参数资料
型号: LTC3427EDC#TRPBF
厂商: Linear Technology
文件页数: 6/12页
文件大小: 0K
描述: IC REG BOOST SYNC ADJ 0.5A 6DFN
标准包装: 2,500
类型: 升压(升压)
输出类型: 可调式
输出数: 1
输出电压: 1.8 V ~ 5.25 V
输入电压: 1.8 V ~ 5 V
PWM 型: 电流模式
频率 - 开关: 1.25MHz
电流 - 输出: 500mA
同步整流器:
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 6-WFDFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 6-DFN-EP(2x2)
LTC3427
OPERATIO
(Refer to Block Diagram)
LOW NOISE FIXED FREQUENCY OPERATION
of input or output voltage. The current signal is blanked for
approximately 25ns to enhance noise rejection.
Shutdown
The LTC3427 is shut down by pulling the SHDN pin below
0.35V, and activated by pulling the SHDN pin above 1V.
Note that SHDN can be driven above V IN or V OUT as long
as it is limited to less than the absolute maximum rating.
Current Limit
The current limit circuitry shuts off the internal N-channel
MOSFET switch when the current limit threshold is reached.
The current limit comparator delay to output is typically
40ns.
Soft-Start
The LTC3427 provides soft-start by ramping the peak
inductor current from zero to its peak value of 500mA. The
soft-start time is typically 2ms. A soft-start cycle is re-
initiated in the event of a commanded shutdown or a
Zero Current Comparator
The zero current comparator monitors the inductor cur-
rent to the output and shuts off the synchronous rectifier
once this current reduces to approximately 20mA.
thermal shutdown.
Anti-Ringing Control
Oscillator
The frequency of operation is set by an internal oscillator
to 1.25MHz for the LTC3427.
Error Amplifier
The error amplifier is a transconductance type with its
positive input internally connected to the 1.24V reference
and the negative input connected to FB. Internal clamps
limit the minimum and maximum error amplifier output
voltage for improved large-signal transient response.
Power converter control loop compensation is provided
internally by the error amplifier. A voltage divider from
V OUT to ground programs the output voltage via FB from
1.8V to 5.25V.
The anti-ringing control connects a resistor across the
inductor to damp the ringing on the SW pin in discontinu-
ous conduction mode. The LC SW ringing (L = Inductor,
C SW = capacitance on the SW pin) is low energy, but can
cause EMI radiation.
Output Disconnect and Inrush Limiting
The LTC3427 provides true output disconnect by elimi-
nating body diode conduction of the internal P-channel
MOSFET rectifier. This allows V OUT to go to zero volts
during shutdown without drawing any current from the
input source. It also provides inrush current limiting at
turn-on, minimizing surge currents seen by the input
supply. Note that to obtain the advantages of output
V OUT = 1 . 24 V ? ? 1 +
?
?
R1 ?
R 2 ? ?
disconnect, there must not be any external Schottky diode
connected between SW and V OUT .
Thermal Shutdown
The error amplifier also provides a soft-start feature
internal to the device.
Current Sensing
Lossless current sensing converts the peak current signal
of the N-channel MOSFET switch into a voltage that is
summed with the internal slope compensation. The
summed signal is compared to the error amplifier output to
provide a peak current control command for the PWM. Peak
switch current is limited to 500mA minimum, independent
If the die temperature reaches approximately 145 ° C, the
part will go into thermal shutdown. All switches will be
turned off. The device will be enabled and initiate a soft-
start sequence when the die temperature drops by
approximately 10 ° C.
Note: Due to the high frequency operation of the LTC3427,
board layout is extremely critical to minimize transients
due to stray inductance. Keep the output filter capacitor as
close as possible to the V OUT pin and use very low ESR/
ESL ceramic capacitors tied to a good ground plane.
3427fa
6
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