Page 22 - EngineerIT May 2022

ELECTRONICS

A new breed of highly integrated

devices for negative output

DC-DC converters

By Thong “Anthony” Huynh, Principal Member of the Technical Staff, Industrial &
Healthcare Business Unit, Maxim Integrated

Introduction case is the negative output voltage, not the system ground
Electronic equipment uses predominantly positive voltage (GND). When using negative voltage rails, designers need
rails for power. Occasionally, some negative voltage rails are to implement level shifter circuits for the system micro-
also used. For this reason, negative (or inverting) output DC- controller to communicate with the DC-DC converter. Figure
DC converter solutions are not as common as their positive 2 illustrates a simplified schematic of a system with two
output DC-DC counterparts. Nevertheless, when powering high level shifters.
performance devices in factory automation, building Again, for simplicity, only one negative output DC-DC
automation and communications systems such as high-speed converter is shown here. But the principle applies to systems
DACs, Op-Amps, RF power amplifiers, AFEs, GaN FET gate with multiple negative voltage rails or with a mix of both
drivers, IGBT gate drivers, etc., a negative voltage rail is needed. positive and negative voltage rails. One level shifter is needed
Designers face a big challenge looking for a negative voltage per I/O pin of each negative output DC-DC converter.
solution where most legacy devices require external level shifter
circuits with which to communicate. They are also outdated,
inefficient, complex and bulky. This article discusses in detail
the drawbacks of legacy solutions, and then investigates a new
breed of highly integrated devices that addresses the deficiency
and offers a compact, easy-to-use, and highly efficient negative
output DC-DC solution.

The negative output dc-dc converter challenges
A typical power system has its lowest voltage potential as
ground reference, or GND. For a positive output DC-DC
Figure 1: Example of a simplified schematic of system using solely
output converter, the ground reference is simply the GND (0V positive voltage rails.
potential). Its input/output signals are naturally referenced
to this ground. The system controller communicates with the
DC-DC converter simply and directly to those I/O pins. Figure
1 illustrates such a system where the system microcontroller
drives the EN (enable) pin of the converter to turn it on and off.
The controller also reads the status of the converter through its
PGOOD (i.e., RESET) pin to know whether the converter power
output is within its regulation and is ready for powering up the
whole system. For simplicity, only one DC-DC converter is shown
here, but the principle also applies to systems with multiple
positive voltage rails.
When a negative DC-DC is used, communication to the
system controller is not trivial. The converter has its I/O’s Figure 2: Example of a simplified schematic of system using negative
pin referenced to its lowest voltage potential, which in this voltage rails.

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