Controller. UC3825 Datasheet

UC3825 Datasheet PDF


Part

UC3825

Description

High Speed PWM Controller

Manufacture

Unitrode

Page 20 Pages
Datasheet
Download UC3825 Datasheet


UC3825 Datasheet
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 fre-
quency 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 cur-
rent-mode or voltage mode systems with the capability for input volt-
age 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 out-
puts 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

UC3825 Datasheet
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


Features Datasheet pdf High Speed PWM Controller application I NFO available UC1825 UC2825 UC3825 FE ATURES • Compatible with Voltage or C urrent Mode Topologies • Practical Op eration Switching Frequencies to 1MHz 50ns Propagation Delay to Output • High Current Dual Totem Pole Outputs ( 1.5A Peak) • Wide Bandwidth Error Amp lifier • Fully Latched Logic with Dou ble Pulse Suppression • Pulse-by-Puls e Current Limiting • Soft Start / Max . Duty Cycle Control • Under-Voltage Lockout with Hysteresis • Low Start U p Current (1.1mA) DESCRIPTION The UC18 25 family of PWM control ICs is optimiz ed for high frequency switched mode pow er supply applications. Particular care was given to minimizing propagation de lays through the comparators and logic circuitry while maximizing bandwidth an d slew rate of the error amplifier. Thi s controller is designed for use in eit her current-mode or voltage mode system s with the capability for input voltage feed-forward. Protection circuitry includes a current limit comparator with a 1V t.
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