ML4825
100k
10k
1k
FUNCTIONAL DESCRIPTION
100nF
47nF
OSCILLATOR
22nF
The ML4825 oscillator charges the external capacitor (C )
T
with a current (I ) equal to 3/R . When the capacitor
SET
SET
0nF
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.
4.7nF
2.2nF
The oscillator period can be described by the following
relationship:
1nF
470pF
t
= t
+ t
OSC
RAMP DEADTIME
100
1k
10k
100k
1M
FREQUENCY (Hz)
where:
tRAMP
C (Ramp Valley to Peak)
ISET
Figure 2. Oscillator Timing Resistance vs Frequency
=
and:
C (Ramp Valley to Peak)
tDEADTIME
=
160
IQ1
1.0nF
140
I
SET
5.1V
5
6
120
100
R
T
I
SET
3V
+
–
I
Q1
C
T
470pF
4
Q1
80
10k
100k
1M
FREQUENCY (Hz)
Figure 3. Oscillator Deadtime vs Frequency
CLOCK
t
D
RAMP PEAK
4.70
2.20
1.00
0.47
0.22
0.10
0.047
C
T
RAMP VALLEY
Figure 1. Oscillator Block Diagram
0.47
1.0
2.2
4.7
10.0
(nF)
22
47
100
C
T
Figure 4. Oscillator Deadtime vs C (3kΩ ≤ R ≤ 100kΩ)
T
T
5
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
