ML4812
FUNCTIONAL DESCRIPTION
OSCILLATOR
TOSC = TRAMP + TDEADTIME
The ML4812 oscillator charges the external capacitor (C )
where:
VOUT
T
with a current (I ) equal to 5/R . When the capacitor
SET
SET
V
voltage reaches the upper threshold, the comparator
changes state and the capacitor discharges to the lower
threshold through Q1. While the capacitor is discharging,
Q2 provides a high pulse.
IN
=
1- DON
and:
CT ´ VRAMP VALLEY TO PEAK
The Oscillator period can be described by the following
relationship:
TDEADTIME
=
8.4mA - ISET
90%
10
8
5nF
2nF
85%
1nF
10nF
EXTERNAL
CLOCK
5
80%
70%
C
SYNC
SYNC
10
Q
2
3
2
I
SET
20nF
R
T
R
SYNC
9
R
T
I
SET
C
T
1
10
16
+
-
100
OSCILLATOR FREQUENCY (kHz)
1000
C
T
5.6V
8.4mA
Figure 2. Oscillator Timing Resistance vs. Frequency
Q
1
15
V
= 15V
CC
V
CC
80µs PULSED LOAD
120Hz RATE
CLOCK
14
13
t
D
SOURCE SATURATION
LOAD TO GROUND
RAMP PEAK
SINK SATURATION
V(C )
T
LOAD TO V
CC
3
2
1
0
RAMP VALLEY
Figure 1. Oscillator Block Diagram
GND
0
200
400
600
800
OUTPUT CURRENT (mA)
Figure 3. Output Saturation Voltage vs. Output Current
5
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
