OR Circuit Battery Backup Solution
Backup Power Supply Solutions using an OR Circuit
Battery backup circuits are circuit types that immediately shift the load to the battery when there’s no main supply. However, if there is a main supply, the load shifts to the power supply as the backup battery enters a charge mode.
A simple back up circuit can be implemented using a Supercap (or EDLC short for Electric Double Layer Capacitor), or a Lithium-Titanium-Oxide (LTO) battery. These energy storage devices can be quickly recharged using an inexpensive LDO Voltage Regulator and if you wish to find out more about LTO batteries please click here.
Depending on VBAT level and the required system Voltage there are different solutions to consider as illustrated in the article below
Backup power supply with LTO battery or supercapacitor (EDLC)
- Seamless switching to backup when the main power is lost
- Efficient charging and discharging of the backup batteries or Supercaps
|(1) Ideal Diode
Ideal diode IC, VF=20mV, 500mA (XC8110) or 1A (XC8111)
|(2) Step-up DC/DC
1.2MHz/ or 3MHz, 750mA @ 3.3V→5V. For OR connection
N-channel MOSFET 20V, 0.3A for Ship-Mode Function
High speed PSRR=65dB, 700mA, true reverse current prevention
|(5) Charging IC (LDO)
For LTO charging, 150mA, Topr=105°C with XC6242
2A, External adj. current limit, True reverse current prevention
|(6) LTO Battery Voltage Monitor
LTO battery voltage monitor, release voltage=2.475V/2.450V, Iq=104nA. For 105°C compatible LTO battery use XC6142
OR Circuit Examples
Case (1) Apply backup battery voltage directly to the MCU
- Implementing an OR circuit using an Ideal diode. (XC8110/11) with lower VF means the leakage current loss is significantly reduced compared to a Schottky Barrier Diode.
Case (2) Apply a Step-up voltage such as 3.3V to the MCU
- Use a step-up DC/DC that supports OR connection. (XC9148C/F/M/L), please note that OR connection availability differs depending on the product and its options.
(3) Method to extend battery life with the Ship function
- Before shipping, turn on the Nch FET to cut off the supply from the backup battery. It is possible to significantly suppress the discharge from the battery until the start of use.
(4) LDO, DC/DC for main power
- LDO with reverse current prevention function prevents reverse current to the main power supply input. (XC6227).
- Alternatively, a Schottky Barrier Diode and Step-down DC/DC can also be used for an OR circuit.
(5) Charging LTO Battery or Super-cap
- The dedicated LDO XC6240 or XC6242 is used to charge the LTO battery.
- An LDO with current limit external adjustment / reverse current prevention is the best for charging a Super-cap. (XC6230B)
(6) Monitoring LTO Battery
- The XC6140 or XC6142 have the optimal release and detection Voltage for LTO batteries