MCP2140AT-ISLASHSS datasheet(22/60 Pages) MICROCHIP

22 / 60 page

MCP2140A

DS22050A-page 22

2.13

Optical Interface

The MCP2140A requires an infrared transceiver for the

optical interface. This transceiver can be a single-chip

solution (integrated) or be implemented with discrete

devices.

The MCP2140A was designed to interface to a

integrated Optical Transceiver, although it can interface

to a discrete solution as long as the MCP2140A

specifications are meet.

The MCP2140 required a wave shaping circuit to inter-

face to typical integrated optical transceivers. An

Example circuit is shown in the user guides of the

MCP2140 Demo and evaluation boards. This circuit is

shown in Figure 2-16. This circuit inverts the optical

transceivers RXD signal.

The MCP2140A requires that the RXD signal is not

inverted.

Figure 2-17

shows

how

the

Microchip

example wave shaping circuit can be modified with

simple

component

replacement

support

the

MCP2140A. Figure 2-19 shows the RXD signal

characteristics before and after the modified wave

shaping circuit (Figure 2-17).

Table 2-2 shows the schematic symbols for the

example MCP2140 wave shaping circuit, and the

component changes required to make the PCB layout

compatible with the MCP2140A. The layout is not

required to be changed since the BAT54 is a Schottky

Diode in a SOT-23-3 package with the desired pin

connections, the capacitor footprint can easily be

replaced by a resistor (0

Ω), and the R16 resistor can be

removed since it is not involved with the circuit.

Figure 2-18 shows a simple “Blue Wire” modification

that can be done.

TABLE 2-2:

EXAMPLE MCP2140 WAVE

SHAPING CIRCUIT TO

MCP2140A COMPONENT

CHANGES

Table 2-4 shows a list of common manufacturers of

integrated optical transceivers.

FIGURE 2-16:

MCP2140 WAVE SHAPING

CIRCUIT FOR

INTEGRATED OPTICAL

TRANSCEIVER

FIGURE 2-17:

MCP2140A

MODIFICATIONS OF

MCP2140 WAVE SHAPING

CIRCUIT

Component

Symbol

MCP2140 Device

(value)

MCP2140A

Device (value)

C19

Capacitor (47pF)

Resistor (0

Ω) (1)

R11

—

R13

—

R16

Resistor

(100

Ω)

—

R20

Resistor

(4.7 k

Ω)

Resistor

(4.7 K

Ω) (1)

(SOT-23-3)

PNP Transistor

(MMUN2111LT1)

Schottky Diode

(BAT54) (1)

Note 1: This device is changed from MCP2140

Wave Shaping Circuit implementation.

R13

RXPD

(MCP2140

C19

47 pF

MMUN2111LT1

+5V

RXPDREF

(MCP2140 Pin 1)

10 k

R14

10 k

R15

R20

4.7 k

+5V

100

R16

R11

Pin 18)

RXD

optional

R13

RXPD

(MCP2140A

C19

BAT54

+5V

RXPDREF

(MCP2140A Pin 1)

10 k

R14

10 k

R15

R20

4.7 k

+5V

R16 (Open)

R11

Pin 18)

RXD

optional

Schottky

Diode

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