ADPD4100 Few Questions

Hi all!

I'm just getting started with ADPD 4100 and had a few questions based on my read of the datasheet + eval board datasheet.

1. Hoping to better understand the INP12_x register (pg. 91 on the datasheet). If INP12_x is set to 0111 (IN1 and IN2 connected to Channel 1. Single-ended or differential, based on PAIR12) and PAIR12 is set to 0 (single-ended), what is the final configuration? How are two single-ended inputs connected to the same channel?

2. The ADPD4100 datasheet mentions adding caps at each led (CVLED), but I don't see these on the eval board. Am I missing something or is there a reason these aren't used?

3. The ADPD4100 datasheet mentions adding a flyback diode reverse biased across the LED power to reduce voltage spikes if using "long" wires. Any intuition on when this is required? My longest wire to an LED will be ~12cm - could estimate based on wire inductance but not sure how fast the turn-off time is.

Thanks so much!


  • 0
    •  Analog Employees 
    on Mar 12, 2021 6:55 PM

    Hi Tyler,

    Thanks for your great questions! 

    1. Input pair setting: differential pair vs. two-single ended 

    The timeslot-specific register you referred to is 0x0102/0x0122/0x0142/... If the pair of inputs are connected to a single AFE channel (CH1 or CH2), it is a differential measurement regardless if the pair of inputs are differential or two single-ended during data acquisition. However, the input connections are different during sleep. If the input pair are configured as differential pair, the two inputs are shorted together during sleep. Please refer to the global registers 0x0020 and 0x0021 for details.

    2. CVLED

    There are 22uF capacitors on VDD_3V for red and IR LEDs and VBOOST for green LEDs on the evaluation board. Please refer to Figure 12 on Page#9 of the user guide

    3. LED driver protection diode

    The reverse biased protection diode is required to protect the LED driver only if long wires are used, such as in clinical monitoring devices where several feet long cable connects the devices on the bedside rack and the LEDs/PDs on the patient. For your application with ~12 cm wire, it is fine without the protection diode.


    Glen B.