UCC28180
www.ti.com
SLUSBQ5A –NOVEMBER 2013–REVISED NOVEMBER 2013
The Switching Frequency
The UCC28180 switching frequency is user programmable with a single resistor on the FREQ pin to ground. For
this design, the switching frequency, fSW, was chosen to be 120 kHz. Figure 31 (same as Figure 1) could be
used to select the suitable resistor to program the switching frequency or the value can be calculated using
constant scaling values of fTYP and RTYP. In all cases, fTYP is a constant that is equal to 65 kHz, RINT is a constant
that is equal to 1 MΩ, and RTYP is a constant that is equal to 32.7 kΩ. Simply applying the calculation below
yields the appropriate resistor that should be placed between FREQ and GND:
f
TYP ´RTYP ´RINT
RFREQ
=
(fSW ´RINT ) + (RTYP ´ fSW ) - (RTYP ´ fTYP
65kHz ´32.7kW ´1MW
)
(12)
(13)
RFREQ
=
= 17.451kW
(120kHz ´1MW) + (32.7kW ´120kHz) - (32.7kW ´ 65kHz)
A typical value of 17.8 kΩ for the FREQ resistor results in a switching frequency of 118 kHz.
265
215
165
115
65
15
0
20
40
60
80
100
120
140
RFREQ (K)
C001
Figure 31. Frequency vs. RFREQ
Copyright © 2013, Texas Instruments Incorporated
Submit Documentation Feedback
25
Product Folder Links :UCC28180
TI [ TEXAS INSTRUMENTS ]
