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參數(shù)資料
| 型號(hào)： | RC5057 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | High Performance Programmable Synchronous DC-DC Controller for Low Voltage Microprocessors |
| 中文描述： | 高性能可編程同步DC - DC控制器低壓微處理器 |
| 文件頁數(shù)： | 15/20頁 |
| 文件大?。?/td> | 177K |
| 代理商： | RC5057 |
PRODUCT SPECIFICATION
RC5057
REV. 1.2.0 2/10/00
15
MOSFET Selection
This application requires N-channel Logic Level Enhance-
ment Mode Field Effect Transistors. Desired characteristics
are as follows:
Low Static Drain-Source On-Resistance,
R
DS,ON
< 20m (lower is better)
Low gate drive voltage, V
GS
= 4.5V rated
Power package with low Thermal Resistance
Drain-Source voltage rating > 15V.
The on-resistance (RDS,ON) is the primary parameter for
MOSFET selection. The on-resistance determines the power
dissipation within the MOSFET and therefore significantly
affects the efficiency of the DC-DC Converter. For details
and a spreadsheet on MOSFET selection, refer to Applica-
tions Bulletin AB-8.
Inductor Selection
Choosing the value of the inductor is a tradeoff between
allowable ripple voltage and required transient response. The
system designer can choose any value within the allowed
minimum to maximum range in order to either minimize rip-
ple or maximize transient performance. The first order equa-
tion (close approximation) for minimum inductance is:
where:
V
in
= Input Power Supply
V
out
= Output Voltage
f = DC/DC converter switching frequency
ESR = Equivalent series resistance of all output capacitors in
parallel
V
ripple
= Maximum peak to peak output ripple voltage budget.
The first order equation for maximum allowed inductance is:
where:
C
o
= The total output capacitance
I
pp
= Maximum to minimum load transient current
V
tb
= The output voltage tolerance budget allocated to load
transient
D
m
= Maximum duty cycle for the DC/DC converter
(usually 95%).
Some margin should be maintained away from both Lmin
and L
max
. Adding margin by increasing L almost always
adds expense since all the variables are predetermined by
system performance except for C
o
, which must be increased
to increase L. Adding margin by decreasing L can be done
by purchasing capacitors with lower ESR. The RC5057 pro-
vides significant cost savings for the newer CPU systems
that typically run at high supply current.
RC5057 Short Circuit Current Characteristics
The RC5057 protects against output short circuit by turning
off both the high-side and low-side MOSFETs and resetting
softstart. The short circuit limit is set with the R
5
resistor, as
given by the formula
with I
Detect
≈
50μA, I
SC
the desired current limit, and R
DS,on
the high-side MOSFET’s on resistance. Remember to make
R
5
large enough to include the effects of initial tolerance and
temperature variation on the MOSFET’s R
DS,on
. However,
the value of R
5
should be less than 8.3K
. If a greater value
is necessary, a lower R
DS,on
MOSFET should be used
instead. Alternately, use of a sense resistor in series with the
source of the MOSFET, as shown in Figure 6, eliminates this
source of inaccuracy in the current limit. Note the addition of
the diode, which is necessary for proper operation of this cir-
cuit.
As an example, Figure 5 shows the typical characteristic of
the DC-DC converter circuit with an FDB6030L high-side
MOSFET (R
DS
= 20m
maximum at 25°C * 1.25 at 75°C =
25m
) and a 8.2K
R
5
.
Figure 5. RC5057 Short Circuit Characteristic
The converter exhibits a normal load regulation characteristic
until the voltage across the MOSFET exceeds the internal
short circuit threshold of 50μA * 8.2K
= 410mV, which
occurs at 410mV/25m
= 16.4A. (Note that this current limit
level can be as high as 410mV/15m
= 27A, if the MOSFET
L
min
(Vin
–
V
out
)
f
x
V
out
V
in
x
ESR
V
ripple
=
L
max
(Vin
–
V
out
) D
m
V
tb
I
pp2
= 2C
0
R
5
I
SC
x R
DS, on
I
Detect
=
V
O
Output Current (A)
0 5 10 15 20 25
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| RC5057M | High Performance Programmable Synchronous DC-DC Controller for Low Voltage Microprocessors |
| RC5058 | High Performance Programmable Synchronous DC-DC Controller for Multi-Voltage Platforms |
| RC5058M | Current-Mode SMPS Controller |
| RC5060 | ACPI Switch Controller |
| RC5060M | Power Supply Switching Circuit |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| RC5057M | 功能描述:DC/DC 開關(guān)控制器 Syn DC-DC Controller Programmable 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 |
| RC5057MT | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 Syn DC-DC Controller Programmable RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| RC5057N | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 DIP-16 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| RC5058 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:High Performance Programmable Synchronous DC-DC Controller for Multi-Voltage Platforms |
| RC5058M | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 SOIC-24 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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