Datasheet

Non-Linear Gain Generation
Layout Guidelines
Cutoutin
groundplane
Signal
GND
Power
GND
GND
ICOMP
ISENSE
VINS VCOMP
VSENSE
VCC
GATE
UCC28019A
SLUS828B – DECEMBER 2008 – REVISED APRIL 2009 .................................................................................................................................................. www.ti.com
The voltage at VCOMP is used to set the current amplifier gain and the PWM ramp slope. This voltage is
buffered internally and is then subject to modification by the SOC function, as discussed earlier.
Together the current gain and the PWM slope adjust to the different system operating conditions (set by the
ac-line voltage and output load level) as VCOMP changes, to provide a low-distortion, high-power-factor input
current wave-shape following that of the input voltage.
As with all PWM controllers, the effectiveness of the filter capacitors on the signal pins depends upon the
integrity of the ground return. The pin out of the UCC28019A is ideally suited for separating the high di/dt
induced noise on the power ground from the low current quiet signal ground required for adequate noise
immunity. A star point ground connection at the GND pin of the device can be achieved with a simple cut out in
the ground plane of the printed circuit board. As shown in Figure 27 , the capacitors on ISENSE, VINS, VCOMP,
and VSENSE must all be returned directly to the quiet portion of the ground plane, indicated by Signal GND, and
not the high current return path of the converter, shown as the Power GND. Because the example circuit in
Figure 27 uses surface mount components, the ICOMP capacitor, C10, has its own dedicated return to the GND
pin.
Layout Components
LAYOUT COMPONENTS
REFERENCE
FUNCTION
DESIGNATOR
U1 UCC28019A
Q1 Main switch
R1 R
GATE
R5 Pull-down resistor on GATE
C13, C14 VCC bypass capacitors
C10 ICOMP compensation, C
ICOMP
R6 Inrush current limiting resistor, R
ISENSE
C11 I
SENSE
filter, C
ISENSE
R12, R13, R14 R
FB1
on VSENSE
R18 R
FB2
on VSENSE
C16 C
VSENSE
R16, C17, C15 VCOMP compensation components,
R
VCOMP
, C
VCOMP
, C
VCOMP_P
C12, R17 C
VINS
, R
VINS2
on VINS
D2 Boost diode
Figure 27. Recommended Layout for the
UCC28019A
22 Submit Documentation Feedback Copyright © 2008 – 2009, Texas Instruments Incorporated
Product Folder Link(s): UCC28019A