参数资料
型号: LTC3830ES#PBF
厂商: Linear Technology
文件页数: 16/24页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 16-SOIC
标准包装: 50
PWM 型: 电压模式
输出数: 1
频率 - 最大: 250kHz
占空比: 95%
电源电压: 3 V ~ 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: 16-SOIC(0.154",3.90mm 宽)
包装: 管件
产品目录页面: 1336 (CN2011-ZH PDF)
LTC3830/LTC3830-1
APPLICATIO S I FOR ATIO
[ ]
The output capacitor in a buck converter under steady-
state conditions sees much less ripple current than the
input capacitor. Peak-to-peak current is equal to inductor
ripple current, usually 10% to 40% of the total load
current. Output capacitor duty places a premium not on
power dissipation but on ESR. During an output load
transient,  the  output  capacitor  must  supply  all  of  the
additional load current demanded by the load until the
LTC3830 adjusts the inductor current to the new value.
ESR in the output capacitor results in a step in the output
voltage equal to the ESR value multiplied by the change in
load current. An 5A load step with a 0.05 ? ESR output
capacitor results in a 250mV output voltage shift; this is
7.6% of the output voltage for a 3.3V supply! Because of
the strong relationship between output capacitor ESR and
output load transient response, choose the output capaci-
tor for ESR, not for capacitance value. A capacitor with
suitable ESR will usually have a larger capacitance value
than is needed to control steady-state output ripple.
Electrolytic capacitors rated for use in switching power
supplies with specified ripple current ratings and ESR can
be used effectively in LTC3830 applications. OS-CON
electrolytic capacitors from Sanyo and other manufactur-
ers give excellent performance and have a very high
performance/size ratio for electrolytic capacitors. Surface
mount applications can use either electrolytic or dry
tantalum capacitors. Tantalum capacitors must be surge
tested and specified for use in switching power supplies.
Low cost, generic tantalums are known to have very short
a maximum rated ESR of 0.04 ? ; three in parallel lower
the net output capacitor ESR to 0.013 ? .
Feedback Loop Compensation
The LTC3830 voltage feedback loop is compensated at the
COMP pin, which is the output node of the error amplifier.
The feedback loop is generally compensated with an RC +
C network from COMP to GND as shown in Figure 10a.
Loop stability is affected by the values of the inductor, the
output capacitor, the output capacitor ESR, the error
amplifier transconductance and the error amplifier com-
pensation network. The inductor and the output capacitor
create a double pole at the frequency:
f LC = 1 / 2 π ( L O )( C OUT )
The ESR of the output capacitor and the output capacitor
value form a zero at the frequency:
f ESR = 1 / [ 2 π ( ESR )( C OUT ) ]
The compensation network used with the error amplifier
must provide enough phase margin at the 0dB crossover
frequency for the overall open-loop transfer function. The
zero and pole from the compensation network are:
f Z = 1/[2 π (R C )(C C )] and
f P = 1/[2 π (R C )(C1)] respectively
lives followed by explosive deaths in switching power
supply applications. Other capacitors that can be used
include the Sanyo POSCAP and MV-WX series.
A common way to lower ESR and raise ripple current
capability is to parallel several capacitors. A typical
COMP
10
LTC3830
ERR
7 SENSE +
R2
R1
V FB
6
C2
LTC3830 application might exhibit 5A input ripple cur-
rent. Sanyo OS-CON capacitors, part number 10SA220M
(220 μ F/10V), feature 2.3A allowable ripple current at
R C
C C
C1
V REF
SENSE –
5
3830 F10a
85 ° C; three in parallel at the input (to withstand the input
ripple current) meet the above requirements. Similarly,
Sanyo POSCAP 4TPB470M (470 μ F/4V) capacitors have
Figure 10a. Compensation Pin Hook-Up
3830fa
16
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