Miniature Liquid Cooling for Next-Generation Personal Computing Devices: Why the Driver IC Is the Key

1.Introduction
2.The Micro-Channel Problem
3.Power Consumption
4.Silent Operation
5.BESTAR
6.Conclusion

Introduction
Smartphones are getting thinner every year. AR and VR headsets are becoming increasingly compact. While users may have different preferences regarding size and appearance, everyone expects a headset that can be worn comfortably for hours. Achieving this level of comfort, however, presents significant challenges in thermal management and system design. With each new generation, smart wearables become more powerful with less space. These very powerful and light laptops can now battle it out for computing power and weight.
What all these trends have in common is more heat in less space.
More powerful and dense chips are being employed in the latest generation of PCs, and this increase cannot be matched by traditional heat management solutions. The tools used by the engineers over the years are coming up against their lifespan.
The ultra-thin heat pipes have been efficient in distributing heat, but under steady high loads, not fast enough. Vapor Chambers offer great heat spreading area, but they become too thick and heavy for many of the types of devices. Miniature fans can offer a few solutions to issues, other issues arise. They cause noise and need physical space and room, which is not available in compact designs of devices. Passive cooling components can only manage with light work-loading, but fail to cope with the high and short bursts of heat.
A new method is needed in the industry. Miniature liquid cooling is the type of cooling. There are problems involved in miniaturizing a traditional water-cooling loop that go beyond a mere shrinking down, that must be overcome before it is possible for someone to do so, thin smartphone, a light AR headset or a smart wearable. It is at the bottom of the miniature liquid cooling pump(the driver and control system) that most of those problems are resolved.

The Micro-Channel Problem: High Performance Creates High Resistance
The micro-channel heat exchanger is used in miniature liquid cooling systems to achieve maximum heat transfer area within a small heat exchanger. These are structures that have channels ranging orders of magnitude from ten-micrometers to hundreds of micrometers. The area for heat exchange is very large relatively to the volume of a coolant at this scale. This is what you want when providing efficient heat removal in a compact space.
The fluid dynamics problem is a serious one with micro-channels. If the liquid runs through very narrow openings, the resistance due to viscosity is large. This type of resistance is known as back-pressure. The smaller the channels, the greater the back pressure for a given flow rate.
The back-pressure level that the micro-channel cold plate can create is enough to cause a complete stalling of the small pump in a smartphone cooling system, or a VR headset thermal module. The operating pressure on a pump that is intended for use in liquid cooling in the desktop or server environments is very different. It simply will not do what is expected it would do in this environment if it were made smaller.
This needs to be accounted for by the driver IC controlling the miniature pump. It must sustain a steady pump rate in the presence of a wide range of variations in back pressure. The driver must sense this rise in pressure and change drive parameters to achieve constant flow if one of these conditions applies, or both-if the viscosity of the coolant is affected by temperature, or a flow path is partially restricted. A drive that is incapable of doing this will result in pump stalling when under load and in turn will prevent the coolant from flowing and make the cooling chip temperature rise rapidly. Worst case scenario is this will result in thermal shutdown or permanent damage. This makes the driver IC not a "canned" part in a miniature liquid cooling system. It is the entity that controls the functioning of the system in actual operations.

Power Consumption: The Cooling System Cannot Be the Battery's Enemy
All phones are battery-powered; AR headsets have battery power limits; smart wearables are also battery-operated; thin and light laptops have inordinately small power budgets. Every milliwatt matters. A thermal management system which consumes noticeable continuous power does part of the shuttle's job for it. Generation of additional heat for the purpose of heat removal, as well as accelerated depletion of the battery.
A small-scale liquid cooling driver IC is a solution to this problem. The aim is to provide all and only the pump power that the system requires at any time.
The thermal output of the chip during light loads is low. The flow rate of the coolant may be decreased. The pump functions at slower speed and the driver lowers the outflow rate quickly. When the chip experiences a sudden burst of computational activity, the driver IC immediately increases the pump speed to handle the resulting thermal load. As soon as the workload decreases, it lowers the pump speed accordingly, maintaining efficient cooling while minimizing energy consumption.
During normal operation, the cooling system's average power consumption is maintained in the milliwatt range with this dynamic power management. The driver IC accomplishes this using power conversion circuits with high efficiency, and algorithms that dynamically adjust pump output to meet the real time thermal demand.
With battery-powered wearable devices, smart watches and those with total system power budgets of a couple hundred mW, this efficiency is more than a performance parameter. The reason for that is that it makes liquid cooling possible as a technology in that device at all.

Silent Operation: Noise Is a Product Quality Issue
Most users will find a cooling fan within a laptop. An AR headset equipped with a cooling fan on the ears is not a cooling fan. Any noise made by a pump or vibration of the fluid against the skin when the smartwatch is on the body will be easily felt at once. But for next-generation personal devices, consumers don't view quiet operation as a high-end item, more than as a base.
An electromagnetic noise and mechanical vibration harmonics are produced by simple square-wave or step-drive signals to miniature pumps. These harmonics, at the pumps' operating frequencies, lie within a range that is acoustically audible and perceptible physically. Hot system but no sound and vibration output for consumer product.
To overcome this problem, a high quality driver IC is available and provides sinusoidal drive waveforms or sinusoidal variable-frequency control. The driver doesn't jump the pump motor, it is programmed to create smooth sinusoidal currents, creating gradual continuous motion of the rotor. Eliminates the switching harmonics that create electromagnetic noise like with a switcher. It also decreases the mechanical vibration that is passed throughout the device chassis from the pump body, the vibration or the structural resonance felt or heard by users.
This ensures smooth, quiet speed throughout the pump's operating range. This difference between the square-wave drive and sinusoidal drive is very apparent in AR and VR headsets where the device is physically next to the user's ears. The same applies for wearables directed against the skin, because their smooth functioning without vibrations is also vital.

BESTAR: Committed to the Liquid Cooling Technology Frontier
BESTAR experiences a vast amount of knowledge in precision electroacoustic components, piezoelectric technology and micro-electromechanical system, which have been accumulated for many years. That knowledge of working at the micro-scale in vibration control, energy conversion and miniaturisation of actuator design could all be directly applied to the knowledge required for the development of drivers for miniature liquid cooled cooling.
The vision of BESTAR for the next generation of personal computing terminals—smartphones, AR and VR, smart wearables, and high-performance thin-and-light laptops—is to see liquid cooling driver technology as a core feature.
Continuous development work has resulted in concrete advancements of the core technical challenges in this area from BESTAR. At the fundamental level as well as reaching the intelligent control level, BESTAR has worked with the miniaturized hardware, as well as the firmware that enables the delivery of reliably working miniature liquid cooling systems in real product applications. The application of that knowledge to both the actual components and the control intelligence will make it possible for BESTAR to put forward customers a complete solution and not random parts of solutions.

Conclusion
By adopting the Liquid Cooling approach on a miniature scale, high performance personal computing devices are moving in this direction. Tight device miniaturization and chip power density constraints provide few options. Thermal management will remain one of the trickiest challenges during the development of any smartphone, AR or VR headset and smart wearables that keep monitoring health parameters and now also edge computing capabilities on a constant basis.
BESTAR's engineering staff is ready to provide support for customers to resolve thermal challenges for new trendy personal computing equipment. Whether you are developing an AR/VR headset, a smart wearable, a thin and light high-performance laptop or a project using a smartphone and wanting to consider miniaturised liquid cooling as your solution for thermal management we want to know about it.
Contact BESTAR and begin the discussion, take the next steps towards a thermal management solution that is tailored to the challenges of next-generation personal devices.