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AN11254
TEF668x Application Note
Rev. 1.13 — 9 October 2015
Application note
Document information
Info
Content
Keywords
TEF6686, TEF6687, TEF6688, TEF6689, Lithio, Car Radio, /V101,
/V102, /V205
Abstract
The TEF668x (family name: Lithio) are high performance, very small,
single chip car radio receivers. This application note describes the
hardware application for these devices.

NXP Semiconductors
AN11254
TEF668x Application Note
AN11254
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2015. All rights reserved.
Application note
Rev. 1.13 — 9 October 2015
2 of 41
Contact information
For additional information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: salesaddresses@nxp.com
Revision history
Rev
Date
Description
1.13
8 October 2015
Changes from Rev 1.12 marked by change bar
Update to device version V205
1, 2.1, 2.5, 3.2, 3.3, 4; Update to reference board 4322_071_11402
2.5: removed old buffer circuit
2.5: added digital radio DR I
2
S current mode connection as available from V205
2.7, 2.7.1, 2.9; added information on crystal applications as available from V205
2.8; added note regarding shared bus requirement for V101 and V102 only
2.9; rephrased GPIO control overview
1.12
24 April 2015
1, 2.1, 2.2, 2.5, 3.2, 3.3, 4; Update to reference board 4322_071_11401
2.1: Trimmed note on transformer type and moved to Fig 4.
2.5: Updated 4 wire and 3 wire digital radio buffer circuit for improved timing
2.5.1: Moved subsection on digital radio baseband I
2
S signal polarity
2.6: Moved and updated information on audio I
2
S interface
Corrected lost cross-reference
1.11
20 Feb. 2015
2.5: Added subsection about polarity of the BB I
2
S signal.
2.7: Added that no BLM should be used in series with pin 1.
2.8: Added information on I²C bus requirements during startup
1.10
29 April 2014
2.5: Changed values of R1, R4 and R5 in the 3 wire BB I
2
S interface. This change is
required to make the 3 wire interface function. Added advice to avoid long PCB tracks
on the BB I
2
S buffer in- and output and for the I
2
S buffer have resistors with not more
than 5 % tolerance.
2.7.1: Added two crystal type suggestions
The amplitude range of the 55.46667MHz signal was brought in line with the datasheet,
added advice on the PCB track length and not to deviate from the proposed 220pF.
1.9
19 Dec. 2013
Added section 2.1.1 describing an FM performance limitation on ultimate SNR when
very strong RF signals at certain frequencies are applied.
Added section 2.3 about selecting different coil types.
1.8
22 Oct. 2013
2.7.1: Added footnote about optimizing the two 15pF capacitors in case of a Lithio
sharing a crystal with a Sabre.
4: Updated GH1664 schematics with new pin naming.
7: Updated Legal information.
1.7
16 Oct. 2013
Small corrections
2.7.1: The note beneath the table of crystal requirements, stating that only the 9.216MHz
crystal specification allowed for dual tuner crystal sharing, has been integrated in the
text of crystal sharing.
1.6
14 Oct. 2013
Grey lines in the right margin indicate changes compared to V1.3.
2.7.1: 12MHz crystal can now be used for all Lithio types.
1.5
27 Sept. 2013
Pin names are brought in line with datasheet.
Added the TEF6687 and TEF6689 types
2.1: The circuit of the external AGC step has been changed.
2.7.1: Added part number KDS crystal, added requirements 12MHz crystal.

NXP Semiconductors
AN11254
TEF668x Application Note
AN11254
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2015. All rights reserved.
Application note
Rev. 1.13 — 9 October 2015
3 of 41
Contact information
For additional information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: salesaddresses@nxp.com
1.3
27 June 2013
2.5: The section of the Digital Radio interface has been extended and rewritten. An
alternative transistor buffer has been added, that can also be used for the 3 wire
interface.
The GH1557 reference design has been updated to the GH1664. There is only one
change: the PCB tracks of IC pin 1 are rerouted. See sect. 3.1 for more info.
1.2
19 June 2013
2.1: Added transfer balun and transformer FM antenna filter and impedance of FM LNA
2.2: Added AM LNA input impedance at 50Hz
3.1: Added new section to draw attention to pin 1 marker on package between pins 1
and 32.
6: Added new EMC chapter
1.1
8 Mar. 2013
2.5: Legal rephrasing HD radio
TM
signals.
In picture of external clock signal: clarified that VDDA_IF should be connected to
+3V3_ANA
2.10: New section about not used pins.
1.0
8 Feb. 2013
2.1: Added note about AM and FM configuration of external AGC step, mentioned LO
leakage, added gain distribution, updated type nr. FM transformer and changed value
capacitor 2003 because of new FM transformer.
2.2: Updated AM LNA input impedance in Fig 10, added subsection for active antenna.
2.4: Added section about ESD protection.
2.5: Changed value components 3043 and 3044, the GH1557 default application now
matches publication.
2.7: Added section about crystal oscillator and external clock reference.
2.9: Added section ‘General’, mentioning that care has to be taken for the GPIO_1 & 2
voltages during startup.
4: The circuit diagrams of the reference design are updated, note that in the previous
version the I
2
C address selection table was wrong.
5.2: Added LW, MW, SW and FM whistle checks
0.5
5 Oct. 2012
First distribution

NXP Semiconductors
AN11254
TEF668x Application Note
AN11254
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2015. All rights reserved.
Application note
Rev. 1.13 — 9 October 2015
4 of 41
1. Introduction
NXP supports the design-in of Lithio by supplying a reference design (4322_071_11402),
a datasheet, a computer control program (the 'GUI'), a User Manual, this application note
and the possibility to ask technical questions.
1
This application note focusses on the hardware design, but some hints are given for the
software application as well. For software development the UM, reference board and GUI
are the most useful tools. The Lithio is not difficult to control by software. The most easy
way to develop software is to connect the reference board to a PC, run the GUI, enable
the I
2
C debugging messages in the console and copy the behavior of the GUI. The UM
explains the I
2
C API calls in some more detail.
The Application Note focusses on the process of making the circuit diagram and the PCB
layout. Some options are available for the circuit diagram, usually involving different
compromises between costs and performance. To support these decisions measurement
results are given. The measurement results also serve as reference to what performance
can be obtained with the Litho.
The layout of radio PCBs is important to have good sensitivity and have undisturbed
reception at all frequencies. For this reason one chapter is dedicated to the PCB layout.
Another chapter gives the 4322_071_11402 reference design which realizes a good
layout.
Further note that the defaults in the GUI, especially the ones for the Weak Signal
Handling, are carefully optimized during field tests. Circumstances, such as an active
antenna, special customer requirements, may require these settings to be changed but
the defaults result in good sound quality under a wide range of signal conditions.
This Application Note is a combined AN for all four Lithio variants. Regarding hardware
the only difference is that the TEF6688 and -89 have a digital radio I
2
S bus, and the
TEF6686 and -87 not. If a subject is only relevant for the TEF6688 and -89 this is
indicated.
This application note describes the application of device versions TEF668xA /V205 as
well as earlier TEF668x versions /V101 and /V102.
1
Address technical questions to your local Field Application Engineer.

NXP Semiconductors
AN11254
TEF668x Application Note
AN11254
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2015. All rights reserved.
Application note
Rev. 1.13 — 9 October 2015
5 of 41
2. Application
2.1 FM Antenna applications
The purpose of the FM antenna application is to pass the FM frequencies and block out
of band signals. Four different FM antenna applications are available: two types using a
transformer and two types without, the so called balun applications. Both the transformer
and the balun applications have a variant with and without an additional external AGC
step. This AGC step extends the IC integrated AGC realizing better performance when
the car is close to a very strong transmitter.
Features of the antenna applications are:
The component cost of the balun applications is usually lower than for transformer
applications.
The transformer applications perform better on very strong signal IM3 conditions. See
Fig 7 for the performance differences.
The additional AGC step also improves the performance on very strong signal IM3
conditions. It is expected that the balun application with ext. AGC step performs
sufficient for most customers.
The transformer applications make the application less critical for pickup of radio
interference signals.
Part of the Local Oscillator signal leaks to the antenna connector. This LO signal is a
few hundred kHz to 1.7MHz away from the tuned frequency and might disturb
reception of a second tuner connected to the same antenna. The biggest leakage is
found at high RF frequencies and is typical +9dBuV at 108MHz for the balun
application and -11dBuV at 108MHz for the transformer application. 108MHz can be
considered the worst case frequency.
The ultimate SNR is reduced when very strong FM antenna signals are applied at
certain frequencies, the transformer application gives the best performance under
these conditions. This effect is described in section 2.1.1.
The external AGC step, when being used, has to be configured for the FM band via API
calls Set_RFAGC (FM cmd. 11) and Set_GPIO (APPL cmd. 3). In AM mode this GPIO
should be set to a fixed high voltage to avoid sensitivity loss and intermodulation
problems (via API call Set_GPIO (APPL cmd. 3).
For the coils Sagami C2012C types are advised; in general these perform well and other
types may degrade the (very strong signal) IM3 performance.
The input impedance between pins FM_IN_M and FM_IN_P behaves as 300Ω parallel to
a 9pF capacitance.
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