AFE4490 not driving LEDs

Puja,


I'm moving this post to the Medical Forum where the AFE4490 is supported. I'm sure you'll get an answer here.


Joseph Wu

Hi Puja,

What are you writing to the AFE, and what are you reading back from the AFE? Could I also see the schematic for the custom board?

Best Regards,
Lakeishia

Hi Lakeishia,

Thanks for the quick response!
I am currently writing one byte, i.e., 0x0000aa to register 0x01 and reading back the same register, obtaining 'aa' on the MISO line.
I am including the schematic for AFE4490 and the layer of my custom board containing it. I have used CC2541 as the main SOC in my design. The PCB consists of four layers.

pulsev6 copy_afe.pdf

This is the schematic for AFE4490.

Following are the images of the custom board:

Top layer with CC2541

Bottom layer with AFE4490

Following are the register settings that I am doing:

void TI_ADS1293_WriteRegSettings(void)
{

TI_ADS1293_SPIWriteReg(0x01,0x003ae8); //// start of the sample LED2 signal with respect to the pulse repetition period (PRP)
TI_ADS1293_SPIWriteReg(0x02,0x004e1e); //// end of the sample LED2 signal with respect to the pulse repetition period (PRP)
TI_ADS1293_SPIWriteReg(0x03,0x003a98); //// start of the LED2 with respect to the PRP
TI_ADS1293_SPIWriteReg(0x04,0x004e1F); //// TI_ADS1293_SPIWriteReg(0x04,0x001F3F); 4e1F end of the LED2 with respect to the PRP
TI_ADS1293_SPIWriteReg(0x05,0x000050); //// start of the sample ambient LED2 signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x06,0x001386); //// end of the sample ambient LED2 signal with respect to the PRP,
TI_ADS1293_SPIWriteReg(0x07,0x0013d8); //// start of the sample LED1 signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x08,0x00270e); //// end of the sample LED1 signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x09,0x001388); //// start of the LED1 signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x0A,0x00270f); //// TI_ADS1293_SPIWriteReg(0x0A,0x000F9F); 270f end of the LED1 signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x0B,0x002760); //// start of the sample ambient LED1 signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x0C,0x003a96); //// end of the sample ambient LED1 signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x0D,0x000006); //// start of the LED2 conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x0E,0x001387); //// end of the LED2 conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x0F,0x00138e); //// start of the LED2 ambient conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x10,0x00270f); //// end of the LED2 ambient conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x11,0x002716); //// start of the LED1 conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x12,0x003a97); //// end of the LED1 conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x13,0x003a9e); //// start of the LED1 ambient conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x14,0x004e1f); //// end of the LED1 ambient conversion signal with respect to the PRP
TI_ADS1293_SPIWriteReg(0x15,0x000000); //// start of the ADC reset0 conversion signal
TI_ADS1293_SPIWriteReg(0x16,0x000005); //// end of the ADC reset0 conversion signal
TI_ADS1293_SPIWriteReg(0x17,0x001388); //// start of the ADC reset1 conversion.
TI_ADS1293_SPIWriteReg(0x18,0x00138d); //// end of the ADC reset1 conversion.
TI_ADS1293_SPIWriteReg(0x19,0x002710); //// start of the ADC reset2 conversion.
TI_ADS1293_SPIWriteReg(0x1A,0x002715); //// end of the ADC reset2 conversion.
TI_ADS1293_SPIWriteReg(0x1B,0x003a98); //// start of the ADC reset3 conversion.
TI_ADS1293_SPIWriteReg(0x1C,0x003a9d); //// end of the ADC reset3 conversion.
TI_ADS1293_SPIWriteReg(0x1D,19999); //// The contents of this register can be used to set the pulse repetition period (PRP)(in number of clock cycles of the 4-MHz clock).
TI_ADS1293_SPIWriteReg(0x1E,0x000101); //// This register configures the clock alarm pin, timer, and number of averages.
TI_ADS1293_SPIWriteReg(0x1F,0x000000); //// This register is a spare register and is reserved for future use.
TI_ADS1293_SPIWriteReg(0x20,0x000000); //// This register sets the device transimpedance amplifier gain mode and feedback resistor and capacitor values.
TI_ADS1293_SPIWriteReg(0x21,0x000000); //// This register configures the ambient light cancellation amplifier gain, cancellation current, and filter corner frequency.
TI_ADS1293_SPIWriteReg(0x22,0x011f08); //// This register sets the LED current range and the LED1 and LED2 drive current.
TI_ADS1293_SPIWriteReg(0x23,0x020000); //// This register controls the LED transmitter, crystal, and the AFE, transmitter, and receiver power modes.
TI_ADS1293_SPIWriteReg(0x24,0x000000); //// This register is a spare register and is reserved for future use.
TI_ADS1293_SPIWriteReg(0x25,0x000000); //// This register is a spare register and is reserved for future use.
TI_ADS1293_SPIWriteReg(0x26,0x000000); //// This register is a spare register and is reserved for future use.
TI_ADS1293_SPIWriteReg(0x27,0x000000); //// This register is reserved for factory use. Readback values vary between devices.
TI_ADS1293_SPIWriteReg(0x28,0x000000); //// This register is reserved for factory use. Readback values vary between devices.
TI_ADS1293_SPIWriteReg(0x29,0x000000); //// This register controls the Alarm pin functionality
TI_ADS1293_SPIWriteReg(0x2A,0x000000); //// This register contains the digital value of the latest LED2 sample converted by the ADC. The ADC_RDY signal goes high each time that the contents of this register are updated
TI_ADS1293_SPIWriteReg(0x2B,0x000000); //// This register contains the digital value of the latest LED2 ambient sample converted by the ADC. The ADC_RDY signal goes high each time that the contents of this register are updated
TI_ADS1293_SPIWriteReg(0x2C,0x000000); //// This register contains the digital value of the latest LED1 sample converted by the ADC. The ADC_RDY signal goes high each time that the contents of this register are updated
TI_ADS1293_SPIWriteReg(0x2D,0x000000); //// This register contains the digital value of the latest LED1 ambient sample converted by the ADC. The ADC_RDY signal goes high each time that the contents of this register are updated
TI_ADS1293_SPIWriteReg(0x2E,0x000000); //// This register contains the digital value of the LED2 sample after the LED2 ambient is subtracted
TI_ADS1293_SPIWriteReg(0x2F,0x000000); //// This register contains the digital value of the LED1 sample after the LED1 ambient is subtracted
TI_ADS1293_SPIWriteReg(0x30,0x000000); //// This register is read only. This register contains the status of all diagnostic flags at the end of the diagnostics sequence

///// Led 2 is RED and LED in IR

delaym(10);
}

Hi Puja,

After programming the registers, do the LEDs turn on? If not, could you please send what you are reading back from the AFE? 

Best Regards,

Lakeishia

Hi Lakeishia,

I am facing a strange problem now. The LEDs did light up finally, but after a few iterations of testing, they again got switched off. I am not being able to figure out the reason.

Regards,
Puja

Hi Every one,

I am Madhusudan, i was working on AFE4490 IC for Pulse oxymeter which will interface with the TI CC2640 controller,

i am facing the issue with perfusion, when the device subjected for thin and a white finger(high perfusion) signal is getting saturated(1.2V), i tried changing the intensity and then changed the gain also but still it is getting saturated, i need help on this,

Hi Madhusudan,

What the LED current set for both the LEDs?
Also what is the gain?

Regards,
Prabin

Hi Prabin,

I have set current for IR = 62mA and Red = 72mA,
Gain = cf = 10pf and rf = 500kohm,

when I checked with the eastern countries i am not getting any signal out, it is getting saturated

Hi Madhusudan,

Signal received by the devices greatly depends on skin tone as seen by you.

To avoid the saturation you can either reduce the LED currents or RF.

Regards,

Prabin