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參數(shù)資料
| 型號： | IR3637STRPBF |
| 廠商： | International Rectifier |
| 英文描述： | 1% ACCURATE SYNCHRONOUS PWM CONTROLLER |
| 中文描述： | 1％準確的同步PWM控制器 |
| 文件頁數(shù)： | 6/21頁 |
| 文件大小： | 655K |
| 代理商： | IR3637STRPBF |
6
Rev.1.1
06/16/05
IR3637SPBF
www.irf.com
Figure 5 - Typical application of the IR3637 for pro-
gramming the output voltage.
APPLICATION INFORMATION
Design Example:
The following example is a typical application for IR3637.
Appliaction circuit is shown in page 12.
V
IN
= Vcc = 5V
Vc=12V
V
OUT
= 1.8V
I
OUT
= 6A
V
OUT
= 50mV
F
S
= 400kHz
Output Voltage Programming
Output voltage is programmed by reference voltage and
external voltage divider. The Fb pin is the inverting input
of the error amplifier, which is internally referenced to
0.8V. The divider is ratioed to provide 0.8V at the Fb pin
when the output is at its desired value. The output volt-
age is defined by using the following equation:
( )
When an external resistor divider is connected to the
output as shown in Figure 5.
Equation (1) can be rewritten as:
( )
Choose R
5
= 1K
This will result to
R
6
= 1.25K
If the high value feedback resistors are used, the input
bias current of the Fb pin could cause a slight increase
in output voltage. The output voltage set point can be
more accurate by using precision resistor.
Soft-Start Programming
The soft-start timing can be programmed by selecting
the soft-start capacitance value. The start-up time of the
converter can be calculated by using:
Fb
IR3637
V
OUT
R
5
R
6
R
6
= R
5
×
- 1
REF
V
OUT
V
OUT
= V
REF
×
1 +
---(1)
5
R
6
For a start-up time of 4ms, the soft-start capacitor will
be 0.1
μ
F. Choose a ceramic capacitor at 0.1
μ
F.
Boost Supply for Single 5V appliaction
To drive the high side switch, it is necessary to supply a
gate voltage at least 4V grater than the bus voltage. This
is achieved by using a charge pump configuration as
shown in Figure 6. This method is simple and inexpen-
sive. The operation of the circuit is as follows: when the
lower MOSFET is turned on, the capacitor (C1) is pulled
down to ground and charges, up to V
BUS
value, through
the diode (D1). The bus voltage will be added to this
voltage when upper MOSFET turns on in next cycle,
and providing supply voltage (Vc) through diode (D2). Vc
is approximately:
Capacitors in the range of 0.1
μ
F and 1
μ
F are generally
adequate for most applications. The diode must be a
fast recovery device to minimize the amount of charge
fed back from the charge pump capacitor into V
BUS
. The
diodes need to be able to block the full power rail volt-
age, which is seen when the high side MOSFET is
switched on. For low voltage application, schottky di-
odes can be used to minimize forward drop across the
diodes at start up.
Figure 6 - Charge pump circuit.
Input Capacitor Selection
The input filter capacitor should be based on how much
ripple the supply can tolerate on the DC input line. The
ripple current generated during the on time of upper
MOSFET should be provided by input capacitor. The RMS
value of this ripple is expressed by:
Css
25
×
t
START
(
μ
F) ---(2)
Where
t
START
is the desired start-up time (ms)
L
IR3637
D1
C1
Vc
HDrv
Q1
Q2
C2
V
BUS
D2
C3
V
BUS
Vc
2V
BUS
- (V
D1
+ V
D2
)
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| IR3638STRPBF | 功能描述:電壓模式 PWM 控制器 HI FREQ SYNC PWM 400kHz 0.6V Track RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 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 |
| IR3640MPBF | 功能描述:IC REG CTRLR BUCK PWM VM 20-MLPQ RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
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