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 a typical discrete optical
transceiver circuit.
FIGURE 2-11:
CIRCUIT FOR A
DISCRETE OPTICAL
TRANSCEIVER
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.
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.
MCP2140
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
+5 V
R14 (2)
10 kΩ
R15 (2)
10 kΩ
+5 V
RXPDREF
(To MCP2140 Pin 1)
C19 (1)
Q1 (1)
MUN211T1
68 pF
RXPD
(To MCP2140 Pin 18)
+5 V
+5 V
R13
47Ω
C18
.1 µF
U6
1
2
3
4
8
7
6
5
R11
22Ω
TXIR
(To MCP2140 Pin 2)
TFDS4500
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.
Table 2-6 shows a list of common manufacturers of
integrated optical transceivers.
2003 Microchip Technology Inc.
Preliminary
DS21790A-page 17