PRODUCT SPECIFICATION

ML4803

REV. 1.1.3 8/3/01

7

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.

R

f

COMP

COMP

1

2

× π ×

R

Hz

k

Ω

COMP

1

6.28

16

330

C

f

R

ZERO

COMP

1

2

× π ××

10

C

Hz

×

k

Ω

µF

ZERO

1

628

330

016

.

.

=

==

=

=

=

Figure 4. Voltage Control Loop

ML4803

ML4803

IVEAO

35

µA

IOUT

VO

220

µF

RLOAD

667

Ω

330k

Ω

11.3M

Ω

0.15

µF

15nF

POWER

STAGE

COMPENSATION

VEAO

∆VEAO +

–

Figure 5. Voltage Loop Gain

60

40

20

0

–20

–40

–60

FREQUENCY (Hz)

0.1

10

1000

1

100

Power Stage

Overall Gain

Compensation

Network Gain

Figure 6. Voltage Loop Phase

0

50

100

150

200

FREQUENCY (Hz)

0.1

1

10

1000

100

Power Stage

Overall

Compensation

Network

Figure 7. Internal Ramp Current vs. VEAO

50

40

30

20

10

0

VEAO (V)

02

7

5

13

6

4

FF @ –55ºC

TYP @ –55ºC

TYP @ 155ºC

SS @ 155ºC

TYP @ ROOM TEMP