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| 型号： | LT3507AEUHF#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PQCC38 |
| 封装： | 5 X 7 MM, LEAD FREE, PLASTIC, QFN-38 |
| 文件页数： | 8/28页 |
| 文件大小： | 372K |
| 代理商： | LT3507AEUHF#PBF |
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LT3507A
16
3507af
Frequency Compensation
The LT3507A uses current mode control to regulate the
output. This simplifies loop compensation. In particular,
the LT3507A does not depend on the ESR of the output
capacitor for stability so you are free to use ceramic ca-
pacitors to achieve low output ripple and small circuit size.
The components tied to the VC pin provide frequency
compensation. Generally, a capacitor and a resistor in
series to ground determine loop gain. In addition, there
is a lower value capacitor in parallel. This capacitor filters
noise at the switching frequency and is not part of the
loop compensation.
Loop compensation determines the stability and transient
performance.Designingthecompensationnetworkisabit
complicated and the best values depend on the application
and 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 compensation network
to optimize the performance. Check stability 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. Application
Note 76 is an excellent source as well.
Figure6showsanequivalentcircuitfortheLT3507Acontrol
loop. The error amp is a transconductance amplifier with
finite output impedance. The power section, consisting of
the modulator, power switch and inductor is modeled as a
transconductance amplifier generating an output current
proportional to the voltage at the VC pin. The gain of the
power stage (gmp) is 6S for chanel 1 and 4.3S for chanels
2 and 3. Note that the output capacitor integrates this cur-
rent and that the capacitor on the VC pin (CC) integrates
the error amplifier output current, resulting in two poles
in the loop. In most cases, a zero is required and comes
either from the output capacitor ESR or from a resistor
in series with CC. This model works well as long as the
inductor current ripple is not too low (
ΔIRIPPLE > 5% IOUT)
and the loop crossover frequency is less than fSW/5. A
phase lead capacitor (CPL) across the feedback divider
may improve the transient response.
SHUTDOWN
The RUN pins are used to place the individual switching
regulatorsandtheinternalbiascircuitsinshutdownmode.
When all three RUN pins are pulled low, the LT3507A is in
shutdown mode and draws less than 1A from the input
supply. When any RUN pin is pulled high (>1.5V) the inter-
nal reference, LDO and selected channel are all turned on.
The RUN pins draw a small amount of current to power
the reference. The current is less than 3A at 1.8V, so the
RUN pin can be driven directly from 1.8V logic. The RUN
pins are rated up to 36V and can be connected directly to
the input voltage.
A RUN pin cannot be pulled up by logic powered by its
own output, i.e., RUN1 can’t be pulled up by logic powered
by OUT1.
POWER GOOD INDICATORS
The PGOOD pin is the open-collector output of an internal
comparator. PGOOD remains low until the FB pin is within
10% of the final regulation voltage. Tie the PGOOD to any
supply with a pull-up resistor that will supply less than
200A. Note that this pin will be open when the LT3507A
is in shutdown mode (all three RUN pins at ground)
regardless of the voltage at the FB pin. PGOOD is valid
when the LT3507A is enabled (any RUN pin is high) and
VIN is greater than ~3.5V.
APPLICATIONS INFORMATION
Figure 6. Loop Response Model
–
+
VFB
800mV
VSW
VC
LT3507A
GND
3507A F06
R1
OUTPUT
ESR
CF
CC
RC
500k
ERROR
AMPLIFIER
FB
R2
C1
CURRENT MODE
POWER STAGE
gmp
330S
+
POLYMER
OR
TANTALUM
CERAMIC
CPL
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3507AHFE#PBF | 功能描述:IC REG QD BUCK/LINEAR 38TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507AHFE#TRPBF | 功能描述:IC REG QD BUCK/LINEAR 38TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507AHUHF#PBF | 功能描述:IC REG QD BUCK/LINEAR 38QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507AHUHF#TRPBF | 功能描述:IC REG QD BUCK/LINEAR 38QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT3507AIFE#PBF | 功能描述:IC REG QD BUCK/LINEAR 38TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
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