參數(shù)資料
型號(hào)： SP6123ACN
英文描述： CAP .033UF 100V PPS FILM ECH-S
中文描述： 低，同步降壓電壓降壓PWM控制器，適合2A至10A條，占地面積小，DC - DC電源轉(zhuǎn)換器
文件頁(yè)數(shù)： 11/18頁(yè)
文件大小： 154K
代理商： SP6123ACN
11
Date: 5/25/04
SP6123 Low Voltage, Synchronous Step Down PWM Controller Copyright 2004 Sipex Corporation
power sources. Certain tantalum capacitors, such
as AVX TPS series, are surge tested. For generic
tantalum capacitors, use 2:1 voltage derating to
protect the input capacitors from surge fallout.
MOSFET Selection
The losses associated with MOSFETs can be
divided into conduction and switching losses.
Conduction losses are related to the on resis-
tance of MOSFETs, and increase with the load
current. Switching losses occur on each on/off
transition when the MOSFETs experience both
high current and voltage. Since the bottom
MOSFET switches current from/to a paralleled
diode (either its own body diode or an external
Schottky diode), the voltage across the MOSFET
is no more than 1V during switching transition.
As a result, its switching losses are negligible.
The switching losses are difficult to quantify
due to all the variables affecting turn on/off
time. However, making the assumption that the
turn on and turn off transition times are equal,
the transition time can be approximated by:
t
T
= C
ISS
V
IN
,
I
G
where C
ISS
is the MOSFET’s input capacitance,
or the sum of the gate-to-source capacitance,
C
GS
, and the drain-to-gate capacitance, C
GD
.
This parameter can be directly obtained from
the MOSFET’s data sheet.
I
G
is the gate drive current provided by the
SP6123 (approximately 1A at V
IN
=5V) and V
IN
is the input supply voltage.
Therefore an approximate expression for the
switching losses associated with the high side
MOSFET can be given as:
P
SH(max)
= (V
IN(max)
+ V
F
)I
OUT(max)
t
T
F
S
,
where t
T
is the switching transition time and V
F
is the free wheeling diode drop.
Switching losses need to be taken into account
for high switching frequency, since they are
directly proportional to switching frequency.
The conduction losses associated with top and
bottom MOSFETs are determined by
P
CH(max)
= R
DS(ON)
I
OUT(max)
2
D
P
CL(max)
= R
DS(ON)
I
OUT(max)
where:
P
CH(max)
= conduction losses of the high side
MOSFET
P
CL(max)
= conduction losses of the low side
MOSFET
R
DS(ON)
= drain to source on resistance.
The total power losses of the top MOSFET are
the sum of switching and conduction losses. For
synchronous buck converters of efficiency over
90%, allow no more than 4% power losses for
high or low side MOSFETs. For input voltages
of 3.3V and 5V, conduction losses often domi-
nate switching losses. Therefore, lowering the
R
DS(ON)
of the MOSFETs always improves effi-
ciency even though it gives rise to higher switch-
ing losses due to increased C
ISS
.
Total gate charge is the charge required to turn
the MOSFETs on and off under the specified
operating conditions (V
GS
and V
DS
). The gate
charge is provided by the SP6123 gate drive
circuitry. (At 500kHz switching frequency, the
gate charge is the dominant source of power
dissipation in the SP6123). At low output levels,
this power dissipation is noticeable as a reduc-
tion in efficiency. The average current required
to drive the high side and low side MOSFETs is:
2
(1 - D),
I
G(av)
= Q
GH
F
S
+ Q
GL
F
S
, where
Q
GH
and Q
GL
are the total charge for the high
side and the low side MOSFETs respectively.
Considering that the gate charge current comes
from the input supply voltage V
IN
, the power
dissipated in the SP6123 due to the gate drive is:
P
GATE DRIVE
= V
IN
I
G(av)
Top and bottom MOSFETs experience unequal
conduction losses if their on time is unequal. For
applications running at large or small duty cycle,
it makes sense to use different top and bottom
MOSFETs. Alternatively, parallel multiple
MOSFETs to conduct large duty factor.
R
DS(ON)
varies greatly with the gate driver volt-
age. The MOSFET vendors often specify R
DS(ON)
on multiple gate to source voltages (V
GS
), as
well as provide typical curve of R
DS(ON)
versus
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SP6123ACN/TR 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Voltage, Synchronous Step-Down PWM Controller Ideal for 2A to 10A, Small Footprint, DC-DC Power Converters
SP6123ACN-L 功能描述:電壓模式 PWM 控制器 Low Voltage, Micro 8 Synchronous, Cntrllr RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開(kāi)關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
SP6123ACN-L/TR 功能描述:電壓模式 PWM 控制器 Low Voltage, Micro 8 Synchronous, Cntrllr RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開(kāi)關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
SP6123AEN-L 制造商:Rochester Electronics LLC 功能描述: 制造商:Exar Corporation 功能描述:
SP6123CN 制造商:Exar Corporation 功能描述:Swithed-Mode Power Supply Controller, Voltage Mode Type, 8 Pin, Plastic, SOP
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