参数资料
型号: LT3509IDE#PBF
厂商: Linear Technology
文件页数: 9/24页
文件大小: 0K
描述: IC REG BUCK ADJ 0.7A DL 14DFN
标准包装: 91
类型: 降压(降压)
输出类型: 可调式
输出数: 2
输出电压: 0.8 V ~ 35.3 V
输入电压: 3.6 V ~ 36 V
PWM 型: 电流模式
频率 - 开关: 260kHz ~ 2.15MHz
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: 14-WFDFN 裸露焊盘
包装: 管件
供应商设备封装: 14-DFN-EP(4x3)
LT3509
APPLICATIONS INFORMATION
Shutdown and Soft Start
When the RUN/SS pins are pulled to ground, the part will
shut down to its lowest current state of approximately
9μA. If driving a large capacitive load it may be desirable
Setting The Output Voltage
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistors
according to:
to use the current limiting soft-start feature. Connecting
capacitors to ground from the RUN/SS pins will control
the delay until full current is available. The pull-up current
R1 = R2 ?
V OUT
0.8
–1
is 1μA and the full current threshold is 2V so the start-up
time is given by:
T = 2 ? C ? 10 6 s
For example a 0.005μF capacitor will give a time to full
current of 10ms. If both outputs can come up together
then the two inputs can be paralleled and tied to one ca-
pacitor. In this case use twice the capacitor value to obtain
The designators correspond to Figure 1. R2 should be 20k
or less to avoid bias current errors.
Frequency Setting
The timing resistor, R T , for any desired frequency in the
range 264kHz to 2.2MHz can be calculated from the
following formula:
the same start-up time. During the soft-start time both
the peak current threshold and the DA current threshold
will track so the part will skip pulses as required to limit
R T =
1.215
f SW
– 0.215 ? 40.2
the maximum inductor current. Starting up into a large
capacitor is not much different to starting into a short-
circuit in this respect.
where f SW is in MHz and R T is in kΩ.
Table 1. Standard E96 Resistors for Common Frequencies
FREQUENCY
TIMING RESISTOR R T (kΩ)
V SW
10V/DIV
I L
0.2A/DIV
V OUT
5V/DIV
264 kHz
300 kHz
400kHz
500kHz
1MHz
2MHz
2.2MHz
178
154
113
88.7
40.2
15.8
13.7
TIME 1ms/DIV
3509 F02
Note: The device is speci?ed for operation down to 300kHz. The 264kHz
value is to allow external synchronization at 300kHz
Figure 2. Soft-Start
3509fc
9
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