Current limit chip cuts GbE and xDSL protection paracitics
Bourns has introduced a family of transient current suppressors (TCSs) for protecting and reducing parasitic capacitance on fast serial busses, including xDSL and Gigabit Ethernet (GbE).
Dubbed the DL-Series, they are bidirectional, automatically reset, and are intended to be installed between the protected device and a transient voltage suppressor (see diagram below).
“The TCS can block voltages up to 40V. This enables very low voltage electronics to be protected by a lower capacitance, higher voltage transient voltage suppressor [TVS], thus achieving very low capacitive loading on high-speed signal lines,” said Bourns. “For example, on a 3.3V driver, a 12V rated TVS may be used, having much lower and more linear capacitance than a lower voltage type.”
Even though a high voltage TVS is used, the maximum stress seen by the protected device is lower than would be seen by using a low voltage TVS by itself, claims the firm, as the current is limited to within the maximum limits of the current protector.
The current suppressors typically switch from normal operation to current limiting in 50ns, and the 40V can be withstood for 1ms.
Parasitic capacitance figures are not yet included on the data sheet.
To avoid asymmetry between protected lines, the two current limiters within a package are matched.
For example, the two elements in a TCS-DL004-250-WH typically exhibit a resistance of 2.3? (1.6min – 3.0max), matched to +/-50m?.
This particular device limits to between 250 and 500mA (375mA typical).
diag, a typical circuit protecting Gigabit Ethernet drivers from line-bourn transients.
“DSL and Ethernet interfaces are increasingly exposed to surge threats. Bourns solutions protect low voltage driver and receiver components from damage from lightning surges without compromising performance,” claimed product line manager Ian Doyle. “The small footprint simplifies retrofitting or upgrading of existing equipment. In most cases, designers can simply add a device to an existing transient voltage suppressor protection design.”
Current limits have a temperature dependence of around +50% at the minimum operating temperature of -40°C, and -60% at the maximum operating temperature of 125°C.
Storage is allowed between -65 and 150°C.
The above device, the smallest and lowest current in the family, is 4×2.5mm and 0.85mm high.
The largest one (1? 1.1A) is 4.0×4.4×0.84mm.