参数资料
型号: LTC3642EDD-3.3#TRPBF
厂商: Linear Technology
文件页数: 13/22页
文件大小: 0K
描述: IC REG BUCK SYNC 3.3V 50MA 8DFN
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: 3.3V
输入电压: 4.5 V ~ 45 V
PWM 型: Burst Mode?
电流 - 输出: 50mA
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: 8-WFDFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 8-DFN-EP(3x3)
LTC3642
APPLICATIONS INFORMATION
Output Voltage Programming
For the adjustable version, the output voltage is set by
an external resistive divider according to the following
equation:
controller is enabled. Figure 7 shows examples of con-
figurations for driving the RUN pin from logic.
V SUPPLY V IN
V OUT = 0.8V ? ? 1 +
R2 ?
?
?
R1 ?
?
LTC3642
RUN
4.7M
LTC3642
RUN
The resistive divider allows the V FB pin to sense a fraction
of the output voltage as shown in Figure 6. Output voltage
adjustment range is from 0.8V to V IN .
Figure 7. RUN Pin Interface to Logic
3642 F07
R3
? I VIN = ? OUT ? ? ? OUT ?
Rising ? V IN ? UVLO ? Threshold = 1.21V ? ? 1 +
R2 ?
Falling ? V IN ? UVLO ? Threshold = 1.10V ? ? 1 +
R2 + R3 ?
V OUT
R1
V FB
LTC3642 R2
GND
Figure 6. Setting the Output Voltage
To minimize the no-load supply current, resistor values in
the megohm range should be used; however, large resistor
values should be used with caution. The feedback divider
is the only load current when in shutdown. If PCB leak-
age current to the output node or switch node exceeds
the load current, the output voltage will be pulled up. In
normal operation, this is generally a minor concern since
the load current is much greater than the leakage. The
increase in supply current due to the feedback resistors
can be calculated from:
? V ? ? V ?
? R1 + R2 ? ? V IN ?
Run Pin with Programmable Hysteresis
The LTC3642 has a low power shutdown mode controlled
by the RUN pin. Pulling the RUN pin below 0.7V puts the
LTC3642 into a low quiescent current shutdown mode
(I Q ~ 3μA). When the RUN pin is greater than 1.2V, the
The RUN pin can alternatively be configured as a precise
undervoltage lockout (UVLO) on the V IN supply with a
resistive divider from V IN to ground. The RUN pin com-
parator nominally provides 10% hysteresis when used in
this method; however, additional hysteresis may be added
with the use of the HYST pin. The HYST pin is an open-
drain output that is pulled to ground whenever the RUN
comparator is not tripped. A simple resistive divider can
be used as shown in Figure 8 to meet specific V IN voltage
requirements.
V IN
R1
RUN
R2 LTC3642
HYST
3642 F08
Figure 8. Adjustable Undervoltage Lockout
Specific values for these UVLO thresholds can be computed
from the following equations:
? R1 ?
?
?
? R1 ?
?
?
3642fc
13
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