參數(shù)資料
型號(hào)： MAX8553
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(diǎn)應(yīng)用
文件頁(yè)數(shù)： 20/24頁(yè)
文件大?。?/td> 483K
代理商： MAX8553
Setting the Current Limit
Constant Current Limit
The adjustable current limit accommodates MOSFETs
with a wide range of on-resistance values. The current-
limit threshold is adjusted with an external resistor con-
nected from ILIM to GND (R
ILIM_
). The adjustment
range is 50mV to 200mV measured across the low-side
MOSFET. The value of R
ILIM
is calculated using the fol-
lowing formula:
where I
VALLEY
is the valley current limit and R
DS(ON)
is
the on-resistance of the low-side MOSFET. To avoid
reaching the current at a lower current than expected,
use the maximum value for R
DS(ON)
at elevated junc-
tion temperature. Refer to the MOSFET manufacturer
’
s
data sheet for maximum values.
Foldback Current Limit
Foldback current limit is used to reduce power dissipa-
tion during overload and short-circuit conditions. This is
accomplished by lowering the current-limit threshold as
the output voltage drops due to the overload.
To use foldback current limit, connect a resistor
(R
FOBK
) from ILIM to the output, and connect a resistor
(R
ILIM
) from ILIM to GND (
Figure
5). The values of R
ILIM
and R
FOBK
are calculated as follows:
First, select the percentage of foldback, P
FB
. This per-
cent corresponds to the current limit when V
OUT
equals
zero divided by the current limit when V
OUT
equals its
nominal voltage. Typical values range from 15% to
30%. To solve for the resistor values, use the following
equations:
If R
ILIM
results in a negative number, select another low-
side MOSFET with lower R
DS(ON)
or increase P
FB
or a
combination of both for the best compromise of cost,
efficiency, and lower short-circuit power dissipation.
Adjusting the Switching Frequency
The switching frequency of the MAX8553/MAX8554 can
be lowered from the value set by FSEL by adding a
resistor voltage-divider to EN/HSD (HSD) as shown in
Figure
6. This voltage-divider lowers the voltage the IC
measures on EN/HSD (HSD), which increases the on-
time. The switching frequency with the added resistor-
divider is calculated as follows:
where K = 1.7μs and N is given in Tables 1 and 2. To set
the frequency, select a value for R2 between 10k
and
100k
, then calculate R1 from the following equation:
With the minimum input voltage, make sure that the
voltage present at EN/HSD (HSD) is greater than 1.5V
when the resistor-divider is used:
V
R
R
R
V
IN MIN
(
1
)
+
1 5
×
>
2
2
R
K N
R
f
R
S
1
1
2
2
=
×
-
f
K
N
R
+
1
R
R
S
×
×
1
2
2
R
R
I
P
R
V
R
I
P
ILIM
DS ON
(
VALLEY
FB
FOBK
OUT
DS ON
(
VALLEY
FB
=
×
×
×
(
)
×
×
(
×
×
)
)
(
)
)
10
1
10
1
-
-
-
R
P
V
A
P
FOBK
FB
μ
OUT
-
FB
=
×
(
)
5
1
R
I
A
R
ILIM
VALLEY
5
μ
DS ON
(
=
×
×
)
10
M
4.5V to 28V Input, Synchronous PWM Buck Controllers
for DDR Termination and Point-of-Load Applications
20
______________________________________________________________________________________
MAX8553
DH
R
ILIM
R
FOBK
V
OUT
LX
DL
PGND
ILIM
Figure
5. Setting the Foldback Current Limit with Two
Resistors, RILIMand RFOBK
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX8553EEE 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(shí)間: 下降時(shí)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
MAX8553EEE+ 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(shí)間: 下降時(shí)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
MAX8553EEE+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(shí)間: 下降時(shí)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
MAX8553EEE-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(shí)間: 下降時(shí)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 RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)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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