Design Article
Tackling power conversion in auto electronics
By Jeff Greutter, Linear Technology Corp.
10/24/2012 10:45 AM EDT
Tackling transients
Its synchronous rectification design includes internal top and bottom MOSFETs to deliver efficiencies as high as 96%. Figure 3 shows that it can deliver over 95% efficiency when powering a 5V load from a nominal 12V input, even with a relatively high 800kHz switching frequency. This high efficiency operation minimizes wasted power and eliminates the need for heat sinks even in the most space constrained applications. In electric vehicles and hybrids, this can directly translate into increased driving range between battery recharges.
Additionally, the LT8610’s Burst Mode operation reduces no load quiescent current to a mere 2.5uA, making it ideal for always-on applications that must maintain constant voltage regulation even at no loads while maximizing battery life. Additionally, a very low ripple Burst Mode operation topology minimizes output noise to below 10mVPK-PK, making it suitable for noise-sensitive applications. If the application requires external synchronization, the Burst Mode function can be replaced with a pulse-skipping frequency scheme.
The LT8610s very low dropout performance is also very beneficial, particularly in applications which must regulate outputs through use stop-start or cold-crank conditions. Figure 4 shows that even when the input voltage drops below the programmed output voltage, 5V in this case, the output is always 200mV (@1A) below the input voltage once the input exceeds 2.9V. This is important because such ECUs drive require one or multiple microprocessors/microcontrollers.
Although these are designed to operate from a nominal 5V, they continue to operate with supply voltages as low as 3V. So in a cold-crank scenario, the input can drop as low as 3.2V and the microprocessor can continue to operate, enabling the ECU to operate seamlessly through cold crank.
Furthermore, the LT8610’s fast minimum on-time of only 50ns enables 2MHz constant frequency operation from a 16V input to a 1.8V output, optimizing efficiency while avoiding critical noise-sensitive frequency bands such as AM radio.
Conclusion
The rapid growth of very complex electronic systems in automobiles has created even higher performance demands on power management ICs. Depending on where the power supply operates on the automotive power bus, they may be subjected to stop/start, cold-crank and load-dump conditions and must be capable of accurately regulating an output voltage throughout these conditions. Additionally, some of these systems will operate in an always on standby mode, requiring minimal supply current. As more electronic systems are added in ever shrinking spaces, minimizing the solution footprint while maximizing efficiency is also critical. Fortunately ICs that meet these demands are already available paving the way for even higher electronic content in future cars.
(Jeff Gruetter is Sr. Product Marketing Engineer, Power Products, at Linear Technology Corp. (Milpitas, Calif.)
Its synchronous rectification design includes internal top and bottom MOSFETs to deliver efficiencies as high as 96%. Figure 3 shows that it can deliver over 95% efficiency when powering a 5V load from a nominal 12V input, even with a relatively high 800kHz switching frequency. This high efficiency operation minimizes wasted power and eliminates the need for heat sinks even in the most space constrained applications. In electric vehicles and hybrids, this can directly translate into increased driving range between battery recharges.
Figure 3. LT8610 Efficiency Graph of Typical Automotive Schematic
Additionally, the LT8610’s Burst Mode operation reduces no load quiescent current to a mere 2.5uA, making it ideal for always-on applications that must maintain constant voltage regulation even at no loads while maximizing battery life. Additionally, a very low ripple Burst Mode operation topology minimizes output noise to below 10mVPK-PK, making it suitable for noise-sensitive applications. If the application requires external synchronization, the Burst Mode function can be replaced with a pulse-skipping frequency scheme.
The LT8610s very low dropout performance is also very beneficial, particularly in applications which must regulate outputs through use stop-start or cold-crank conditions. Figure 4 shows that even when the input voltage drops below the programmed output voltage, 5V in this case, the output is always 200mV (@1A) below the input voltage once the input exceeds 2.9V. This is important because such ECUs drive require one or multiple microprocessors/microcontrollers.
Although these are designed to operate from a nominal 5V, they continue to operate with supply voltages as low as 3V. So in a cold-crank scenario, the input can drop as low as 3.2V and the microprocessor can continue to operate, enabling the ECU to operate seamlessly through cold crank.
Figure 4. LT8610 Dropout Performance
Furthermore, the LT8610’s fast minimum on-time of only 50ns enables 2MHz constant frequency operation from a 16V input to a 1.8V output, optimizing efficiency while avoiding critical noise-sensitive frequency bands such as AM radio.
Conclusion
The rapid growth of very complex electronic systems in automobiles has created even higher performance demands on power management ICs. Depending on where the power supply operates on the automotive power bus, they may be subjected to stop/start, cold-crank and load-dump conditions and must be capable of accurately regulating an output voltage throughout these conditions. Additionally, some of these systems will operate in an always on standby mode, requiring minimal supply current. As more electronic systems are added in ever shrinking spaces, minimizing the solution footprint while maximizing efficiency is also critical. Fortunately ICs that meet these demands are already available paving the way for even higher electronic content in future cars.
(Jeff Gruetter is Sr. Product Marketing Engineer, Power Products, at Linear Technology Corp. (Milpitas, Calif.)
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cupster
10/25/2012 3:41 PM EDT
You mentioned that no diodes are needed. I assume you were referring to flyback diodes since you have a synchronous output. However, automotive also has a reverse battery requirement which means adding a diode in the battery feed, unless the LT8610 has reverse voltage protection. This adds a diode drop at all voltages and means that the low end battery voltage is now 3.7Volts (assuming we can use a schottky diode). USB charging and data application require 5Volts. We really need a buck-boost supply.
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JefW
11/3/2012 6:57 AM EDT
You don't need an input diode for reverse battery protection. You can use a fet. This is a no-brainer if your low-battery-voltage operating-current is above half an amp or so.
Sepic seems easier to keep rf-clean. You have to use a boost controller rather than buck but with modern ceramic caps it's fairly plain sailing.
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