参数资料
型号: LTC3633EUFD#TRPBF
厂商: Linear Technology
文件页数: 14/28页
文件大小: 0K
描述: IC REG BUCK ADJ 3A DL 28QFN
标准包装: 2,500
类型: 降压(降压)
输出类型: 可调式
输出数: 2
输出电压: 0.6 V ~ 14.7 V
输入电压: 3.6 V ~ 15 V
PWM 型: 电流模式,混合
频率 - 开关: 500kHz ~ 4MHz
电流 - 输出: 3A
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: 28-WFQFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 28-QFN(4x5)
LTC3633
APPLICATIONS INFORMATION
C OUT ≈
must instantaneously supply the current to support the load
until the feedback loop raises the switch current enough
to support the load. The time required for the feedback
loop to respond is dependent on the compensation and the
output capacitor size. Typically, 3 to 4 cycles are required
to respond to a load step, but only in the first cycle does
the output drop linearly. The output droop, V DROOP , is
usually about 3 times the linear drop of the first cycle.
Thus, a good place to start is with the output capacitor
size of approximately:
3 ? ?I OUT
f ? V DROOP
Though this equation provides a good approximation, more
capacitance may be required depending on the duty cycle
and load step requirements. The actual V DROOP should be
verified by applying a load step to the output.
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are available
in small case sizes. Their high ripple current, high voltage
rating and low ESR make them ideal for switching regulator
applications. However, due to the self-resonant and high-
Q characteristics of some types of ceramic capacitors,
care must be taken when these capacitors are used at
the input. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
V IN input. At best, this ringing can couple to the output and
be mistaken as loop instability. At worst, a sudden inrush
of current through the long wires can potentially cause a
voltage spike at V IN large enough to damage the part. For
a more detailed discussion, refer to Application Note 88.
When choosing the input and output ceramic capacitors,
choose the X5R and X7R dielectric formulations. These
dielectrics have the best temperature and voltage char-
acteristics of all the ceramics for a given value and size.
INTV CC Regulator Bypass Capacitor
An internal low dropout (LDO) regulator produces the
3.3V supply that powers the internal bias circuitry and
drives the gate of the internal MOSFET switches. The
INTV CC pin connects to the output of this regulator and
must have a minimum of 1μF ceramic decoupling capaci-
tance to ground. The decoupling capacitor should have
low impedance electrical connections to the INTV CC and
PGND pins to provide the transient currents required by
the LTC3633. This supply is intended only to supply ad-
ditional DC load currents as desired and not intended to
regulate large transient or AC behavior, as this may impact
LTC3633 operation.
Boost Capacitor
The LTC3633 uses a “bootstrap” circuit to create a voltage
rail above the applied input voltage V IN . Specifically, a boost
capacitor, C BOOST , is charged to a voltage approximately
equal to INTV CC each time the bottom power MOSFET is
turned on. The charge on this capacitor is then used to
supply the required transient current during the remainder
of the switching cycle. When the top MOSFET is turned on,
the BOOST pin voltage will be equal to approximately V IN
+ 3.3V. For most applications, a 0.1μF ceramic capacitor
closely connected between the BOOST and SW pins will
provide adequate performance.
Low Power 2.5V Linear Regulator
The V2P5 pin can be used as a low power 2.5V regulated
rail. This pin is the output of a 10mA linear regulator
powered from the INTV CC pin. Note that the power from
V2P5 eventually comes from V IN1 since the INTV CC power
is supplied from V IN1 . When using this output, this pin
must be bypassed with a 1μF ceramic capacitor. If this
output is not being used, it is recommended to short this
output to INTV CC to disable the regulator.
3633fc
14
For more information www.linear.com/LTC3633
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