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| 型号： | LTC3775IMSE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/34页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 16-MSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 80% |
| 电源电压： | 4.5 V ~ 38 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-TFSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 带卷 (TR) |
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LTC3775
APPLICATIONS INFORMATION
Operation (Refer to Block Diagram)
The LTC3775 is a constant frequency, voltage mode con-
troller for DC/DC step-down converters. It is designed to
be used in a synchronous switching architecture with two
external N-channel MOSFETs. For circuit operation, please
refer to the Block Diagram.
The LTC3775 uses voltage mode control in which the duty
cycle is controlled directly by the error ampli?er output.
The error ampli?er adjusts the voltage at the COMP pin
by comparing the V FB pin with the 0.6V internal refer-
ence. When the load current increases, it causes a drop
in the feedback voltage relative to the reference. The
COMP voltage then rises, increasing the duty cycle until
the LTC3775 output feedback voltage again matches the
reference voltage.
In normal operation, the top MOSFET is turned on when
the PWM comparator changes state and is turned off by
the internal oscillator. The PWM comparator maintains
the proper duty cycle by comparing the error ampli?er
output (after being “compensated” by the line feedfor-
ward multiplier) to a sawtooth waveform generated by
the oscillator. When the top MOSFET is turned off, the
bottom MOSFET is turned on until the next cycle begins,
or if pulse-skipping mode operation is enabled, until the
inductor current reverses as determined by the reverse
current comparator.
Feedback Control
The LTC3775 senses the output voltage at V OUT with an
internal feedback op amp (see Block Diagram). This is a
true op amp with a low impedance output, 80dB of open-
loop gain and a 25MHz gain-bandwidth product. The
positive input is connected to an internal 0.6V reference,
while the negative input is connected to the FB pin. The
output is connected to COMP, which is in turn connected
to the line feedforward circuit and from there to the PWM
generator.
At steady state, as shown in the Block Diagram, the output of
the switching regulator is given the following equation
Unlike many regulators that use a transconductance (g m )
ampli?er, the LTC3775 is designed to use an inverting
summing ampli?er topology with the FB pin con?gured
as a virtual ground. This allows the feedback gain to be
tightly controlled by external components. In addition, the
voltage feedback ampli?er allows ?exibility in choosing
pole and zero locations. In particular, it allows the use of
“Type 3” compensation, which provides a phase boost
at the LC pole frequency and signi?cantly improves the
control loop phase margin.
In a typical LTC3775 circuit, the feedback loop consists
of the line feedforward circuit, the modulator, the external
inductor, the output capacitor and the feedback ampli?er
with its compensation network. All these components
affect loop behavior and need to be accounted for in the
loop compensation. The modulator consists of the PWM
generator, the output MOSFET drivers and the external
MOSFETs themselves. The modulator gain varies linearily
with the input voltage. The line feedforward circuit com-
pensates for this change in gain, and provides a constant
gain from the error ampli?er output to the inductor input
regardless of input voltage. From a feedback loop point of
view, the combination of the line feedforward circuit and
the modulator looks like a linear voltage transfer function
from COMP to the inductor input and has a gain roughly
equal to 30V/V. It has fairly benign AC behavior at typical
loop compensation frequencies with signi?cant phase shift
appearing at half the switching frequency.
The external inductor/output capacitor combination
makes a more signi?cant contribution to loop behavior.
These components cause a second order LC roll-off at the
output with 180° phase shift. This roll-off is what ?lters
the PWM waveform, resulting in the desired DC output
voltage, but this phase shift causes stability issues in the
feedback loop and must be frequency compensated. At
higher frequencies, the reactance of the output capacitor
approaches its ESR, and the roll-off due to the capacitor
stops, leaving –20dB/decade and 90° of phase shift.
V OUT = V REF ? 1 +
R A
R B
3775fa
10
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| LTC3775IUD#PBF | 功能描述:IC REG CTRLR BUCK PWM VM 16-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3775IUD#TRPBF | 功能描述:IC REG CTRLR BUCK PWM VM 16-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC3776EGN | 制造商:Linear Technology 功能描述:DC DC Cntrlr Dual-OUT Sync Step Down 2.75V to 9.8V Input 24-Pin SSOP N |
| LTC3776EGN#PBF | 功能描述:IC CTLR SYNC DUAL 24-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:2,000 系列:- 应用:控制器，DSP 输入电压:4.5 V ~ 25 V 输出数:2 输出电压:最低可调至 1.2V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:30-TFSOP（0.173"，4.40mm 宽） 供应商设备封装:30-TSSOP 包装:带卷 (TR) |
| LTC3776EGN#TRPBF | 功能描述:IC CNTRLR SYNC DUAL 24-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:43 系列:- 应用:控制器，Intel VR11 输入电压:5 V ~ 12 V 输出数:1 输出电压:0.5 V ~ 1.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:48-VFQFN 裸露焊盘 供应商设备封装:48-QFN（7x7） 包装:管件 |
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