ML4825CS datasheet(5/9 Pages) MICRO-LINEAR

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ML4825

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:

C Ramp Valley to Peak

RAMP

SET

= ()

and:

C Ramp Valley to Peak

DEADTIME

= ()

Figure 1. Oscillator Block Diagram

ISET

5.1V

IQ1

CLOCK

RAMP PEAK

RAMP VALLEY

–

100k

10k

FREQUENCY (Hz)

100

10k

100k

100nF

47nF

22nF

0nF

4.7nF

2.2nF

1nF

470pF

160

140

120

100

FREQUENCY (Hz)

10k

100k

1.0nF

470pF

4.70

2.20

1.00

0.47

0.22

0.10

0.047

CT (nF)

0.47

2.2

100

1.0

4.7

10.0

Figure 2. Oscillator Timing Resistance vs Frequency

Figure 3. Oscillator Deadtime vs Frequency

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

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