參數(shù)資料
型號： MAX1777
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
文件頁數(shù)： 29/32頁
文件大?。?/td> 497K
代理商： MAX1777
M
High-Effic ienc y, Quad Output, Main Power-
S upply Controllers for Notebook Computers
______________________________________________________________________________________
29
Use of Coupled Induc tors to Create
Auxiliary Outputs
A coupled inductor or transformer can be substituted for
the inductor in the 5V or 3.3V SMPS to create an auxiliary
output (Figure 12). The MAX1777/MAX1977/MAX1999 are
particularly well suited for such applications because they
can be configured in ultrasonic or forced-PWM mode to
ensure good load regulation when the main supplies are
lightly loaded. An additional postregulation circuit can be
used to improve load regulation and limit output current.
The power requirements of the auxiliary supply must be
considered in the design of the main output. The trans-
former must be designed to deliver the required current
in both the primary and the secondary outputs with the
proper turns ratio and inductance. The power ratings of
the synchronous rectifier MOSFETs and the current limit
in the MAX1777/MAX1977/MAX1999 must also be
adjusted accordingly. Extremes of low input-output dif-
ferentials, widely different output loading levels, and high
turns ratios can further complicate the design due to par-
asitic transformer parameters such as interwinding
capacitance, secondary resistance, and leakage induc-
tance. Power from the main and secondary outputs is
combined to get an equivalent current referred to the
main output. Use this total current to determine the cur-
rent limit (see the
Determining the Current Limit
section):
where I
TOTAL
is the equivalent output current referred
to the main output, and P
TOTAL
is the sum of the output
power from both the main output and the secondary
output:
where L
PRIMARY
is the primary inductance, N is the
transformer turns ratio, V
SEC
is the minimum required
rectified secondary voltage, V
FWD
is the forward drop
across the secondary rectifier, V
OUT(MIN)
is the minimum
value of the main output voltage, and V
RECT
is the on-
state voltage drop across the synchronous rectifier
MOSFET. The transformer secondary return is often con-
nected to the main output voltage instead of ground in
order to reduce the necessary turns ratio. In this case,
subtract V
OUT
from the secondary voltage (V
SEC
–
V
OUT
) in the transformer turns ratio equation above.
The secondary diode in coupled-inductor applications
must withstand flyback voltages greater than 60V, which
usually rules out most Schottky rectifiers. Common sili-
con rectifiers, such as the 1N4001, are also prohibited
because they are too slow. This often makes fast silicon
rectifiers such as the MURS120 the only choice. The fly-
back voltage across the rectifier is related to the V
IN
-
V
OUT
difference, according to the transformer turns ratio:
V
FLYBACK
= V
SEC
+ (V
IN
- V
OUT
)
N
where N is the transformer turns ratio (secondary wind-
ings/primary windings), V
SEC
is the maximum secondary
DC output voltage, and V
OUT
is the primary (main) out-
put voltage. If the secondary winding is returned to V
OUT
instead of ground, subtract V
OUT
from V
FLYBACK
in the
equation above. The diode’s reverse breakdown voltage
rating must also accommodate any ringing due to leak-
age inductance. The diode’s current rating should be at
least twice the DC load current on the secondary output.
The optional linear postregulator must be selected to
deliver the required load current from the transformer’s
rectified DC output. The linear regulator should be con-
figured to run close to dropout to minimize power dissi-
pation and should have good output accuracy under
those conditions. Input and output capacitors are cho-
sen to meet line regulation, stability, and transient
requirements. There are a wide variety of linear regula-
tors appropriate for this application; consult the specific
linear-regulator data sheet for details.
Widely different output loads effect load regulation. In
particular, when the secondary output is left unloaded
while the main output is fully loaded, the secondary out-
put capacitor may become overcharged by the leakage
inductance, reaching voltages much higher than intend-
ed. In this case, a minimum load or overvoltage protec-
tion may be required on the secondary output to protect
any device connected to this output.
PC Board Layout Guidelines
Careful PC board layout is critical to achieve minimal
switching losses and clean, stable operation. This is
especially true when multiple converters are on the
same PC board where one circuit can affect the other.
The switching power stages require particular attention
(Figure 13). Refer to the MAX1999 EV kit data sheet for
a specific layout example.
Mount all of the power components on the top side of
the board with their ground terminals flush against one
another, if possible. Follow these guidelines for good
PC board layout:
Isolate the power components on the top side from
the sensitive analog components on the bottom side
with a ground shield. Use a separate PGND plane
under the OUT3 and OUT5 sides (called PGND3 and
L
V
V
V
V
I
LIR
N
V
V
+
V
V
PRIMARY
OUT
IN MAX
× ×
+
OUT
×
IN MAX
(
TOTAL
SEC
FWD
OUT MIN
(
RECT
=
=
(
(
)
)
)
I
P
V
TOTAL
TOTAL
OUT
=
/
相關(guān)PDF資料
PDF描述
MAX1777-MAX1999 High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
MAX1977 High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
MAX1999 High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
MAX1977EEI High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
MAX1999EEI High-Efficiency, Quad Output, Main Power- Supply Controllers for Notebook Computers
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX1777EEI 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
MAX1777EEI+ 功能描述:DC/DC 開關(guān)控制器 Quad-Out Main Power Sply Ctlr for Ntbk 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
MAX1777EEI+T 功能描述:DC/DC 開關(guān)控制器 Quad-Out Main Power Sply Ctlr for Ntbk 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
MAX1777EEI-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
MAX1778EUG 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
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