ML4825CQ 查看數據表（PDF） - Micro Linear Corporation

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ML4825CQ

High Frequency Power Supply Controller

Micro Linear Corporation 

FUNCTIONAL DESCRIPTION

OSCILLATOR

The ML4825 oscillator charges the external capacitor (CT)

with a current (ISET) equal to 3/RSET. 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.

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)

ISET

5

RT

3V

5.1V

ISET

6

+

CT

IQ1

–

Q1

4

CLOCK

tD

RAMP PEAK

CT

RAMP VALLEY

Figure 1. Oscillator Block Diagram

ML4825

100k

100nF

47nF

22nF

0nF

10k

4.7nF

2.2nF

1k

100

1nF

470pF

1k

10k

100k

1M

FREQUENCY (Hz)

Figure 2. Oscillator Timing Resistance vs Frequency

160

1.0nF

140

120

100

80

10k

470pF

100k

1M

FREQUENCY (Hz)

Figure 3. Oscillator Deadtime vs Frequency

4.70

2.20

1.00

0.47

0.22

0.10

0.047

0.47 1.0 2.2 4.7 10.0 22

47 100

CT (nF)

Figure 4. Oscillator Deadtime vs CT (3kΩ ≤ RT ≤ 100kΩ)

5

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