A reconfigurable DMOS control chip for an electronic typewriter

A custom chip combining complex signal circuits and power sections is described. It provides the power subsystem for a portable typewriter, including drivers for three different loads, the associated control logic, and a switched-mode power supply (SMPS). This IC can exchange load drive and control strategy information with a standard microprocessor by means of an 8-bit common-I/O data bus. The microprocessor interface decodes the first four bits, which, depending on the content of the remaining four, are used to operate the power transistors, activate the PWM (pulse width modulation) loop, and set the D/A (digital/analog) output value. The fabrication technique used for the integrated circuit combines the DMOS process with some steps typical of the junction-isolated technique. The regulated voltage used to drive the internal circuit blocks and the external microprocessor can deliver 5 W (5 V, 1 A) with an efficiency greater than 90% at a typical frequency of 100 kHz.<>