UCC28951
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ZHCSIQ7A –AUGUST 2018 –REVISED DECEMBER 2021
VP = 2V
(99)
Calculate current sense resistor (RCS) and leave 300 mV for slope compensation using 方程式 100. Include a
1.1 factor for margin:
VP - 0.3V
RCS
=
» 47W
IP1
´1.1
CTRAT
(100)
(101)
Select a standard resistor for RCS
:
RCS = 47W
Estimate the power loss for RCS using 方程式102:
æ
ç
è
ö2
÷
IPRMS1
CTRAT
P
=
´RCS » 0.03W
RCS
ø
(102)
Calculate maximum reverse voltage (VDA) on DA using 方程式103:
DCLAMP
P 1-DCLAMP
VDA = V
» 29.8V
(103)
(104)
(105)
Estimate the DA power loss (PDA) using 方程式104:
POUT ´0.6V
P
=
» 0.01W
DA
VINMIN ´ h´CTRAT
Calculate reset resistor R7:
Resistor R7 is used to reset the current sense transformer CT:
R7 = 100´RCS = 4.7kW
Resistor RLF1 and capacitor CLF form a low-pass filter for the current sense signal (Pin 15). For this design,
chose the following values. This filter has a low frequency pole (fLFP) at 482 kHz, (which is appropriate for most
applications) but may be adjusted to suit individual layouts and EMI present in the design.
R
LF1 = 1kW
(106)
(107)
CLF = 330pF
1
fLFP
=
= 482kHz
2pf ´RLF1 ´CLF
(108)
The UCC28951 VREF output (Pin 1) needs a high frequency bypass capacitor to filter out high frequency noise.
This pin needs at least 1 µF of high-frequency bypass capacitance (CREF).
CREF = 1mF
(109)
Copyright © 2023 Texas Instruments Incorporated
English Data Sheet: SLUSDB2
56
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