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參數(shù)資料
| 型號(hào)： | AS2842 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Current Mode Controller |
| 中文描述： | 電流模式控制器 |
| 文件頁數(shù)： | 12/20頁 |
| 文件大?。?/td> | 94K |
| 代理商： | AS2842 |
AS2842/3/4/5
Current Mode Controller
ASTEC Semiconductor
48
1.3 Oscillator
The newly designed oscillator of the AS2842 is
enhanced to give significantly improved perfor-
mance. These enhancements are discussed in
the following paragraphs. The basic operation of
the oscillator is as follows:
A simple RC network is used to program the
frequency and the maximum duty ratio of the
AS2842 output. See Figure 15. Timing capacitor
(C
T
) is charged through timing resistor (R
T
) from
the fixed 5.0 V at V
REG
. During the charging time,
the OUT (pin 6) is high. Assuming that the output
is not terminated by the PWM latch, when the
voltage across C
T
reaches the upper oscillator
trip point (
≈
3.0 V), an internal current sink from
pin 4 to ground is turned on and discharges C
T
towards the lower trip point. During this dis-
charge time, an internal clock pulse blanks the
output to its low state. When the voltage across
C
T
reaches the lower trip point (
≈
1.3 V), the
current sink is turned off, the output goes high,
and the cycle repeats. Since the output is blanked
during the discharge of C
T
, it is the discharge time
which controls the output deadtime and hence,
the maximum duty ratio.
Figure 15.
Oscillator Set-up and Waveforms
The nature of the AS2842 oscillator circuit is such
that, for a given frequency, many combinations of
R
T
and C
T
are possible. However, only one value
of R
T
will yield the desired maximum duty ratio at
a given frequency. Since a precise maximum
duty ratio clamp is critical for many power supply
designs, the oscillator discharge current is
trimmed in a unique manner which provides
significantly improved tolerances as explained
later in this section. In addition, the AS2844/5
options have an internal flip-flop which effectively
blanks every other output pulse (the oscillator
runs at twice the output frequency), providing an
absolute maximum 50% duty ratio regardless of
discharge time.
1.3.1 Selecting timing components R
T
and
C
T
The values of R
T
and C
T
can be determined
mathematically by the following expressions:
5 V REG
OSCILLATOR
AS2842
6 OUTPUT
7 V
CC
8
R
T
C
T
I
D
5 GND
CLOCK
PWM
C
T
OUTPUT
Large R
T
/Small C
T
C
T
OUTPUT
Small R
T
/ Large C
T
4
C
D
R
D
R
T
T
T
=
=
( )
1
OSC
L
H
OSC
K
K
ln
1.63
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AS2843 | Current Mode Controller |
| AS2844 | Current Mode Controller |
| AS2845D-8 | Current Mode Controller |
| AS2845N | Current Mode Controller |
| AS2850AT-1.5 | Analog IC |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AS2843 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
| AS2844 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
| AS2845 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
| AS28450FLF | 制造商:TT Electronics / IRC 功能描述:AS28450FLF |
| AS28450HLF | 制造商:TT Electronics / IRC 功能描述:AS28450HLF |
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