參數(shù)資料
型號： MAX1902
廠商： Maxim Integrated Products, Inc.
英文描述： 500kHz Multi-Output, Low-Noise Power-Supply Controllers for Notebook Computers
中文描述： 500kHz、多路輸出、低噪聲、電源控制器，用于筆記本電腦
文件頁數(shù)： 23/33頁
文件大?。?/td> 649K
代理商： MAX1902
M
500kHz Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
______________________________________________________________________________________
23
P
TOTAL
= The sum of the output power from all outputs
I
TOTAL
= P
TOTAL
/ V
OUT
= The equivalent output cur-
rent referred to V
OUT
where: V
SEC
= the minimum required rectified sec
ondary output voltage
V
FWD
= the forward drop across the secondary
rectifier
V
OUT(MIN)
= the minimum value of the main out
put voltage (from the
Electrical
Characteristics
tables)
V
RECT
= the on-state voltage drop across the
synchronous rectifier MOSFET
V
SENSE
= the voltage drop across the sense
resistor
In positive-output applications, the transformer sec-
ondary return is often referred to the main output volt-
age, rather than to ground, to reduce the needed turns
ratio. In this case, the main output voltage must first be
subtracted from the secondary voltage to obtain V
SEC
.
Selecting Other Components
MOSFET Switches
The high-current N-channel MOSFETs must be logic-
level types with guaranteed on-resistance specifica-
tions at V
GS
= 4.5V. Lower gate threshold
specifications are better (i.e., 2V max rather than 3V
max). Drain-source breakdown voltage ratings must at
least equal the maximum input voltage, preferably with
a 20% derating factor. The best MOSFETs will have the
lowest on-resistance per nanocoulomb of gate charge.
Multiplying R
DS(ON)
Q
G
provides a good figure for
comparing various MOSFETs. Newer MOSFET process
technologies with dense cell structures generally per-
form best. The internal gate drivers tolerate >100nC
total gate charge, but 70nC is a more practical upper
limit to maintain best switching times.
In high-current applications, MOSFET package power
dissipation often becomes a dominant design factor.
I
2
R power losses are the greatest heat contributor for
both high-side and low-side MOSFETs. I
2
R losses are
distributed between Q1 and Q2 according to duty fac-
tor (see the following equations). Generally, switching
losses affect only the upper MOSFET, since the
Schottky rectifier clamps the switching node in most
cases before the synchronous rectifier turns on. Gate
charge losses are dissipated by the driver and don
’
t
heat the MOSFET. Calculate the temperature rise
according to package thermal-resistance specifications
to ensure that both MOSFETs are within their maximum
junction temperature at high ambient temperature. The
worst-case dissipation for the high-side MOSFET
occurs at both extremes of input voltage, and the
worst-case dissipation for the low-side MOSFET occurs
at maximum input voltage:
where: On-state voltage drop V
Q_
= I
LOAD
R
DS(ON)
C
RSS
= MOSFET reverse transfer capacitance
I
GATE
= DH driver peak output current capability
(1A typ)
20ns = DH driver inherent rise/fall time
Under output short-circuit, the MAX1904 synchronous
rectifier MOSFET suffers extra stress because its duty
factor can increase to greater than 0.9. It may need to
be oversized to tolerate a continuous DC short circuit.
During short circuit, the MAX1901/MAX1902
’
s output
undervoltage shutdown protects the synchronous recti-
fier under output short-circuit conditions.
To reduce EMI, add a 0.1μF ceramic capacitor from the
high-side switch drain to the low-side switch source.
Rectifier Clamp Diode
The rectifier diode is a clamp across the low-side MOS-
FET that catches the negative inductor swing during
the 60ns dead time between turning one MOSFET off
and each low-side MOSFET on. The latest generations
of MOSFETs incorporate a high-speed Schottky diode,
which serves as an adequate clamp diode. For
MOSFETs without integrated Schottky diodes, place a
Schottky diode in parallel with the low-side MOSFET.
PD
I
+
R
DUTY
V
I
f
V
C
I
ns
PD
I
(
R
DUTY
)
1
DUTY
V
V
V
V
upperFET
LOAD
DS ON
× ×
IN
LOAD
IN
RSS
GATE
2
upperFET
LOAD
DS(
) (
2
OUT
Q
IN
Q
=
×
×
×
×
+
=
=
×
×
-
+
2
20
1
(
)
/
)
(
)
-
L
V
V
× ×
V
V
f
I
LIR
Turns Ratio N
V
V
V
V
V
PRIMARY
OUT
IN MAX
(
OUT
×
+
IN MAX
(
TOTAL
SEC
+
)
FWD
OUT MIN
(
RECT
SENSE
=
=
+
(
)
)
)
-
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MAX1902EAI+ 功能描述:DC/DC 開關(guān)控制器 500kHz Multi-Output Power-Supply Ctlr 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
MAX1902EAI+T 功能描述:DC/DC 開關(guān)控制器 500kHz Multi-Output Power-Supply Ctlr 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
MAX1902EAI-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
MAX1904BEAI 制造商:Maxim Integrated Products 功能描述:
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