There are many different types of batteries and they often need specialised charging IC and dedicated protection devices. Below we discuss the new generation of re-chargeable batteries which can be charged simply, with inexpensive Linear LDO Voltage Regulators. Before moving to the main topic, let us first review and compare some of the different types of batteries.
In the tables below (Fig.1), we show some of the widely used battery chemistries that are readily available in the market. For each we show the operating voltage and provide a summary of the strengths and weaknesses associated with each type of cell. The table is intended as a quick overview and we acknowledge that there are other chemistries available and that the specifications of each battery will vary from manufacturer to manufacturer.
Battery Name |
Type (Positive electrode) |
Nominal Voltage |
Voltage Range |
Features |
||
---|---|---|---|---|---|---|
Lithium battery | Manganese dioxide (Li-MnO2) |
3.0 V | 1.8 V ~ 3.2 V | CR battery. Lower impedance than Li-SOCl2. | ||
Thionyl chloride (Li-SOCl2) |
3.6 V | 2.4 V ~ 3.6 V | ER battery. Large capacity for incorporation into smart meters, etc. Beware of high impedance. | |||
Alkaline battery | 1.5 V | 0.9 V ~ 1.6 V | High capacity, high current output dry cell. | |||
Zinc-carbon battery | 1.5 V | 0.9 V ~ 1.6 V | Dry cell suitable for long-term use with low output current |
Battery Name |
Type (Positive electrode) |
Nominal Voltage |
Voltage Range |
Features |
||
---|---|---|---|---|---|---|
Li-ion battery |
Lithium Cobalt Oxide (LiCoO2) |
3.7 V |
2.8 V ~ 4.2 V, |
General lithium rechargeable battery. Solid-state type is ready. |
||
Lithium iron phosphate (LiFePO4) | 3.2 V | 2.8 V ~ 3.6 V | Lower capacity than above, but safe and long life. | |||
[Negative node] |
2.3 V | 1.6 V ~ 2.6 V |
Rechargeable by LDO. Semi-solid state types are ready. |
|||
Ni-MH battery | Nickel oxide hydroxide (NiOOH) | 1.2 V | 1.0 V ~ 1.3 V | Higher current, larger capacity and smaller memory effect than Ni-Cd | ||
Ni-Cd battery | Nickel oxide hydroxide (NiOOH) | 1.2 V | 1.0 V ~ 1.3 V | Be careful to the memory effect. |
(Fig.1: Typical primary and rechargeable batteries)
Typically, conventional Li-ion batteries have a nominal voltage of 3.7V and they require a dedicated CC / CV charging IC plus a dedicated external protection circuit. They often have a narrow operating and charging temperature range, making them difficult to use in some industrial equipment.
A new generation of Li-ion rechargeable batteries with a nominal voltage between 2V and 3V are now emerging and they offer many benefits over the traditional Li-ion products. Some of these new batteries can be charged with a constant voltage between 2.5V to 3.0V and these offer exciting opportunities for the designer as outlined below:
Benefits include:
|
Ready for constant voltage charging by LDO. No need for a dedicated expensive CV / CC charging IC. |
|
Resistant to over-discharge and can be used with simple low voltage detection |
|
Because it is a battery, it can maintain a constant voltage around 2.2V to 2.3V for a long time. Energy can be used more easily and efficiently than a Supercap, which drops the voltage linearly. |
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There are also products that can handle high temperatures such as 70°C and 105°C. |
|
Reflow / Hot laminating compatible products are also available. |
|
Semi-solid-state battery types and Coin battery-shaped types that support reflow soldering are readily available. |
In Fig.2 below we illustrate a typical circuit for charging a small Li battery and offer an explanation of the operation during different states.
(Fig.2: Typical circuit for charging rechargeable batteries)
The operation of the Voltage Regulator circuit is shown in detail below:
(Fig.3: Typical Voltage Regulator Circuit)
The XC6240 and XC6215 typically consume 0.8µA when operating and they sink only 0.24µA in standby (battery sink current). The XC6240 has a fixed VOUT of 2.63V ± 1.5% specifically for NGK’s EnerCera products. Whereas the XC6215 is available with VOUT selectable from 0.9V to 5.0V ±2% in 0.1V steps.
If size is important, both series are available in ultra-small USPN-4 (1.2 x 0.9 x Max 0.40 mm) or low profile USP-6B06 (1.5 x 1.8 x Max 0.33 mm) as well as the larger SSOT-24 (2.1 x 2.0 x Max 1.1 mm).
The XC6136 and XC6140 typically consume 110nA when operating and the detect voltage threshold (VDF) is user selectable, normally VDF is between 1.6V and 2.2V for these batteries’ types.
With the XC6140 the Detect Release Voltage (VDR) is fixed at 2.475V and this is the optimum value for this type of cell (see notes in Fig.2). The VDR for the XC6136 is calculated with a fixed hysteresis on 5% (VDR=VDF+5%) so it is dependent on VDF. Both series are available in the ultra-small USPQ-4B05 package (1.0 x 1.0 x Max 0.33 mm).
In the circuit example below, we illustrate a typical use case for these new batteries.
Many industrial applications need a back-up circuit to provide an emergency supply in the event of a main power failure. Typically, a non-rechargeable coin cell or Supercap is be used today, but now these can easily be replaced by a small rechargeable Li cell as shown in Fig.4.
(Fig.4 Back up circuit for 5V to 3.3V or unstable 5V to 5V cases)
The ease of charging combined with superior strength against over discharge and the extended operating temperature range all mean these batteries are a good choice for use as a back-up in industrial equipment.
Other common applications include small IoT modules, battery power systems and next generation smartcards. Often space is constrained in these applications and our charging solution fits perfectly due to the small size and low profile of our USP packaging. A solution can easily be implemented with a height ≦ 0.35mm, making it ideal for smartcard applications.
In the circuit example below, we illustrate a typical use case:
(Fig.5 Circuit for IoT modules, battery power systems and smartcards)
There are a growing number of manufacturers promoting these new batteries and you can find out more by exploring the links below:
NGK insulators Chip-type Ceramic Rechargeable Battery "EnerCera" Series
https://www.ngk-insulators.com/en/product/electron/enercera/
Murata Small Li-ion secondary batteries
https://www.murata.com/en-eu/products/batteries/small/
Nichicon Small Li-ion Rechargeable Batteries
https://www.nichicon.co.jp/english/products/slb/about/
Samples for all the Torex products mentioned in this feature are readily available, so please ask your local Torex representative for details or contact us directly via our website.
We also offer dedicated evaluation boards for testing the circuits with NGK EnerCera batteries. These evaluation boards include two portions, one for the charging function and one for the power supply. Customers can use the Power Supply Unit to test the rest of their circuit.
The Power Supply Unit has a Boost Micro DC/DC (with integrated coil) and an LDO fitted as standard. Layout for an an optional Buck Micro DC/DC (with integrated coil) is also included.
Our standard Power Supply Unit features a 3.3V Boost Micro DC/DC and a 1.8V Low Power LDO, but the Buck Micro DC/DC is not mounted.
Semi-custom versions of the Power Supply unit are also available for customers with special Voltage requirements or if a Buck Micro DC/DC is required.
Please note Torex does not supply batteries, but these can be sourced from the battery manufacturers directly.
The Torex IC included are shown in the following table
Charging unit |
Power supply unit |
||||
---|---|---|---|---|---|
LDO for charge | XC6240A2638R-G | Low lq LDO | XC6215B182NR-G | ||
RESET IC for battery voltage monitor |
XC6140C20A9R-G |
Step-up Micro DC/DC | XCL103D333CR-G | ||
Wireless power receiver | XCM414B050D2-G | Step-down Micro DC/DC (Optional) | XCL206xxx3CR-G |
The circuit for these evaluation boards are shown below:
The evaluation board is ready for both DC and ANT inputs, however if only the DC input is used the Schottky Barrier Diode on DC input side is not necessary.
The CE pin of each IC can be connected to the RESETB output of XC6140 or Pull up/down to VIN/GND
For more information on the Torex products highlighted in this article please see:
XC6140 Series: https://www.torex-europe.com/products/voltage-supervisors/low-power/xc6140/
XC6215 Series: https://www.torex-europe.com/products/voltage-regulators/low-iq/xc6215/
XC6240 Series: https://www.torex-europe.com/products/voltage-regulators/low-iq/xc6240/
XCM414 Series: https://www.torex-europe.com/products/multi-chip-modules/xcm414/
XCL103 Series: https://www.torex-europe.com/products/micro-dc-dc/step-up-1/xcl103/
XCL206 Series: https://www.torex-europe.com/products/micro-dc-dc/step-down-1/xcl206/