参数资料
型号: LT3684EMSE#TRPBF
厂商: Linear Technology
文件页数: 16/24页
文件大小: 0K
描述: IC REG BUCK ADJ 2A 10MSOP
标准包装: 2,500
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 1.27 V ~ 20 V
输入电压: 3.6 V ~ 34 V
PWM 型: 电流模式
频率 - 开关: 300kHz ~ 3MHz
电流 - 输出: 2A
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: 10-TFSOP,10-MSOP(0.118",3.00mm 宽)裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 10-MSOP 裸露焊盘
LT3684
APPLICATIONS INFORMATION
Soft-Start
D4
MBRS140
The RUN/SS pin can be used to soft-start the LT3684,
reducing the maximum input current during start-up.
V IN
V IN
BOOST
LT3684
The RUN/SS pin is driven through an external RC ?lter to
RUN/SS
SW
V OUT
create a voltage ramp at this pin. Figure 7 shows the start-
up and shut-down waveforms with the soft-start circuit.
By choosing a large RC time constant, the peak start-up
current can be reduced to the current that is required to
regulate the output, with no overshoot. Choose the value
V C
GND FB
BACKUP
of the resistor so that it can supply 20μA when the RUN/SS
pin reaches 2.3V.
3684 F07
Figure 7. Diode D4 Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output. It Also
Protects the Circuit from a Reversed Input. The LT3684
Runs Only When the Input is Present
RUN
15k
I L
1A/DIV
LT3684 can pull large currents from the output through
the SW pin and the V IN pin. Figure 7 shows a circuit that
0.22 μ F
RUN/SS
GND
V RUN/SS
2V/DIV
V OUT
2V/DIV
will run only when the input voltage is present and that
protects against a shorted or reversed input.
PCB Layout
For proper operation and minimum EMI, care must be
2ms/DIV
3481 F06
taken during printed circuit board layout. Figure 8 shows
Figure 6. To Soft-Start the LT3684, Add a Resisitor
and Capacitor to the RUN/SS Pin
Shorted and Reversed Input Protection
If the inductor is chosen so that it won’t saturate exces-
sively, an LT3684 buck regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT3684 is absent. This may occur in battery charging ap-
plications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT3684’s
output. If the V IN pin is allowed to ?oat and the RUN/SS
pin is held high (either by a logic signal or because it is
tied to V IN ), then the LT3684’s internal circuitry will pull
its quiescent current through its SW pin. This is ?ne if
your system can tolerate a few mA in this state. If you
ground the RUN/SS pin, the SW pin current will drop to
essentially zero. However, if the V IN pin is grounded while
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
currents ?ow in the LT3684’s V IN and SW pins, the catch
diode (D1) and the input capacitor (C1). The loop formed
by these components should be as small as possible. These
components, along with the inductor and output capacitor,
should be placed on the same side of the circuit board,
and their connections should be made on that layer. Place
a local, unbroken ground plane below these components.
The SW and BOOST nodes should be as small as possible.
Finally, keep the FB and V C nodes small so that the ground
traces will shield them from the SW and BOOST nodes.
The Exposed Pad on the bottom of the package must be
soldered to ground so that the pad acts as a heat sink. To
keep thermal resistance low, extend the ground plane as
much as possible, and add thermal vias under and near
the LT3684 to additional ground planes within the circuit
board and on the bottom side.
the output is held high, then parasitic diodes inside the
3684f
16
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