA = 25°C
VOUT = 5V
TO START
TO RUN
Minimum Input Voltage, VOUT = 3.3V
Minimum Input Voltage, VOUT = 5V
相关PDF资料 |
PDF描述 |
|---|---|
| LT3508EUF | 3.2 A DUAL SWITCHING CONTROLLER, 1060 kHz SWITCHING FREQ-MAX, PQCC24 |
| LT3509HMSE#TRPBF | 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3509IMSE#PBF | 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3509IMSE#TRPBF | 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16 |
| LT3509EMSE#TRPBF | 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3508IFE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Monolithic 1.4A Step-Down Switching Regulator |
| LT3508IUF#PBF | 功能描述:IC REG BUCK ADJ 1.4A DL 24QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 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:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT3508IUF#PBF | 制造商:Linear Technology 功能描述:DC-DC CONVERTER BUCK 1MHZ Q 制造商:Linear Technology 功能描述:DC-DC CONVERTER, BUCK, 1MHZ, QFN-24 |
| LT3508IUF#TRPBF | 功能描述:IC REG BUCK ADJ 1.4A DL 24QFN 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 |
| LT3508IUF-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Monolithic 1.4A Step-Down Switching Regulator |
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