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AFE4403 with 2 Green LEDs?

Ming Liao
Intellectual 450 points
Other Parts Discussed in Thread: AFE4403

Hello,

 

I tried to set LED2 and LED1 to be turned on/off at the same time (for example (PRF = 250Hz), LED2’s LED start and end count are 0 and 1999 respectively, and LED1’s is set as LED2), but it didn’t work. Or is the only way to connect the 2 green LEDs’ cathode to TX3 pin?

 

Thanks.

Best regards,

Ming

  • 0
    TI__Mastermind 18285 points

    Ming,

    We have received your post and should have a response back to you soon.

  • 0
    TI__Mastermind 49176 points

    Hello Ming, 

    Yes the configuration you are suggesting (turning on/off LED1 and LED2 simultaneously) will not work.

    You will need to tie the cathodes of the 2 LEDs together and connect it to TX3 or TXP or TXN.

    Figure 60 of AFE4403 datasheet shows a possible configuration driving 2 LEDs simultaneously.

  • 0 in reply to Praveen Aroul
    Intellectual 450 points

    Hi Praveen,

    Got your point. Thanks.

    One more question is: in common anode configuration, can these LEDs’ anode and LED_DRV_SUP connect together to VBAT that is from 4.2 to 3.3V, and TX_CTRL_SUP connect to 3.0V? 

    Best regards,

    Ming

  • 0 in reply to Ming Liao
    TI__Mastermind 49176 points

    Hello Ming,

    Depending on the type of LED (green, red or IR) (Vfb of the LED) connected between TXN and TXP and the TX_REF voltage, the LED_DRV_SUP might require to be high as 5V. The datasheet mentions the recommended operating conditions for LED_DRV_SUP.

    You can connect the LED_DRV_SUP and LEDs' anode to VBAT so long as the recommended operating condition for LED_DRV_SUP is maintained. But since you are driving Green LEDs (Vfb in general is about 3.2V), you may not be able to directly connect the LED_DRV_SUP to VBAT. You may require a boost regulator.

    The voltage difference between LED_DRV_SUP and TX_CTRL_SUP voltage must be within +/- 0.3V. So you can connect the same supply to both LED_DRV_SUP and TX_CTRL_SUP pins.

    Regards

    Praveen.