参数资料
型号: LT3689IUD-5#TRPBF
厂商: Linear Technology
文件页数: 20/34页
文件大小: 0K
描述: IC REG BUCK 5V 0.7A 16QFN
标准包装: 2,500
类型: 降压(降压)
输出类型: 固定
输出数: 1
输出电压: 5V
输入电压: 3.6 V ~ 36 V
PWM 型: 电流模式,Burst Mode?
频率 - 开关: 500kHz ~ 2MHz
电流 - 输出: 700mA
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: 16-WFQFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 16-QFN-EP(3x3)
LT3689/LT3689-5
APPLICATIONS INFORMATION
BST and OUT Pin Considerations
Capacitor C3 and the internal boost Schottky diode (see
the Block Diagram) are used to generate a boost voltage
that is higher than the input voltage. In most cases, a 0.1μF
capacitor will work well. Figure 6 shows three ways to ar-
range the boost circuit. The BST pin must be more than
2.3V above the SW pin for best efficiency. For outputs of
3V and above, the standard circuit (Figure 6a) is best. For
outputs between 2.8V and 3V, use a 0.47μF boost capaci-
tor. A 2.5V output presents a special case because it is
marginally adequate to support the boosted drive stage
while using the internal boost diode. For reliable BST pin
operation with 2.5V outputs, use a good external Schottky
diode (such as ON Semiconductor’s MBR0540), and a
0.47μF boost capacitor (see Figure 6b). For lower output
voltages, the boost diode can be tied to the input (Figure 6c),
or to another supply greater than 2.8V. The circuit in
Figure 6a is more efficient because the BST pin current
and OUT pin quiescent current comes from a lower
V OUT
voltage source. Ensure that the maximum voltage ratings
of the BST and OUT pins are not exceeded.
The minimum operating voltage of an LT3689 application
is limited by the minimum input voltage (3.7V) and by the
maximum duty cycle, as outlined in the Minimum Operating
Voltage Range section. For proper start-up, the minimum
input voltage is also limited by the boost circuit. If the input
voltage is ramped slowly, or the LT3689 is turned on with
its EN/UVLO pin when the output is already in regulation,
then the boost capacitor may not be fully charged. Because
the boost capacitor is charged with the energy stored in
the inductor, the circuit will rely on some minimum load
current to get the boost circuit running properly. This
minimum load will depend on input and output voltages,
and on the arrangement of the boost circuit. The minimum
load generally goes to zero once the circuit has started.
For lower start-up voltage, the boost diode can be tied to
V IN ; however, this restricts the input range to one-half of
the absolute maximum rating of the BST pin.
V OUT
OUT
BST
OUT
BST
D2
V IN
2.2μF
V IN
LT3689
GND
SW
C3
V IN
2.2μF
V IN
LT3689
GND
SW
C3
(6a) For V OUT > 2.8V
OUT
BST
(6b) For 2.5V < V OUT < 2.8V
V OUT
V IN
2.2μF
V IN
LT3689
GND
SW
C3
3689 F06
(6c) For V OUT < 2.5V; V IN(MAX) = 30V
Figure 6. Three Circuits for Generating the Boost Voltage
3689fe
20
For more information www.linear.com/LT3689
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