AFE4403 datasheet(39/97 Pages) TI

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AFE4403

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SBAS650B – MAY 2014 – REVISED JULY 2014

8.3.5.1 Third LED Support

A third LED can be optionally connected on the TX3 pin, as shown in Figure 53. An example application involving

a third LED is where the Red and IR LEDs are connected on the TXP, TXN pins for pulse oximeter applications

and a third LED (for example a Green LED) is connected on the TX3 pin for a heart rate monitoring application.

The third LED can be connected only in common anode configuration. By programming the TX3_MODE register

bit, the timing engine controls on TXP can be transferred to the TX3 pin. In this mode, the register bits that

indicate the diagnostic results on the TXP pin now indicate the diagnostic results on the TX3 pin. The selection

between using TX3 versus using TXP, TXN is intended as a static mode selection as opposed to a dynamic

switching selection. A typical time delay of approximately 20 ms is required for the receive channel to settle after

a change to the TX3_MODE setting. During this transition time, the receive signal chain should be active so that

the filters are able to settle to the new signal level from the third LED.

Figure 53. Multiplexing Third LED

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