MCP2140A Datasheet, PDF (22/60 Pages) Microchip Technology – IrDA® Standard Protocol Stack Controller With Fixed 9600 Baud Communication Rate

MCP2140A
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 to 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 (0Ω), 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
Component
Symbol
MCP2140 Device
(value)
MCP2140A
Device (value)
C19
Capacitor (47pF) Resistor (0 Ω) ⁽¹⁾
R11
—
—
R13
—
—
R16
Resistor
—
(100Ω)
R20
Resistor
(4.7 kΩ)
Resistor
(4.7 KΩ) ⁽¹⁾
Q1
PNP Transistor Schottky Diode
(SOT-23-3) (MMUN2111LT1) (BAT54) ⁽¹⁾
Note 1: This device is changed from MCP2140
Wave Shaping Circuit implementation.
Table 2-4 shows a list of common manufacturers of
integrated optical transceivers.
FIGURE 2-16:
MCP2140 WAVE SHAPING
CIRCUIT FOR
INTEGRATED OPTICAL
TRANSCEIVER
+5V
R16
100Ω
R13
optional
RXD
C19 _R11
47 pF _optional
+5V
2 ^Q1
1 ^MMUN2111LT1
3
R20
4.7 kΩ
RXPD
(MCP2140
Pin 18)
R14
10 kΩ
R15
10 kΩ
RXPDREF
(MCP2140 Pin 1)
FIGURE 2-17:
MCP2140A
MODIFICATIONS OF
MCP2140 WAVE SHAPING
CIRCUIT
+5V
R16 (Open)
R13
optional
RXD
C19
0Ω
R11
optional
+5V
Q1
1 BAT54
3
Schottky
Diode ^R20
4.7 kΩ
RXPD
(MCP2140A
Pin 18)
R14
10 kΩ
R15
10 kΩ
RXPDREF
(MCP2140A Pin 1)
DS22050A-page 22
© 2007 Microchip Technology Inc.