参数资料
型号: LTC3890MPUH#PBF
厂商: Linear Technology
文件页数: 20/40页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 32-QFN
标准包装: 73
系列: PolyPhase®
PWM 型: 电流模式
输出数: 2
频率 - 最大: 850kHz
占空比: 99%
电源电压: 4 V ~ 60 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -55°C ~ 150°C
封装/外壳: 32-WFQFN 裸露焊盘
包装: 管件
LTC3890
APPLICATIONS INFORMATION
Tracking and Soft-Start (TRACK/SS Pins)
The start-up of each V OUT is controlled by the voltage on
the respective TRACK/SS pin. When the voltage on the
TRACK/SS pin is less than the internal 0.8V reference,
the LTC3890 regulates the V FB pin voltage to the voltage
on the TRACK/SS pin instead of 0.8V. The TRACK/SS pin
can be used to program an external soft-start function
or to allow V OUT to track another supply during start-up.
V X(MASTER)
V OUT(SLAVE)
Soft-start is enabled by simply connecting a capacitor
from the TRACK/SS pin to ground, as shown in Figure 6.
An internal 1μA current source charges the capacitor,
providing a linear ramping voltage at the TRACK/SS pin.
The LTC3890 will regulate the V FB pin (and hence V OUT )
according to the voltage on the TRACK/SS pin, allowing
V OUT to rise smoothly from 0V to its final regulated value.
The total soft-start time will be approximately:
0.8V
t SS = C SS ?
1μA
3890 F07a
TIME
(7a) Coincident Tracking
V X(MASTER)
V OUT(SLAVE)
1/2 LTC3890
TIME
3890 F07b
C SS
TRACK/SS
SGND
(7b) Ratiometric Tracking
Figure 7. Two Different Modes of Output Voltage Tracking
3890 F06
Figure 6. Using the TRACK/SS Pin to Program Soft-Start
Alternatively, the TRACK/SS pin can be used to track two
(or more) supplies during start-up, as shown qualitatively
in Figures 7a and 7b. To do this, a resistor divider should
be connected from the master supply (V X ) to the TRACK/
SS pin of the slave supply (V OUT ), as shown in Figure 8.
During start-up V OUT will track V X according to the ratio
set by the resistor divider:
R TRACKB
R TRACKA
V x V OUT
R B
R A
1/2 LTC3890
V FB
TRACK/SS
3890 F08
R + R TRACKB
V X
V OUT
=
R A
R TRACKA
? TRACKA
R A + R B
Figure 8. Using the TRACK/SS Pin for Tracking
For coincident tracking (V OUT = V X during start-up):
R A = R TRACKA
R B = R TRACKB
3890fc
20
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