ML4811CP MICRO-LINEAR [Micro Linear Corporation], ML4811CP Datasheet - Page 6

• Manufacturer Part Number: ML4811CP
• Description: High Frequency Power Supply Controller
• Manufacturer: MICRO-LINEAR [Micro Linear Corporation]

V(1)
V(1)
Figure 4. Switching Current and Pin 4 Voltage — Normal
Figure 5. Switching Current and Pin 4 Voltage — Load Fault
I(1)
I(1)
ML4810, ML4811
OSCILLATOR
The ML4811 oscillator charges the external capacitor (C
with a current (I
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. A
discharge of the oscillator con be initiated by applying a
high level to the Sync pin. A short pulse of a frequency
higher than the oscillator’s free running frequency can be
used to synchronize the ML4811 to an external clock. The
pulse can be equal to the desired deadtime (T
deadtime can be determined by I
greater.
6
Figure 7. Oscillator Timing Resistance vs Frequency
100k
10k
1k
100
100nF
SET
) equal to 3/R
47nF
1k
22nF
FREQUENCY (Hz)
10k
0nF
T
. When the capacitor
DIS
4.7nF
100k
and C
2.2nF
T
1nF
, whichever is
1M
470pF
D
) or the
T
)
The oscillator period can be described by the following
relationship:
where:
and:
Figure 6. Simplified Oscilator Block Diagram and Timing
t
t
t
OSC
RAMP
DEADTIME
Figure 8. Oscillator Deadtime vs Frequency
SYNC
I
= t
SET
R
C
RAMP VALLEY
160
140
120
100
T
T
80
RAMP PEAK
RAMP
10k
C Ramp Valley to Peak
10
6
7
CLOCK
(
I
C Ramp Valley to Peak
SET
+ t
3V
I
DIS
(
DEADTIME
Q1
1.0nF
470pF
C
I
T
SET
FREQUENCY (Hz)
100k
t
I
D
Q
1
5V
Q2
)
+
–
)
1M
CLOCK
OUT
5