HCS473 datasheet(7/68 Pages) MICROCHIP

7 / 68 page

 2002 Microchip Technology Inc.

Preliminary

DS40035C-page 5

HCS473

2.0

DEVICE DESCRIPTION

The HCS473 is designed for small package outline,

cost-sensitive applications by minimizing the number of

external components required for RKE and PKE appli-

cations.

Figure 2-1 shows a typical 3-axis HCS473 RKE/PKE

application.

• The switch inputs have internal pull-down resis-

tors and integrated debouncing allowing a switch

to be directly connected to the inputs.

The transponder circuitry requires only the addition of

external LC-resonant circuits for inductive communica-

tion capability.

• The open-drain LED output allows an external

resistor for customization of LED brightness - and

current consumption.

• The DATA output can be directly connected to the

RF circuit or connected in conjunction with S3/

RFEN to a PLL.

2.1

Pinout Overview

A description of pinouts for the HCS473 can be found

in Table 2-1.

TABLE 2-1:

PINOUT SUMMARY

2.2

LF Antenna Considerations

A typical magnetic low frequency sensor (receiving

antenna) consists of a parallel inductor-capacitor circuit

that is sensitive to an externally applied magnetic sig-

nal. This LC circuit is tuned to resonate at the source

signal's base frequency. The real-time voltage across

the sensor represents the presence and strength of the

surrounding magnetic field. By amplitude modulating

the source's magnetic field, it is possible to transfer

data

over

short

distances.

This

communication

approach is successfully used with distances up to 1.8

meters, depending on transmission strengths and sen-

sor sensitivity. Two key factors that greatly affect com-

munication range are:

Sensor tuning

A properly tuned sensor's relative sensitivity

An LC antenna’s component values may be initially cal-

culated using the following equation. “Initially” because

there are many factors affecting component selection.

It is not this data sheet’s purpose to present in-depth

details regarding LC antenna and their tuning. Please

refer to “Low Frequency Magnetic Transmitter Design

Application Note”, AN232, for appropriate LF antenna

design details.

Pin Name

Number

Description

Button input pin with Schmitt Trigger detector and internal pull-down resistor (Figure 2-3).

S3/RFEN

Multi-purpose input/output pin (Figure 2-4).

• Button input pin with Schmitt Trigger detector and internal pull-down resistor.

• RFEN output driver.

DDT

Transponder supply voltage. Regulated voltage output for strong inductive field.

LCX

Sensitive transponder input X (Figure 2-7). A strong signal on this pin is internally regulated

and supplied on V

DD for low-battery operation/recharging.

LCY

Sensitive transponder input Y (Figure 2-7)

LCZ

Sensitive transponder input Z (Figure 2-7)

LCCOM

Transponder bias output (Figure 2-7)

SST

Transponder ground reference, must be connected to V

SS.

Ground reference

DATA

Transmission data output (Figure 2-5)

LED

Open drain LED output (Figure 2-6)

Positive supply voltage

Note:

Microchip also has a confidential Applica-

tion Note on Magnetic Sensors (AN832C).

Contact Microchip for a Non-Disclosure

Agreement in order to obtain this applica-

tion note.

2πF

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