ML4825 Datasheet, PDF (1/9 Pages) Micro Linear Corporation – High Frequency Power Supply Controller

May 1997
ML4825*
High Frequency Power Supply Controller
GENERAL DESCRIPTION
FEATURES
The ML4825 High Frequency PWM Controller is an IC
controller optimized for use in Switch Mode Power
Supply designs running at frequencies to 1MHz.
Propagation delays are minimal through the comparators
and logic for reliable high frequency operation while slew
rate and bandwidth are maximized on the error amplifier.
This controller is designed to work in either voltage or
current mode and provides for input voltage feed forward.
A 1V threshold current limit comparator provides cycle-
by-cycle current limit while exceeding a 1.4V threshold
initiates a soft-start cycle. The soft start pin doubles as a
maximum duty cycle clamp. An under-voltage lockout
circuit with 800mV of hysteresis assures low startup
current and drives the outputs low.
This controller is similar in architecture and performance
to the UC1825 controller, however the ML4825 includes
many features not found on the 1825. These features are
set in Italics.
s Practical operation at switching frequencies to 1.0MHz
s High current (2A peak) dual totem pole outputs
s Wide bandwidth error amplifier
s Fully latched logic with double pulse suppression
s Pulse-by-pulse current limiting
s Soft start and maximum duty cycle control
s Under voltage lockout with hysteresis
s Precision trimmed 5.1V bandgap reference
s Pin compatible improved replacement for UC1825
s Fast shut down path from current limit to outputs
s Outputs preset to known condition after under voltage
lockout
s Soft start latch ensures full soft start cycle
s Outputs pull low for undervotage lockout
BLOCK DIAGRAM (Pin configuration shown for 16-pin version) *Some Packages Are Obsolete or End Of Life
5 ^RT
C_T
6
RAMP
7
E/A OUT
3
2 ^NI
INV
1
8 ^SS
OSC
1.25V
+
+ ^COMP
–
ERROR
+ AMP
–
V+
9µA
CQ
TF.F.
P
Q
1V –
ILIM/SD
9
+
+
1.4V ^–
1V
RQ
S
CLOCK OUT
4
R
SQ
POWER GND
POWER V_C
ENABLE
VREF
VREF GEN
9V
UNDER
VOLTAGE
LOCKOUT
INTERNAL
BIAS
PWR VC ₁₃
OUT A
11
OUT B
14
PWR GND
12
4V
1.5V VREF
16
VCC ₁₅
SIGNAL GND
10
1