ML4823
FUNCTIONAL DESCRIPTION
OSCILLATOR
The ML4823 oscillator charges the external capacitor (C
T
)
with a current (I
SET
) equal to 3/R
SET
. 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:
T
OSC
= T
RAMP
+ T
DEADTIME
where: T
RAMP
= C (Ramp Valley to Peak)/I
SET
and:
T
DEADTIME
= C (Ramp Valley to Peak)/I
Q1
I
SET
R
T
R
T
3V
5.1V
I
SET
C
T
I
Q1
Q1
+
–
160
Q
2
CLOCK
OUT
140
1.0nF
T
D
(ns)
400µA
120
100
470pF
CLOCK OUT
80
10k
100k
FREQ (Hz)
1M
T
D
RAMP PEAK
C
T
RAMP VALLEY
Figure 3. Oscillator Deadtime vs Frequency
Figure 1. Oscillator Block Diagram
100k
100nF
47nF
22nF
RT (OHMS)
10nF
10k
4.7nF
2.2nF
1nF
470pF
1k
0.1k
1k
10k
100k
1M
10M
T
D
(µs)
30
25
20
15
10
5
0
0.47
1.0
2.2
4.7
10.0
22
47
100
FREQ (Hz)
C
T
(nF)
Figure 2. Oscillator Timing Resistance vs Frequency
Figure 4. Oscillator Deadtime vs C
T
(3kΩ
≤
R
T
≤
100kΩ)
5
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
