topic LPC55S DC/DC converter inductor in LPC Microcontrollers

LPC55S DC/DC converter inductor

jpowning — Thu, 13 Oct 2022 12:42:52 GMT

I would like to specify an inductor for the LPC55S DC/DC converter, but I do not see any requirements other than the inductance. Can anyone tell me what other characteristics are important?

Re: LPC55S DC/DC converter inductor

ZhangJennie — Tue, 18 Oct 2022 06:30:19 GMT

Hi @jpowning

inductance L1 of 4μ7H and the capacitance C1 of 22μF are calculated by LPC55xx internal circuit. When designing, we must strictly follow the parameters recommended in the manual, otherwise DCDC circuit can’t work normally.

For more about DCDC power supply circuit analysis and detection method, see

https://community.nxp.com/t5/LPC-Microcontrollers-Knowledge/LPC55xx-Power-Supply-Circuit-Design-and-Detection-Method/ta-p/1429011

Hope this helps,

Jun Zhang

Re: LPC55S DC/DC converter inductor

jpowning — Thu, 20 Oct 2022 15:53:04 GMT

Thank you for your help. I have some more questions:

1, What is the control scheme of the converter? (constant frequency, burst mode, pulse skipping, current controlled….).

2. Are there any features in the converter to minimize emissions? (spread spectrum, dithering….)

3. What is the operating frequency of the internal DC-DC Converter?

4. What is the max/peak cycle current?

5. What is the max average current? What is the spec for the supply current into VDD_PMU?

6. AN12325 recommends minimum saturation current for the inductor >350mA, but tables 16, 17, 18 in the data sheet would imply the max average current <6.1mA.

John

Re: LPC55S DC/DC converter inductor

jpowning — Thu, 20 Oct 2022 16:06:40 GMT

Also, what is the min/max duty cycle of the DC-DC controller MOSFET switch?

thank you,

John

Re: LPC55S DC/DC converter inductor

ZhangJennie — Fri, 21 Oct 2022 07:29:16 GMT

John

LPC5500 DCDC uses PFM control scheme. See AN13532 chapter 4 DC-DC operating mechanism and control regulation

https://www.nxp.com.cn/docs/en/application-note/AN13532.pdf

The DCDC converter spec that we can share is listed in above AN as well, chapter 5 DC-DC converter specs. Besides we don’t have other spec record for external.

Inductor >350mA. This is requirement for selecting inductor. see below

While Datasheet table 16-18 is for Idd. They are different.

Hope this helps,

Jun Zhang