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Home > News > [Torex] How to use LDO regulator to charge small lithium-ion batteries (2/3)

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[Torex] How to use LDO regulator to charge small lithium-ion batteries (2/3)

  • Author:Torex
  • Release on:2021-01-12

Choose the right regulator and detector

The operation of the voltage regulator circuit is as follows:

(image 3:Typical voltage regulator circuit)

XC6240 and XC6215 usually consume 0.8µA of current during operation, and only absorb 0.24µA of current (battery sink current) in standby mode.Fixed V of XC6240 OUTIt is 2.63V±1.5%, specially used in NGK's EnerCera product.XC6215 V OUTIt can be selected in 0.1V steps within the range of 0.9V to 5.0V±2%.

If size is important, both series can use ultra-small USPN-4 (1.2 x 0.9 x max 0.40 mm) or thin USP-6B06 (1.5 x 1.8 x max0.33 mm) And the larger SSOT-24 (2.1 x 2.0 x maximum 1.1 mm).

XC6136 and XC6140 usually consume 110nA of current when working,User can chooseDetection voltage threshold (V DF),For these battery types, Usually V DFBetween 1.6V and 2.2V.

Use XC6140 to detect the release voltage (V DR) Is fixed at 2.475V, which is the best value for this type of battery (see the note in Figure 2).XC6136V DRIs at 5% (V DR = V DF + 5%)Calculated with a fixed hysteresis,So it depends on V DF.Both series are in the ultra-small USPQ-4B05 package (1.0 x 1.0 x 0.33 mm maximum).

Application example: standby circuit

In the circuit example below, we illustrate typical use cases for these new batteries.

Many industrial applications require backup circuits to provide emergency power in the event of a main power failure.Usually, non-rechargeable button batteries or Supercaps are used today, but they can now be easily replaced with small rechargeable lithium batteries, as shown in Figure 4.

(Figure 4 Backup circuit under 5V to 3.3V or 5V to 5V unstable conditions)

Instructions

For VIN = 5V to VOUT = 5V

  • XC9142 C or F type maintains VOUT 5V.
  • The backup capacitor or battery is always charged by XC6240/15 LDO.
  • When VIN is cut off, the lower side boost DC/DC provides voltage.
  • XC9142 C or F type is ready and can be used for "OR" connection of VOUT.
  • XC9140 / XCL101 can also be used for downside boost.

For VIN = 5V to VOUT = 3.3V

  • XC6227 is suitable for upper-side LDO to generate 3.3V voltage, because it has reverse current protection function, so no external isolation diode is needed.

notes:

  • The boost DC/DC works every time, and VOUT2 should be 0.1V~0.2V lower than VOUT1
  • Supercapacitors usually have a maximum of 2.5V, so engineers need to be wary of overvoltages.
  • If you use LDO Li rechargeable batteries, they can maintain 2.2V~2.3V longer, and all the stored energy can be used (unlike Supercap).

Ease of charging, super strength against overdischarge and extended operating temperature range all mean that these batteries are ideal for use as backup batteries for industrial equipment.

Application examples: IoT modules, battery modules and smart cards

Other common applications include small IoT modules, battery power systems and next-generation smart cards.These applications often limit space, and due to the small size and compact size of our USP package, our charging solution is very suitable.Solutions with a height of ≤0.35mm are easy to implement and very suitable for smart card applications.

In the following circuit example, we illustrate a typical use case:

(Figure 5IOT module, battery power system and smart card circuit)

notes:

  • Although the voltage of Supercap drops linearly during discharge, this lithium battery can keep the output voltage constant at around 2.3 to 2.3V, making the effective use of energy easier.
  • Lithium batteries and Li capacitors that are rechargeable via LDO can be charged with a constant voltage of 2.5 to 3.0V via LDO and are easy to use, making them ideal for backup applications.
  • Has also developedHigher operating temperature type than Li primary battery (e.g. CR2032), e.g. ~70 O C and ~105 O C, suitable for industrial equipment applications.It also supports reflow and thermal lamination.
  • The XC6140 is ready as a dedicated IC to match the discharge detection circuit of Li batteries that can be charged through LDO and Li capacitors.