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| 型号： | SP7655EB |
| 厂商： | Exar Corporation |
| 文件页数： | 8/16页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD FOR SP7655 |
| 标准包装： | 1 |
| 系列： | * |
APPLICATIONS INFORMATION
Output Capacitor Selection
The required ESR (Equivalent Series Resis-
tance) and capacitance drive the selection of the
type and quantity of the output capacitors. The
ESR must be small enough that both the resis-
tive voltage deviation due to a step change in the
load current and the output ripple voltage do not
exceed the tolerance limits expected on the
output voltage. During an output load transient,
the output capacitor must supply all the addi-
tional current demanded by the load until the
SP7655 adjusts the inductor current to the new
value.
In order to maintain V OUT ,the capacitance must
be large enough so that the output voltage is held
up while the inductor current ramps to the value
corresponding to the new load current. Addi-
tionally, the ESR in the output capacitor causes
a step in the output voltage equal to the current.
Because of the fast transient response and inher-
ent 0% to100% duty cycle capability provided
by the SP7655 when exposed to an output load
transient, the output capacitor is typically cho-
sen for ESR, not for capacitance value.
The ESR of the output capacitor, combined with
the inductor ripple current, is typically the main
contributor to output voltage ripple. The maxi-
mum allowable ESR required to maintain a
specified output voltage ripple can be calculated
by:
F S = Switching Frequency
D = Duty Cycle
C OUT = Output Capacitance Value
Input Capacitor Selection
The input capacitor should be selected for ripple
current rating, capacitance and voltage rating.
The input capacitor must meet the ripple current
requirement imposed by the switching current.
In continuous conduction mode, the source cur-
rent of the high-side MOSFET is approximately
a square wave of duty cycle V OUT /V IN . More
accurately the current wave form is trapezoidal,
given a finite turn-on and turn-off, switch tran-
sition slope. Most of this current is supplied by
the input bypass capacitors. The RMS current
handling capability of the input capacitors is
determined at maximum output current and
under the assumption that the peak-to-peak in-
ductor ripple current is low, it is given by:
I CIN(RMS) = I OUT(max) D(1 - D)
The worst case occurs when the duty cycle D is
50% and gives an RMS current value equal to
I OUT /2.
Select input capacitors with adequate ripple
current rating to ensure reliable operation.
The power dissipated in the input capacitor is:
P CIN = I CIN ( rms ) R ESR ( CIN )
R ESR
V OUT
I PK-PK
2
where:
V OUT = Peak-to-Peak Output Voltage Ripple
I PK-PK = Peak-to-Peak Inductor Ripple Current
The total output ripple is a combination of the
ESR and the output capacitance value and can
be calculated as follows:
This can become a significant part of power
losses in a converter and hurt the overall energy
transfer efficiency. The input voltage ripple
primarily depends on the input capacitor ESR
and capacitance. Ignoring the inductor ripple
current, the input voltage ripple can be deter-
mined by:
(
F S IN IN
C V
V OUT = I PP (1 – D)
C OUT F S
)
2
+
(I PP R ESR ) 2
V IN = I out (max) R E SR ( CIN ) +
I OUT ( MAX ) V OUT ( V I N V OUT )
2
Rev E: 3/2 /07
SP7655 Wide Input Voltage Range 8A, 300kHz, Buck Regulator
8
? 2007 Sipex Corporation
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SP7655ER | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Evaluation Board Manual |
| SP7655ER/TR | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Wide Input Voltage Range, 8Amp 300kHz, Buck Regulator |
| SP7655ERL | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Wide Input Voltage Range, 8Amp 300kHz, Buck Regulator |
| SP7655ER-L | 功能描述:线性稳压器 - 标准 Buck Regulator RoHS:否 制造商:STMicroelectronics 输出类型: 极性: 输出电压:1.8 V 输出电流:150 mA 负载调节: 最大输入电压:5.5 V 线路调整率: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOT-323-5L |
| SP7655ERL/TR | 制造商:SIPEX 制造商全称:Sipex Corporation 功能描述:Wide Input Voltage Range, 8Amp 300kHz, Buck Regulator |
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