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Table 1. Part Selection Guide
- Frequency Band Definition and Selection
according to the frequency range desired. Table 2. Band Sequence Definition for Si4836-A
12.25 MHz
13.87 MHz
21.85 MHz
Table 2. Band Sequence Definition for Si4836-A (Continued)
Table 3. Band Sequence Definition for Si4825-A
Table 3. Band Sequence Definition for Si4825-A (Continued)
- Total value of resistance from the BAND to GND is equal to the value specified in Table 2.
- Total resistance from TUNE1 to GND is 500 k in 1% tolerance.
The following sections describe some commonly used bands and their respective selection circuits. Table 4 and Figure 1 illustrate the band and resistor value details for a typical 12-band application for Si4836-A. Table 4. Typical 12-Band Selection
Figure 1. Typical 12-Band Selection Circuit
Table 5 and Figure 2 show the band and resistor value details for a typical European 2-band application. Figure 2. Typical 2-Band Selection Circuit for Europe Table 5. Typical European 2-Band Selection
Table 6 and Figure 3 show the band and resistor value details for a typical 2-band application for the U.S. Figure 3. Typical 2-Band Selection Circuit for US Table 6. Typical U.S. 2-Band Selection
(32.768 kHz) to XTALI, leave XTALO floating. control function or stereo/station indicator function. VR1 (100k /10%), R27, C1, C13 constitute the tuning circuit. 100K at 10% tolerance is recommended for VR1. and SW bands as defined in Section “2.1. Band Definition” . bands. The LNA is switched off by the LNA_EN signal in AM and FM mode controlled by the chip. Figure 5. Si4825-A Basic Applications Circuit
Figure 6. Si4836-A Basic Applications Circuit
the minimum or maximum, respectively. Figure 7. Si4825-A Applications Circuit with Internal Volume Adjustment 11, which sets the default volume to Max.
Figure 9. Si4836-A Applications Circuit with Bass/Treble Control
RSTB voltage to below 0.3*VDD to power off Si4825/36. pole of S3 short Pin 9 RSTB to GND to power off the tuner. Figure 10. Si4825-A Applications Circuit with User Setting Memory
Table 7. Si4825-A Basic Applications Circuit BOM
Table 8. Additional BOM for Si4825-A Applications Circuit with Internal Volume Adjustment Table 9. Additional BOM for Si4825-A Applications Circuit with User Setting Memory Table 7. Si4825-A Basic Applications Circuit BOM (Continued)
Table 10. Si4836-A Basic Applications Circuit BOM
Table 11. Additional BOM for Si4836-A Applications Circuit with Bass/Treble Control Table 10. Si4836-A Basic Applications Circuit BOM (Continued)
Place VDD bypass capacitor C16, C15 as close as possible to the power supply pin (Pin 14). Place the crystal as close to XTALO (Pin 12) and XTALI (Pin 13) as possible. underneath and around the chip. Do not route Pin 5. This pin must be left floating to guarantee proper operation. Keep the Tune1 and Tune2 traces away from Pin 5, route Tune1 and Tune2 traces in parallel and the same way. Place C1, C13 as close to Pin 2 TUNE1 as possible. Refer to the Si4836-A Layout example as much as possible when doing Si4825/36-A PCB layout. Figure 11. Si4836-A PCB Layout Example
- Headphone Antenna for FM Receive
approximately half the FM wavelength (FM wavelength is ~3 m). of a typical application is shown in Figure 12. Figure 12. Typical Headphone Antenna Application
With the specified BOM components, the corner frequency of the headphone amplifier is approximately 20 Hz. manufacturer is not critical for resistors and capacitors. Table 12. Headphone Antenna Bill of Materials
Rev. 0.2 25 4.4. Headphone Antenna Layout To minimize inductive and capaciti ve coupling, inductor LMATCH and headphone jack J24 should be placed together and as far from noise sources (such as clocks and digital circuits) as possible. LMATCH should be placed near the headphone connector to keep audio currents away from the chip. To minimize CSHUNT and CP, place ferrite beads F1 and F2 as closely as possible to the headphone connector. To maximize ESD protection diode effectiveness, plac e diodes D1, D2, and D3 as near to the headphone connector as possible. If capacitance larger than 1 pF is required for D1 and D2, both components should be placed between FB1, FB2, and the headphone amplifier to minimize CSHUNT. Place the chip as near to the headphone connector as possible to minimize antenna trace capacitance, CPCBANT. Keep the trace length short and narrow and as far above the reference plane as possible, restrict the trace to a microstrip topology (trace routes on the top or bottom PCB layers only), minimize trace vias, and relieve ground fill on the trace layer. Note that minimizing capacitance has the effect of maximizing characteristic impedance. It is not necessary to design for 50 transmission lines. To reduce the level of digital noise passed to the antenna, RF shunt capacitors C5 and C6 may be placed on the left and right audio traces close to the headphone ampl ifier audio output pins. The recommended value is 100 pF or greater; however, the designer sh ould confirm that the headphone amplifie r is capable of driving the selected shunt capacitance. 4.5. Headphone Antenna Design Checklist Select an antenna length of 1.1 to 1.45 m. Select matching inductor LMATCH to maximize signal strength across the FM band. Select matching inductor LMATCH with a Q of 15 or greater at 100 MHz and minimal dc resistance. Place inductor LMATCH and headphone connector together and as far from potential noise sources as possible to reduce capacitive and inductive coupling. Place the chip close to the headphone connector to minimize antenna trace length. Minimizing trace length reduces CP and the possibility for inductive and capacitive coupling into the antenna by noise sources. This recommendation must be followed for optimal device performance. Select ferrite beads F1-F2 with 2.5 k or greater resistance at 100 MHz to maximize RSHUNT and, therefore, RP. Place ferrite beads F1-F2 close to the headphone connector. Select ESD diodes D1-D3 with minimum capacitance. Place ESD diodes D1-D3 as close as possible to the headphone connector for maximum effectiveness. Place optional RF shunt capacitors near the headphone amplifier’s left and right audio output pins to reduce the level of digital noise passed to the antenna.
input connector for maximum effectiveness. Maximize whip antenna length for optimal performance. Select matching inductor L1 with a Q of 15 or greater at 100 MHz and minimal dc resistance. capacitive and inductive coupling. recommendation must be followed for optimal device performance. Place ESD U3 as close as possible to the whip antenna for maximum effectiveness. Select ESD diode U3 with minimum capacitance. Place the ac coupling capacitor, C5, as close to the FMI pin as possible. Table 13. FM Whip Antenna Bill of Materials
- Ferrite Loop Antenna for AM Receive
prone to device noise activity and may result in better AM reception. a better sensitivity than the miniature one. Figure 16. Standard and Miniature Ferrite Loop Antennas and 450 uH for the Si4825/36-A AM Receiver. Table 14 lists the recommended ferrite loop antenna for the Si4825/36-A AM Receiver. Table 14. Recommended Ferrite Loop Antenna
Figure 17. AM Ferrite Loop Antenna Schematic C1 is the ac coupling cap going to the AMI pin and its value should be 0.47 µF. D1 is an optional ESD diode if there is an exposed pad going to the AMI pin. AM band. Noise sources can come from clock signals, sw itching power supply, and digital activities (e.g., MCU). chip. This will minimize capacitive coupling between the plane(s) and the antenna. To tune correctly, the total capacitance seen at the AMI input needs to be minimized and kept under a certain value. capacitance at the AM input can be calculated using the formula shown in Equation 3. Table 15. Ferrite Loop Antenna Bill of Materials *Note: Optional; only needed if there is any exposed pad going to the AMI pin.
30 Rev. 0.2 Equation 3. Expected Total Capacitance at AMI The total allowable capacitance, when interfacing a ferrite loop stick antenna, is the effective capacitance resulting from the AMI input pin, the capacitance from the PCB, and the capacitance from the ferrite loop stick antenna. The inductance seen at the AMI in this ca se is primarily the inductance of the ferrite loop stick antenna. The total allowable capacitance in the case of an air loop antenna is the effective capacitance resulting from the AMI input pin, the capacitance of the PCB, the capacitance of the transformer, and the capacitance of the air loop antenna. The inductance in this case should also take all the elem ents of the circuit into account. The input capacitance of the AMI input is 8 pF. The formula shown in Equation 3 gives a total capacitance of 28 pF when a 300 uH ferrite loop stick antenna is used for an AM band, where the highest frequency in the band is 1750 kHz. 6.5. Ferrite Loop Antenna Design Checklist Place the chip as close as possible to the ferrite loop antenna feedline to minimize parasitic capacitance and the possibility of noise coupling. Place the ferrite loop stick antenna away from any sources of interference and even away from the I/O signals of the chip. Make sure that the AM antenna is as far away as possible from circuits that switch at a rate which falls in the AM band (504–1750 kHz). Recommend keeping the AM ferrite loop antenna at least 5 cm away from the tuner chip. Place optional component D1 if the antenna is exposed. Select ESD diode D1 with minimum capacitance. Do Not Place any ground plane under the ferrite loop stick antenna if the ferrite loop stick antenna is mounted on the PCB. The recommended ground separation is 1/4 inch or the width of the ferrite. Route traces from the ferrite loop stick connectors to the AMI input via the ac coupling cap C1 such that the capacitance from the traces and the pads is minimized. CTotal 1 2fmax 2Leffective Where: CTotal Total capacitance at the AMI input Leffective Effective inductance at the AMI input fmax Highest frequency in AM band=
Table 16. Recommended Transformers
Figure 19. AM Air Loop Antenna Schematic C1 is the ac coupling cap going to the AMI pin and its value should be 0.47 µF. D1 is a required ESD diode since the antenna is exposed. trace going to the air loop antenna, which will minimize parasitic capacitance and the possibility of noise coupling. transformer. Use a shielded transformer if possible. falls in the AM band (504–1750 kHz). from the traces and the pads is minimized. Select ESD diode D1 with minimum capacitance. Table 17. Air Loop Antenna Bill of Materials
Maximize whip antenna length for optimal performance. capacitive and inductive coupling. recommendation must be followed for optimal device performance. Place the ac coupling capacitor C33, as close to the AMI pin as possible. Table 18. SW Whip Antenna Bill of Materials
36 Rev. 0.2 DOCUMENT CHANGE LIST Revision 0.1 to Revision 0.2 Added new Table 3 for the band definition of Si4825- Updated all the Si4825 schematic figures and the BOM tables.
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