HCS473-SLROM datasheet(10/68 Pages) MICROCHIP

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

CCT

Noise

Filter

Signal In

Damp/Clamp

Control

LCX

LCY

LCZ

LCCOM

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