UCC28951
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ZHCSIQ7A –AUGUST 2018 –REVISED DECEMBER 2021
The voltage at the ADEL input of the controller (VADEL) must be set with RA based on the following conditions:
• If tABSET > 155 ns, set VADEL = 0.2 V. tABSET can be programmed between 155 ns and 1000 ns.
• If tABSET ≤155 ns, set VADEL = 1.8 V. tABSET can be programmed between 29 ns and 155 ns.
Based on VADEL selection, calculate RA:
R
AHI ´ VADEL
RA =
» 344W
5V - VADEL
(132)
(133)
The closest standard resistor value for RA selected is 348 Ω.
Recalculate VADEL based on resistor divider selection:
5V ´RA
VADEL
=
= 0.202V
R
AHI + RA
Resistor RAB programs tABSET. Variable CS is the voltage at the CS pin with respect to ground and ratio KA was
calculated in 方程式5:
TABSET
RAB
=
´ 0.26 + CS´K ´1.3 » 30.6kW
A
(
)
5
(134)
The standard resistor value for RAB selected for the design is 30.1 kΩ.
备注
After a prototype oprational, fine tune tABSET during light-load operation to the peak and valley of the
resonance between LS and the switch node capacitance. In this design, the delay was set at 10%
load.
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Product Folder Links: UCC28951
English Data Sheet: SLUSDB2
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