Texas Instruments AFE4405YZR

Description
The AFE4405 is an analog front-end (AFE) for optical biosensing applications such as heart rate monitoring (HRM) and blood oxygen saturation (SpO2) measurement. The device supports three light-emitting diodes (LEDs) and up to two photodiodes. The photodiode currents are converted to voltages by transimpedance amplifiers (TIAs) and digitized using analog-to-digital converters (ADCs). The ADC codes can be stored in a deep, programmable 234-sample first-in, first-out (FIFO) memory block. The FIFO depth can be partitioned as needed to accommodate the storage requirements of different phases. The contents of the FIFO can be read out using either an IC or SPI interface. The AFE also features a fully integrated LED driver with 8-bit current control. The device has wide dynamic range transmit and receive paths to facilitate sensing of very small signal levels.

Features
Transmit:
Supports common-anode LED configuration
Optical heart rate monitoring (HRM) (wearables and hearables)
Heart rate variability (HRV)
Dynamic range: 100 dB
Blood oxygen saturation (SpO2) measurement:
8-bit programmable LED current up to 50 mA (expandable to 100 mA for VO2 max)
Programmable LED on-time
Supports three LEDs simultaneously for optimized SpO2 measurement, HRM, or multi-wavelength HRM
Receive:
Supports two time-division multiplexed photodiode inputs
24-bit two's complement representation of photodiode current at TIA input
Independent DC offset subtraction DACs (±15.75 µA range) at TIA inputs
Digital ambient subtraction for each LED and ambient ADC output
Transimpedance gain: 10 kΩ to 2 MΩ
Dynamic range: 100 dB
Dynamic power-saving mode reduces receiver current to 200 µA
Pulse rate: 5 SPS to 1000 SPS
Flexible pulse sequencing and timing control
Flexible clocking options:
External clock: 4 MHz to 60 MHz input clock
Internal clock: 4 MHz oscillator
FIFO with 240-sample depth: Partitioning can be programmed for each phase
IC, Serial Peripheral Interface (SPI)™ interface
Selectable operating temperature range via pin
2.6 mm × 2.1 mm DSBGA package, 0.4 mm pitch

Applications
Calorie expenditure