ML4812IQ Datasheet ML4812IQX, ML4812CP, ML4812CQ | P7-P9

PRODUCT SPECIFICATION ML4812

REV. 1.0.4 5/31/01 7

EA–

–

0.5mA

EA OUT

VOL

, OPEN LOOP GAIN (dB)

FREQUENCY (Hz)

10 1k 1M

100 10k 10M100k

100

-20

EXCESS PHASE (degrees)

-30

-60

-90

-120

-150

-180

GAIN

PHASE

RAMP COMP

GM OUT

SINE

ERROR CURRENT

RAMP COMP

SINE

ERROR CURRENT

– I

RAMP COMP

500

400

300

200

100

MULTIPLE OUTPUT CURRENT (µA)

ERROR AMP OUTPUT VOLTAGE (V)

SINE INPUT CURRENT (µA)

0 200 300 500400100

4.5

4.0

3.5

3.0

2.5

2.0

1.5

Output Driver Stage

The ML4812 output driver is a 1A peak output high speed

totem pole circuit designed to quickly drive capacitive loads,

such as power MOSFET gates. (Figure 3)

Error Ampliﬁer

The ML4812 error ampliﬁer is a high open loop gain, wide

bandwidth, ampliﬁer.(Figures 4-5)

Gain Modulator

The ML4812 gain modulator is of the current-input type to

provide high immunity to the disturbances caused by high

power switching. The rectiﬁed line input sine wave is con-

verted to a current via a dropping resistor. In this way, small

amounts of ground noise produce an insigniﬁcant effect on

the reference to the PWM comparator. The output of the gain

modulator is a current of the form: I

OUT

is proportional to

SINE

↔ I

, where I

SINE

is the current in the dropping

resistor, and I

is a current proportional to the output of the

error ampliﬁer. When the error ampliﬁer is saturated high,

the output of the gain modulator is approximately equal to

the I

SINE

input current. The gain modulator output current is

converted into the reference voltage for the PWM compara-

tor through a resistor to ground on the gain modulator out-

put. The gain modulator output is clamped to 5V to provide

current limiting.

Ramp compensation is accomplished by subtracting 1/2 of

the current ﬂowing out of RAMP COMP through a buffer

transistor driven by C

which is set by an external resistor.

Under Voltage Lockout

On power-up the ML4812 remains in the UVLO condition;

output low and quiescent current low. The IC becomes oper-

ational when V

reaches 16V. When V

drops below

10V, the UVLO condition is imposed. During the UVLO

condition, the 5V VREF pin is “off”, making it usable as a

“ﬂag” for starting up a downstream PWM converter.

Figure 4. Error Amplifier Configuration

Figure 5. Error Amplifier Open-Loop Gain and

Figure 6. Gain Modulator Block Diagram

Figure 7. Gain Modulator Linearity

Phase vs Frequency

ML4812 PRODUCT SPECIFICATION

8 REV. 1.0.4 5/31/01

Typical Applications

Input Inductor (L1) Selection

The central component in the regulator is the input boost

inductor. The value of this inductor controls various critical

operational aspects of the regulator. If the value is too low,

the input current distortion will be high and will result in low

power factor and increased noise at the input. This will

require more input ﬁltering. In addition, when the value of

the inductor is low the inductor dries out (runs out of current)

at low currents. Thus the power factor will decrease at lower

power levels and/or higher line voltages. If the inductor

value is too high, then for a given operating current the

required size of the inductor core will be large and/or the

required number of turns will be high. So a balance must be

reached between distortion and core size.

One more condition where the inductor can dry out is ana-

lyzed below where it is shown to be maximum duty cycle

dependent.

For the boost converter at steady state:

Where D

is the duty cycle [T

/(T

+ T

OFF

)]. The

input boost inductor will dry out when the following condi-

tion is satisﬁed:

INDRY

: voltage where the inductor dries out.

OUT

: output DC voltage.

Effectively, the above relationship shows that the resetting

volt-seconds are more than setting volt-seconds. In energy

transfer terms this means that less energy is stored in the

inductor during the ON time than it is asked to deliver during

the OFF time. The net result is that the inductor dries out.

Figure 8. Under-Voltage Lockout Block Diagram

Figure 9a. Total Supply Current vs. Supply Voltage

Figure 9b. Supply Current (I

) vs. Temperature

Figure 10. Reference Load Regulation

OUT

–

--------------------=

(1)

t() V

OUT

< 1D

–()×

(2)

INDRY

max()–[]=V

OUT

(3)

ENABLE

REF

GEN.

INTERNAL

BIAS

5V V

REF

–

(mA)

(V)

3020 4010

SUPPLY CURRENT (mA)

TEMPERATURE (degrees)

–60 20 60 140100–20

–40 40 80 1200

OPERATING CURRENT

STARTUP

∆V

REF

(mV)

REF

(mA)

0 40 100

20 60 12080

-4

-8

-12

-16

-20

-24

PRODUCT SPECIFICATION ML4812

REV. 1.0.4 5/31/01 9

The recommended maximum duty cycle is 95% at 100KHz

to allow time for the input inductor to dump its energy to

the output capacitors. For example, if: V

OUT

= 380V and

(max) = 0.95, then substituting in (3) yields V

INDRY

= 20V. The effect of drying out is an increase in distortion at

low voltages.

For a given output power, the instantaneous value of the

input current is a function of the input sinusoidal voltage

waveform, i.e. as the input voltage sweeps from zero volts to

a maximum value equal to its peak so does the current.

The load of the power factor regulator is usually a switching

power supply which is essentially a constant power load. As

a result, an increase in the input voltage will be offset by a

decrease in the input current.

By combining the ideas set forth above, some ground rules

can be obtained for the selection and design of the input

inductor:

Step 1: Find minimum operating current.

then:

Step 2: Choose a minimum current at which point the

inductor current will be on the verge of drying out. For this

example 40% of the peak current found in step 1 was chosen.

then:

Step 3: The value of the inductance can now be found using

previously calculated data.

The inductor can be allowed to decrease in value when the

current sweeps from minimum to maximum value. This

allows the use of smaller core sizes. The only requirement is

that the ramp compensation must be adequate for the lower

inductance value of the core so that there is adequate com-

pensation at high current.

Step 4: The presence of the ramp compensation will change

the dry out point, but the value found above can be consid-

ered a good starting point. Based on the amount of power

factor correction the above value of L1 can be optimized

after a few iterations.

Gapped Ferrites, Molypermalloy, and Powdered Iron cores

are typical choices for core material. The core material

selected should have a high saturation point and acceptable

losses at the operating frequency.

One ferrite core that is suitable at around 200W is the

#4119PL00-3C8 made by Philips Components (Ferroxcube).

This ungapped core will require a total gap of 0.180" for this

application.

Oscillator Component Selection

The oscillator timing components can be calculated by using

the following expression:

For example:

Step 1: At 100kHz with 95% duty cycle T

OFF

= 500ns

calculate C

using the following formula:

Step 2: Calculate the required value of the timing resistor.

Current Sense and Slope (Ramp)

Compensation Component Selection

Slope compensation in the ML4812 is provided internally.

Rather than adding slope to the noninverting input of the

PWM comparator, it is actually subtracted from the voltage

present at the inverting input of the PWM comparator. The

amount of slope compensation should be at least 50% of the

downslope of the inductor current during the off time, as

reﬂected to the inverting input of the PWM comparator. Note

that slope compensation is required only when the inductor

current is continuous and the duty cycle is more than 50%.

The downslope of the inductor current at the verge of

discontinuity can be found using the expression given below:

The downslope as reﬂected to the input of the PWM

comparator is given by:

min()

PEAK

1.414 P

× min()

max()

-------------------------------------------=

min()50W=

max()260V=

(4)

min()

PEAK

0.272A=

LDRY

100mA=

INDRY

max()×

LDRY

OSC

-------------------------------------------------------

20V 0.95×

100mA 100KHz×

---------------------------------------------- 2mH===

(5)

OSC

1.36

--------------------=

(6)

OFF

DIS

OSC

----------------------------- 1 0 0 0 p F==

(7)

(8)

1.36

OSC

-------------------------

1.36

100KHz 100pF×

------------------------------------------- 13.6kΩ== =

choose R

= 14kΩ

--------

OUT

INDRY

–

-----------------------------------------

380V 20V–

2mH

------------------------------ 0.18A µs⁄===

(9)

PWM

OUT

INDRY

–

-----------------------------------------

-------==

(10)

PWM

380V 20V–

2mH

------------------------------=

100

---------

× 0.225V µs⁄=

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

ML4812IQ

Mfr. #:

Buy ML4812IQ

Manufacturer:

ON Semiconductor

Description:

IC POWER FACTOR CTRLR 20-PLCC

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

ML4812IQ

ML4812IQ

Products related to this Datasheet