MCP2140-IP datasheet(17/58 Pages) MICROCHIP

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 2003 Microchip Technology Inc.

Preliminary

DS21790A-page 17

MCP2140

2.13

Optical Interface

The MCP2140 requires an infrared transceiver for the

optical interface. This transceiver can be a single-chip

solution (integrated) or be implemented with discrete

devices.

2.13.1

DISCRETE TRANSCEIVER

SOLUTION

The MCP2140 was designed to use a discrete imple-

mentation that allows the lowest system power

consumption as well as a low cost implementation.

Figure 2-12

shows

typical

discrete

optical

transceiver circuit.

FIGURE 2-11:

CIRCUIT FOR A

DISCRETE OPTICAL

TRANSCEIVER

Care must be taken in the design and layout of the

photo-detect circuit, due to the small signals that are

being detected and their sensitivity to noise.

2.13.2

INTEGRATED TRANSCEIVER

The MCP2140 was designed to use a discrete imple-

mentation that allows the lowest system power con-

sumption and a low cost implementation (see

Section 2.12.1, “Discrete Transceiver Solution”). It is

possible to use an integrated optical transceiver solu-

tion, with the addition of four components. Two com-

ponents are required to condition the input signal to

ensure that the RXIR pulse width is not greater than

1.5 µs (see Parameter IR131A). The other two com-

ponents are required to set the RXIR signal trip point

(typically VDD/2). Figure 2-12 shows an example

MCP2140 optical transceiver circuit, using a Vishay®/

Temic TFDS4500.

FIGURE 2-12:

CIRCUIT FOR AN

INTEGRATED OPTICAL

TRANSCEIVER

Table 2-6 shows a list of common manufacturers of

integrated optical transceivers.

This figure will be available in Revision B of the

MCP2140 data sheet. Please conact the Microchip

factory via email (tech.support@microchip.com)

for additional information.

+5 V

R11

Ω

TFDS4500

Ω

R13

C18

.1 µF

RXPD

(To MCP2140 Pin 2)

TXIR

(To MCP2140 Pin 18)

+5 V

C19 (1)

Q1 (1)

68 pF

MUN211T1

+5 V

RXPDREF

(To MCP2140 Pin 1)

10 k

Ω

R14 (2)

10 k

Ω

R15 (2)

Note 1: These components are used to control

the width of the TFDS4500 RXD output

signal. Q1 is a digital transistor, which

includes the bias resistors.

2: These components are used to set the

reference voltage that the RXPD signal

needs to cross to “detect” a bit.

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