ML4828 Micro Linear, ML4828 Datasheet - Page 5

• Manufacturer Part Number: ML4828
• Description: BiCMOS Phase Modulation/Soft Switching Controller
• Manufacturer: Micro Linear

FUNCTIONAL DESCRIPTION
PHASE MODULATOR
The ML4828 controls the power of a full bridge power
section by modulating the phases of the switches of the A
and B sides (Figure 1). The power cycle starts with A2 and
B1 high, as shown in the timing diagram (Figure 2).
1. With A2 and B1 high, Q1 and Q2 are ON. Current
2. After either the
3. B2 goes high after time t
flows through the primary of the transformer, and
power is delivered to the output through the secondary
winding (not shown).
goes low, turning off Q2. Energy in the primary winding
charges the parasitic capacitances of Q2 and Q3 to
+VIN during t
connected from RB (pin 2) to GND. t
large enough such that the source of Q3 has been
DB
Figure 2. Phase Modulation control waveforms (Shaded areas indicate a power cycle).
.
MOD or I
A2
A1
ML4828
I
LIM
DB
Figure 1. Simplified diagram of Phase Modulated power Outputs.
, which is set by the resistor
LIM
B2
B1
CLOCK
comparator trips, B1
A2
A1
C
B1
B2
B
A
T
DB
T
B
T
should be set
B
t
PD1
t
DB
B
t
DA
Q3
Q2
4. CLOCK then goes high and A2 goes low, while A1
5. A1 goes high after time t
The above sequence is then repeated with the roles of
side A and B interchanged.
The ML4828 can also be used in current mode by sensing
the load current on the RAMP input (pin 11).
L
charged to +VIN. At this time, Q3 turns on at zero
voltage. The transformer is now effectively shorted
through Q1 and Q3, with the primary magnetizing
current circulating in the loop formed by the
transformer primary, Q1, and Q3.
remains low for time t
connected from RA (pin 1) to GND. During this time,
both Q1 and Q4 are OFF. The primary magnetizing
current discharges the parasitic capacitances of Q1 and
Q4 to GND.
Q4 is discharged to GND, and Q4 turns on at zero
voltage. With both Q3 and Q4 ON, a new power cycle
starts, and power is delivered to the output.
TRANSFORMER
t
LEAKAGE
PD1
t
DB
+VIN
R
t
DA
SENSE
Q1
Q4
t
PD1
t
DB
t
DA
DA
DA
, which is set by the resistor
A
. At this point, the drain of
T
A
T
A
ML4828
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