que 4 delete

WIP - TODO - Split MAX31855 breakout board points from LDO regulator and move LDO regulator context to main LDO review document

Torex Semiconductor's XC6204/XC6205 series

Datasheet for Torex Semiconductor's XC6204/XC6205, Mark 4B2X - LDO regulator, CMOS based.

• This part shows up on a lot of ESP8266 development boards and breakout boards. It is on the MAX31855K breakout board that I am using. This board looks like an unbranded version of the Adafruit board; however, it has several component selection differences. It is clearly built to a different bill of materials. The Adafruit schematic shows a TI LP298XS for the LDO regulator, along with 10μF CAPs. My unbranded board uses the Torex Semiconductor's XC6204 with ~0.5μF CAPs. The Adafuit board photo clearly shows different size CAPs on the board and the SMD mark on the LDO does not match up with the TI datasheet. So their schematic may not be current.
• I find Torex's datasheet to be long and hard to follow. It is very tedious to find the details you need for a part variation.
• At least for all the variations in parameters that are listed, there is only one "Absolute Maximum Ratings" section shown for all variations.

For additional information and reference:

• TI also has a CMOS-based regulator TLV701 with a different pinout. See Application Information for additional guidance that I think can be applied to the XC6204 as well.

• A distant cousin, the TI LP298XS has a similar pinout and also supports using low ESR ceramic capacitors.

  • Datasheet for TI's LP298XS bipolar based.
  • TI has always had good application note information. In this datasheet, they have important details on selecting ceramic capacitors and for values >= 2.2μF their value can be seriously affected by temperature. 8.2.2.2 Capacitor Characteristics
  • Also supporting the idea of using type X7R ceramic CAPs, the Component List (Bill of materials) for the MAX31855PMB1 Peripheral Module (AKA Breakout board) also specifies them. I have since found some older WeMos Mini schematics that show the 1μF as an X7R though the LDO is different.

Torex's Datasheet TMI Breakdown

For a deeper discussion on the XC6204 go here

Unbranded MAX31855K Breakout Board Change Summary

1. The two ~0.5μF ceramic CAPs are almost okay. The net value falls just under 1μF. This may be due to part tolerances. To guarantee stability, add an additional CAP to make the net value, a temperature stable value over 1.0μF.
2. The breakout board is missing a CAP for CIN. Add a CIN to the backside of the board where the header is connected.
3. The MAX31855 is missing a 0.1μF bypass CAP. This value would have a different resonant frequency than the ~0.5μF CAP. I don't know if it matters. No harm in paring one on to the existing CAP near the chip.

TODO Thoughts to be integrated into the above discussion

• From various Application Information descriptions, it is clear that for an ESP8266 which can idle at ~85mA or less and spike upward to 300mA, more capacitance is needed for CL. Looking at Espressif's Hardware Design Guideline, Sections 1.4.1.2., 1.6.5. 1. for requirements. It looks like 10μF should have been used in the module near pin AVDD. This is in addition to the 10μF referenced in Section 1.4.1.2. Looking at the Board Schematic used for testing, it has both 10μF CAPs at VDDA and VDD3P3. I am confused, if these CAPs are needed to get test data, why would they not always be needed. What am I missing?
  • AI Thinker modules have about a lump (Total) capacitance of 11.1μF, more is usually supplied at the module power pin. NodeMCU's DEV board has a 100uf CAP!
  • while DOIT measures at 3.88μF - this seems too light
  • TODO look at what Sonoff has for lump capacitances well as other IoT devices.
• 1.0μF alone at the LDO would be grossly inadequate. Espressif Design Guide additional capacitance on the ESP8266 Modules, and a CAP specified to be next to it. To address transients it is usually best for CAPs to be placed next to the transient load. Maybe the >=1.0μF capacitor to stabilize the LDO is enough/correct. CL-total already measures at 20 to 30μF.
• There is a longer discussion to be made about the current limit and current ratings of this part over the operating range of the ESP8266; however, this is not a concern for my breakout board.
• May need to expand on the need for doubling some classes of ceramic CAPs in order to get the required minimum over the operating temperature range. Also, need to consider CAP value tolerances.