参数资料
型号: LTC3836EUFD#TRPBF
厂商: Linear Technology
文件页数: 17/30页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 28-QFN
标准包装: 2,500
系列: PolyPhase®
PWM 型: 电流模式
输出数: 2
频率 - 最大: 825kHz
占空比: 97%
电源电压: 2.75 V ~ 4.5 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: 28-WFQFN 裸露焊盘
包装: 带卷 (TR)
LTC3836
APPLICATIONS INFORMATION
A small (0.1μF to 1μF) bypass capacitor between the chip
V IN pin and ground, placed close to the LTC3836, is also
suggested. A 10 Ω resistor placed between C IN (C1) and
the V IN pin provides further isolation between the two
channels.
The selection of C OUT is driven by the effective series
resistance (ESR). Typically, once the ESR requirement
is satis?ed, the capacitance is adequate for ?ltering. The
output ripple ( ? V OUT ) is approximated by:
To improve the frequency response, a feedforward ca-
pacitor, C FF , may be used. Great care should be taken to
route the V FB line away from noise sources, such as the
inductor or the SW line.
Run/Soft-Start Function
The RUN/SS pin is a dual purpose pin that provides the
optional external soft-start function and a means to shut
down the LTC3836.
V OUT I RIPPLE ESR +
1
8fC OUT
Pulling the RUN/SS pin below 0.65V puts the LTC3836 into
a low quiescent current shutdown mode (I Q = 6.5μA). If
RUN/SS has been pulled all the way to ground, there will
where f is the operating frequency, C OUT is the output
capacitance and I RIPPLE is the ripple current in the induc-
be a delay before the LTC3836 comes out of shutdown
and is given by:
tor. The output ripple is highest at maximum input voltage
since I RIPPLE increases with input voltage.
t DELAY = 0.65V ?
C SS
0.65 μ A
= 1s/ μ F ? C SS
Setting Output Voltage
The LTC3836 output voltages are each set by an external
feedback resistor divider carefully placed across the out-
put, as shown in Figure 5. The regulated output voltage
is determined by:
This pin can be driven directly from logic as shown in
Figure 6. Diode D SS in Figure 6 reduces the start delay
but allows C SS to ramp up slowly providing the soft-start
function. This diode (and capacitor) can be deleted if the
external soft-start is not needed.
V OUT = 0.6V ? 1 + B
R
R A
V OUT
3.3V OR 5V
D SS
RUN/SS
C SS
RUN/SS
C SS
1/2 LTC3836
V FB
R B
R A
C FF
V DD ≤ V IN
RUN/SS
(INTERNAL SOFT-START)
3836 F05
3836 F06
Figure 5. Setting Output Voltage
Figure 6. RUN/SS Pin Interfacing
3836fb
17
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