ML4825
ERROR AMPLIFIER
The ML4825 error amplifier is a 5.5MHz bandwidth 12V/µs
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.
SOFT START AND CURRENT LIMIT
The ML4825 employs two current limits. When the
voltage at I
LIM
/SD exceeds 1V, the outputs are
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
LIM
/SD reaches 1.4V before the outputs have turned
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.
5
100
80
4
V
IN
60
AV
40
20
0
0
–20
0
0
–90
–180
100M
(V)
3
V
OUT
2
1
0
0.2
0.4
0.6
0.8
1.0
100
1k
10k
100k
1M
10M
TIME (µs)
FREQUENCY (Hz)
Figure 5. Unity Gain Slew Rate
V
CC
3
POWER V
C
13
Q2
VSAT (V)
AV (dB)
OUT A
Figure 6. Open Loop Frequency Response
2
11
SOURCE
OUT B
14
1
Q1
POWER
GND
SINK
12
0
0
0.5
IOUT (A)
1.0
1.5
Figure 7. Simplified Schematic
Figure 8. Saturation Curves
6
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
