HCS412SN datasheet(29/44 Pages) MICROCHIP

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Preliminary

DS41099C-page 29

HCS412

4.4.3

INTELLIGENT DAMPING (IDAMP)

A high Q-factor LC antenna circuit connected to the

HCS412 will continue to resonate after a strong LF field

is removed, slowly decaying. The slow decay makes

fast communication near the reader difficult as data bit

low times disappear.

If the Intelligent Damping option is enabled, the

HCS412 will clamp the LC pins through a 2 k

Ω resistor

for 5

µs every 1/4 LFTE, whenever the HCS412 is

expecting data from the transponder reader. The intel-

ligent damping pulses start 12.5 LFTE after the

Acknowledge sequence is complete and continue for

12.5 LFTE. If the HCS412 detects data from the reader

while sending out damping pulses, it will continue to

send the damping pulses.

TABLE 4-11:

INTELLIGENT DAMPING

(IDAMP)

FIGURE 4-19: INTELLIGENT DAMPING

TABLE 4-12:

LF TIMING SPECIFICATIONS

IDAMP

Description

Intelligent damping enabled

Intelligent damping disabled

12.5 LFTE

µs

1/4 LFTE

µs

DAMP PULSES

Bit From

reader

Field

ACK

Parameter

Symbol

Min.

Typ.

Max.

Units

Time Element

IFFB = 0

IFFB = 1

LFTE

180

200

100

220

110

µs

Power-up Time

TPU

4.2

7.8

Acknowledge to Opcode Time

TATO

LFTE

PPM Command Bit Time

Data = 0

Data = 1

TBITC

—

LFTE

PPM Response Bit Time

Data = 0

Data = 1

TBITR

—

LFTE

Read Response Time

TRT

—13—

LFTE

IFF Response Time

TIT

3.87

4.3

4.73

Opcode to Data Input Time

TOTD

2.6

—

Transport Code to Data Input Time

TTTD

2.2

—

Encoder Select Acknowledge Time

TESA

—LFTE+100

—

µs

IFF EEPROM Write Time (16 bits)

TWR

—30—

Op Code to Hop Code Response Time

TOTH

10.26

11.4

12.54

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