Technical Note TN1202.04 XE1202 to XE1202A TrueRF™ Migration TN1202.04 Technical Note XE1202 to XE1202A TrueRFTM migration Rev 1 February 2006 www.semtech.com 1 Technical Note TN1202.04 XE1202 to XE1202A TrueRF™ Migration 1 INTRODUCTION This technical note provides the information about the main differences between the XE1202 and the new XE1202A TrueRF™ circuits. It also explains what has to be done at the application level to switch from one circuit to the other. 2 XE1202A TRUERFTM BENEFITS • • • 3 Full FCC/ETSI compliancy without a SAW filter Unconditional stability even at 15 dBm output power Improved transmission efficiency if the SAW filter is omitted (no filter insertion loss) XE1202A TRUERFTM PART NUMBERING The XE1202A TrueRF™ version part number is XE1202AI027. The ‘non TrueRF™ version part number is XE1202I027. Please contact XEMICS technical support if in doubt. 4 PCB MIGRATION TM Because the XE1202A TrueRF is pin-compatible with the XE1202, PCB layout changes are required only if the SAW filter is omitted (substitution with an L-C filter is required). Clients deciding not to change the PCB layout can use the XE1202ATrueRFTM and keep the SAW filter. 4.1 PIN NAME CHANGE Pin 11, TVCO connected to ground in the previous version of the chip becomes now VSSP (VSS for the power amplifier) connected to ground. No PCB layout modification is necessary for this. 4.2 VCO TANK The tank of the VCO can be implemented with one inductor in parallel with one capacitor, as in the previous TM version of the XE1202. The values for these components have to be changed when using the XE1202A TrueRF . The characteristics of the external tank components must be as follows: Name Typical Value for 434 MHz Typical Value for 868 MHz Typical Value for 915 MHz Tolerance CV1 NC NC NC ± 5% LV1 39 nH 6.8 nH 5.6 nH ± 2% The values above are typical and may differ for different PCB layouts. For 915 MHz and 869 MHz frequency bands the use of the external capacitor CV1 should be avoided. The value of the inductor LV1 and its position (between the two footprints) should be changed to centre the VCO tuning range. Depending on the minimum supply voltage available, the VCO tuning voltage, Vlfb, should be centred as follows: Minimum supply voltage Typical Vlfb for 434 MHz Typical Vlfb for 868 MHz Typical Vlfb for 915 MHz VDDmin = 2.7 V 0.9 V 1.2 V 1.1 V VDDmin = 2.4 V 0.8 V 1.1 V 1.0 V © Semtech 2006 www.semtech.com 2 Technical Note TN1202.04 XE1202 to XE1202A TrueRF™ Migration 4.3 LOOP FILTER OF THE FREQUENCY SYNTHESIZER The loop filter of the frequency synthesizer is shown below: XE1202A 2 Figure 1: Loop filter of the frequency synthesizer. TM The XE1202A TrueRF VCO has an increased Kvco. So the loop filter components values should be changed accordingly. The recommended values are given in the table below. 4.4 Name Typical Value for 434 MHz Typical Value for 868 MHz Typical Value for 915 MHz Tolerance CL1 22 nF 22 nF 22 nF ± 5% CL2 1 nF 1 nF 1 nF ± 5% RL1 560Ω 470Ω 470Ω ± 5% MATCHING NETWORK OF THE TRANSMITTER The optimum load impedances for 15 dBm at the three main frequencies are given in the following table. PA optimum load 434 MHz 868 MHz 915 MHz 66 – 5j 66 + 14j 64 + 13j The schematic of the recommended matching network at the output of the transmitter is given on the next page. The two Π-sections are used to provide harmonic filtering to pass FCC and ETSI regulations with sufficient margin. © Semtech 2006 www.semtech.com 3 Technical Note TN1202.04 XE1202 to XE1202A TrueRF™ Migration LT1 VDD CT2 CT1 LT2 CT4 CT5 XE1202A CT3 LT3 Figure 2: Transmitter output network. The typical component values of this matching circuit are given below. 5 Name Typical Value for 434 MHz Typical Value for 868 MHz Typical Value for 915 MHz Tolerance CT1 6.8 pF 1.5 pF 1.8 pF ± 5% CT2 1.0 pF 0.56 pF NC ± 5% CT3 22 pF 15 pF 33 pF ± 5% CT4 6.8 pF 3.3 pF 3.3 pF ± 5% CT5 4.7 pF 2.2 pF 2.2 pF ± 5% LT1 33 nH 39 nH 47 nH ± 5% LT2 22 nH 10 nH 10 nH ± 5% LT3 22 nH 8.2 nH 8.2 nH ± 5% REGISTER CONFIGURATION There is no change in the way of configuring the circuit. All the settings used for the XE1202 can be left unchanged in the XE1202A TrueRF™. 6 CONCLUSIONS This application note describes the necessary changes when migrating from the existing XE1202 to the XE1202A TrueRFTM. PCB layout changes are necessary only when removing the SAW filter. If the SAW filter is retained then only some component values should be changed, as described above. © Semtech 2006 www.semtech.com 4 Technical Note TN1202.04 XE1202 to XE1202A TrueRF™ Migration © Semtech 2006 All rights reserved. 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