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參數(shù)資料
| 型號： | MAX8554 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 4.5V to 28V Input. Synchronous PWM Buck Controllers for DDR Termination and Point-of-Load Applications |
| 中文描述： | 4.5V至28V輸入、同步PWM buck控制器，適合DDR端接和負(fù)載點應(yīng)用 |
| 文件頁數(shù)： | 19/24頁 |
| 文件大小： | 483K |
| 代理商： | MAX8554 |
M
4.5V to 28V Input, Synchronous PWM Buck Controllers
for DDR Termination and Point-of-Load Applications
______________________________________________________________________________________
19
peak inductor current at the maximum-defined load
current (I
LOAD(MAX)
):
Output-Capacitor Selection
The key selection parameters for the output capacitor
are the actual capacitance value, the ESR, the equiva-
lent series inductance (ESL), and the voltage-rating
requirements, which affect the overall stability, output
ripple voltage, and transient response.
The worst-case output ripple has three components:
variations in the charge stored in the output capacitor,
the voltage drop across the capacitor
’
s ESR, and ESL
caused by the current into and out of the capacitor.
This can be approximated by:
The output voltage ripple due to the ESR is:
The output voltage ripple due to the output capacitance is:
The output voltage ripple due to the ESL of the output
capacitor is:
V
RIPPLE (ESL)
= (V
IN
x ESL) / (L+ESL)
I
P-P
is the peak-to-peak inductor current:
After a load transient, the output voltage instantly
changes by ESR x
I
LOAD
+ ESL x di/dt and the con-
trollers respond within 100ns and try to regulate back to
the nominal output value.
Solid polymer or OSCON electrolytic capacitors are
recommended due to their low ESR and ESL at the
switching frequency. Higher output-current applications
require multiple output capacitors connected in parallel
to meet the output ripple-voltage requirements. Do not
exceed the capacitor
’
s voltage or ripple-current ratings.
Output-Capacitor Stability Consideration
Stability is determined by the value of the ESR zero rel-
ative to the switching frequency. To ensure stability, the
following condition must be met:
where f
S
is the switching frequency and:
For a typical 300kHz application, the ESR zero frequen-
cy must be well below 95kHz, preferably below 50kHz.
Do not put high-value ceramic capacitors directly
across the feedback sense point without taking precau-
tions to ensure stability. Large ceramic capacitors can
have a high-ESR zero frequency and cause erratic,
unstable operation. However, it is easy to add enough
series resistance by placing the capacitors a couple of
inches downstream from the feedback sense point,
which should be as close as possible to the inductor.
The easiest method for checking stability is to apply a
very fast zero-to-max load transient and carefully
observe the output voltage-ripple envelope for over-
shoot and ringing. It can help to simultaneously monitor
the inductor current with an AC current probe. Do not
allow more than one cycle of ringing after the initial
step-response under- or overshoot.
Input-Capacitor Selection
The input capacitor (C
IN
) reduces the current peaks
drawn from the input supply and reduces noise injec-
tion. The source impedance to the input supply largely
determines the value of C
IN
. High source impedance
requires high input capacitance. The input capacitor
must meet the ripple current requirement (I
RMS
)
imposed by the switching currents. The RMS input rip-
ple current is given by:
I
RMS
has a maximum value of 1/2 I
LOAD
, which occurs
when V
IN
is twice V
OUT
.
For optimal circuit reliability, choose a capacitor that
has less than 10
°
C temperature rise at the peak ripple
current.
I
I
V
V
V
V
RMS
LOAD
OUT
IN
OUT
IN
=
×
×
(
)
-
f
R
C
ESR
ESR
OUT
=
×
×
1
2
π
f
f
ESR
S
π
<
I
V
V
V
P P
-
IN
OUT
L
OUT
IN
S
f
- V
×
=
×
V
I
C
f
RIPPLE( )
P P
OUT
S
=
×
×
-
8
V
I
ESR
RIPPLE ESR
P P
-
(
)
×
=
V
V
V
V
RIPPLE
RIPPLE ESR
RIPPL( )
RIPPLE ESL
+
(
)
(
)
=
+
I
I
LIR
2
I
PEAK
LOAD MAX
LOAD MAX
(
)
(
)
=
+
×
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX8554EEE | 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8554EEE+ | 功能描述:電流型 PWM 控制器 4.5-28V Input Synch Buck Controller RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8554EEE+T | 功能描述:電流型 PWM 控制器 4.5-28V Input Synch Buck Controller RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8554EEE-T | 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| MAX8554EVKIT | 功能描述:電流型 PWM 控制器 Evaluation Kit for the MAX8553 MAX8554 RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
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