参数资料
型号: LT3505IDD#PBF
厂商: Linear Technology
文件页数: 8/24页
文件大小: 0K
描述: IC REG BUCK ADJ 1.2A 8DFN
标准包装: 121
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 0.78 V ~ 33.8 V
输入电压: 3.6 V ~ 36 V
PWM 型: 电流模式
频率 - 开关: 200kHz ~ 3.01MHz
电流 - 输出: 1.2A
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: 8-WFDFN 裸露焊盘
包装: 管件
供应商设备封装: 8-DFN-EP(3x3)
LT3505
BLOCK DIAGRAM
V IN
3
V IN
C2
INT REG
AND
UVLO
ON OFF
R3
SLOPE
COMP
Σ
R
Q
BOOST
1
D2
C4
4
SHDN
OSC
S
Q
DRIVER
Q1
SW
2
C3
L1
V OUT
FREQUENCY
FOLDBACK
D1
C1
V C
g m
780mV
5
GND
8
V C
7
FB
6
R T
R1
3505 BD
R2
OPERATION
(Refer to Block Diagram)
The LT3505 is a constant frequency, current mode step-
down regulator. A resistor-programmed oscillator enables
an RS ?ip-?op, turning on the internal 1.4A power switch
Q1. 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 the V C pin. An error ampli?er measures the
output voltage through an external resistor divider tied to
the FB pin and servos the V C node. 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
(not shown) on the V C node provides current limit. The
V C node is also clamped to the voltage on the SHDN pin;
soft-start is implemented by generating a voltage ramp at
the SHDN pin using an external resistor and capacitor.
An internal regulator provides power to the control circuitry.
This regulator includes an undervoltage lockout to prevent
switching when V IN is less than ~3.4V. The SHDN pin is
used to place the LT3505 in shutdown, disconnecting the
output and reducing the input current to less than 2μA.
The switch driver operates from either the input or from
the BOOST pin. An external capacitor and diode are used
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 opera-
tion.
When the FB pin is low, the voltage at the R T pin decreases
to reduce the oscillator frequency. This frequency foldback
helps to control the output current during start-up and
overload.
3505fc
8
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