The Tech Blog

When designing circuits for reasonably high-power DC applications you will run across the case of handling thermals. It’s not just about picking the right IC for your DC power conversion; thermal management plays a key role. Here’s a primer on designing with thermals in mind.

For linear power regulators, the math is straightforward. Subtract the output voltage from the input voltage, multiply by the output current, and voilà, you have the power dissipation. This lost power needs to be dissipated in the IC package. So get the datasheet of the IC, find the thermals section, and hunt for Junction-to-ambient thermal resistance. Say it’s 45°C/W; this means for every watt lost, the IC temperature spikes by 45°C above ambient. So if it’s 25°C ambient, the IC hits 70°C.

For a DC-DC converter, it’s a bit more trickier. Here Efficiency = Pout/Pin and Power Loss = Pout – Pin. Now in a DC-DC converter datasheet, you need to find your efficiency value. You will get this mostly from a graph in the datasheet that shows the efficiency of the converter for a particular load and particular output current. Put that value in and you get the power lost.

As a designer, it’s your task to manage this dissipated heat somehow. It can be via a large heatsink(which has a smaller thermal resistance) or can even be via PCB ground planes. There is a TI app note (AN2020 worth reading) that tells you what size of PCBs you want to have to dissipate heat properly without heatsinks. Check images for the rule-of-thumb calculations. Don’t overlook thermal vias and multi-layer PCB stacks as other ways to remove this heat.

In summary, always keep thermals in mind else the moment you power on the circuit the first time, you will see the magic smoke. Speaking from experience.

Most tech enthusiasts will know that Li-ion batteries in your phones, laptops, tablets, and watches can have a longer life cycle if they’re not always charged to 100%. If you didn’t know this, it’s true, and it’s not a myth. Let’s delve into why today.

When a Li-ion battery is recharged, from an external power source, it forces Lithium ions to move from positive to negative terminals through the electrolyte, when discharged the reverse happens and power is delivered to the load. During the discharge process, all the Lithium ions don’t reach back to the positive terminal and with repeated usage, it forms a layer of Li atoms on the negative terminal(reducing efficiency for the next cycle). Another key thing is the depth of Discharge(DoD) of Li-ion batteries. Here’s where Depth of Discharge (DoD) comes in. DoD is the percentage of battery capacity that’s been used up. For instance, a 60% DoD means 60% of the battery power has been discharged.

The larger the DoD value, more the deposition of Li atoms on the terminal and the thicker it becomes in further discharge cycles. This is what is causing the drop in battery capacity over multiple cycles. It can reduce the overall lifetime to say around 500 charge cycles before overall capacity drastically drops.

To increase your battery’s lifespan, you need to reduce the DoD, meaning limit the level to which a battery discharges and also the maximum level to which it can be charged. A 60% DoD can potentially triple your battery recharge lifetime cycles(Check the table). However, this means power output in a single cycle is smaller. So, if possible, keep your devices at 60-80% max capacity and charge only when it’s below 20%. It’s a small change that can make a big difference to your battery’s lifespan!

BTW, If you’re keen on diving deeper into batteries and related topics, drop comments or DM! I’m considering creating a detailed BackToBasics series if there is enough interest, but it’ll take some time.