AFE4490 datasheet(68/85 Pages) TI2

68 / 85 page

AFE

INP

INM

TX_SUP

TX3

TX2

TX1

RX_SUP

I2C_CLK

I2C_DAT

RESETZ

ADC_RDY

TX_SUP

IO_SUP

CLK

MCU

GND

LEDs

Rseries

Rshunt

AFE4404

SBAS689D – JUNE 2015 – REVISED DECEMBER 2016

www.ti.com

Product Folder Links: AFE4404

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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The AFE is designed to operate with a minimal number of external components. Deriving the power supplies for

the AFE from the available source of power in the system can require an additional external LDO or boost

converter. A reset is essential after power-up to ensure that all registers are reset to their default values. TI also

recommends that the entire system be operated using a single master clock. The AFE can either be set to

accept an external clock derived from a master clock generated elsewhere in the system, or the AFE can provide

its internal oscillator as an output clock to serve as the master clock for the rest of the system. If a single master

clock is not possible, extra care must be taken to ensure that spurious energy from unrelated clocks does not get

coupled into the AFE. If this energy does couple into the AFE the spurs get aliased based on the sampling

operation. These aliased spurs can result in a faulty detection of parameters (such as heart rate). The

photodiode outputs are specifically prone to picking up noise. Especially when operating in coexistence and

close proximity with RF communication circuitry [such as Bluetooth® low energy (BLE)], a common-mode choke

may become essential to add in the path of the AFE inputs to reject the interference.

9.2 Typical Application

NOTE: Use Rseries in external clock mode and Rshunt in internal oscillator mode.

Figure 92. Typical AFE Connection

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