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參數(shù)資料
| 型號： | 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)： | 16/20頁 |
| 文件大?。?/td> | 94K |
| 代理商： | AS2842 |
AS2842/3/4/5
Current Mode Controller
ASTEC Semiconductor
52
Resistors R
1
and R
F
set the low frequency gain
and should be chosen to provide the highest
possible gain, without exceeding the unity gain
crossing frequency limit of f
SW
/4. R
BIAS
, in con-
junction with R
1
, sets the converter’s output volt-
age; but has no effect on the loop gain/phase
response.
There are a few converter design considerations
associated with the error amplifier. First, the
values of the divider network (R
1
and R
BIAS
)
should be kept low in order to minimize errors
caused by the error amplifier’s input bias current
( –1.0
μ
A). An output voltage error equal to the
product of the input bias current and the equiva-
lent divider resistance, can be quite significant
with divider values greater than 5 k
. Low divider
resistor values also help to improve the noise
immunity of the sensitive V
FB
input.
The second consideration is that the error ampli-
fier will typically source only 0.8 mA; thus, the
value of feedback resistance (R
F
) should be no
lower than 5 k
in order to maintain the error
amplifier’s full output range. In practice, how-
ever, the feedback resistance required is usually
much greater than 5 k
, hence this limitation is
normally not a problem.
Some power supply topologies may require a
more elaborate compensation network. For ex-
ample, flyback and boost converters operating
with continuous current have transfer functions
that include a right half plane (RHP) zero. These
types of systems require an additional pole
element within the compensation network.
A detailed discussion of loop compensation, how-
ever, is beyond the scope of this application note.
1.5 I
SENSE
current comparator/PWM latch
The current sense comparator (sometimes called
the PWM comparator) and accompanying
latch circuitry make up the pulse width modulator
(PWM). It provides pulse-by-pulse current
sensing/limiting and generates a variable duty
ratio pulse train which controls the output voltage
of the power supply. Included is a high speed
comparator followed by ECL type logic circuitry
which has very low propagation delays and switch-
ing noise. This is essential for high frequency
power supply designs. The comparator has been
designed to provide guaranteed performance
with the current sense input below ground. The
PWM latch ensures that only one pulse is al-
lowed at the output for each oscillator period.
The inverting input to the current sense compara-
tor is internally connected to the level shifted
output of the error amplifier (V
E
)
as discussed in
the previous section. The non-inverting input is
the I
SENSE
input (pin 3). It monitors the switched
inductor current of the converter.
Figure 20 shows the current sense/PWM cir-
cuitry of the AS2842, and associated waveforms.
The output is set high by an internal clock pulse
and remains high until one of two conditions
occur; 1) the oscillator times out (Section 1.3 )or
2) the PWM latch is set by the current sense
comparator. During the time when the output is
high, the converter’s switching device is turned
on and current flows through resistor R
S
. This
produces a stepped ramp waveform at pin 3 as
shown in Figure 20. The current will continue to
ramp up until it reaches the level of V
E
at the
inverting input. At that point, the comparator’s
output goes high, setting the PWM latch and the
output pulse is then terminated. Thus, V
E
is a
variable reference for the current sense com-
parator, and it controls the peak current sensed
by R
S
on a cycle-by-cycle basis. V
S
varies in
proportion to changes in the input voltage/cur-
rent (inner control loop) while V
E
varies in propor-
tion to changes in the converters output voltage/
current (outer control loop). The two control loops
merge at the current sense comparator, produc-
ing a variable duty ratio pulse train that controls
the output of the converter.
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| AS2843 | Current Mode Controller |
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| AS2845D-8 | Current Mode Controller |
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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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