Renesas RL78/G14 Application Note
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Renesas RL78/G14 Application Note

Renesas RL78/G14 Application Note

Recommended pcb layout for reducing noise
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RL78/G14
Recommended PCB Layout for Reducing Noise
Introduction
The purpose of this document is to help the user understand how to design a good PCB layout with high reducing noise
performance. A thorough system evaluation is necessary after taking the countermeasures mentioned in this document.
This document provides an explanation using RL78/G14 sample boards.
Target Device
RL78/G14
The test results are applied to the following conditions:
• MCU:
RL78/G14 64-pin
• PCB type:
Single-side printed board without a polygon
R01AN1876EC0100 Rev. 1.00
Feb. 28, 2014
APPLICATION NOTE
R01AN1876EC0100
Rev. 1.00
Feb. 28, 2014
Page 1 of 14

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Summary of Contents for Renesas RL78/G14

  • Page 1 The purpose of this document is to help the user understand how to design a good PCB layout with high reducing noise performance. A thorough system evaluation is necessary after taking the countermeasures mentioned in this document. This document provides an explanation using RL78/G14 sample boards. Target Device...

  • Page 2: Table Of Contents

    RL78/G14 Recommended PCB Layout for Reducing Noise Contents Preface ..........................3 Recommended PCB Layout .................... 4 Wiring of VDD and VSS ......................4 Oscillator Concerns ........................4 Bypass Capacitor........................4 Wiring of RESET Pin ........................4 Wiring of REGC Pin........................4 Wiring of TOOL0 Pin ........................

  • Page 3: Preface

    RL78/G14 Recommended PCB Layout for Reducing Noise Preface This application note describes how to design PCB layout to achieve high reducing noise performance. The countermeasures of recommended PCB layout are shown in this application note. And the AC line noise contrast test with two types of PCB layout boards is introduced to verify these countermeasures.

  • Page 4: Recommended Pcb Layout

    RL78/G14 Recommended PCB Layout for Reducing Noise Recommended PCB Layout Good PCB layout is very important in reducing noise design. Some countermeasures of improving reducing noise performance are shown below. Wiring of VDD and VSS • Connect the MCU and main power supply with the shortest possible wiring.

  • Page 5: Description Of The Test Board

    RL78/G14 Recommended PCB Layout for Reducing Noise Description of the Test Board This section shows examples of the recommended layout and non-recommended layout. Both the recommended board and non-recommended board are made with the same schematics and components. Only the PCB layouts are different.

  • Page 6: Differences Between Recommended Layout And Non-Recommended Layout

    RL78/G14 Recommended PCB Layout for Reducing Noise Figure 3.2 Recommended Layout (Left) and Non-recommended Layout (Right) Differences between Recommended Layout and Non-recommended Layout This section introduces the main differences between the recommended layout and the non-recommended layout. 3.3.1 Wiring of VDD and VSS The VDD and VSS wiring of the recommended board are separated from peripheral power supply wiring at the entrance of the main power supply.

  • Page 7: Wiring Of Reset Pin

    RL78/G14 Recommended PCB Layout for Reducing Noise 3.3.4 Wiring of RESET Pin Reset circuits R1, D1, and C6 on the recommend board are closer to the MCU than the non-recommended one. And the wiring from the reset circuit to the MCU is shorter than the non-recommended one. On the non-recommended board, the leads of R1, D1, and C6 are not directly connected to the MCU VDD and VSS wiring, but connected to the main power supply VDD and VSS wiring.
  • Page 8 RL78/G14 Recommended PCB Layout for Reducing Noise Reset System initialization Interrupt Interrupt handler initialization Illuminated LEDs All LEDs ON for 5 sec..All LEDs OFF Illuminated LEDs ..LED OFF LED ON Note: The red LEDs are controlled by the main loop and the yellow LEDs are controlled by the interrupt handler.

  • Page 9: Reducing Noise Test Of Different Layout

    RL78/G14 Recommended PCB Layout for Reducing Noise Reducing Noise Test of Different Layout Test Description In this test, two types of PCB were used. One is designed according to the countermeasures. The other is designed without the countermeasures. The PCB layouts around the MCU are shown as Figure 3.2. The peripheral circuits on the two boards are same.

  • Page 10: Test Results

    RL78/G14 Recommended PCB Layout for Reducing Noise Test Results Table 4.1 Test Results of Recommended Board and Non-recommended Board Layout Recommended Board Test Results Non-recommended Board Test Results Polarity − − Voltage 4000 3900 3800 3700 3600 3500 3400 3300...

  • Page 11: Test Conclusions

    RL78/G14 Recommended PCB Layout for Reducing Noise Test Conclusions The test results only show the reducing noise performance of the tested boards. As is shown in Table 4.1, the result of noise interference test on the recommended board is about 4000 V (the maxim value of test condition), and the non-recommended one is below 2500 V.

  • Page 12: Improve The Non-Recommended Board

    RL78/G14 Recommended PCB Layout for Reducing Noise Improve the Non-recommended Board After the above test, modifications were made on the non-recommended board and retested under the same conditions. In this test, the non-recommended PCB board was modified provisionally to improve reducing noise performance.

  • Page 13: Test Results Of The Modified Board

    RL78/G14 Recommended PCB Layout for Reducing Noise Test Results of the Modified Board Table 5.1 Test Results of Non-recommended Board Improvement Non-recommended After Modification Before Modification Layout Polarity − − Voltage 4000 3900 3800 3700 3600 3500 3400 3300 3200...

  • Page 14: Documents For Reference

    User’s Manual: RL78/G14 User's Manual: Hardware (R01UH0186EJ) RL78 Family User's Manual: Software (R01US0015EJ) The latest versions can be downloaded from the Renesas Electronics website. Technical Updates/Technical News The latest information can be downloaded from the Renesas Electronics website. Website and Support Renesas Electronics Website http://www.renesas.com/index.jsp...
  • Page 15 Revision History Description Rev. Date Page Summary 1.00 Feb. 28, 2014 — First edition issued...
  • Page 16 General Precautions in the Handling of MPU/MCU Products The following usage notes are applicable to all MPU/MCU products from Renesas. For detailed usage notes on the products covered by this document, refer to the relevant sections of the document as well as any technical updates that have been issued for the products.
  • Page 17 10. It is the responsibility of the buyer or distributor of Renesas Electronics products, who distributes, disposes of, or otherwise places the product with a third party, to notify such third party in advance of the contents and conditions set forth in this document, Renesas Electronics assumes no responsibility for any losses incurred by you or third parties as a result of unauthorized use of Renesas Electronics products.

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