Page 14 - EngineerIT July 2022

ELECTRONICS

Performance data integrated bootstrap capacitor inside of LTC705x DrMOS family. This will translate to lower
Efficiency and power loss overshoot on the switch node, meaning reduced EMI, as well as radiated and conducted
The test result in figure 5 shows that, noise, and higher reliability as switch-node overvoltage stresses are reduced.
at a switching frequency of 500 kHz,
the LTC7051 managed to have higher Device output ripple performance
efficiency (0.70% better) compared to Another parameter is the output voltage ripple shown in Figure 8. It can be seen that the
its competitor. With a further increase in noise exhibited by LTC7051 is less compared to that of the competitor’s part. Reduced
switching frequency from 500 kHz to 1 noise is due to the lower V DS spike and minimal oscillation on the switching node, which
MHz, the LTC7051 also provided better are the result of Silent Switcher technology. If switch-node spikes are not generated, then
efficiency (0.95% greater). there is no conducted noise to the output.
Likewise, the LTC7051 and the competitor device were also subjected to output noise
Efficiency performance spread spectrum measurements as shown in Figure 9. LTC7051 outperformed the other
Noteworthy here is the higher efficiency DrMOS device, and showed that the noise generated at the switching frequency is lower
performance of the LTC7051 over the compared to that of the competitor’s part. The noise difference was approximately 1 mV rms.
competitor at high output load current
and at elevated switching frequency.
This is the benefit of ADI’s patented
Silent Switcher technology where
improvements in both switching edge
rate and shorter dead-times reduce
total power losses. This enables higher
switching frequency operation for a
smaller solution size without a significant
impact in overall efficiency. With
lower total power loss comes lower
temperature operation for higher current Figure 5. Efficiency and power loss at 1 V from 0 A to 60 A load with 500 kHz and 1 MHz switching
outputs, thereby significantly increasing frequency, respectively.
power density.

Thermal performance
Advantages in efficiency and power losses
brought about by LTC7051 also translate
to its better thermal performance. A
temperature difference of approximately
3°C to 10°C was observed between the
LTC7051 and the competitor offering,
with the former being cooler, as shown
in Figure 6. This superior performance
of LTC7051 is due to its well-designed, Figure 6. Thermal performance at 1 V output, 60 A load with 500 kHz and 1.0 MHz switching
frequency, respectively.
thermally enhanced package.
With increased ambient temperature
from 25°C to 80°C, the temperature
difference observed between LTC7051
and its competitor widened to
approximately 15°C, with the former
again being cooler.

Device switch node performance
It can be observed from Figure 7 that the Figure 7. Switch node waveforms at 1 V evaluated at 0 A and 60 A load, respectively.
LTC7051 drain-to-source voltage (V DS)
peak is less than that of the competitor’s
device. Also, with the load increased to 60
A, V DS measured on the competitor’s part
is at its peak while prolonged oscillation
can be seen. The LTC7051, on the other
hand, managed to have a smaller spike
and reduced oscillation, again due to
the Silent Switcher 2 architecture and Figure 8. Output ripple waveforms at 1 V evaluated at 0 A and 60 A load, respectively.

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