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參數(shù)資料
| 型號： | IRU3073 |
| 廠商： | International Rectifier |
| 英文描述： | SYNCHRONOUS PWM CONTROLLER WITH OVER-CURRENT PROTECTION / LDO CONTROLLER |
| 中文描述： | 同步PWM控制器，帶有過電流保護/ LDO控制器 |
| 文件頁數(shù)： | 10/21頁 |
| 文件大?。?/td> | 236K |
| 代理商： | IRU3073 |
10
Rev. 1.0
09/17/03
IRU3073
www.irf.com
F
ESR
= 1
2
π×
ESR
×
Co
P
SW(TOTAL)
= 133mW
F
LC
= 1
2
π×
L
O
×
C
O
R
DS(ON)
= 4m
×
1.5 = 6m
I
SET
I
O(LIM)
= 8A
×
1.5 = 12A
(50% over nominal output current)
This results to: R
SET
4.8K
Select: R
SET
= 5K
Feedback Compensation
The IRU3073 is a voltage mode controller; the control
loop is a single voltage feedback path including error
amplifier and error comparator. To achieve fast transient
response and accurate output regulation, a compensa-
tion circuit is necessary. The goal of the compensation
network is to provide a closed loop transfer function with
the highest 0dB crossing frequency and adequate phase
margin (greater than 45
8
).
V
DS
90%
V
GS
10%
t
d
(ON)
t
d
(OFF)
t
r
t
f
Figure 9 - Switching time waveforms.
From IRF7832 data sheet we obtain:
IRF7832
t
r
= 12.3ns
t
f
= 21ns
These values are taken under a certain condition test.
For more details please refer to the IRF7832 datasheet.
By using equation (12), we can calculate the total switch-
ing losses.
Programming the Over-Current Limit
The over-current threshold can be set by connecting a
resistor (R
SET
) from drain of low side MOSFET to the
OCSet pin. The resistor can be calculated by using equa-
tion (2).
The R
DS(ON)
has a positive temperature coefficient and it
should be considered for the worse case operation.
Gain
F
LC
0dB
Phase
0
8
F
LC
-180
8
Frequency
Frequency
-40dB/decade
The output LC filter introduces a double pole, –40dB/
decade gain slope above its corner resonant frequency,
and a total phase lag of 180
8
(see Figure 10). The Reso-
nant frequency of the LC filter is expressed as follows:
Figure 10 shows gain and phase of the LC filter. Since
we already have 180
8
phase shift just from the output
filter, the system risks being unstable.
Figure 10 - Gain and phase of LC filter.
The IRU3073’s error amplifier is a differential-input
transconductance amplifier. The output is available for
DC gain control or AC phase compensation.
The E/A can be compensated with or without the use of
local feedback. When operated without local feedback,
the transconductance properties of the E/A become evi-
dent and can be used to cancel one of the output filter
poles. This will be accomplished with a series RC circuit
from Comp pin to ground as shown in Figure 11.
Note that this method requires that the output capacitor
should have enough ESR to satisfy stability requirements.
In general, the output capacitor’s ESR generates a zero
typically at 5KHz to 50KHz which is essential for an
acceptable phase margin.
The ESR zero of the output capacitor expressed as fol-
lows:
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| IRU3137CS | 制造商:IRF 制造商全稱:International Rectifier 功能描述:8-PIN SYNCHRONOUS PWM CONTROLLER |
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