Compact temperature compensation of inductive fly-back clamps for integrated power switches using a high-voltage base-current-compensated Vbe multiplier

In advanced power systems controlling inductive loads, integrating a power switch with clamping functionality that protects against inductive fly-back with other control circuitry can achieve a lower system cost. However, the conventional active clamp typically consists of many reverse-biased diodes that exhibit a positive temperature coefficient which is counterbalanced by several forward-biased diodes that consume a large chip area. A compact high-voltage V_be multiplier with base-current compensation circuit is presented to introduce a negative temperature coefficient within the clamp that occupies 50% less chip area than an equivalent clamp compensated with forward-biased diodes. The active clamp along with an LDMOS power transistor and driving circuitry have been fabricated in an 180nm high-voltage BiCMOS process and measurement results show that a negative temperature coefficient was introduced to achieve a 4V reduction in clamping voltage over a -40°C to 160°C range.