参数资料
型号: LTC3809IDD-1#TRPBF
厂商: Linear Technology
文件页数: 16/24页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 10-DFN
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 600kHz
占空比: 100%
电源电压: 2.75 V ~ 9.8 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 10-WFDFN 裸露焊盘
包装: 带卷 (TR)
LTC3809-1
APPLICATIONS INFORMATION
For most applications, a 59k resistor is suggested for R A .
In applications where minimizing the quiescent current is
critical, R A should be made bigger to limit the feedback
divider current. If R B then results in very high impedance,
it may be bene?cial to bypass R B with a 50pF to 100pF
capacitor C FF .
V OUT
Once the controller is enabled, the start-up of V OUT is con-
trolled by the state of the TRACK/SS pin. If the TRACK/SS
pin is connected to V IN , the start-up of V OUT is controlled
by internal soft-start, which slowly ramps the positive
reference to the error ampli?er from 0V to 0.6V, allowing
V OUT to rise smoothly from 0V to its ?nal value. The default
internal soft-start time is around 0.74ms. The soft-start
time can be changed by placing a capacitor between the
LTC3809-1
R B
C FF
TRACK/SS pin and GND. In this case, the soft-start time
will be approximately:
V FB
R A
38091 F03
t SS = C SS ?
600mV
1 μ A
Figure 3. Setting Output Voltage
Run and Soft-Start/Tracking Functions
The LTC3809-1 has a low power shutdown mode which is
controlled by the RUN pin. Pulling the RUN pin below 1.1V
puts the LTC3809-1 into a low quiescent current shutdown
mode (I Q = 9μA). Releasing the RUN pin, an internal 0.7μA
where 1μA is an internal current source which is always on.
When the voltage on the TRACK/SS pin is less than the
internal 0.6V reference, the LTC3809-1 regulates the V FB
voltage to the TRACK/SS pin voltage instead of 0.6V.
Therefore the start-up of V OUT can ratiometrically track
an external voltage V X , according to a ratio set by a resis-
tor divider at TRACK/SS pin (Figure 5a). The ratiometric
relation between V OUT and V X is (Figure 5c):
= TA ?
(at V IN = 4.2V) current source will pull the RUN pin up
to V IN , which enables the controller. The RUN pin can be
driven directly from logic as showed in Figure 4.
V OUT
V X
R
R A
R A + R B
R TA + R TB
V OUT
3.3V OR 5V
V X
LTC3809-1
RUN
LTC3809-1
RUN
R TB
LTC3809-1
V FB
TRACK/SS
R B
R A
38091 F04
R TA
38091 F5a
Figure 4. RUN Pin Interfacing
Figure 5a. Using the TRACK/SS Pin to Track V X
38091fc
16
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