Optimum for backup circuit Ship function that suppresses battery discharge at shipment

Problems and purposes

For a backup circuit that mainly uses a primary battery, OR connection using an ideal diode IC is one of the optimum circuit configurations.
However, for the ideal diode IC, about 1 μA of current generally flows into CE terminal (EN terminal). There has been a problem in that the battery level of primary battery decreased due to this current flowing into CE terminal.

Here introduces a method for adding Ship function that reduces current consumption for CE terminal during long-term storage after shipment by adding an external circuit.

[Appendix] What is ship function?

Ship function is a function that prevents battery power from decreasing during long-term storage after product shipment.
Electronic devices without Ship function are shipped while consuming current from the batteries even after the shipment. In this status, the battery level decreases during long-term storage after shipment. When the product is in the hands of the end user, the product may not operate due to low battery level or it may not operate for the expected driving time.

How to realize

The current that flows into CE terminal is supplied from output side by applying CE terminal voltage from output side.
With this countermeasure, the power of the primary battery is not uselessly consumed by CE terminal.
However, it is not possible to shift to Ship mode by just connecting CE terminal to output side. Additional circuit and procedure are required for mounting it for Ship mode.

Shift to Ship mode

1. Set the main power supply to OPEN and keep power supply only from the battery.
2. Input "H" to SHDN signal so that CE="L".
3. Keep "H" for SHDN signal until the output voltage becomes 0 V.
4. After the output voltage becomes 0 V, set SHDN to OPEN.
5. The Ship mode that keeps the output voltage to 0 V is kept until the power is supplied to the main power supply.

Shift from Ship mode to usual mode

1. If the power is supplied to the main power supply, the output voltage increases.
2. If the output voltage increases, becomes CE="H", and then the ideal diode operates and the mode shift to the usual mode.

Advantage

• Minimizing the voltage drop of battery during long-term storage

Disadvantage

• Additional circuits of FET and resistance are required

Comparison of current consumption

Now, let's check how much the current consumption (battery current) from the battery can be reduced by adding Ship function with the frequently used circuit configuration for the backup circuit.

The current consumption (battery current) measured with the experimental circuit shown in Figure 1 becomes as Figure 2.

In this experiment, the current consumption from the battery can be reduced by about 87% by using Ship function for XC8110/XC8111 series although the value depends on the current consumption of an ideal diode IC.

The battery life can be extended approximately 8 times longer by using Ship mode compared to non-use of this mode.

Conclusion

Adding the Ship function can minimize the current consumption of a battery at the shipment. In addition, the current consumed by CE terminal can be supplied from output side because CE terminal can be connected to output side, so the consumption of primary battery while the main power is supplied can be minimized.