AFE4490_14 Datasheet, PDF (1/96 Pages) Texas Instruments – Integrated Analog Front-End for Pulse Oximeters

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AFE4490
SBAS602G – DECEMBER 2012 – REVISED JUNE 2014
AFE4490 Integrated Analog Front-End for Pulse Oximeters
1 Features
•1 Fully-Integrated Analog Front-End for
Pulse Oximeter Applications:
– Flexible Pulse Sequencing and
Timing Control
• Transmit:
– Integrated LED Driver (H-Bridge, Push, or Pull)
– 110-dB Dynamic Range Across Full Range
(Enables Low Noise at Low LED Current)
– LED Current:
– Programmable Ranges of 50 mA, 75 mA,
100 mA, 150 mA, and 200 mA,
Each with 8-Bit Current Resolution
– Low Power:
– 100 µA + Average LED Current
– LED On-Time Programmability from
(50 µs + Settle Time) to 4 ms
– Independent LED2, LED1 Current Reference
• Receive Channel with High Dynamic Range:
– Input-Referred Noise:
50 pA_RMS (at 5-µA PD Current)
– 13.5 Noise-Free Bits (at 5-µA PD Current)
– Analog Ambient Cancellation Scheme with
Selectable 1-µA to 10-µA Ambient Current
– Low Power: < 2.3 mW at 3.0-V Supply
– Rx Sample Time: 50 µs to 4 ms
– I-V Amplifier with Seven Separate LED2 and
LED1 Programmable Feedback R and C
Settings
– Integrated Digital Ambient Estimation and
Subtraction
• Integrated Fault Diagnostics:
– Photodiode and LED Open and
Short Detection
– Cable On or Off Detection
• Supplies:
– Rx = 2.0 V to 3.6 V
– Tx = 3.0 V or 5.25 V
• Package: Compact VQFN-40 (6 mm × 6 mm)
• Specified Temperature Range: –40°C to 85°C
2 Applications
• Medical Pulse Oximeter Applications
• Industrial Photometry Applications
3 Description
The AFE4490 is a fully-integrated analog front-end
(AFE) that is ideally suited for pulse-oximeter
applications. The device consists of a low-noise
receiver channel with a 22-bit analog-to-digital
converter (ADC), an LED transmit section, and
diagnostics for sensor and LED fault detection. The
device is a very configurable timing controller. This
flexibility enables the user to have complete control of
the device timing characteristics. To ease clocking
requirements and provide a low-jitter clock to the
device, an oscillator is also integrated that functions
from an external crystal. The device communicates to
an external microcontroller or host processor using an
SPI™ interface.
The device is a complete AFE solution packaged in a
single, compact VQFN-40 package (6 mm × 6 mm)
and is specified over the operating temperature range
of –40°C to 85°C.
Device Information⁽¹⁾
PART NUMBER
PACKAGE
BODY SIZE (NOM)
AFE4490
VQFN (40)
6.00 mm × 6.00 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Simplified Schematic
Rx Supply
(2.0 V to 3.6 V)
Rx
+
CPD
TIA
+
Stage 2
Gain
Photodiode
Diagnostic
PD Open or Short
Cable Off
LED Open or Short
LED2
AMBLED2
LED1
AMBLED1
+
Buffer
ûADC
Timing
Controller
LED2 Data
Amb (LED2) Data
(LED2 ± Amb) Data
LED1 Data
Amb (LED1) Data
(LED1 ± Amb) Data
AFE
SPI
SPI Interface
LED
Driver
LED
LED Current
Control
DAC
Tx Supply
(3.0 V or 5.25 V)
OSC
8 MHz
AFE
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.