參數(shù)資料
型號(hào)： MAX1977
廠商： Maxim Integrated Products, Inc.
英文描述： High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
中文描述： 高效率、四路輸出、主電源控制器，用于筆記本電腦
文件頁(yè)數(shù)： 28/32頁(yè)
文件大?。?/td> 497K
代理商： MAX1977
M
High-Effic ienc y, Quad Output, Main Power-
S upply Controllers for Notebook Computers
28
______________________________________________________________________________________
an MBR0530 (500mA-rated) type for loads up to 1.5A, a
1N5819 type for loads up to 3A, or a 1N5822 type for
loads up to 10A. The rectifier’s rated reverse breakdown
voltage must be at least equal to the maximum input volt-
age, preferably with a 20% derating factor.
Boost S upply Diode
A signal diode, such as a 1N4148, works well in most
applications. Use a small (20mA) Schottky diode for
slightly improved efficiency and dropout characteris-
tics, if the input voltage can go below 6V. Do not use
large power diodes, such as 1N5817 or 1N4001, since
high-junction capacitance can force LDO5 to excessive
voltages.
Applic ations Information
Dropout Performanc e
The output voltage-adjust range for continuous-conduc-
tion operation is restricted by the nonadjustable 350ns
(max) minimum off-time one-shot. Use the slower 5V
SMPS for the higher of the two output voltages for best
dropout performance in adjustable feedback mode. The
duty-factor limit must be calculated using worst-case val-
ues for on- and off-times, when working with low input
voltages. Manufacturing tolerances and internal propaga-
tion delays introduce an error to the t
ON
K factor. Also,
keep in mind that transient response performance of
buck regulators operated close to dropout is poor, and
bulk output capacitance must often be added (see the
V
SAG
equation in the
Output Capacitor Selection
section).
The absolute point of dropout occurs when the inductor
current ramps down during the minimum off-time
(
I
DOWN
) as much as it ramps up during the on-time
(
I
UP
). The ratio h =
I
UP
/
I
DOWN
indicates the ability to
slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
the inductor current is less able to increase during each
switching cycle and V
SAG
greatly increases unless
additional output capacitance is used.
A reasonable minimum value for h is 1.5, but this may
be adjusted up or down to allow tradeoffs between
V
SAG
, output capacitance, and minimum operating
voltage. For a given value of h, the minimum operating
voltage can be calculated as:
(
×
where V
DROP1
and V
DROP2
are the parasitic voltage
drops in the discharge and charge paths (see the
On-
Time One-Shot
section), t
OFF(MIN)
is from the EC table,
and K is taken from Table 2. The absolute minimum
input voltage is calculated with h = 1.
Operating frequency must be reduced or h must be
increased and output capacitance added to obtain an
acceptable V
SAG
if calculated V+
(MIN)
is greater than
the required minimum input voltage. Calculate V
SAG
to
be sure of adequate transient response if operation
near dropout is anticipated.
Dropout Design Example
MAX1977: With V
OUT5
= 5V, fsw = 400kHz, K = 2.25μs,
t
OFF(MIN)
= 350ns, V
DROP1
= V
DROP2
= 100mV, and h = 1.5,
the minimum V+ is:
(
μ
×
μ
.
2 25
Calculating with h = 1 yields:
Therefore, V+ must be greater than 6.65V. A practical
input voltage with reasonable output capacitance
would be 7.5V.
V
V
V
s
μ
s
V
V
V
MIN
+
=
+
(
)
μ ×
+
=
(
)
.
.
.
.
.
.
5
0 1
1
0 35
2 25
1
0 1
0 1
6 04
V
V
V
s
s
V
V
V
MIN
+
=
+
)
1 5
+
=
(
)
.
.
.
.
.
.
5
0 1
1
0 35
0 1
0 1
6 65
V
V
V
t
h
K
V
V
MIN
OUT
DROP
OFF MIN
(
DROP
DROP
+
=
+
)
+
(
)
_
)
1
2
1
1
MAX1777
MAX1977
MAX1999
V+
12V
POSITIVE
SECONDARY
OUTPUT
5V
MAIN
OUTPUT
DL_
DH_
T1
10
μ
H
1:2.2
T1 = TRANSPOWER TECHNOLOGIES TTI-5870
MAX1658/
MAX1659
LDO
Figure 12. Transformer-Coupled Secondary Output
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX1977EEI 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1977EEI+ 功能描述:DC/DC 開關(guān)控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1977EEI+T 功能描述:DC/DC 開關(guān)控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1977EEI-T 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
MAX1977EEI-TG068 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述:
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