Texas Instruments TMS3705A Installation guide

J.A.G Aug 2006
LF Technical Training
TMS3705A Transceiver IC

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J.A.G Aug 2006
z5V device
zAutomatic sleep mode (TXCT idle for 100 ms)
zTransponder resonance frequency measurement
zInternal Full Bridge antenna driver
zDigital demodulator
zDiagnosis function
zSeveral operating modes
♦self adapting or fixed frequency charge-up
♦automatic or fixed demodulator threshold
♦asynchronous or synchronous data to µP
zReduced additional component count
zPLL for internal clock generation
z2/4 MHz crystal or low cost ceramic resonator can
be used
16 Pin SO Package
►Main Features
9.35 mm
6.12 mm

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►A Transceiver Module with antenna

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►Pin Names & Functions
SENSE
SFB
D_TST
A_TST
ANT1
VSSA
ANT2
VDDA
TXCT
F_SEL
SCIO
VSSB
VSS
OSC1
OSC2
VDD
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
PIN NAME I/O DESCRIPTION
1 SENSE
2 SFB
3 D_TST
4 A_TST
5 ANT1
6 VSSA
7 ANT2
8 VDDA
9 VDD
10 OSC2
11 OSC1
12 VSS
13 VSSB
14 SCIO
15 FSEL
16 TXCT
I
O
O
O
O
I
O
I
I
O
I
I
I
O
I
I
Input of RF amplifier
Output of RF amplifier
Test output for digital signals
Test output for analog signals
Antenna output 1
Ground for full bridge drivers
Antenna output 2
Voltage supply for full bridge drivers
Voltage supply for non-power blocks
Oscillator output
Oscillator input
Ground for non-power blocks
Ground for PLL
Data output to microprocessor
Control input for frequency selection
Control input for microprocessor
D Package
(Top view)

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SCI-
Encoder
►Block Diagram
Band Pass
Limiter
Vref
ANT1
ANT2
VDDA
VSSA
Control Logic
with Mode Control
Register
Pre-
drivers
Full Bridge
RF
Amplifier
SFB
SENSE
Diagnosis
Power-
on reset
Controlled
Frequency Divider
VDD
VSS
OSC1
OSC2
TXCT
F_SEL
SCIO
PLL
D_TST
A_TST
VSSB
10k
Digital
Demodulator
Tag Resonant -
Freq. Measurement

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►Generic Circuit Diagram
SENSE
SFB
D_TST
A_TST
ANT1
VSSA
ANT2
VDDA
TXCT
F_SEL
SCIO
VSSB
VSS
OSC1
OSC2
VDD
L1
C1
R1
R2
C2
C1
C4
Q1
4 MHz
116
89
TXCT (input)
SCIO (output)
Supply Voltage
Ground
U1
ANTENNA

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►Power Supply and Blocking Capacitance
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VDD
VDDA VDD
zConnect the blocking capacitors as
close as possible to the supply pins
zTantalum capacitors are recommended
zTo prevent uncontrolled radiation it is
recommended to connect the supply
voltage symmetrically to VDDA and VDD

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►Oscillator - PLL
zIf a Ceramic Oscillator is to be used, one with an internal load
capacitance of around 56 pF is recommended
zAn external oscillator signal can be fed into OSC1. OSC2 has
to be left open - a decoupling capacitor is recommended.
OSC1
OSC2
F_SEL
PLL
VSSB

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►The Digital
Demodulator
zThe input frequency is measured by counting the oscillation clock for the time
period of the input signal.
zThe demodulator distinguishes between the high-bit frequency and the low-bit
frequency by the shift values and not by the absolute values.
zThe threshold between the high-bit and the low-bit is defined as 6.5 kHz lower
than that measured for the low-bit frequency
zAfter the charge phase, the transponder response frequency is measured to
determine the counter state for the low-bit and high-bit threshold
VDD
SCIO
Digital
Demodulator
Transponder Resonance -
Frequency Measurement
SCI-
Encoder

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►Tag Resonant Frequency Measurement
z1.6 ms after TXCT goes high, an internal measuring cycle of 100 µs
will start to measure the low bit frequency of the 16 tag pre-bits.
100 µs
1.6 ms 1.7 ms
TXCT
SCIO Start Bit
Frequency measuring
starts (Pre-bits)
Begins looking for start
byte (0x7E, 0x7F))
zWhen TXCT goes high, the module enters the read phase
z1.7 ms after TXCT goes high, the IC starts looking for a valid
start byte.

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zThe diagnostics byte is sent 2 ms after the start of the charge
phase
♦If normal antenna operation is detected then 0xAF is sent
♦If no antenna oscillation is detected or a short detection occurs,
then 0xFF is sent
►Diagnostics Byte
SFB
SENSE
Diagnosis
A_TST
10k

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zThe OP Amp has a fixed internal voltage reference
zA voltage gain of 5 is controlled by external resistance
►RX Amplifier
R2 150k
G = = = 3.19
R1 47k
Band Pass
Limiter
Vref
RFAmplifier
SFB
SENSE
Diagnosis
A_TST
10k

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zNo external components required for filtering and amplification
zThe analog sine-wave is converted to a digital signal
zHigh gain - at least 1000
►Band-Pass Filter & Limiter
Band Pass
Limiter
Vref
RFAmplifier
SFB
SENSE
Diagnosis
A_TST
10k

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zAn 8-bit shift register is used to buffer and send the received
data byte-wise to the micro controller (Least Significant Bit
first)
zIn Synchronous Mode, a high state at the SCSI output
indicates that a new byte is ready to be transmitted
zThe transmission rate is 15625 baud (in asynchronous mode)
with 1 start byte (high) and 1 stop byte (low).
►SCI Encoder for Data Transmission to the
Controller
SCIO
VDD
Digital
Demodulator
Transponder Resonance -
Frequency Measurement
SCI-
Encoder

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zThe Start-Byte is the first byte sent to the microcontroller.
zData bits at the SCIO output are inverted compared with the
data from a transponder. Typical transponder values:
♦R/O Transponder = 0x81 (0x7E inverted)
♦R/W Transponder = 0x01 (0xFE inverted)
♦DST Transponder = 0x81 (0x7E inverted)
►SCI Encoder for Data Transmission to the
Controller (2)
SCIO
VDD
Digital
Demodulator
Transponder Resonance -
Frequency Measurement
SCI-
Encoder

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►SCIO Asynchronous Transmission
zTiming diagram
SCIO Start
Bit
Stop
Bit
tsci tsci
LSB 1 2 3 4 5 6 MSB

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►SCIO Synchronous Transmission
zTiming diagram
SCIO
tsync tready
LSB 1 2 3 4 5 6 MSB
tsyn
c
TxCT
Byte
ready Stop
‘bit’
tL_sync
tt_sync
µP Reads data
Shift data

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►SCIO in Synchronous Transmission Mode
zThe SCI encoder can be switched into synchronous
transmission mode by setting the SCI_Sync bit in the Mode
Control Register (MCR)
zThe micro-controller has to clock out the data bytes by
sending 8 clock signals to the TXCT input
zA high state on the SCIO indicates that a new byte is ready to
be transmitted.
zThe advantage of synchronous transmission:
♦Higher speed of the byte transmission
♦Minimum clock period of 4µs x 8.5 = 34 µs per byte

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►Mode Control Register (MCR)
Control Logic
with
Mode Control
Register
Power-on
Reset
VDD
TXCT
SCIO
D_TST
Digital
Demodulator
Transponder Resonance -
Frequency Measurement
SCI-
Encoder
zBy writing to the MCR the
mode of operation of the IC
can be changed.
zThe options include:
♦Asynchronous/ Synchronous
data
♦Frequency changing
♦Demodulator threshold
adjustment
♦Test Mode

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►Timing Diagram
zMode Control Register Write Protocol
PHASE Low Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 CHARGE
Start bit Test bit
Init. Transmission End of transmission
tinit tmcr tmcr
TxCT