ml4818 Microsemi Corporation, ml4818 Datasheet - Page 6
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ml4818
Manufacturer Part Number
ml4818
Description
Phase Modulation/soft Switching Controller
Manufacturer
Microsemi Corporation
Datasheet
1.ML4818.pdf
(12 pages)
Available stocks
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Part Number
Manufacturer
Quantity
Price
Part Number:
ml4818CS
Manufacturer:
ML
Quantity:
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ML4818
The ML4818 can also be used in current mode by sensing
load current on the RAMP input (pin 3).
The four output delay timers are programmed via an
external R
value should be no less than 1k . Expressing R
k the delay, in ns is:
The ML4818 contains special logic circuits to provide for
voltage mode feed-forward and lock out long pulses into
the internal logic. This prevents instability from occuring
when the
The collector of Q
cycle. When the power cycle terminates, RAMP is pulled
low. In voltage mode operation, a capacitor is connected
from RAMP to GND with a resistor from RAMP to V
provide input voltage feed forward.
OSCILLATOR
The ML4818 oscillator charges the external capacitor, C
with a current (I
reaches the upper threshold (Ramp Peak), the comparator
changes state, turning on the current sink which
discharges C
C
prevent inaccuracy due to undershoot on C
To use the CLOCK output for driving external synch-
ronization circuitry, a pull-down resistor is required from
CLOCK to GND.
6
T
RAMP VALLEY
pin is clamped to Ramp Valley by Q1 (Figure 5) to
RAMP PEAK
CLOCK
Figure 3. Voltage Feed-Forward Circuit.
DELAY
OSC
OUTPUT
Figure 4. Ocillator Timing Diagram
Comparator trips in voltage mode.
T
MOD
C
to the lower threshold (Ramp Valley). The
T
SET
resistor as shown below. This resistor
T
DELAY
R
) equal to 5/R
S
R
in figure 3 is high only during a power
T
C
T
33
D
Q
R
DELAY
T
. When the C
45
Q
RAMP
R
T
.
T
DELAY
3
voltage
IN
in
to
(1)
T
,
For frequencies of less than 500kHz, oscillator frequency
can be set by using the following formulae:
ERROR AMPLIFIER
The ML4818 error amplifier is a 2.5MHz bandwidth,
8.5V/ s slew rate op-amp with provision for limiting the
positive output voltage swing (output inhibit line) to
implement the soft start function. The error amplifier
output source current is limited to 4.5mA.
I
R
SET
T
C
T
11
2
5.5mA
Figure 5. Ocillator Block Diagram
1.7V
f
OSC
Q1
0 52
.
C R
T T
I
SET
1
+
–
5V
500
C
T
5V
CLOCK
250
OUT
(2)
13