ML4810 데이터 시트보기 (PDF) - Micro Linear Corporation

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ML4810

High Frequency Power Supply Controller

Micro Linear Corporation 

ML4810, ML4811

OSCILLATOR

The ML4811 oscillator charges the external capacitor (CT)

with a current (ISET) equal to 3/RT. When the capacitor

voltage reaches the upper threshold (Ramp Peak), the

comparator changes state and the capacitor discharges to

the lower threshold (Ramp Valley) through Q1. While the

capacitor is discharging, Q2 provides a high pulse. A

discharge of the oscillator con be initiated by applying a

high level to the Sync pin. A short pulse of a frequency

higher than the oscillator’s free running frequency can be

used to synchronize the ML4811 to an external clock. The

pulse can be equal to the desired deadtime (TD) or the

deadtime can be determined by IDIS and CT, whichever is

greater.

The oscillator period can be described by the following

relationship:

tOSC = tRAMP + tDEADTIME

where:

tRAMP

=

C

(Ramp

Valley

ISET

to

Peak)

and:

tDEADTIME

=

C

(Ramp

Valley

IQ1

to

Peak)

I(1)

V(1)

Figure 4. Switching Current and Pin 4 Voltage — Normal

SYNC 10

ISET

3V

6

RT

ISET

7

CT

IDIS

Q1

5V

Q2

+

–

CLOCK

OUT

5

I(1)

V(1)

Figure 5. Switching Current and Pin 4 Voltage — Load Fault

100k

100nF

47nF

22nF

0nF

10k

4.7nF

2.2nF

1k

100

1nF

470pF

1k

10k

100k

1M

FREQUENCY (Hz)

Figure 7. Oscillator Timing Resistance vs Frequency

6

CLOCK

tD

RAMP PEAK

CT

RAMP VALLEY

Figure 6. Simplified Oscilator Block Diagram and Timing

160

1.0nF

140

120

100

80

10k

470pF

100k

1M

FREQUENCY (Hz)

Figure 8. Oscillator Deadtime vs Frequency

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