High Speed PWM Controller
application INFO available
UC1825 UC2825 UC3825
FEATURES • Compatible with Voltage or Current Mode
Topologies
• Practical Operation Switching Frequencies to 1MHz
• 50ns Propagation Delay to Output
• High Current Dual Totem Pole Outputs (1.5A Peak)
• Wide Bandwidth Error Amplifier
• Fully Latched Logic with Double Pulse Suppression
• Pulse-by-Pulse Current Limiting
• Soft Start / Max. Duty Cycle Control
• Under-Voltage Lockout with Hysteresis
• Low Start Up Current (1.1mA)
DESCRIPTION
The UC1825 family of PWM control ICs is optimized for high frequency switched mode power supply applications. Particular care was given to minimizing propagation delays through the comparators and logic circuitry while maximizing bandwidth and slew rate of the error amplifier. This controller is designed for use in either current-mode or voltage mode systems with the capability for input voltage feed-forward.
Protection circuitry includes a current limit comparator with a 1V threshold, a TTL compatible shutdown port, and a soft start pin which will double as a maximum duty cycle clamp. The logic is fully latched to provide jitter free operation and prohibit multiple pulses at an output. An under-voltage lockout section with 800mV of hysteresis assures low start up current. During under-voltage lockout, the outputs are high impedance.
These devices feature totem pole outputs designed to source and sink high peak currents from capacitive loads, such as the gate of a power MOSFET. The on state is designed as a high level.
BLOCK DIAGRAM
SLUS235A - MARCH 1997 - REVISED MARCH 2004
UDG-92030-2
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (Pins 13, 15) . . . . . . . . . . . . . . . . . . . . . . . . 30V Output Current, Source or Sink (Pins 11, 14) DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A Pulse (0.5m s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0A Analog Inputs (Pins 1, 2, 7). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 7V (Pin 8, 9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6V Clock Output Current (Pin 4) . . . . . . . . . . . . . . . . . . . . . . . -5mA Error Amplifier Output Current (Pin 3) . . . . . . . . . . . . . . . . 5mA Soft Start Sink Current (Pin 8) . . . . . . . . . . . . . . . . . . . . . 20mA Oscillator Charging Current (Pin 5) . . . . . . . . . . . . . . . . . . -5mA Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C Lead Temperature (Soldering, 10 seconds) . . . . . . . . . . 300°C
CONNECTION DIAGRAMS
DIL-16 (Top View) J or N Package
UC1825 UC2825 UC3825
SOIC-16 (Top View) DW Package
PLCC-20 & LCC-20 (Top View) Q & L Packages
PACKAGE PIN FUNCTION
FUNCTION
PIN
N/C 1
INV 2
NI 3
E/A Out
4
Clock
5
N/C 6
RT 7
CT 8
Ramp
9
Soft Start
10
N/C 11
ILIM/SD
12
Gnd 13
Out A
14
Pwr Gnd
15
N/C 16
VC 17
Out B
18
VCC
19
VREF 5.1V
20
THERMAL RATINGS TABLE
Package DIL-16J DIL-16N PLCC-20 LCC-20 SOIC-16
Q
QJA
80-120 90(1)
43-75(1)
70-80 50-120(1)
QJC 28(2)
45
34 20(2)
35
Q
2
UC1825 UC2825 UC3825
ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for , RT = 3.65k, CT = 1nF, VCC
= 15V, -55°C