UCC28500-12 Datasheet, PDF (1/35 Pages) Texas Instruments – BiCMOS PFC/PWM COMBINATION CONTROLLER

UCC28500, UCC28501, UCC28502, UCC28503
UCC38500, UCC38501, UCC38502, UCC38503
SLUS419C − AUGUST 1999 − REVISED NOVEMBER 2001
BiCMOS PFC/PWM
COMBINATION CONTROLLER
FEATURES
D Combines PFC and Downstream Converter
Controls
D Controls Boost Preregulator to Near-Unity
Power Factor
D Accurate Power Limiting
D Improved Feedforward Line Regulation
D Peak Current-Mode Control in Second Stage
D Programmable Oscillator
D Leading-Edge/Trailing-Edge Modulation for
Reduced Output Ripple
D Low Start-up Supply Current
D Synchronized Second Stage Start-Up, with
Programmable Soft-start
D Programmable Second Stage Shutdown
DESCRIPTION
The UCC2850x family provides all of the control
functions necessary for an active power-factor-
corrected preregulator and a second-stage dc-to- dc
converter. The controller achieves near-unity power
factor by shaping the ac input line current waveform to
correspond to the ac input-line voltage using average
current-mode control. The dc-to-dc converter uses
peak current-mode control to perform the step-down
power conversion.
The PFC stage is leading-edge modulated while the
second stage is trailing-edge synchronized to allow for
minimum overlap between the boost and PWM
switches. This reduces ripple current in the bulk-output
capacitor.In order to operate with over three-to-one
range of input-line voltages, a line feedforward (V_FF) is
used to keep input power constant with varying input
voltage. Generation of V_FF is accomplished using I_AC in
conjunction with an external single-pole filter. This not
only reduces external parts count, but also avoids the
use of high-voltage components, offering a lower-cost
solution. The multiplier then divides the line current by
the square of V_FF.
The UCC2850x PFC section incorporates a low
offset-voltage amplifier with 7.5-V reference, a
highly-linear multiplier capable of a wide current range,
a high-bandwidth, low offset-current amplifier, with a
novel noise-attenuation configuration, PWM
comparator and latch, and a high-current output driver.
Additional PFC features include over-voltage
protection, zero-power detection to turn off the output
when VAOUT is below 0.33 V and peak current and
power limiting.
The dc-to-dc section relies on an error signal generated
on the secondary-side and processes it by performing
peak current mode control. The dc-to-dc section also
features current limiting, a controlled soft-start, preset
operating range with selectable options, and 50%
maximum duty cycle.
The UCC28500 and UCC28502 have a wide UVLO
threshold (16.5 V/10 V) for bootstrap bias supply
operation. The UCC28501 and UCC28503 are
designed with a narrow UVLO range (10.5 V/10 V) more
suitable for fixed bias operation. The UCC28500 and
UCC28501 have a narrow UVLO threshold for PWM
stage (to allow operation down to 75% of nominal bulk
voltage), while the UCC28502 and UCC38503 are
configured for a much wider operation range for the
PWM stage (down to 50% of bulk nominal voltage).
Available in 20-pin N and DW packages.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
www.ti.com
Copyright  2001, Texas Instruments Incorporated
1