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參數(shù)資料
| 型號： | IRU3048 |
| 廠商： | International Rectifier |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | DUAL SYNCHRONOUS PWM CONTROLLER CIRCUITRY AND LDO CONTROLLER |
| 中文描述： | 雙同步PWM控制器電路和LDO控制器 |
| 文件頁數(shù)： | 10/18頁 |
| 文件大?。?/td> | 154K |
| 代理商： | IRU3048 |
10
Rev. 1.7
09/12/02
IRU3048
www.irf.com
Cross Over Frequency:
The stability requirement will be satisfied by placing the
poles and zeros of the compensation network according
to following design rules. The consideration has been
taken to satisfy condition 14 regarding transconduc-
tance error amplifier.
1)
Select the crossover frequency:
2)
Select R
7
, so that R
7
>>
3)
Place first zero before LC’s resonant frequency pole.
F
Z1
75% F
LC
1
2
π ×
F
Z1
×
R
7
4)
Place third pole at the half of the switching frequency.
F
P3
=f
S
2
1
2
π ×
R
7
×
F
P3
C
12
> 50pF
If not, change R
7
selection.
5)
Place R
7
in (15) and calculate C
10
:
6)
Place second pole at ESR zero.
F
P2
= F
ESR
Check if R
8
>
If R
8
is too small, increase R
7
and start from step 2.
7)
Place second zero around the resonant frequency.
F
Z2
= F
LC
8)
Use equation (1) to calculate R
5
:
These design rules will give a crossover frequency ap-
proximately one-tenth of the switching frequency. The
higher the band width, the potentially faster the load tran-
sient speed. The gain margin will be large enough to
provide high DC-regulation accuracy (typically -5dB to -
12dB). The phase margin should be greater than 45
8
for
overall stability.
LDO Section
Output Voltage Programming
Output voltage for LDO is programmed by reference volt-
age and external voltage divider. The Fb3 pin is the in-
verting input of the error amplifier, which is internally ref-
erenced to 1.25V. The divider is ratioed to provide 1.25V
at the Fb3 pin when the output is at its desired value.
The output voltage is defined by using the following equa-
tion:
( )
R
LOW
Results to: R
HIGH
=1K
LDO Power MOSFET Selection
The first step in selecting the power MOSFET for the
linear regulator is to select the maximum R
DS(ON)
based
on the input to the dropout voltage and the maximum
load current.
Results to: R
DS(ON)(MAX)
= 0.4
Note that since the MOSFET R
DS(ON)
increases with tem-
perature, this number must be divided by ~1.5 in order
to find the R
DS(ON)(MAX)
at room temperature. The IRLR2703
has a maximum of 0.065
R
DS(ON)
at room temperature,
which meets our requirements.
1
g
m
C
12
=
C
10
≤
×
2
π ×
Lo
×
F
O
×
Co
R
7
V
OSC
V
IN
R
8
=
1
2
π ×
C10
×
F
P2
R
6
= 1
8
2
π ×
C10
×
F
Z2
R
5
= V
×
R
6
V
OUT
- V
REF
REF
R
DS(ON)
=V
IN3
- V
OUT2
I
OUT2
For:
V
IN3
= 3.3V
V
OUT2
= 2.5V
I
OUT2
= 2A
Where:
V
IN
= Maximum Input Voltage
V
OSC
= Oscillator Ramp Voltage
Lo = Output Inductor
Co = Total Output Capacitors
F
O1
= R
7
×
C
10
×
×
V
IN
V
OSC
1
2
π×
Lo
×
Co
---(15)
Fo < F
ESR
and Fo
≤
(1/10 ~ 1/6)
×
f
S
2
g
m
C
11
=
For:
V
OUT2
= 2.5V
V
REF
= 1.25V
R
LOW
= 1K
R
HIGH
V
OUT2
= V
REF
×
1+
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