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LT8900 Datasheet Revision 1.1 LT8900 Low Cost 2.4GHz Radio Transceiver FEATURES GENERAL DESCRIPTION z Complete 2.4 GHz radio transceiver includes fully integrated RF PLL and channel filtering z Supports Frequency-Hopping Spread Spectrum z Supports SPI and I2C bus interface z Built-in smart auto-acknowledge Tx/Rx protocol simplifies usage z Packet data rate 1 Mbps over-the-air z FIFO flag signal permits continuous streaming data at 1 Mbps over-the-air z Power management for minimizing current consumption z Digital readout of RSSI and temperature z Lead-free 4x4mm QFN Package & SOP16 for best RF performance Application z Remote controls z Wireless keyboards and mice z Proprietary Wireless Networks z Home automation z Commercial and industrial short-range wireless z Wireless voice, VoIP, Cordless headsets z Robotics and machine connectivity The LT8900 is a low-cost, fully integrated CMOS RF transceiver, GFSK data modem, and packet framer, optimized for use in the 2.4 GHz ISM band. It contains transmit, receive, RF synthesizer, and digital modem functions, with few external components. The transmitter supports digital power control. The receiver utilizes extensive digital processing for excellent overall performance, even in the presence of interference and transmitter impairments. The LT8900 transmits GFSK data at approximately 1 dBm output power. The low-IF receiver architecture produces good selectivity, with sensitivity down to approx. -87 dBm. Digital RSSI values are available to monitor channel quality. On-chip transmit and receive FIFO registers are available to buffer the data transfer with MCU. Over-the-air data rate is always 1 Mbps even when connected to a slow, low-cost MCU. Built-in CRC, FEC, data whitening, and automatic retry/acknowledge are all available to simplify and optimize performance for individual applications. The digital baseband interface can be either 4-wire SPI or 2-wire I2C-bus. Three additional pins are available for optional reset and buffer control. For extended battery life, power consumption is minimized all key areas. A sleep mode is available to reduce standby current consumption to just 1 uA typ. while preserving register settings. This product is available in RoHS compliant 24-lead 4x4 mm JEDEC standard QFN package, featuring an exposed pad on the bottom for best RF characteristics. Also available in bare die form. 1. Block Diagram LT8900 Datasheet Revision 1.1 Page 2 July 2010 2. Absolute Maximum Ratings LT8900 Datasheet Revision 1.1 Table 1. Absolute Maximum Rating Parameter Operating Temp. Storage Temp. LDO_VDD, VDD_IO Voltage VDD pins Applied Voltages to Other Pins Input RF Level Output Load mismatch (Z0=50Ω) Symbol TOP TSTORAGE VIN_MAX VDD_MAX VOTHER PIN VSWROUT MIN TYP MAX -40 +85 -55 +125 +3.7 +2.5 -0.3 +3.7 +10 10:1 Unit ºC ºC VDC VDC dBm VSWR Notes: 1. Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Recommended operating conditions indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics section below. 2. These devices are electro-static sensitive. Devices should be transported and stored in anti-static containers. Equipment and personnel contacting the devices need to be properly grounded. Cover workbenches with grounded conductive mats. Page 3 July 2010 3. Electrical Characteristics LT8900 Datasheet Revision 1.1 Table 2. Electrical Characteristics The following specifications are guaranteed for TA = 25 C, LDO_VDD= VDD_IO = 3.3 VDC, unless otherwise noted. Parameter Symbol MIN Supply Voltage DC power supply voltage range 1.9 Current Consumption Current Consumption - TX IDD_TXH IDD_TXL Current Consumption - RX IDD_RX Current Consumption –IDLE IDD_IDLE1 IDD_IDLE2 Current Consumption - SLEEP IDD_SLP Digital Inputs Logic input high Logic input low 0.8 VIH VDD_IN VIL 0 Input Capacitance C_IN Input Leakage Current I_LEAK_IN Digital Outputs Logic output high Logic output low VOH VOL 0.8 VDD_IN Output Capacitance C_OUT Output Leakage Current I_LEAK_OUT Rise/Fall Time (SPI) T_RISE_OUT Clock Signals CLK rise, fall time (SPI) Tr_spi CLK frequency range (SPI) FSPI 0 Overall Transceiver Operating Frequency Range Antenna port mismatch (Z0=50Ω) F_OP VSWR_I VSWR_O 2400 TYP 18 12 17 1.4 1.1 1 12 <2:1 <2:1 MAX Units Test Condition and Notes 3.6 VDC` Input to VDD_IO and LDO_VDD pins. mA POUT = high power setting mA POUT = low power setting mA mA Configured for BRCLK output running. mA Configured for BRCLK output OFF. uA 1.2 V VDD_IN 0.8 V 10 pF 10 uA VDD_IN V 0.4 V 10 pF 10 uA 5 nS 25 nS Requirement for error-free register reading, writing. MHz 2482 MHz VSWR VSWR Receive mode. Transmit mode. Page 4 July 2010 LT8900 Datasheet Revision 1.1 Parameter Symbol MIN TYP MAX Unis Test Condition and Notes Receive Section Receiver sensitivity Measured using 50 Ohm balun. For BER ≤ 0.1%: -87 dBm FEC off. Maximum useable signal -20 1 dBm Data (Symbol) rate Ts 1 us Min. Carrier/Interference ratio For BER ≤ 0.1% Co-Channel Interference CI_cochannel +9 dB -60 dBm desired signal. Adjacent Ch. Interference, CI_1 +6 dB -60 dBm desired signal. 1MHz offset Adjacent Ch. Interference, CI_2 -12 dB -60 dBm desired signal. 2MHz offset Adjacent Ch. Interference, CI_3 -24 dB -67 dBm desired signal. 3MHz offset Out-of-Band Blocking OBB_1 -10 OBB_2 -27 For additional test conditions, see OBB_3 -27 footnote1. OBB_4 -10 dBm dBm dBm dBm 30 MHz to 2000 MHz 2000 MHz to 2400 MHz 2500 MHz to 3000 MHz 3000 MHz to 12.75 GHz Meas. with ACX BF2520 ceramic filter 2 on ant. pin . Desired sig. -67 dBm, BER ≤ 0.1%. Transmit Section Measured using 50 Ohm balun3: RF Output Power PAV 6 POUT= maximum output power Reg09=0x4000 2 dBm POUT = nominal output power, Reg09=0x1840 -17 POUT=minimum power,Reg09=1FC0 output Second harmonic -50 dBm Conducted to ANT pin. Third harmonic -50 dBm Conducted to ANT pin. Modulation Characteristics Peak FM 00001111 pattern Deviation 01010101 pattern ∆f1avg ∆f2max 280 kHz 225 kHz In-Band Spurious Emission 2MHz offset IBS_2 -40 dBm >3MHz offset IBS_3 -60 dBm Out-of-Band Spurious Emission, Operation Note: OBS_O_1 OBS_O_2 OBS_O_3 OBS_O_4 < -60 -36 dBm 30 MHz ~ 1 GHz -45 -30 dBm 1 GHz ~ 12.75 GHz, excludes desired signal and harmonics. < -60 -47 dBm 1.8 GHz ~ 1.9 GHz < -65 -47 dBm 5.15 GHz ~ 5.3 GHz 1. The test is run at one midband frequency, typically 2460 MHz. With blocking frequency swept in 1 MHz steps, up to 24 exception frequencies are allowed. Of these, no more than 5 shall persist with blocking signal reduced to -50dBm. For blocking frequencies below desired receive frequency, in-band harmonics of the out-of-band blocking signal are the most frequent cause of failure, so be sure blocking signal has adequate harmonic filtering. 2. In some applications, this filter may be incorporated into the antenna, or be approximated by the effective antenna bandwidth. 3. Transmit power measurement is corrected for insertion loss of Balun, in order to indicate the transmit power at the IC pins. Page 5 July 2010 LT8900 Datasheet Revision 1.1 Parameter RF VCO and PLL Section Typical PLL lock range Tx, Rx Frequency Tolerance Channel (Step) Size SSB Phase Noise Crystal oscillator freq. range Symbol FLOCK (Reference Frequency) Crystal oscillator digital trim range, typ. RF PLL Settling Time THOP Spurious Emissions OBS_1 OBS_2 LDO Voltage Regulator Section Dropout Voltage Vdo MIN TYP MAX Unit Test Condition and Notes 2366 -1 ≤ -95 ≤ -115 2516 12.00 0 ±20 75 150 < -75 -57 -68 -47 MHz ppm MHz dBc/Hz dBc/Hz Same as XTAL pins frequency tolerance 550kHz offset 2MHz offset MHz ppm uS dBm dBm Designed for 12 MHz crystal reference freq. See Register 27 description. Amount of pull depends on crystal spec. and operating point. Settle to within 30 kHz of final value. 30 MHz ~ 1 GHz 1 GHz ~ 12.75 GHz IDLE state, Synthesizer and VCO ON. 0.17 0.5 V Measured during Receive state Page 6 July 2010 4. Typical Application LT8900 Datasheet Revision 1.1 2.4 GHz Wireless Data Transceiver with SPI Figure 1. LT8900 Typical Application Schematic R3 10K C3 12pF R2 680K VDD VDD ANTb ANT VDD VDD XTALI XTALO VDD R1 2.2K C4 12pF VDD1.8V VDD_IO C5 1uF VDD LDO_VDD LDO_OUT RST_n RESET_n MISO/I2C_DAT SPI_miso VDD_IO R3 1K MOSI/A4 SPI_mosi I2C_SEL SPI_CLK SPI_CLK VDD_IO R4 1K PKT PKT_flag RESET_n SPI_miso SPI_mosi SPI_CLK PKT_flag SPI_SS VDD_IO VDD_IO SPI_SS BRCLK VSS FIFO VDD SPI_SS BRCLK FIFO_FLAG VDD1.8V VDD_IO R4:1K R3:1K R2:680K VDD18 Page 7 July 2010 5. Pin Description LT8900 Datasheet Revision 1.1 Pin No. 1, 2, 5, 6, 7, 19, 22 3, 4 8 9 10 Pin Name VDD ANTb, ANT FIFO GND VDD_IO 11 SPI_SS 12 BRCLK 13 PKT 14 SPICLK 15 I2C_SEL 16 MOSI/A4 17 MISO/I2C_DAT 18 RST_n 20 LDO_VDD 21 LDO_OUT 23 XTALO 24 25 (Exposed pad) XTALI GND Table 3. Pin Description QFN24 Type Description PWR Power supply voltage. Balanced RF O GND PWR I O O I I I I/O I PWR PWR AO AI RF input/output. FIFO status indicator bit. Ground connection. Vdd for the digital interface. SPI: Enable input for the SPI bus, active low. Also used to bring device out of SLEEP state. I2C: Used to bring device out of SLEEP state. Output from internal clock Transmit/Receive packet status indicator bit. Clock input for SPI/I2C interface. Mode selection: 0: Interface is SPI 1: Interface is I2C SPI: Data input for the SPI bus. I2C: Specifies I2C address bit 4. SPI: Data output (tri-state when not active) I2C: Data in/out When RST_n is low, most of the chip shuts down to conserve power. Register values will be lost. To preserve register values, use SLEEP mode instead. When raised high, RST_n is used to turn on the chip, restoring all registers to their default value. Input power to the on-chip LDO. +1.8V output from the on-chip LDO voltage regulator. Normally this will connect to all VDD pins of the chip, supplying clean, well-regulated power to all critical sections. DO NOT CONNECT TO EXTERNAL LOADS. Output of the crystal oscillator gain block. Input to the crystal oscillator gain block. GND Ground reference connection. Page 8 July 2010 6. SPI Interface LT8900 Datasheet Revision 1.1 6.1. SPI Default Format Figure 2. SPI Signal Format when CKPHA = 1 (Standard configuration for QFN packaged parts) 6.2. SPI Optional Format Figure 3. SPI Signal Format when CKPHA = 0 (For QFN packaged parts, this option available by special order only) Notes: 1. Polarity of SPI read/write bit: Write= 0, Read= 1. 2. Access to FIFO Register 50 is byte-by-byte (always integer multiples of 8-bits). Access to multiple FIFO bytes may be combined into one or more SPI_SS cycle(s) if desired. 3. Access to all registers other than FIFO is always word length (16-bits per register). 4. Access to multiple registers (except FIFO register) may be combined into one SPI_SS cycle. If combined, address is written only once at the beginning of the SPI cycle, then each 16-bit register value follows. The LT8900 will auto-increment the register number that each word of data is placed into. If in doubt, simply use separate SPI_SS cycles for each 16-bit register write. 5. MISO return status byte S7:S0 will be the same as the top byte of Register 48 (contains result of CRC and FEC error check, and framer state status). Page 9 July 2010 LT8900 Datasheet Revision 1.1 6.3. SPI Timing Requirements Name T1 T2a, T2b T3 T4 T5 T6 Table 4. SPI Timing Requirements Min Typ. Max Description 250ns 41.5ns Note 1 Note 1 Note 2 Interval between two SPI accesses Relationship between SPI_SS & SPI_CLK Interval time between address and data Interval time between high byte and low byte data Interval time between two register data 83ns SPI_CLK period Notes: 1. When MCU/application reads register 50 FIFO data, at least 450ns wait time is required for framer to get correct FIFO read point. For all other registers, T3min = 41.5ns. 2. When reading register 50 FIFO data, at least 450ns wait time is required. For all other registers, T5min = 41.5ns. Page 10 July 2010 7. IIC Interface LT8900 Datasheet Revision 1.1 7.1. I2C Command Format Figure 4. Example I2C Data Transfers 7.2. I2C Supported Features Table 5. I2C Supported Feature List I2C device Slave Mode Optional Feature List Standard-mode – 100 kbps Fast-mode – 400 kbps Fast-mode Plus – 1000 kbps High-speed mode – 3200 kbps Clock Stretching 10-bit slave address general call address software reset device ID LT8900 Support? Yes Yes Yes No No No No No No Page 11 July 2010 LT8900 Datasheet Revision 1.1 7.3. I2C Device Address In I2C mode, the LT8900 responds to the following device address: A6 A5 A4 A3 A2 A1 A0 R/W Determined jumper. by bonding pad Determined by bonding pad jumper. QFN packaged parts: Standard is ‘1’. QFN packaged determined by parts: As Read=1 0 10 0 0 Special order option is ‘0’. pin 15, MOSI/A4. Write=0 Bare Die: can be bonded however required. Bare Die: can be bonded however required. Page 12 July 2010 8. Top Level State Diagram LT8900 Datasheet Revision 1.1 Page 13 July 2010 9. Register Information LT8900 Datasheet Revision 1.1 The following registers are accessed using SPI or I2C serial interface protocol. Some of the internal registers and bit fields are not intended for end-user adjustment. Such registers are not described herein, and should not be altered from the factory-recommended value. 9.1. Register 3 – Read only Bit No. 15:13 Bit Name (Reserved) 12 RF_SYNTH_LOCK 11:0 (Reserved) Table 6. Register 3 information Description (Reserved) Indicates the phase lock status of RF synthesizer. 1: Locked. 0: Unlocked. (Reserved) 9.2. Register 6 – Read only Bit No. Bit Name Table 7. Register 6 information Description 15:10 RAW_RSSI[5:0] Indicate 4-bit raw RSSI values from analog circuit. 9:0 (Reserved) (Reserved) 9.3. Register 7 Bit No. 15:9 Bit Name (Reserved) 8 TX_EN 7 RX_EN 6:0 RF_PLL_CH_NO [6:0] Table 8. Register 7 information Description (Reserved) Initiate the Transmit Sequence for state machine control. Note that TX_EN and RX_EN cannot be “HIGH” at the same time. Initiate the Receive Sequence for state machine control. Note that TX_EN and RX_EN cannot be “HIGH” at the same time. This will be the 7 bit RF channel number. The on-air frequency will be: f = 2402 + RF_PLL_CH_NO. Page 14 July 2010 9.4. Register 9 Bit No. 15:12 11 10:7 6:0 Bit Name PA_PWCTR[3:0] (Reserved) PA_GN[3:0] (Reserved) LT8900 Datasheet Revision 1.1 Table 9. Register 9 information Description PA current control (Reserved) 4-bit power amplifier gain setting. (Reserved) 9.5. Register 10 Bit No. 15:1 Bit Name (Reserved) 0 XTAL_OSC_EN Table 10. Register 10 information Description (Reserved) 1: Enable crystal oscillator gain block. 0: Disable crystal oscillator gain block. 9.6. Register 11 Bit No. 15:9 Bit Name (Reserved) 8 RSSI_PDN 7:0 (Reserved) Table 11. Register 11 information Description (Reserved) 1: Power down RSSI. 0: RSSI operates normally. (Reserved) 9.7. Register 23 Bit No. 15:3 Bit Name (Reserved) 2 TxRx_VCO_CAL_EN 1:0 (Reserved) Table 12. Register 23 information Description (Reserved) 1: Calibrate VCO before each and every Tx/Rx enable. 0: Do not calibrate VCO before each and every Tx/Rx enable. (Reserved) Page 15 July 2010 9.8. Register 27 Bit No. 15:6 5:0 Bit Name (Reserved) XI_trim[5:0] LT8900 Datasheet Revision 1.1 Table 13. Register 27 information Description (Reserved) Crystal frequency trim adjust. 9.9. Register 29 – Read only Bit No. 15:8 7:4 3 2:0 Bit Name (Reserved) RF_VER_ID [3:0] (Reserved) Digital version Table 14. Register 29 information Description (Reserved) This field is used to identify minor RF revisions to the design. (Reserved) This field is used to identify minor digital revisions to the design. 9.10. Register 30 – Read only Bit No. Bit Name 15:0 ID_CODE_L [15:0] Table 15. Register 30 information Description Lower bits of JEDEC JEP106-K Manufacture’s ID code, containing manufacturer, part number, and version. The LSB is always “1”. 9.11. Register 31 – Read only Bit No. 15:12 11:0 Bit Name RF_CODE_ID ID_CODE_M [31:16] Table 16. Register 31 information Description JEDEC JEP106-K revision level. Upper bits of Manufacture’s ID code. Page 16 July 2010 9.12. Register 32 Bit Name 15:13 PREAMBLE_LEN 12:11 SYNCWORD_LEN 10:8 TRAILER_LEN 7:6 DATA_PACKET_TYPE 5:4 FEC_TYPE LT8900 Datasheet Revision 1.1 Table 17. Register 32 information R/W Description 000: 1byte, 001: 2bytes, R/W 010: 3 bytes, … 111: 8 bytes 11: 64 bits {Reg39[15:0],Reg38[15:0],Reg37[15:0],Reg36[15:0]} R/W 10: 48bits, {Reg39[15:0],Reg38[15:0],Reg36[15:0]} 01: 32bits, {Reg39[15:0],Reg36[15:0] 00: 16 bits,{Reg36[15:0]} 000: 4 bits, 001: 6bits, 010: 8 bits, R/W 011: 10 bits …. 111: 18 bits 00: NRZ law data 01: Manchester data type R/W 10: 8bit/10bit line code 11: Interleave data type 00: No FEC 01: FEC13 R/W 10: FEC23 11: reserved default 010B 11B 000B 00B 00B Page 17 July 2010 Bit Name 3:1 BRCLK_SEL 0 (Reserved) R/W Description LT8900 Datasheet Revision 1.1 default Selects output clock signal to BRCLK pin: 3’b000: keep low 3’b001: crystal buffer out 3’b010: crystal divided by 2 R/W 3’b011: crystal divided by 4 3’b100: crystal divided by 8 3’b101: TXCLK 1 MHz 3’b110: APLL_CLK (12 MHz during Tx, Rx) 3’b111: keep low 011B W/R (Reserved) 0B Page 18 July 2010 LT8900 Datasheet Revision 1.1 9.13. Register 33 Bit Name Table 18. Register 33 information R/W Description default 15-8 VCO_ON_DELAY_CNT[7:0] R/W After set TX or RX wait delay timer for internal VCO setting time. Each time increment is 1 uS. 63H 7-6 TX_PA_OFF_DELAY[1:0] R/W Set PA off after PA_OFF command, 1 represents 1us, base is 4us 00B 5:0 TX_PA_ON_DELAY[5:0] R/W After set VCO_ON, it will wait this timer , than internal PA fully on, 07H 9.14. Register 34 Bit Name 15 Bpktctl_direct Table 19. Register 34 information R/W Description default When direct mode, it is used control PA on at TX and R/W 0B wide/narrow mode control at RX 14-8 TX_CW_DLY[6:0] R/W Transmit CW modulation data at before transmit data, after PA on, continue TX CW mode time. 03H 7-6 Reserved 5:0 TX_SW_ON_DELAY[5:0] R/W 0B R/W Set VCO_ON, wait this timer, internal TW switch turn on, 1 represents 1us 0BH 9.15. Register 35 Page 19 Table 20. Register 35 information July 2010 Bit Name 15 POWER_DOWN 14 SLEEP_MODE 13 (Reserved) 12 BRCLK_ON_SLEEP 11:8 RE-TRANSMIT_TIMES 7 MISO_TRI_OPT 6:0 SCRAMBLE_DATA R/W Description LT8900 Datasheet Revision 1.1 default 1: First set crystal off, then set LDO low-power mode W (register values will be lost). 0B 0: Leave power on. 1: Enter SLEEP state (set crystal gain block to off. Keep LDO regulator on (register values will be preserved). W Wakeup begins when SPI_SS goes low. This will restart the 0B on-chip clock oscillator to begin normal operation. 0: Normal (IDLE) state. (Reserved) 1: crystal running at sleep mode. Draws more current but enables fast wakeup. R/W 1B 0: crystal stops during sleep mode. Saves current but takes longer to wake up. Max. re-transmit packet attempts when auto_ack function is R/W 3H enabled. 1: MISO stays low-Z even when SPI_SS=1. R/W 0B 0: MISO is tri-state when SPI_SS=1. Whitening seed for data scramble. Must be set the same at R/W 00H both ends of radio link (Tx and Rx). 9.16. Register 36 Bit Name 15:0 SYNC_WORD[15:0] Table 21. Register 36 information R/W Description R/W LSB bits of sync word is sent first. default 0000H 9.17. Register 37 Bit Name 15:0 SYNC_WORD[31:16] Table 20. Register 37 information R/W Description R/W LSB bits of sync word is sent first. default 0000H Page 20 July 2010 9.18. Register 38 Bit Name 15:0 SYNC_WORD[47:32] LT8900 Datasheet Revision 1.1 Table 21. Register 38 information R/W Description R/W LSB bits of sync word is sent first. default 0000H 9.19. Register 39 Bit Name 15:0 SYNC_WORD[63:48] Table 22. Register 39 information R/W Description R/W LSB bits of sync word is sent first. default 0000H 9.20. Register 40 Table 23. Register 40 information Bit Name R/W Description 15:11 FIFO_EMPTY_THRESHOLD 10:6 FIFO_FULL_THRESHOLD 5:0 SYNCWORD_THRESHOLD R/W R/W The minimum allowable error bits of SYNCWORD, R/W 07 means 6 bits,01 means 0 bit default 00100B 00100B 07H 9.21. Register 41 Bit Name 15 CRC_ON 14 SCRAMBLE_ON 13 PACK_LENGTH_EN 12 FW_TERM_TX Page 21 Table 24. Register 41 information R/W Description 1: CRC on. R/W 0: CRC off. Removes long patterns of continuous 0 or 1 in transmit data. Automatically restores original unscrambled data on receive. R/W 1: scramble on. 0: scramble off. 1: LT8900 regards first byte of payload as packet length R/W descriptor byte. 1: When FIFO write point equals read point, LT8900 will R/W terminate TX when FW handle packet length. 0: FW (MCU) handles length and terminates TX. default 1B 0B 1B 1B July 2010 Bit Name 11 AUTO_ACK 10 PKT_FIFO_POLARITY 9:8 (Reserved) 7:0 CRC_INITIAL_DATA R/W Description LT8900 Datasheet Revision 1.1 default 1: After receiving data, automatically send ACK/NACK. R/W 1B 0: After receive, do not send ACK or NACK; just go to IDLE. 1: PKT flag, FIFO flag Active low. R/W 0B 0: Active high R/W (Reserved) 00B R/W Initialization constant for CRC calculation. 00H 9.22. Register 42 Bit Name 15:10 SCAN_RSSI_CH_NO 9:8 (Reserved) 7:0 Rx_ACK_TIME[7:0] Table 25. Register 42 information R/W Description R./W Number of consecutive channels to scan for RSSI value. RSSI result of each channel is returned in FIFO registers. R/W (Reserved) R/W Wait RX_ack ID timer setting. 1 represents 1us default 00H 01B 6BH 9.23. Register 43 Bit Name Table 26. Register 43 information R/W Description 15 SCAN_RSSI_EN R./W 1: Start scan_RSSI process. 14:8 SCAN_STRT_CH_OFFST[6:0] 7:0 WAIT_RSSI_SCAN_TIM[7:0] Normally an RSSI scan would start at 2402 MHz (channel 0). This field introduces a starting offset. R/W EXAMPLE: If offset= +10, Starting channel will be 2412 MHz (ch. 10). Set VCO & SYN setting time when scan different channel R/W RSSI default 0B 01B 6BH Page 22 July 2010 LT8900 Datasheet Revision 1.1 9.24. Register 48 – Read only Bit Name 15 CRC_ERROR 14 FEC23_ERROR 13:8 FRAMER_ST 7 SYNCWORD_RECV 6 PKT_FLAG 5 FIFO_FLAG 4:0 (Reserved) Table 27. Register 48 information R/W Description R Received CRC error R Indicate FEC23 error R Framer status 1: syncword received, it is just available in receive status, R After out receive status, always keep ‘0’. R PKT flag indication R FIFO flag indication R (Reserved) default 9.25. Register 50 Bit Name 15:0 TXRX_FIFO_REG 9.26. Register 52 Bit Name 15 CLR_W_PTR 14 (Reserved) 13:8 FIFO_WR_PTR 7 CLR_R_PTR 6 (Reserved) 5:0 FIFO_RD_PTR Page 23 Table 30. Register 50 information R/W Description default For MCU read/write data between the FIFO. R/W Reading this register removes data from FIFO; Writing to this register adds data to FIFO. 00H Note: FW (MCU) access to FIFO is byte-by-byte. Table 31. Register 51 information R/W Description 1: clear TX FIFO point to 0 when write this bit to “1”. W It is not available in RX status. W R FIFO write pointer. 1: clear RX FIFO point to 0 when write this bit to “1”. W It is not available in TX status. R FIFO read pointer (number of bytes to be read by MCU). default 0B 0B July 2010 10. Recommended Register Values LT8900 Datasheet Revision 1.1 The following register values are recommended for most typical applications. Some changes may be required depending on application. Register number 0 1 2 4 5 7 8 9 10 11 12 13 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Table 32. Recommended Register Values Power-up reset value (hex) 6fef 5681 6619 5447 f000 0030 Recommended value for many applications (hex) 6fef 5681 6617 9cc9 6637 0030 Notes Use for setting RF frequency, and to start/stop Tx/Rx packets. 71af 3000 7ffd 4008 0000 4855 c0ff 8005 307b 1659 1833 9100 1800 00x0 f413 1002 1806 6c90 1840 7ffd 0008 0000 48bd 00ff 8005 0067 1659 19e0 1200 1800 read-only read-only read-only 1806 Sets Tx power level Crystal osc. enabled. RSSI enabled. Calibrate VCO before each and every Tx/Rx. No crystal trim. Stores p/n, version information. Stores p/n, version information. Stores p/n, version information. Packet data type: NRZ, no FEC, BRCLK=12 div. by 4= 3MHz 6307 030b 1300 0000 0000 0000 0000 2107 b800 fd6b 000f 63f0 3000 0380 Configures packet sequencing. Configures packet sequencing. AutoAck max Tx retries = 3 Choose unique sync words for each over-the-air network. Similar to a MAC address. 2107 b000 fd6b 000f Configure FIFO flag, sync threshold. CRC on. SCRAMBLE off. 1st byte is packet length. Configure scan_rssi. Page 24 July 2010 11. Usage Notes LT8900 Datasheet Revision 1.1 The LT8900 Low-Cost RF Transceiver can be used to add wireless capability to many applications. The following notes are intended to answer common questions regarding the LT8900. 11.1. Power On and Register Initialization Sequence Figure below shows the timing diagram of power-on sequence after VDD is ready. Figure 5. Power on and register programming sequence 1. After VDD power is ready, make sure to have valid reset on pin RST_n, which is active-low. 2. After RST_n =1, BRCLK will be running at 12MHz clock. 3. Wait T1 (1 to 5 ms) for crystal oscillator to stabilize, then MCU/application can perform register initialization. 4. After register initialization, LT8900 is ready to transmit or receive. Figure 6. Initialization flowchart Page 25 July 2010 LT8900 Datasheet Revision 1.1 11.2. Enter Sleep and Wake-Up When MCU writes LT8900 register to enter sleep mode and pulls SPI_SS back to high, LT8900 will enter sleep state where the current consumption is extremely low. When SPI_SS is pulled low, LT8900 will automatically wake up from sleep state. MCU needs to keep SPI_SS low a certain time (the time required for RFIC crystal to be stabilized) before driving SPI_CLK and SPI data. 11.3. Packet Data Structure Each over-the-air LT8900 packet is structured as follows: z Preamble: 1~8 bytes, programmable. z SYNC: 16/32/48/64 bits, programmable as device syncword. z Trailer: 4~18 bits, programmable. z Payload: TX/RX data. There are 4 data types: „ Raw data „ 8 bit / 10 bit line code „ Manchester „ Interleave with FEC option z CRC: 16-bit CRC is optional. 11.4. FIFO Pointer Clear For transmit, it is required to clear FIFO write pointer before application writes data to FIFO for transmit. This is accomplished by writing ‘0’ to Register 52[15]. After receiving a packet, the read pointer will indicate how many bytes of receive data are waiting in FIFO buffer, waiting to be read by user MCU or application. FIFO write pointer will automatically be cleared when receiver receives SYNC. FIFO read pointer will automatically be cleared when receiver receives SYNC, or after transmitting SYNC in transmit mode. 11.5. Packet Payload Length LT8900 provides two ways to handle TX/RX packet length. If Register 41[13]= 1, the LT8900 internal framer will detect packet length based on the value of the 1st payload byte. If Register 41[13]= 0, the 1st byte of the payload has no particular meaning, and packet length is determined by either TX FIFO running empty, or TX_EN bit cleared. See table below: Page 26 July 2010 LT8900 Datasheet Revision 1.1 Register 41[13] PACK_LENGTH_EN Table 33. Packet Payload Length Register 41[12] FW_TERM_TX 0 0 (MCU/application handles packet length) 1 Transmit stops only when Register 7 TX_EN= 0. See page 31 for details. Receive stops only when Register 7 RX_EN= 0. See page 33 for details. Transmit automatically stops whenever FIFO runs empty. Receive stops only when Register 7 RX_EN= 0. See page 29 for details. 1 (LT8900 framer handles packet length) x (don’t care) 1st byte of payload is regarded as packet length, 0 to 255 bytes. Transmit automatically stops when all 0 to 255 bytes are transmitted. See page 25 for details. Detailed timing diagrams are shown below. All timing diagrams show active-high for PKT and FIFO flags. Active-low is also available via Register 41[10] setting. Page 27 July 2010 LT8900 Datasheet Revision 1.1 11.6. Framer handles packet length Framer of LT8900 will handle packet length by setting Register 41[13]=1. The first byte of payload is regarded as packet length (this length byte is not counted in the packet length). Maximum allowed packet length is 255 bytes. Framer will handle Tx/Rx start and stop. 11.6.1. Transmit Timing Tx timing diagram is shown below. After MCU writes Register 7[8]=1 and selects transmit channel (refer to Register 7 definition), the framer will automatically generate the packet using payload data from FIFO. MCU needs to fill in transmit data before framer sends trailer bits. If packet length exceeds FIFO length, the MCU will need to write FIFO data multiple times. FIFO flag indicates whether FIFO is empty in transmit state or not. Figure 7. Tx Timing Diagram when Register 41[13]= 1 (Framer Handles Packet Length). PKT and FIFO flags are Active High Page 28 July 2010 LT8900 Datasheet Revision 1.1 Figure 8. Example Tx packet flowchart where FIFO and PKT flags are interrupt signals to MCU. Page 29 July 2010 LT8900 Datasheet Revision 1.1 11.7. Receive Timing Rx timing diagram is shown in figure below. When MCU writes Register 7[7]= 1 and selects receiving channel, LT8900 framer will turn on the receiver and wait while attempting to detect a valid syncword. If valid syncword is found, the LT8900 framer will process packet automatically. When received packet processing is complete, LT8900 framer will set state to IDLE. If received packet length is longer than 63 bytes, FIFO flag will go active, which means MCU must read out data from FIFO. A valid syncword will not always be found, due to weak signal, multipath signal cancellation, devices out of range, etc. To accommodate such a condition and prevent lockup, the MCU/application should incorporate a receive timeout timer. In most applications, receive packets are expected to arrive within a defined time ‘window’. If the packet does not arrive, the system can use either timer polling or timer-based interrupt to take corrective or alternative action. Figure 9. Rx Timing Diagram when Register 41[13]=1 (Framer Handles Packet Length). Write reg 7 SPI_SS PKT and FIFO flags are Active High Internal Rx on Received data 2us Receive on delay Rx package PKT_flag FIFO_flag PKG_flag=1 when Rx packet has been received by framer FIFO_flag=1 when FIFO is full Page 30 July 2010 LT8900 Datasheet Revision 1.1 Figure 10. Example Rx packet flowchart where FIFO and PKT flag signals interrupt MCU. RX Start Write Reg7 as RX on and select RX channel Wait 10us Set RX timeout timer RX timeout interrupt Disable PKT_flag interrupt Write Reg7 RX_EN=0 Enable interrupt RETI FIFO_flag interrupt Disable FIFO_flag interrupt No More data to read in? Yes Read FIFO Enable FIFO_flag interrupt RETI PKT_flag interrupt Disable PKT_flag interrupt No Read FIFO Yes Read FIFO Enable FIFO_flag interrupt RETI 11.8. MCU/Application handles packet length When Register 41[13]= 0, the 1st byte of the payload data has no special significance. Instead, packet length depends on Register 41[12]. Page 31 July 2010 11.8.1. FW_TERM_TX= 1 LT8900 Datasheet Revision 1.1 If Register 41[12] = 1, the LT8900 framer will continue to compare FIFO write point and FIFO read point during packet transmission. If MCU/application stops writing data to FIFO, the framer eventually detects that there is no data to send (FIFO empty), and LT8900 will exit cease transmission automatically. The timing diagram is shown in Figure below. Figure 11. Tx timing when Register 41[13:12]= ‘b01. PKT and FIFO flags are set as active high. Note: When Register 41[13] = 0 (MCU/application handles packet length), never let FIFO underflow or over flow. FIFO full/empty thresholds can be controlled via Register 40 FIFO_EMPTY_THRESHOLD and FIFO_FULL_THRESHOLD settings. The best value will depend on SPI speed, and speed at which MCU/application can stream the data into FIFO. Page 32 July 2010 LT8900 Datasheet Revision 1.1 Figure 12. Example transmit flowcharts for Register 41[13:12]= ‘b01 using interrupts for PKT and FIFO flags. Page 33 July 2010 LT8900 Datasheet Revision 1.1 11.8.2. FW_TERM_TX= 0 (Transmit) When Register 41[13:12] = ‘b00, the LT8900 framer does not stop packet transmission until MCU/application writes Register 7[8] TX_EN bit = 0. Packet transmission continues even if FIFO is empty. The timing diagram is shown in Figure below. Figure 13. TX timing diagram when Register 41[13:12] = ‘b00. PKT and FIFO flags are shown high active. Note: When Register 41[13] = 0 (MCU/application handles packet length), never let FIFO underflow or over flow. FIFO full/empty thresholds can be controlled via Register 40 FIFO_EMPTY_THRESHOLD and FIFO_FULL_THRESHOLD settings. The best value will depend on SPI speed, and speed at which MCU/application can stream the data into FIFO. Page 34 July 2010 LT8900 Datasheet Revision 1.1 Figure 14. Example Transmit flowcharts for Register 41[13:12]= ‘b00 using interrupts for PKT and FIFO flags. Page 35 July 2010 LT8900 Datasheet Revision 1.1 11.8.3. FW_TERM_TX= 0 (Receive) When Register 41[13] =0, packet reception starts when MCU/application writes Register 7[7] RX_EN = 1. At this time, the framer will automatically turn on the receiver to the frequency/channel specified in register 7. After waiting for the internal synthesizer and receiver delays to transpire, the framer circuitry of the LT8900 will begin searching the incoming signal for a syncword. When detected, it will set PKT flag active, then start to fill FIFO with receive data bytes. The PKT flag will remain active until MCU/application reads out the first byte of data from FIFO register. After MCU/application reads the first byte of receive data, PKT flag goes inactive until next Tx/Rx period. With Register 41[13:12] = ‘b00 or ‘b01, the LT8900 framer will always need the MCU/application to write Register 7[7] to 0 to stop Rx state. Rx timing diagram is shown in Figure below. Figure 15. RX timing diagram when Register 41[13:12] = ‘b00 or ‘b01. PKT_flag and FIFO_flag are active high. Page 36 July 2010 LT8900 Datasheet Revision 1.1 Figure 16. Example Receive flowcharts for Register 41[13:12]= ‘b00 or ‘b01 using interrupts for PKT and FIFO flags. Page 37 July 2010 LT8900 Datasheet Revision 1.1 11.9. Crystal Oscillator The LT8900 supports quartz crystal, or external clock input. 11.9.1. Quartz crystal application Series resistor R2 limits power to the crystal, and contributes to the phase shift necessary for oscillation. Crystal loading capacitors C7 and C8 largely determine the load seen by the crystal, which should match the crystal vendor’s specification. These capacitor values can be trimmed, to fine-tune the frequency of oscillation. Self- bias resistor R1, from buffer output to input, serves to self-bias the on-chip buffer to the center of the linear region for maximum gain. 11.9.2. External clock application Self-bias resistor R1 should still be used, but the external clock may be coupled to the XTALI pin via a series DC blocking capacitor. See circuit below. Output resistor R0 is used to sample a small amount of power from an existing oscillator or clock circuit. The best value of R0 may need to be determined experimentally, but around 3k Ohms is a good starting point. In the extreme case of R0 being much too large, the RFIC will fail to initialize to the IDLE state properly. Regarding PCB layout: The CLK trace should be kept short and direct. The trace should be relatively narrow (high impedance), and must route away from other traces on the PCB that may inject or couple noise onto the CLK trace. The LT8900 will receive the clock signal relative to ground; therefore, the ground between chips should be a good low-noise, low-inductance ground. Ideally, this GND return should be a single ground plane on the PCB layout. Figure 17. External Clock Application Additional Notes: 1. Clock duty cycle should be 50%. If not 50%, some additional drive voltage may be required (i.e. reduce R0). 2. If received Bit Error Rate (BER) is high, it can be caused by insufficient clock drive to the RFIC (i.e. reduce R0). 3. Another cause for high BER is phase noise on the clock signal. Try putting 0.1 and 2.2 uF ceramic bypass capacitors across the baseband chip VDD/VSS pins that power the oscillator. Page 38 July 2010 LT8900 Datasheet Revision 1.1 11.9.3. Minimum Pin Count When a low cost MCU drives the LT8900, MCU pin count must be minimized. Consider the following: z FIFO: only needed when Tx or Rx packet length is greater than around 63 bytes, up to infinity. For short packets (< 63 bytes), FIFO is not needed. z PKT: gives a hardware indication of a packet received. If the user is willing to poll register 48 for this information, then this pin is not needed. z SPI lines: All 4 of these lines are needed. z RST_n: This line is sometimes connected through an RC filter to the VDD_IN, which makes the chip self-reset when power is applied, thus eliminating an MCU pin. 11.9.4. CKPHA On the LT8900 die, there is a CKPHA pad. When LT8900 is purchased in QFN package, this pad will normally be connected by bond wire to a source of logic ‘1’. This is to save a pin, thus keeping packaged part cost low. The alternate configuration, CKPHA= 0, is available by special order. Customers ordering bare unpackaged die will be able to bond CKPHA however desired. 11.9.5. Antenna Type and Location Probably the greatest single factor affecting RF performance for the LT8900 or any other over-the-air RF device is the antenna – not just type, but also placement and orientation. Antenna gain is normally measured with respect to isotropic, that is, an ideal radiator that sends/receives power equally from/to any direction. This ideal antenna would be described as 0 dBi, or zero dB’s above/below isotropic. Unfortunately, they don’t really exist in practice. A simple dipole with a theoretical gain of +2 dBi is usually a good choice, but the designer should exercise care when placing the antenna, since dipole antennas have a radiation pattern described as a donut, whereby the null can be very deep. For most wireless applications, the printed full-wave loop antenna shown on the schematic should perform well, provided that the antenna is placed in the clear, away from other circuitry and wires, hands, etc. In particular, the antenna must be kept away from human tissue, particularly sensitive spots like the heart, brain, and eyes. Violating this design principle will not only make the end product perform poorly and possibly become a long term danger to the user, but it will likely not receive FCC or other regulatory agency approval. For best operation, design the product so the main antenna radiation is away from the body, or at least not proximity loaded by the human body, or dielectric objects within the product. Also, be sure to keep the antenna away from clock lines and digital bus signals; otherwise, harmonics of the clock frequency will jam certain receive frequencies. It’s best to just keep the antenna away from all wires and metal objects! Page 39 July 2010 LT8900 Datasheet Revision 1.1 11.10. PCB Layout PCB layout is not too critical, but here are some helpful hints: 1. RF path: Since the LT8900 utilizes 2-conductor balanced transmission line at the RF port, ground plane is not necessary along the balanced line length. Be sure to keep each of the two conductors equal length. 2. Clock traces: It is best to keep the clock traces simple and direct. The self-bias resistor should be close to the XTALI and XTALO pins. The oscillation loop, consisting of the series resistor and crystal, should be a simple, small loop. The crystal loading capacitors should be near the crystal. The ground connection to these capacitors must be to a good, clean, quiet ground. This keeps noise from becoming injected into the oscillator. This is a good reason to have one ground plane for the entire RF section. 3. Power distribution and decoupling: Capacitors should be located near the VDD pins, as shown in the schematic. 4. Antenna Placement: If using an antenna manufactured by a particular company, be sure to follow the manufacturer’s recommendation regarding layout. 5. Digital Interface: In order to provide a good ground return for the digital lines, it is a good idea to provide at least 2 pins for ground, not just one. Good grounding between RF and MCU can help reduce noise ‘seen’ at the antenna, thus improving performance. Page 40 July 2010 12. Package Outline LT8900 Datasheet Revision 1.1 QFN 24 Lead Exposed Pad Package, 4x4 mm, 0.5mm pitch. Dimensions in mm. Dim. A A1 A3 b D/E D2/E2 e Table 28. Package Outline Dimension Min. Nom. Max. 0.70 0.75 0.80 0 0.02 0.05 0.203 REF 0.18 0.25 0.30 3.90 4.00 4.10 1.90 2.00 2.10 0.50 BSC Dim. L y Min. Nom. Max. 0.30 0.40 0.50 0.08 Page 41 July 2010 13. IR Reflow Standard LT8900 Datasheet Revision 1.1 Follow : IPC/JEDEC J-STD-020 B Condition : Average ramp-up rate (183ºC to peak): 3 ºC/sec. max. Preheat: 100~150ºC 60~120sec Temperature maintained above 183ºC: 60~150 seconds Time within 5ºC of actual peak temperature: 10 ~ 30 sec. Peak temperature: 240+0/-5 ºC Ramp-down rate: 6 ºC/sec. max. Time 25ºC to peak temperature: 6 minutes max. Cycle interval: 5 minutes Figure 18. IR Reflow Diagram Page 42 July 2010 14. Document Revision History Mar 2010: Release Preliminary Specification. LT8900 Datasheet Revision 1.1 Page 43 July 2010




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