ML4821CP 데이터 시트보기 (PDF) - Micro Linear Corporation
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ML4821CP Datasheet PDF : 12 Pages
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ML4821
INV
7
+8V
S.S
9
–
+
VREF
+8V
6.2kΩ
EA OUT
6
Figure 3. Error and Current Amplifier Configuration
0
VCC
SOURCE SATURATION
(LOAD TO GROUND)
VCC = 15V
–1.0
TA = 25°C
80µs PULSED LOAD
120 Hz RATE
–2.0
TA = –55°C
3.0
2.0
1.0
0
0
TA = –55°C
SINK SATURATION
(LOAD TO VCC)
TA = 25°C
GND
200
400
600
800
IO, OUTPUT LOAD CURRENT (mA)
Figure 5. Output Saturation Voltage vs. Output Current.
100
0
VCC = 15V
80
GAIN
VO = 1.0V TO 5.0V
RL = 100kΩ
–30
TA= 25°C
60
60
40
90
PHASE
20
120
0
150
–20
180
10
100
1.0k
10k
100k 1.0M
10M
f, FREQUENCY (Hz)
Figure 4. Error Amplifier Open-loop Gain and Phase vs.
Frequency.
0.5
OPERATING BOUNDRY
0.4
0.3
K
DESIGN
FOR
BROWNOUT
0.2
0.23
0.1
DESIGN
FOR
NORMAL
OPERATIONS
THIS IS THE MINIMUM
OPERATING
VOLTAGE POINT
THIS GAIN CURVE TAKES
OUT THE 1/(VIN)2
DEPENDENCY OF THE
VOLTAGE CONTROL LOOP
0
0
1
2
3
4
5
6
7
85VAC 120VAC
220VAC
VRMS
Figure 6. K-factor. Gain Modulator gain with
respect to the voltage at VRMS.
The output of the gain modulator is a current which
appears on IA+ to form the reference for the current error
amplifier and is given as:
IGM = K × ISINE × (VEA − 0.8)
where:
ISINE is the current in the dropping resistor, VEA
is the output of the error amplifier and K is a
constant determined by the VRMS input.
The output current of the gain modulator is limited to:
IGM(MAX)
=
2.5
RT
This sets the system current limit.The multiplier output
current is converted into the reference voltage for the
current (IA) amplifier through a resistor to ground on IA+.
Figure 6 shows the gain adjustor (K) with respect to the
voltage at VRMS. The curve has been separated in two
parts. The right hand part is for operation under normal
conditions in the voltage range from minimum line
voltage to maximum line voltage (90VAC to 260VAC).
85VAC on the curve has been chosen to account for
tolerances. Under normal operating conditions as input
voltage decreases the gain increases compensating for the
drop in the loop gain.
Under brownout conditions (below 85VAC) the gain
decreases to limit the amount of current that is drawn
from the line thus preventing an overload condition. This
is a very useful feature since in many cases the load for a
PFC is a constant power load. The input current has to go
high to compensate for a drop in the input voltage.
Micro Linear
7
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