参数资料
型号: LTC3854EDDB#TRPBF
厂商: Linear Technology
文件页数: 11/28页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 12-DFN
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 440kHz
占空比: 98%
电源电压: 4.5 V ~ 38 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: 12-WFDFN 裸露焊盘
包装: 带卷 (TR)
LTC3854
APPLICATIONS INFORMATION
V IN
V IN
C IN
RUN/SS
TG
M1
C SS
C C
R C
C C2
ITH
BOOST
LTC3854
SW
C B
D BOOST
INDUCTOR
R FB1
R FB2
FB
SENSE –
INTV CC
BG
C VINT
M2
R1
L
DCR
C1
V OUT
C OUT
SENSE +
GND
R2
3854 F02
Figure 2. Buck Regulator Using DCR Current Sense
V OUT ?
V IN(MAX) ? ?
? I L ? f SW
R1 ? C1 =
(R2 not used)
R1||R2 ? C1 =
(at 20°C)
R SENSE (EQ) = DCR(MAX) ?
capacitorisequaltothevoltagedropacrosstheinductor
DCR ? R2/(R1+R2). R2 may be used to scale the voltage
across the same terminals when the DCR is greater than
the target sense resistance. Check the manufacturer’s
datasheet for specifications regarding the inductor DCR, in
order to properly dimension the external filter components.
The DCR of the inductor can also be measured using a
precision RLC meter.
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant-fre-
quency architectures by preventing subharmonic oscil-
lations at high duty cycles. It is accomplished internally
by adding a compensating ramp to the inductor current
signal. Normally, this results in a reduction of maximum
inductor peak current for high duty cycles. However, the
LTC3854 uses a novel scheme that allows the maximum
inductor peak current to remain unaffected throughout
all duty cycles.
Inductor Value Calculation
The inductor value has a direct effect on ripple current.
The inductor ripple current ? I L decreases with higher
inductance or frequency and increases with higher V IN .
1 ?
L MIN = ? V OUT ? 1 ?
?
Accepting larger values of ? I L allows the use of low value
inductors, but results in a higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is I L = 0.4 ? (I MAX ). The maximum
? I L occurs at the maximum input voltage.
Option 1: DCR within desired range
L
DCR
Option 2: DCR > desired R SENSE
L
DCR
R2
R1 + R2
3854fb
11
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