May 1997
ML4810*, ML4811**
High Frequency Power Supply Controller
GENERAL DESCRIPTION
The ML4810 and ML4811 High Frequency PWM
Controllers are optimized for use in Switch Mode Power
Supply designs running at frequencies to 1MHz. The
ML4810/11 contain a unique overload protection circuit
which helps to limit stress on the output devices and
reliably performs a soft-start reset. These controllers are
designed to work in either voltage or current mode and
provide for input voltage feed forward.
A 1.1V threshold current limit comparator provides a
cycle-by-cycle current limit. An integrating circuit
“counts” the number of times the 1.1V limit was reached.
A soft-start cycle is initiated if the cycle-by-cycle current
limit is repeatedly activated. A reset delay function is
provided on the ML4811.
These controllers are similar to the UC1825 controller,
however these controllers include many features not
found on the 1825. These features are set in
Italics.
FEATURES
s
s
s
s
s
s
s
s
s
s
s
Integrating Soft Start Reset
High current (2A peak) dual totem pole outputs
Practical operation to 1MHz (f
OSC
)
5.1V
±2%
trimmed bandgap reference
Under voltage lockout with 7V hysteresis
Soft Start Reset Delay (ML4811)
Oscillator synchronization function (ML4811)
Soft Start latch ensures full soft start cycle
Outputs pull low for undervoltage lockout
Accurately controlled oscillator ramp discharge current
All timing currents “slaved” to R
T
for precise control
* This part is End of Life as of August 1, 2000
** This part is Obsolete
BLOCK DIAGRAM
(Pin numbers shown are for ML4811)
6
7
10
11
8
3
2
1
9
R
T
C
T
SYNC
O.V.P./SHUTDOWN
RAMP
E/A OUT
NI
INV
SOFT START
P
+
–
OSC
2.2V
+
–
CLOCK
5
1.25V
+
–
R
COMP
I(1)
S
Q
PWR V
C
OUT A
C
TF.F.
Q
Q
POWER GND
POWER V
C
OUT B
POWER GND
V+
+
–
ERROR
AMP
I(1)
V+
16
14
17
15
1.1V
–
+
4V
1.5V
2.45V
4
RC (RESET)
20
–
–
RESET DELAY
CLOCK
+
+
+
+
–
–
12
I
LIM
/SD
ENABLE
V
REF
V
REF
GEN
Q
9V
R
–
1.5V V
REF
19
S
S
3× I(1)
Q
R
INTERNAL
BIAS
V
CC
GND
18
5.1V
1.1V
1.1V
UNDER
VOLTAGE
LOCKOUT
+
13
3V
I(1) = 16 x R
T
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
