ML4812
FUNCTIONAL DESCRIPTION
OSCILLATOR
The ML4812 oscillator charges the external capacitor (C
T
)
with a current (I
SET
) equal to 5/R
SET
. When the capacitor
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.
The Oscillator period can be described by the following
relationship:
T
OSC
=
T
RAMP
+
T
DEADTIME
where:
V
OUT
=
V
IN
1
-
D
ON
C
T
´
V
RAM P VALLEY TO PEAK
8.4mA
-
I
SET
and:
T
DEADTIM E
=
10
8
10nF
EXTERNAL
CLOCK
CSYNC
10
90%
5nF
2nF
1nF
85%
MAXIMUM DUTY CYCLE (%)
5
80%
SYNC
Q
2
RT
9
RT (kΩ)
3
70%
20nF
2
ISET
RSYNC
RT
16
CT
8.4mA
ISET
+
CT
1
10
100
OSCILLATOR FREQUENCY (kHz)
1000
5.6V
-
Q
1
Figure 2. Oscillator Timing Resistance vs. Frequency
15
OUTPUT SATURATION VOLTAGE (V)
CLOCK
tD
RAMP PEAK
V(CT)
RAMP VALLEY
VCC
14
13
VCC = 15V
80µs PULSED LOAD
120Hz RATE
SOURCE SATURATION
LOAD TO GROUND
SINK SATURATION
LOAD TO VCC
3
2
1
Figure 1. Oscillator Block Diagram
GND
0
0
200
400
600
800
OUTPUT CURRENT (mA)
Figure 3. Output Saturation Voltage vs. Output Current
5
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
