Providing stable power supply to the printed circuit board of a microprocessor system when connected via a long cable

This article considers the problem of creating a stable input power supply node for a printed circuit board (PCB) of a microprocessor system connected to a power source via a long cable. It is shown that under these conditions, the use of expensive, large-capacity ceramic capacitors without taking damping into account can lead to an unstable transient process, since the cable inductance, together with the input capacitance, form a resonant circuit with a sufficiently high Q factor. An approach to constructing an input power supply node is proposed that ensures damping of resonant processes without excessive voltage drop and overheating, shunting of high-frequency current components, and localization of interference. The main idea of this approach is to use the ESR of the storage input capacitor as a means of resonance damping, and to compensate for the effect of series inductance with small-value ceramic capacitors. It is shown that a similar principle is unacceptable in local decoupling circuits of microcircuits. Recommendations are provided for selecting the range of equivalent series resistance values, the nominal values of input capacitors, and the placement of components on the PCB.

1. Texas Instruments. LMZ21701 1-A Nano Module With 17-V Maximum Input Voltage: Datasheet [Electronic resource] // Texas Instruments : website. — 2018. — URL: https://www.ti.com/lit/ds/symlink/lmz21701.pdf (дата обращения: 14.05.2026).

2. Klein S. Input Filter for DCDC Converter. Design and Application Considerations of Input Filter to Reduce Conducted Emissions Caused by DC/DC Converter: Application Note No. 62AN101E Rev.003 [Electronic resource] // ROHM Co., Ltd. : website. — 2020. — URL: https://fscdn.rohm.com/en/products/databook/applinote/ic/power/switching_regulator/input_filter_for_dcdc_converter_appli-e.pdf (дата обращения: 14.05.2026).

3. H. Johnson, M. Graham. High-Speed Digital Design: A Handbook of Black Magic. Prentice Hall PTR, 1993.

4. Робертс С., Гончаров И. Решение проблем с пусковым током источников питания // Электронные компоненты. — 2020. — № 12. — С. 40–42. —URL: https://www.elcomdesign.ru (дата обращения: 19.03.2026).

5. Toshiba Electronic Devices & Storage Corporation. Load Transient Response of LDO and Methods to Improve It: Application Note [Electronic resource] // Toshiba : website. — 2021. — URL: https://toshiba.semicon-storage.com/info/application_note_en_20210326_AKX00312.pdf?did=66268 (дата обращения: 14.05.2026).

6. Texas Instruments. TPS7B84-Q1 150-mA, 40-V, Adjustable, Low-Dropout Regulator [Electronic resource] // Texas Instruments : website. — 2025. — URL: https://www.ti.com/lit/gpn/tps7b84-q1 (дата обращения: 14.05.2026).

7. Texas Instruments. TPS7A20 300-mA, Ultra-Low-Noise, Low-IQ, High PSRR LDO [Electronic resource] // Texas Instruments : website. — 2024. — URL: https://www.ti.com/product/TPS7A20 (дата обращения: 14.05.2026).

8. Baker B. Is Your Op Amp Filter Ringing? Look at Q! [Electronic resource] // Texas Instruments : website. — 2015. — URL: https://www.ti.com/document-viewer/lit/html/ssztcm1 (дата обращения: 14.05.2026).

9. «Затухающий гармонический осциллятор [Электронный ресурс] // StudFiles : сайт. — URL: https://studfile.net/preview/15835505/page:7/ (дата обращения: 14.05.2026).

10. National Semiconductor. LM1117/LM1117I 800mA Low-Dropout Linear Regulator [Электронный ресурс] URL: https://www.ti.com/lit/ds/symlink/lm1117.pdf (дата обращения:19.12.2025)

11. National Semiconductor. LP2950/LP2951 Series of Adjustable Micropower Voltage Regulators [Электронный ресурс] URL: https://www.ti.com/lit/ds/symlink/lp2950-n.pdf (дата обращения:19.12.2025)