HCS473 Datasheet, PDF (7/68 Pages) Microchip Technology – Code Hopping Encoder and Transponder

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
Pin Name
Pin
Number
Description
S0
S1
S2
S3/RFEN
VDDT
LCX
LCY
LCZ
LCCOM
VSST
VSS
DATA
LED
VDD
1
Button input pin with Schmitt Trigger detector and internal pull-down resistor (Figure 2-3).
2
Button input pin with Schmitt Trigger detector and internal pull-down resistor (Figure 2-3).
3
Button input pin with Schmitt Trigger detector and internal pull-down resistor (Figure 2-3).
4
Multi-purpose input/output pin (Figure 2-4).
• Button input pin with Schmitt Trigger detector and internal pull-down resistor.
• RFEN output driver.
5
Transponder supply voltage. Regulated voltage output for strong inductive field.
6
Sensitive transponder input X (Figure 2-7). A strong signal on this pin is internally regulated
and supplied on VDD for low-battery operation/recharging.
7
Sensitive transponder input Y (Figure 2-7)
8
Sensitive transponder input Z (Figure 2-7)
9
Transponder bias output (Figure 2-7)
10 Transponder ground reference, must be connected to VSS.
11 Ground reference
12 Transmission data output (Figure 2-5)
13 Open drain LED output (Figure 2-6)
14 Positive supply voltage
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:
1. Sensor tuning
2. 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.
2πF = -----1------
LC
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.
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.
 2002 Microchip Technology Inc.
Preliminary
DS40035C-page 5