adpd4100 LED intensity low

Hello sir,

we are working with PPG evaluation Board(ADPD4100Z) ,ADPD4100Z board is interfaced with  nrf52840 Development board.

we are using SPI communication  for reading and writing the registers.


IOVDD connected to 3volts (this power source giving from the nrf52840 controller board)

 AVDD connected to 1.8volts using external power supply 

 VLED(DS1) connected to 4.2 volts anode side using external power supply.


All Grounds shorted.(AGND ,IOGND,DGND)

Observations and issues:-

LED1A is enabled ,LED1A is glowing but with low intensity(anode side 4.2 volts and cathode side enabling using register 0x0105 by writing 0X004A).

voltage measured on  cathode(driver side) wrt to ground = 2.5volts.

voltage measured on anode side(DS1 GREEN LED) wrt to ground = 4.2volts.

setting LED1A driver current 120ma ,but measured current is = 135 microamps.

ADPD4100Z configuration values

{0x00B4, 0x0000},
{0x000B, 0x02EA}, //02CA 1mhz freq adj
{0x0100, 0x0100}, //
{0x000D, 0x2710}, // setting the sampling rate
{0x000f, 0x0006}, //(1Mhz internal low freq osc)
{0x0010, 0x0000}, // time slot A enable *
{0x0020, 0x0002}, // INP sleep in1 is connected to vc1
{0x0022, 0x0003}, // gpio config pin output invert
{0x0023, 0x0002}, // gpio 0 is int x
{0x0014, 0x8000}, // interrupt enable th_fifi
{0x0021, 0x0000}, // in1 connected to the single ended
{0x0006, 0x003B}, // setting the size of fifo thrshould
{0x0100, 0x0000}, // 40DA
{0x0101, 0x40DA}, // setting the analog path
{0x0102, 0x0001}, // IN1 connected to channel1
{0x0103, 0x5002}, // precondition with TIAVref and vc1 sel tia +215mv
{0x0104, 0x03C0}, // 13C2// AFE trim Vref 1,265 &madulatevref1.265 ,channel1 200k
{0x0105, 0x004A}, //
{0x0107, 0x0108}, // number of 4 pulses
{0x0108, 0x0000}, // mode selection
{0x0109, 0x0420}, // led pulse 2micro width, offset 16microsec
{0x010A, 0x0003}, // integrator clock width 3 microsec
{0x010B, 0x0206}, // int offset 16us and led width 2us 0210
{0x010C, 0x0201},
{0x010D, 0x1099}, // CHOPE MODE 99
{0x010E, 0x0000},
{0x0110, 0x0003} // 3 bytesome

 can you please suggest the solutions to increase the intensity.

Thanks &Regards

  • 0
    •  Analog Employees 
    on Sep 14, 2021 7:28 PM

    Hi there,

    You have a setting of LED1A at 0x4A, which is for 111mA. You would need a very big decoupling capacitor (refer to the CVLED in the datasheet) to be able to drive the LED. Have you add any decoupling capacitor?


    Glen B.

  • Good Day.

    Many thanks for your quick response.

    Already 22uF capacitor is connected to CVLED as per ADPD4100Z eval board schematic.

    Whether we need to calculate DCap value again as per ADPD4100 datasheet or 22uF is sufficient for programming current 1.5 mA to 200mA.

    Please confirm.

  • 0
    •  Analog Employees 
    on Sep 15, 2021 12:42 PM in reply to mahee1

    Hi there,

    We strongly recommend that you run the test with EVAL-ADPDUCZ before you try with your own connections. EVAL-ADPDUCZ has the right connections to the EVAL-ADPD4100Z-PPG. A picture of your setup along with specs of your 4.2V power supply can help with the debug, although there is no guarantee.


    Glen B. 

  • PDF

    Hi sir,

    Here i am sharing the connections

    MOSI P1 connector 13th pin
    MISO P1 connector 14th pin
    CSO P1 connector 12th pin
    CLK P1 connector 11th pin
    VDD_3V P1 connector 6th pin  (from controller board)
    VDD_1.8V P1 connector 1st and 2nd pins (external power supply)
    GND_LOCAL P1 connector 16th pin.

    VBOOST 4th pin of p1connector connected 4.2v from external power supply

    Through ribbon cable connected SPI lines and 3 volts.

    let me know where i am doing wrong.

    Thanks $Regards

  • 0
    •  Analog Employees 
    on Sep 15, 2021 6:38 PM in reply to mahee1

    Hi there,

    You may want to connect both pin3 and pin4 of P1 to 4.2V and pin15 and pin16 to ground. Since your IOVDD is 1.8V, you need to set the register 0x00B4 to its default 0x0050. Also please set register 0x010D to 0x0099 or 0x0010. 

    Please also check if there are ripples in your external 4.2 power supply while it drives the LED.

    Hope it can solve your problem but there can be something wrong with your wiring/cable that we don't know.


    Glen B.