参数资料
型号: SP6133ER1-L/TR
厂商: Exar Corporation
文件页数: 12/20页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 16-QFN
标准包装: 3,000
PWM 型: 电压模式
输出数: 1
频率 - 最大: 345kHz
占空比: 92%
电源电压: 5 V ~ 24 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-VFQFN 裸露焊盘
包装: 带卷 (TR)
APPLICATION INFORMATION
? V OUT
I PK - PK
{ }
I PP ? (1-D)
(I PP R ESR ) 2 +
OutputCapacitorSelection
The  required  ESR  (Equivalent  Series  Re -
sistance) and capacitance drive the selec-
tion of the type and quantity of the output 
capacitors. The ESR must be small enough
that both the resistive 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 ad-
ditional current demanded by the load until
the SP6 33 adjusts the inductor current to
the new value.
Therefore, the capacitance must be large
enough so that the output voltage is held up
while the inductor current ramps up or down
to the value corresponding to the new load
current. Additionally, the ESR in the output
capacitor causes a step in the output voltage
equal to the current.  Because of the fast tran -
sient response and inherent  00% and 0%
duty cycle capability provided by the SP6 33
when exposed to output load transients, the
output capacitor is typically chosen for ESR,
not for capacitance value.
The output capacitor ’s ESR, combined with 
the inductor ripple current, is typically the
main contributor to output voltage ripple.
The  maximum  allowable  ESR  required  to 
maintain  a  specified  output  voltage  ripple 
can be calculated by:
R ESR <
  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:
? V OUT =
.
2
C OUT ? F S
where:
Fs = 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 current of the high-side
MOSFET is approximately a square wave 
of duty cycle V OUT /V IN . Most of this current
is supplied by the input bypass capacitors.
The RMS value of input capacitor current is
determined at the maximum output current
and under the assumption that the peak
to peak inductor ripple current is low, it is
given by: 
I CIN ( RMS ) = I OUT ( MAX ) ? D ? ( -D)
Schottky Diode Selection
When paralleled with the bottom MOSFET,
an optional Schottky diode can improve
efficiency  and  reduce  noise.  Without  this 
Schottky diode, the body diode of the bot-
tom MOSFET conducts the current during
the non-overlap time when both MOSFETs
are turned off. Unfortunately, the body di-
ode has high forward voltage and reverse
recovery problems. The reverse recovery of
the body diode causes additional switching
noise when the diode turns off. The Schottky
diode alleviates these sources of noise and
additionally improves efficiency thanks to its 
low forward voltage. The reverse voltage
across the diode is equal to input voltage, 
and the diode must be able to handle the
peak  current  equal  to  the  maximum  load 
current.
Oct 24-06 Rev L
SP6 33 Synchronous Buck Controller
 2
? 2006 Sipex Corporation
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