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LPC3250 Developer’s Kit v2 - User’s Guide

Page 22

4.9 SP6: VBAT/ALARM Handling

The board can power the VBAT input supply (to the OEM board) from two different sources:

 The +3.3V power supply, via D1 (when board is normally powered).

 A 3V Lithium CR1025 size coin battery, via D2. Note that battery is not included.

See the LPC3250 datasheet for details about VBAT voltage range.

The ALARM signal control LED21. It is the LPC3250 signal ONSW that is connected to this signal.

Check the LPC3250 errata for details about some limitations on this signal.

Also note that LED21 will consume a lot of current from the battery and/or super-capacitor. Restrict

on/high time to conserve energy.

Figure 8 – VBAT and ALARM circuit

ALARM-LED

LED21

Battery Holder

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