DAN191
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EXAR UARTS IN BLUETOOTH APPLICATIONS
April 2008
EXAR UARTS IN BLUETOOTH APPLICATIONS
1.0 INTRODUCTION
This application note describes why Exar's XR20M1170 is ideal for adding Bluetooth® capability to any
application. Some example applications where Bluetooth can be used are SmartPhones, PDA and GPS
applications.
2.0 BLUETOOTH ENHANCED DATA RATE
The Bluetooth Core Specification Version 2.1 + EDR was published in July 2007. In this version, the Enhanced
Data Rate (EDR) modulation mode supports data rates up to 3 Mbps.
3.0 UART HOST CONTROLLER INTERFACE
There are usually a few host controller interfaces (HCI) available on Bluetooth modules/chipsets to
communicate with a host controller or system. However, one of the simplest ways is for the host controller/
system to communicate via a UART interface. As a result of the Enhanced Data Rate, newer Bluetooth
modules/chipsets have UARTs on their HCI that support data rates of 3Mbps.
However, the maximum data rate of the built-in UART on the host controller/system can only typically support
data rates up to 115200 bps. Hence, there is a need for high performance Exar UARTs.
F
IGURE 1. BLUETOOTH APPLICATION PROBLEM
Bluetooth
Module/
Chipset
UART
UART
115.2 Kbps
3 Mbps
MCU
?
DAN191
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EXAR UARTS IN BLUETOOTH APPLICATIONS
4.0 XR20M1170 IN BLUETOOTH APPLICATIONS
Exar’s XR20M1170 is a single channel I2C/SPI UART and it is ideal for Bluetooth applications for the reasons
listed below. Since the SPI mode supports a 5MHz clock and the I
2
C interface only supports up to 400kHz, the
SPI mode is recommended to achieve the highest performance.
4.1 High Performance
The XR20M1170 can easily support the 3Mbps data rate requirement. If necessary, the XR20M1170 can
support UART serial data rates of up to 16Mbps. Data throughput and interrupt servicing can be optimized by
utilizing the 64 byte TX and RX FIFOs.
4.2 Low Voltage Operation
The XR20M1170 can operation from 1.62V - 3.63V to directly interface with the lower voltage MCUs as well as
the lower voltage Bluetooth chipsets.
4.3 Low Power Consumption
The XR20M1170 has a sleep mode to minimize the power consumption. In the sleep mode, the XR20M1170
consumes less than 30 uA. This will significantly help extend the battery life of the handheld/portable
applications.
4.4 Small Package Size
The XR20M1170 is available in a 4x4mm QFN package which will require minimal board space.
4.5 Fractional Baud Rate Generator and 8X/4X Sampling Rate
In addition, with the combination of the Fractional Baud Rate Generator and 8X/4X sampling rate features, the
XR20M1170 can take any existing clock source on the board (above 12MHz) to generate the 3Mbps UART
data rate which further saves valuable PCB space.
5.0 CONCLUSION
With its low power consumption, small package size and enhanced features, Exar’s XR20M1170 is the ideal
solution for communication between an MCU and a Bluetooth module/chipset.
F
IGURE 2. XR20M1170 BLUETOOTH APPLICATIONS SOLUTION BLOCK DIAGRAM
Bluetooth
Module/
Chipset
UART
UART
115.2 Kbps
3 Mbps
XR20M1170
SPI
SPI Bus
Master
MCU