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參數(shù)資料
| 型號(hào)： | IRU3047CW |
| 廠商： | International Rectifier |
| 元件分類(lèi)： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | DUAL SYNCHRONOUS PWM CONTROLLER WITH CURRENT SHARING CIRCUITRY AND LDO CONTROLLER |
| 中文描述： | 雙同步PWM控制器，帶有均流電路和LDO控制器 |
| 文件頁(yè)數(shù)： | 6/19頁(yè) |
| 文件大?。?/td> | 141K |
| 代理商： | IRU3047CW |
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6
Rev. 1.0
09/09/02
IRU3047
www.irf.com
APPLICATION INFORMATION
Design Example:
The following example is a typical application for IRU3047
in current sharing mode. The schematic is Figure 12 on
page 16.
PWM Section
Output Voltage Programming
Output voltage is programmed by reference voltage and
external voltage divider. The Fb1 pin is the inverting input
of the error amplifier, which is internally referenced to
1.25V. The divider is ratioed to provide 1.25V at the Fb1
pin when the output is at its desired value. The output
voltage is defined by using the following equation:
( )
R
5
When an external resistor divider is connected to the
output as shown in Figure 3.
Figure 3 - Typical application of the IRU3047 for
programming the output voltage.
Equation (1) can be rewritten as:
( )
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:
t
START
= 75
×
Css (ms) ---(2)
Where:
C
SS
is the soft-start capacitor (
μ
F)
For a start-up time of 75ms, the soft-start capacitor will
be 1
μ
F. Choose a ceramic capacitor at 1
μ
F.
Boost Supply Vc
To drive the high-side switch it is necessary to supply a
gate voltage at least 4V greater than the bus voltage.
This is achieved by using a charge pump configuration
as shown in Figure 1. The capacitor is charged up to
approximately twice the bus voltage. A capacitor in the
range of 0.1
μ
F to 1
μ
F is generally adequate for most
applications.
Sense Resistor Selection
These resistors will determine the current sharing
between two channels. The relationship between the
Master and Slave output currents is expressed by:
For an equal current sharing, R
SEN1
=R
SEN1
Choose R
SEN1
=R
SEN2
=5m
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 control
MOSFET should be provided by input capacitor. The RMS
value of this ripple is expressed by:
Where:
D is the Duty Cycle, simply D=V
OUT
/V
IN.
I
RMS
is the RMS value of the input capacitor current.
I
OUT
is the output current for each channel.
For V
IN1
=12V, I
OUT1
=6A and D1=0.208
Results to: I
RMS1
=2.43A
And for V
IN2
=5V, I
OUT2
=6A and D2=0.5
Results to: I
RMS2
=3A
R
6
= R
5
×
- 1
V
OUT1
V
REF
Will result to:
V
OUT1
= 2.5V
V
REF
= 1.25V
R
5
= 1K
R
6
= 1K
V
IN1(MASTER)
= 12V
V
IN2(SLAVE)
= 5V
V
OUT1
= 1.5V
I
OUT
= 12A
V
OUT
= 75mV
f
S
= 200KHz
Fb1
IRU3047
V
OUT1
R
5
R
6
V
OUT1
= V
REF
×
1+
---(1)
R
6
I
RMS
= I
OUT
D
×
(1-D)
---(4)
R
SEN1
×
I
MASTER
= R
SEN2
×
I
SLAVE
---(3)
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