ICs address speedy Ethernet devices’ need for EMI, ESD protection
By Margery Conner, Technical Editor -- EDN, December 13, 2007
The Ethernet communication standard is morphing into 10/100/1000-Mbps versions and gaining inherent power-delivery capability in POE (power-over-Ethernet) designs. System designers are responding with feature-packed products, such as VOIP (voice-over-Internet Protocol) phones and IP cameras. However, it is becoming increasingly difficult to protect these devices from EMI (electromagnetic-interference) noise and ESD (electrostatic discharge) without degrading system performance. Passive devices, including TVS (transient-voltage-suppression) diodes for ESD protection and external chokes for EMI, offer some protection but often at the expense of system performance. Addressing these problems, Akros Silicon has introduced two devices that it claims are the first active devices for suppressing EMI and ESD and promoting EMC (electromagnetic compatibility).
The integrated AS1602 common-mode-EMI-noise- and ESD-suppression IC provides less-than-0.5Ω common-mode impedance to ground and complies with Ethernet-performance specs. The CMOS chip goes between the Ethernet PHY (physical) layer and the line transformer. External ferrites steer bursts of energy to the chip, which quickly sinks the transient energy; in less than 1 nsec, diodes steer the energy away from the PHY layer. The AS1601 version provides only EMI suppression. The AS1602 and AS1601 CMOS ICs sell for $1.60 and $1.23 (1000), respectively.
