UCC28500, UCC28501, UCC28502,
UCC38500, UCC38501, UCC38502
SLUS419C 鈥?AUGUST 1999 鈥?REVISED NOVEMBER 2001
BiCMOS PFC/PWM
COMBINATION CONTROLLER
FEATURES
D
Combines PFC and Downstream Converter
D
D
D
D
D
D
D
D
D
Controls
Controls Boost Preregulator to Near-Unity
Power Factor
Accurate Power Limiting
Improved Feedforward Line Regulation
Peak Current-Mode Control in Second Stage
Programmable Oscillator
Leading-Edge/Trailing-Edge Modulation for
Reduced Output Ripple
Low Start-up Supply Current
Synchronized Second Stage Start-Up, with
Programmable Soft-start
Programmable Second Stage Shutdown
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
PFC-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.
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
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.
Copyright
錚?/div>
2001, Texas Instruments Incorporated
www.ti.com
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