參數(shù)資料
型號(hào)： PM6641TR
廠商： STMICROELECTRONICS
元件分類： 穩(wěn)壓器
英文描述： SWITCHING REGULATOR, 1100 kHz SWITCHING FREQ-MAX, QCC48
封裝： 7 X 7 MM, 1 MM HEIGHT, LEAD FREE, VQFP-48
文件頁(yè)數(shù)： 29/47頁(yè)
文件大小： 2254K
代理商： PM6641TR
PM6641
Components selection
Doc ID 13510 Rev 3
35/47
8
Components selection
The PM6641 switching regulator sections are buck converters employing a constant
frequency, current mode PWM current loop (see Chapter 7.3: SW regulators control loop on
section for details).
The duty-cycle of the buck converter is, in steady-state conditions, given by
Equation 11
The switching frequency directly affects two parameters:
●
Inductor size: greater frequencies mean smaller inductances. In notebook applications,
real estate solutions (i.e. low-profile power inductors) are mandatory also with high
saturation and root mean square (RMS) currents.
●
Efficiency: switching losses are proportional to the frequency. Generally, higher
frequencies imply lower efficiency.
8.1
Inductor selection
Once the switching frequency has been defined, the inductance value depends on the
desired inductor current ripple. Low inductance value means great ripple current that brings
to poor efficiency and great output noise. On the other hand a great current ripple is
desirable for fast transient response when a load step is applied.
Otherwise, great inductance brings to good efficiency but the load transient response is
critical, especially if VINmin - VOUT is little. The product of the output capacitor’s ESR
multiplied by the inductor ripple current must be taken in consideration; the PM6641
switching regulators current loop doesn’t need a minimum output ripple in order to work
properly, so a ceramic output capacitor can be considered a good choice.
A good trade-off between the transient response time, the efficiency, the cost and the size is
choosing the inductance value in order to maintain the inductor ripple current between 20%
and 50% (usually 30%) of the maximum output current.
The maximum inductor current ripple,
ΔI
L,MAX, occurs at the maximum input voltage.
With these considerations, the inductance value can be calculated with the following
expression:
Equation 12
where fSW is the switching frequency, VIN is the input voltage, VOUT is the output voltage and
ΔI
L is the inductor current ripple.
IN
OUT
V
D
=
IN
OUT
L
OUT
IN
V
I
fsw
V
L
Δ
=
相關(guān)PDF資料
PDF描述
PM6641 SWITCHING REGULATOR, 1100 kHz SWITCHING FREQ-MAX, QCC48
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