Buck/boost module to extend battery life of IoT applications
By Jordi Torrebadell, Representative Director, RECOM Power Japan K.K.
Monday, 01 July, 2019
The RBB10-2.0 series is a 4 A non-isolated buck/boost regulator power module where the input voltage can be higher, lower or the same as output voltage. Transition from buck to boost mode is smooth without any interruption to the output. The output voltage can be easily adjusted from 1 V to 5.5 V with external resistors.
The module uses a 25pad LGA package which is compatible with the DOSA footprint. Although the DOSA footprint uses fewer pads, the position of the functions/features in the RECOM 25pad LGA footprint matches exactly those of the standard DOSA package (Vin, Vout, GND, Sense, Enable, Trim, etc).
This compact DOSA-compatible footprint module has a low profile of only 3.9 mm, but an efficiency of up to 95% allows the RBB10-2.0 module to operate at full load in ambient temperatures as high as 85°C without forced air cooling.
The package also features 6-sided shielding for optimal EMC performance and excellent thermal management, as well as several protections: short-circuit protection (SCP), over current protection (OCP) and over temperature protection (OTP).
Typical applications include USB voltage regenerators, 3.3 V to/from 5 V converters, supercapacitor boosters and Li-Ion battery regulators.
RECOM also offers an easy-to-use evaluation board for quick prototyping with pin connectors for the input/output pads and all other additional features, such as enabling, trimming and sensing functions.
How to use the RBB10-2.0 module to expand battery life and protect the RF modules
Most engineers in the IoT industry will be reticent to add cost by using a regulator after the battery. However, the unique features of this buck/boost module will allow engineers to expand the usage of the battery and extend the battery lifetime, as well as the final product’s lifetime, which can generate additional revenue.
Case Study I: lithium polymer batteries
Let’s imagine that an engineer wants to build an IoT system with LTE/GSM capabilities powered by a Lithium Polymer battery.
For the LTE/GSM module let’s take as an example the SARA-R4/N4 module from Ublox that has an input voltage range of 3.2–4.2 V. And for the battery let’s use a generic 3.7 V LiPo Battery, which has a typical usable voltage range from 2.7–4.2 V.
Looking at a typical battery span life graph of a LiPo battery, you can see that around the 10–15% of the charge capacity level the voltage has already dropped to below 3.2 V. This means that you can’t use that remaining 10–15% of the battery for such an application.
Because of the ability of RECOM’s RBB10-2.0 module to boost the voltage, you can utilise that wasted 10–15% of battery capacity until fully discharged (around 2.7 V) increasing the usable lifetime of not only the battery but the whole LTE/GSM system.
Additionally, the RBB10-2.0 offers an enable control that an engineer can use to even further increase the lifetime of the whole system by putting the RBB-10-2.0 regulator in stand-by operation mode when communication is not necessary — a mode which requires less than 7 µA from the battery. When communication is necessary, the enable control can turn on the RBB10-2.0 and activate the LTE/GSM module to allow data transmission.
If we take an LTE/GPS module, for example the Ublox’s LARA-R3121 module, the issue with the LiPo batteries becomes even more critical since the minimum voltage required by this module is 3.3 V.
Case Study II: lithium-ion batteries
Another concern would be if the system uses a rechargeable lithium-ion (Li-ion) battery that can reach voltages of 4.6 or 4.8 V at full charge capacity. These high voltages can’t be used with the majority of LTE/GSM/GPS modules. In this case a regulator like RECOM’s RBB10-2.0 would be mandatory to avoid damage to the RF module. The RBB10-2.0 can smoothly transition from buck topology when the battery voltage is 3.7–4.8 V to a boost topology when the battery voltage is 2.7–3.7 V, providing a stable 3.7 V to the RF modules across all discharging stages of the batteries.
How to use RBB10-2.0 module to reduce cost by resizing your batteries
Case Study III: AA batteries
Now that we have established a very important reason for using a regulator together with a LiPo or Li-Ion battery to optimise the usage of those batteries in RF systems requiring 3.7 V, why not go one step forward and exploit the boost mode of the RECOM’s RBB10-2.0 by using a simple 2-pack of AA batteries? Two AA batteries will have a realistic usable battery voltage of 2.4 to 3 V.
Typically, two AA batteries could not be used to power a 3.7 V LTE/GSM module, but by adding a RBB10-2.0, the low battery voltage can be boosted to 3.7 V which can be used in such RF applications.
How to use RBB10-2.0 module with supercapacitors for unlimited cycle life
If the goal is to improve the number of cycles or increase speed of charging or operate in relatively lower temperatures, another option would be to use supercapacitors instead of batteries. The linear discharge capacity behavior of the supercapacitors also demands the use of a regulator such as RECOM’s RBB10-2.0 to optimise supercapacitor usage in 3.7 V RF/IoT applications.
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