ML4803IS-2 View Datasheet(PDF) - Micro Linear Corporation
Part Name
Description
MFG CO.
'ML4803IS-2' PDF : 13 Pages View PDF
ML4803
TYPICAL APPLICATIONS (Continued)
R COMP
=
2´
p
´
1
f´
CCOMP
(3)
R COMP
=
6.28
´
1
30Hz
´ 16nF
=
330kW
C ZERO
=
2´
p
´
1
f
10
´
R COMP
(4)
C ZERO
=
6.28 ´
1
3Hz ´
330kW
= 0.16mF
INTERNAL VOLTAGE RAMP
The internal ramp current source is programmed by way of
the VEAO pin voltage. Figure 7 displays the internal ramp
current vs. the VEAO voltage. This current source is used
to develop the internal ramp by charging the internal
30pF +12/–10% capacitor. See Figures 10 and 11. The
frequency of the internal programming ramp is set
internally to 67kHz.
PFC CURRENT SENSE FILTERING
In DCM, the input current wave shaping technique used
by the ML4803 could cause the input current to run away.
In order for this technique to be able to operate properly
under DCM, the programming ramp must meet the boost
inductor current down-slope at zero amps. Assuming the
programming ramp is zero under light load, the OFF-time
will be terminated once the inductor current reaches zero.
Subsequently the PFC gate drive is initiated, eliminating
the necessary dead time needed for the DCM mode. This
forces the output to run away until the VCC OVP shuts
down the PFC. This situation is corrected by adding an
VO
ML4803
∆VEAO +
–
IOUT
220µF
11.3MΩ
RLOAD
667Ω
VEAO
330kΩ
15nF
POWER
STAGE
0.15µF
COMPENSATION
Figure 4. Voltage Control Loop
ML4803
IVEAO
35µA
0
Power Stage
Overall
Compensation
Network
50
100
150
60
Power Stage
Overall Gain
40
Compensation
Network Gain
20
0
–20
–40
–60
0.1
1
10
100
FREQUENCY (Hz)
1000
Figure 5. Voltage Loop Gain
50
FF @ –55ºC
40 TYP @ –55ºC
TYP @ ROOM TEMP
30 TYP @ 155ºC
SS @ 155ºC
20
10
200
0.1
1
10
100
FREQUENCY (Hz)
1000
Figure 6. Voltage Loop Phase
8
0
0
1
2
3
4
5
6
7
VEAO (V)
Figure 7. Internal Ramp Current vs. VEAO
February 1999
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