Page 29 - EngineerIt July 2021

ELECTRONICS

Point-of-load DC-to-DC converters

solve voltage accuracy, efficiency

and latency issues

By Atsuhiko Furukawa, Field Applications Engineer

Question:
Why use point-of-load
(POL) power supplies

where the DC-to-DC
converter is as
close as possible
to the load?

Answer:
Efficiency and
Proximity to power accuracy are two big
It’s one of the best ways
to improve voltage advantages but achieving
accuracy, efficiency and POL conversion requires
the dynamic response
of a power rail. A point-of- some care in regulator
load converter is a power design.
supply DC-to-DC converter
placed as close to the load as
possible to achieve proximity
to power. Applications that benefit from Figure 1: DC-to-DC output voltage drop with narrower PCB trace.
POL converters include high performance CPUs, SoCs and
FPGAs — all of which require ever increasing power levels. In
automotive applications, for example, the number of sensors used
for an advanced driver assistance system (ADAS) — such as
those in radar, LIDAR and vision systems — is steadily multiplying,
resulting in the need for faster data processing (more power) to
detect and track surrounding objects with minimal latency.
Many of these digital systems operate at high current and
low voltages, increasing the need to minimise the distance from
power supply to load. One obvious problem with high currents
is trace-induced voltage drops from converter to load. Figures 1
and 2 show how minimising the resistance of the leads between
supply and load minimises the output voltage drop of the Figure 2: DC-to-DC output voltage drop with wider PCB trace.
converter’s output — in this case, a controller IC and MOSFETs
powering a CPU.
The wider PCB trace shown in Figure 2 reduces the voltage
drop to meet the accuracy requirement, but parasitic inductance
must also be considered. The PCB trace length in Figure 2 has an
estimated inductance of about 14.1 nH, as shown in the LTspice ®
model of Figure 3. Figure 3: An LTspice model for the PCB trace inductance.

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