参数资料
型号: LT3972IMSE#PBF
厂商: Linear Technology
文件页数: 8/24页
文件大小: 0K
描述: IC REG BUCK ADJ 3.5A 10MSOP
标准包装: 50
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 0.79 V ~ 30 V
输入电压: 3.6 V ~ 33 V
PWM 型: 电流模式,Burst Mode?
频率 - 开关: 230kHz ~ 2.45MHz
电流 - 输出: 3.5A
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 10-TFSOP,10-MSOP(0.118",3.00mm 宽)裸露焊盘
包装: 管件
供应商设备封装: 10-MSOP 裸露焊盘
LT3972
OPERATION
The LT3972 is a constant frequency, current mode step-
down regulator. An oscillator, with frequency set by RT,
enables an RS ?ip-?op, turning on the internal power
switch. An ampli?er and comparator monitor the current
?owing between the V IN and SW pins, turning the switch
off when this current reaches a level determined by the
voltage at V C . An error ampli?er measures the output
voltage through an external resistor divider tied to the FB
pin and servos the V C pin. If the error ampli?er’s output
increases, more current is delivered to the output; if it
decreases, less current is delivered. An active clamp on the
V C pin provides current limit. The V C pin is also clamped to
the voltage on the RUN/SS pin; soft-start is implemented
by generating a voltage ramp at the RUN/SS pin using an
external resistor and capacitor.
An internal regulator provides power to the control circuitry.
The bias regulator normally draws power from the V IN pin,
but if the BD pin is connected to an external voltage higher
than 3V bias power will be drawn from the external source
(typically the regulated output voltage). This improves
ef?ciency. The RUN/SS pin is used to place the LT3972
in shutdown, disconnecting the output and reducing the
input current to less than 0.5μA.
The switch driver operates from either the input or from
to generate a voltage at the BOOST pin that is higher than
the input supply. This allows the driver to fully saturate
the internal bipolar NPN power switch for ef?cient
operation.
To further optimize ef?ciency, the LT3972 automatically
switches to Burst Mode operation in light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down, reducing the input supply
current to 75μA in a typical application.
The oscillator reduces the LT3972’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the output current during start-
up and overload.
The LT3972 contains a power good comparator which trips
when the FB pin is at 91% of its regulated value. The PG
output is an open-collector transistor that is off when the
output is in regulation, allowing an external resistor to pull
the PG pin high. Power good is valid when the LT3972 is
enabled and V IN is above 3.6V.
The LT3972 has an overvoltage protection feature which
disables switching action when the V IN goes above 35V
typical (33V minimum). When switching is disabled, the
LT3972 can safely sustain input voltages up to 62V.
the BOOST pin. An external capacitor and diode are used
3972fa
8
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