TPS23753A
www.ti.com
SLVS933B –JULY 2009–REVISED JANUARY 2010
Occasionally, a technique referred to as frequency dithering is utilized to provide additional EMI measurement
reduction. The switching frequency is modulated to spread the narrowband individual harmonics across a wider
bandwidth, thus lowering peak measurements. The circuit of Figure 26 modulates the switching frequency by
feeding a small ac signal into the FRS pin. These values may be adapted to suit individual needs.
VB
6.04kΩ
+
-
TL331IDBV
10kΩ
To
FRS
301kΩ
1uF
RTN
Figure 26. Frequency Dithering
Design Procedure
A detailed design procedure for PDs using the TPS23753A is covered in Designing with the TPS23753 Powered
Device and Power Supply Controller , literature number SLVA305. Several designs with data are provided in the
evaluation module documentation SLVU314 and SLVU315.
References
IEEE Standard for Information Technology … Part 3: Carrier sense multiple access with collision detection
(CSMA/CD) access method and physical layer specifications, IEEE Computer Society, IEEE 802.3™at (Clause
33)
Information technology equipment – Radio disturbance characteristics – Limits and methods of measurement,
International Electrotechnical Commission, CISPR 22 Edition 5.2, 2006-03
Designing with the TPS23753 Powered Device and Power Supply Controller, Eric Wright, TI, SLVA305
Advanced Adapter ORing Solutions using the TPS23753, Eric Wright, TI, SLVA306
Practical Guidelines to Designing an EMI-Compliant PoE Powered Device With Isolated Flyback, Donald V.
Comiskey, TI, SLUA469
TPS23753AEVM-004: Evaluation Module for TPS23753A, SLVU314
TPS23753AEVM-0041 Evaluation Module for TPS23753A, SLVU315
SPACER
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