ML4825 Micro Linear, ML4825 Datasheet - Page 6

• Manufacturer Part Number: ML4825
• Description: High Frequency Power Supply Controller
• Manufacturer: Micro Linear

ML4825
ERROR AMPLIFIER
The ML4825 error amplifier is a 5.5MHz bandwidth 12V/ s
slew rate op-amp with provision for limiting the positive
output voltage swing (Output Inhibit line) for ease in
implementing the soft start function.
OUTPUT DRIVER STAGE
The ML4825 Output Driver is a 2A peak output high
speed totem pole circuit designed to quickly switch the
gates of capacitive loads, such as power MOSFET
transistors.
6
5
4
3
2
1
0
Figure 5. Unity Gain Slew Rate
Figure 7. Simplified Schematic
V
IN
V
CC
0.2
V
OUT
0.4
TIME ( s)
Q2
Q1
0.6
POWER V
POWER
OUT A
OUT B
GND
0.8
C
13
11
14
12
1.0
SOFT START AND CURRENT LIMIT
The ML4825 employs two current limits. When the
voltage at I
immediately shut off and the cycle is terminated for the
remainder of the oscillator period by resetting the RS flip
flop.
If the output current is rising quickly such that the voltage
on I
off, a soft start cycle is initiated. The soft start capacitor is
discharged and outputs are held “off” until the voltage at
SS reaches 1V, ensuring a complete soft start cycle. The
duty cycle on start up is limited by limiting the output
voltage of the error amplifier voltage to the voltage at SS.
LIM
/SD reaches 1.4V before the outputs have turned
Figure 6. Open Loop Frequency Response
100
–20
80
60
40
20
LIM
0
3
2
1
0
100
0
/SD exceeds 1V, the outputs are
Figure 8. Saturation Curves
SOURCE
1k
SINK
10k
0.5
FREQUENCY (Hz)
0
I OUT (A)
AV
100k
1.0
1M
10M
100M
1.5
0
0
–90
–180