Basic Application Schematic
A basic application schematic of the AT86RF212B with a single-ended RF connector is shown in the figure below. The 50Ω single-ended RF input is transformed to the 100Ω differential RF port impedance using balun B1. The capacitors C1 and C2 provide AC coupling of the RF input to the RF port. If the balun pins at the differential side provide no DC path to ground and to the single-ended pin, the capacitors are not necessary.
Regulatory rules like FCC 47 CFR Section 15.247 [5], ETSI EN 300 220-1 [6], and ERC/REC 70-03 [7] may require an external filter F1, depending on used transmit power levels.
The power supply decoupling capacitors (CB2, CB4) are connected to the external analog supply pin 28 (EVDD) and external digital supply pin 15 (DEVDD). Capacitors CB1 and CB3 are bypass capacitors for the integrated analog and digital voltage regulators to ensure stable operation. All bypass capacitors should be placed as close as possible to the pins and should have a low-resistance and low-inductance connection to ground to achieve the best performance.
The crystal (XTAL), the two load capacitors (CX1, CX2), and the internal circuitry connected to pins XTAL1 and XTAL2 form the crystal oscillator. To achieve the best accuracy and stability of the reference frequency, large parasitic capacitances should be avoided. Crystal lines should be routed as short as possible and not in proximity of digital I/O signals. This is especially required for the High Data Rate Modes.
Crosstalk from digital signals on the crystal pins or the RF pins can degrade the system performance. Therefore, a low-pass filter (C3, R1) is placed close to the CLKM output pin to reduce the emission of CLKM signal harmonics. This is not needed if pin 17 (CLKM) is not used as a microcontroller clock source. In this case, pin 17 (CLKM) output should be disabled during device initialization.
- The pins DIG1, DIG2, DIG3, and DIG4 are connected to ground in the Basic Application Schematic; refer to the figure aboe. Special programming of these pins requires a different schematic; refer to the Extended Feature Set Application Schematic.
Symbol | Description | Value | Manufacturer | Part Number | Comment |
---|---|---|---|---|---|
B1 | SMD balun | 800 – 1000MHz |
Wuerth JTI |
748431090 0900BL18B100 |
|
F1 | SMD low pass filter | 902 – 928MHz |
Wuerth JTI |
748131009 0915LP15A026 |
|
B1 + F1 (alternatively) |
Balun/Filter combination | 863 – 928MHz | JTI | 0896FB15A0100 | |
779 – 787MHz | JTI | 0783FB15A0100 | |||
CB1 CB3 |
LDO VREG bypass capacitor |
1mF |
AVX Murata |
0603YD105KAT2A GRM188R61E105KA12 |
X5R, 10%, 16V (0603) |
CB2 CB4 |
Power supply bypass capacitor |
X5R, 15%, 25V (0603) |
|||
CX1, CX2 |
Crystal load capacitor |
12pF |
AVX Murata |
06035A120JA GRM1555C1H120JA01 |
C0G, 5%, 50V (0402 or 0603) |
C1, C2 |
RF coupling capacitor |
100pF |
Epcos Epcos AVX |
B37930 B37920 06035A680JAT2A |
C0G, 5%, 50V (0402 or 0603) |
C3 |
CLKM low-pas filter capacitor |
2.2pF |
AVX Murata |
06035A229DA GRP1886C1H2R0DA01 |
COG, ±0.5pF, 50V (0603) Designed for fCLKM = 1MHz |
R1 |
CLKM low-pass filter resistor |
680W | Designed for fCLKM = 1MHz | ||
XTAL | Crystal |
CX-4025 16MHz SX-4025 16MHz |
ACAL Taitjen Siward |
XWBBPL-F-1 A207-011 |