UC1849
UC2849
UC3849
Secondary Side Average Current Mode Controller
FEATURES
DESCRIPTION
The UC1849 family of average current mode controllers accurately accom-
plishes secondary side average current mode control. The secondary side
output voltage is regulated by sensing the output voltage and differentially
sensing the AC switching current. The sensed output voltage drives a volt-
age error amplifier.The AC switching current, monitored by a current sense
resistor, drives a high bandwidth, low offset current sense amplifier. The
outputs of the voltage error amplifier and current sense amplifier differential-
ly drive a high bandwidth, integrating current error amplifier. The sawtooth
waveform at the current error amplifier output is the amplified and inverted
inductor current sensed through the resistor. This inductor current down-
slope compared to the PWM ramp achieves slope compensation, which
gives an accurate and inherent fast transient response to changes in load.
•
Practical Secondary Side Control
of Isolated Power Supplies
•
•
1MHz Operation
Differential AC Switching Current
Sensing
•
•
Accurate Programmable
Maximum Duty Cycle
Multiple Chips Can be
Synchronized to Fastest
Oscillator
•
•
Wide Gain Bandwidth Product
(70MHz, Acl>10) Current Error
and Current Sense Amplifiers
The UC1849 features load share, oscillator synchronization, undervoltage
lockout, and programmable output control. Multiple chip operation can be
achieved by connecting up to ten UC1849 chips in parallel.The SHARE bus
and CLKSYN bus provide load sharing and synchronization to the fastest
oscillator respectively. The UC1849 is an ideal controller to achieve high
power, secondary side average current mode control.
Up to Ten Devices Can Easily
Share a Common Load
BLOCK DIAGRAM
Pin numbers refer to 24-pin packages.
UDG-94110
7/95
Powered by ICminer.com Electronic-Library Service CopyRight 2003