In many regulated industries who either work directly with High Voltage circuits or may be exposed to High Voltage in a fault condition, Creepage and Clearance requirements exist. The regualtions often come from a safety standard such as IEC60601-1 (medical), IEC60950-1(office) or IEC60112 and are verified and certified by a Nationally Recognized Test Lab (NRTL) such as UL, CSA, VDE, Intertek, etc.
The Creepage distance is defined as the distance across the surface of a dielectric (such as the PCB FR4 material) that a ARC may propagate across.
The Clearance distance is defined as the distance through air that a ARC may cross between two conductors. Clearance is also sometimes referred to as “air gap”.
Safety standards typically specify the required minimum distances for a product to be deemed safe by a NRTL. These distances increase proportional to the maximum expected voltage. Distances may also be derated based on the environment that the product is installed into, also known as contamination level.
A typical requirement may exist for a optocoupler and transformer to isolate a 5VDC “wall wart” power supply from 120VAC mains. In this case a minimum of 1mm of “air gap” or Clearance is required and Creepage of 5mm. If the optocoupler body is only 4mm wide, the device meets the clearance requirement but in order to meet creepage, a slot must be cut in the board such that there is no longer a 4mm direct path across the surface but rather the arc must travel around the slot.
Triad designs ASICs for Medical, Industrial and Automotive customers. In all of these cases, safety consideration influence the design. Often it becomes a challenge for product designers to meet these requirements and still meet the products performance and cost targets with off the shelf parts. In these instances, an ASIC will help to develop a custom isolation strategy to distribute control across the isolation barrier. This strategy can be optimised for cost and performance because of the great flexibility that our technology offers.