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参数资料
| 型号： | APW7093QAI-TR |
| 厂商： | Anpec Electronics Corporation |
| 英文描述： | 3A, 1MHz, Step Down DC/DC Regulator |
| 中文描述： | 第3A，1MHz的，下步直流/直流稳压器 |
| 文件页数： | 13/20页 |
| 文件大小： | 728K |
| 代理商： | APW7093QAI-TR |
Copyright
ANPEC Electronics Corp.
Rev. A.5 - Jun., 2005
APW 7093
www.anpec.com.tw
13
Application I nformation( Cont.)
When sinking current, the switching frequency
increases due to the on-resistances of the internal
switches adding to the voltage across the inductor,
reducing the on-time. Calculate T
ON
when sinking
current using the equation:
Programming the Switching Frequency and
Off-Time and On-Time (Cont.)
+
=
PMOS
V
OUT
V
IN
NMOS
V
OUT
V
OFF
T
ON
V
T
Inductor Selection
The key inductor parameters must be specified: inductor
value (L) and peak current (I
PEAK
). A lower value of
inductor allows smaller size but results in higher losses
and ripple. A good compromise between size and
losses is found at approximately a 25% ripple current
to load current ratio (
I/
I
OUT
= 0.25).
0.25
I
T
V
L
OUT
OFF
OUT
×
×
=
The peak inductor current at full load is calculated by:
L
2
T
V
I
I
OFF
OUT
OUT
PEAK
×
×
+
=
where I
OUT
is the maximum source or sink current.
Choose an inductor with a saturation current at least
as high as the peak inductor current. Additionally, verify
the peak inductor current while sourcing output
current (I
OUT
= I
SOURCE
) does not exceed the positive
current limit. The inductor selected should exhibit low
losses at the chosen operating frequency.
Input Capacitor Selection
The input filter capacitor reduces peak currents and
noise at the voltage source.
A 22μF to 47μF capacitor
may be required for higher power and dynamic loads.
L
ow-ESR and low-ESL
Tantalum or ceramic capacitor
should be suitable.
Output Capacitor Selection
The output filter capacitor affects the output voltage
ripple, output load-transient response, and feedback
loop stability. The output filter capacitor must have low
enough ESR to meet output ripple and load transient
requirements, yet have high enough ESR to satisfy
stability requirements. Also, the capacitance value must
be high enough to guarantee stability and absorb the
inductor energy going from a full-load sourcing to full
load sinking condition without exceeding the maximum
output tolerance.
In applications where the output is subject to large
load transients, the output capacitor’s size typically
depends on how much ESR is needed to prevent the
output from dipping too low under a load transient.
OUT(MAX)
OUT
V
ESR
I
/
R
≤
The actual microfarad capacitance value required is
defined by the physical size needed to achieve low
ESR, and by the chemistry of the capacitor technology.
Thus, the capacitor is usually selected by ESR, size
and voltage rating rather than by capacitance value.
When using low-capacity filter capacitors such as
ceramic or polymer types, capacitor size is usually
determined by the capacity needed to prevent overshoot
and undershoot
from causing problems during load
transients. Generally, once enough capacitance is
added to meet the overshoot requirement, undershoot
at the rising-load edge is no longer a problem.
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相关代理商/技术参数 |
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|---|---|
| APW7093QAI-TRL | 制造商:ANPEC 制造商全称:Anpec Electronics Coropration 功能描述:3A, 1MHz, Step Down DC/DC Regulator |
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