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HCS473-SLSQTP Datasheet(PDF) 10 Page - Microchip Technology |
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HCS473-SLSQTP Datasheet(HTML) 10 Page - Microchip Technology |
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10 / 68 page  HCS473 DS40035C-page 8 Preliminary 2002 Microchip Technology Inc. 2.3.3 TRANSPONDER INTERFACE The transponder interface on the HCS473 consists of the following: • The internal transponder circuitry has separate power supply (V DDT) and ground (VSST) connec- tions. - The V DDT pin supplies power to the transpon- der circuitry and also outputs a regulated volt- age if the LCX antenna input is receiving a strong signal; transponder is placed in a strong LF field. - The V SST pin supplies the ground reference to the transponder circuitry and must be con- nected to the V SS pin. • LF input amplifier and envelope detector to detect and shape the incoming low frequency excitation signal. • Three sensitive transponder inputs with over-volt- age protection (LCX, LCY, LCZ). • Incoming LF energy rectification and regulation on the LCX input to supplement the supply voltage in low-battery transponder instances. • 10V zener input protection from excessive antenna voltage resulting when proximate to very strong magnetic fields. • LCCOM pin used to bias the transponder reso- nant circuits for best sensitivity. • LF antenna clamping transistors for inductive responses back to the transponder reader. The antenna ends are shorted together, ‘clamped’, dissipating the oscillatory energy. The reader detects this as a momentary load on its excitation antenna. • Damping transistors to increase LF communica- tion reliability when using high Q-factor LC anten- nae. The LCCOM pin functions to bias the LCX, LCY, and LCZ AGC amplifier inputs. The amplifier gain control sets the optimum level of amplification in respect to the incoming signal strength. The signal then passes through an envelope detector before interpretation in the logic circuit. A block diagram of the transponder circuit is shown in Figure 2-8. FIGURE 2-8: HCS473 TRANSPONDER CIRCUIT 2.3.4 INTERNAL EEPROM The HCS473 has an on-board non-volatile EEPROM which is used to store: • configuration options - encryption keys - serial number - vehicle ID’s - baud rates - ... see Section 3.1.4 and Section 3.2.1 • 64 bits of user memory • synchronization counter. All options are programmable during production, but many of the security related options are programmable only during production and are further read protected. The user area allows storage of general purpose infor- mation and is accessible only through the transponder communication path. During every EEPROM write, the device ensures that the internal programming voltage is at an acceptable level prior to performing the EEPROM write. Rectifier/ Regulator V CCT Noise Filter Signal In Damp/Clamp Control LCX LCY LCZ LCCOM |
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