UPD17231MC datasheet(45/92 Pages) NEC

45 / 92 page

Data Sheet U14360EJ1V0DS00

µPD17230, 17231, 17232, 17233, 17234, 17235, 17236

5.3.2

Countermeasures against noise during transmission (carrier output)

When a signal is transmitted from the transmitter of a remote controller, a peak current of 0.5 to 1 A may flow through

the infrared LED. Since two batteries are usually used as the power source of the transmitter, several

Ω of equivalent

resistance (r) exists in the power source as shown in Figure 5-2. This resistance increases to 10 to 20

Ω if the supply

voltage drops to 2 V. While the carrier is output from the REM pin (while the infrared LED lights), therefore, a high-

frequency noise may be generated on the power lines due to the voltage fluctuation that may take place especially

during switching.

To minimize the influence on the microcontroller of this high-frequency noise, take the following measures:

<1> Separate the power lines of the microcontroller from the power lines of the infrared LED with the terminals

of the batteries at the center. Use thick power lines and keep the wiring short.

<2> Locate the resonator as close as possible to the microcontroller and shield it with GND lines (as indicated

by the shaded portion in the figure below).

<3> Locate the capacitor for stabilization of the power supply closely to the power lines of the microcontroller.

Also, use a capacitor to eliminate high-frequency noise.

<4> To prevent data from changing, do not execute an interrupt that requires read/write processing and stack,

such as key scan interrupt, and the CALL/RET instruction, while the carrier is output.

<5> To improve the reliability in case of program hang-up, use the watchdog timer.

Figure 5-2. Example of Countermeasures against Noise

0.5 to 1 A

Infrared LED

REM

VDD

Microcomputer

–

Batteries

VSS

UPD17231MC Datasheet(PDF) 45 Page - NEC