Moteino USB - Reduce FTDI current on sleep

[Uncle Buzz]

pullup resistors are on the powered side of the bus, only the I2C sensor is isolated by mosfet while it's power is shut off.

The mosfets don't put the bus at 0V, but isolate the sensor side to avoid power come back to the sensor via the I2C bus.

[perky]

perky - how would you use that app note for powering down the bus? It's clear on how to do level-shifting, not sure how to power down the I2C bus without the resistors still consuming power.

With reference to Fig 1 in that app note, imagine the MCU on the right hand side and the sensor on the left hand side and both at 3.3V. There are pull-up resistors on both sides. If the sensor on the left were to be powered down, the MOSFET diodes will be reversed biased and the MOSFETs would be off thereby isolating it from the MCU. 

There are variants on this, it's possible to have two 'back to back' MOSFETs and have each side at different or the same voltages, and when powered down isolates itself from the other bus. See this article:
http://www.poulpetersen.dk/xfiles/cir/gbi2ciso.html

Mark.

[TomWS]

...
There are variants on this, it's possible to have two 'back to back' MOSFETs and have each side at different or the same voltages, and when powered down isolates itself from the other bus. See this article:
http://www.poulpetersen.dk/xfiles/cir/gbi2ciso.html

The back to back configuration is common in LiPo protection circuits.  See attachment...

Tom

[Felix]

Guys,
I tried to reproduce the higher consumption in the MoteinoUSB, but to my surprise I was not able to.
I used various sketches including the DeepSleep and the one below, all resulting in a ~6.5uA draw on a MoteinoUSB.
This is regardless how the TX/RX serial pins are used (as GPIO set to HIGH, or as Serial printing data).
I tried this with recent R6 and older R4 MoteinoUSBs from 2013 as well. Both perform identically, 6.5uA in WDT sleep.
I recall seeing higher consumption on MoteinoUSBs some years ago (10-20uA?) and I attributed it to the FTDI chip at that time without doing further optimization, now I cannot reproduce that same scenario, so it's possible it could have been an IDE/board definition thing, but I cannot pinpoint the difference. Since I tried an older '13 FTDI chip I have no reason to believe any changes in the FTDI chip has historically caused higher consumption.

Code Select Expand

//***********************************************************************************************************
// Sample sketch that achieves the lowest power on a Moteino of ~6.5uA
// Everything is put to sleep including the MCU, the radio (if any) and the FlashMem chip
//**** SETTINGS *********************************************************************************************
//#define WITH_RFM69              //comment this line out if you don't have a RFM69 on your Moteino
#define WITH_SPIFLASH           //comment this line out if you don't have the FLASH-MEM chip on your Moteino
//***********************************************************************************************************
#include <LowPower.h> //get library from: https://github.com/lowpowerlab/lowpower

#define LED           9 // Moteinos have LEDs on D9
#define FLASH_SS      8 // and FLASH SS on D8

#if defined(WITH_RFM69) || defined(WITH_SPIFLASH)
  #include <SPI.h>                //comes with Arduino IDE (www.arduino.cc)
  #if defined(WITH_RFM69)
    #include <RFM69.h>            //get it here: https://www.github.com/lowpowerlab/rfm69
    RFM69 radio;
  #endif
  #if defined(WITH_SPIFLASH)
    #include <SPIFlash.h>         //get it here: https://www.github.com/lowpowerlab/spiflash
    SPIFlash flash(FLASH_SS, 0xEF30); //EF30 for 4mbit  Windbond chip (W25X40CL)
  #endif
#endif

void setup () {
#ifdef WITH_RFM69
  radio.initialize(RF69_915MHZ,2,100);
  radio.sleep();
#endif


#ifdef WITH_SPIFLASH
  if (flash.initialize())
    flash.sleep();
#endif

  for (uint8_t i=0; i<=A5; i++)
  {
#ifdef WITH_RFM69
    if (i == RF69_SPI_CS) continue;
#endif
#ifdef WITH_SPIFLASH
    if (i == FLASH_SS) continue;
#endif
    pinMode(i, OUTPUT);
    digitalWrite(i, LOW);
  }

  //Serial.begin(115200);
  pinMode(0, OUTPUT);
  digitalWrite(0,HIGH);
  pinMode(1, OUTPUT);
  digitalWrite(1,HIGH);

  pinMode(LED, OUTPUT);

  digitalWrite(LED, HIGH);
  delay(20);
  digitalWrite(LED, LOW);
  delay(20);
  digitalWrite(LED, HIGH);
  delay(20);
  digitalWrite(LED, LOW);
  delay(20);
  digitalWrite(LED, HIGH);
  delay(20);
  digitalWrite(LED, LOW);
  delay(20);
}

void loop () 
{
  //optional blink to know radio/flash sleeping went OK
  digitalWrite(LED, HIGH);
  //LowPower.powerDown(SLEEP_30MS, ADC_OFF, BOD_OFF);
  delay(1000);
  digitalWrite(LED, LOW);
  //LowPower.powerDown(SLEEP_30MS, ADC_OFF, BOD_OFF);
  //digitalWrite(LED, HIGH);
  //LowPower.powerDown(SLEEP_30MS, ADC_OFF, BOD_OFF);
  //digitalWrite(LED, LOW);

  //sleep MCU for 8seconds
  LowPower.powerDown(SLEEP_2S, ADC_OFF, BOD_OFF);
  //LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF);
}

I ended up making a new revision of MoteinoUSB (R7) which includes the footprints for the mods discussed in this thread. However these will not be populated and the MoteinoUSB R7 will be equivalent to the previous revision at least for now or until further proof that R6 is higher consumption somehow. Those users interested in exploring this topic further can simply add the n-mosfet/resistor to the new R7 if they like to do so, here's an example of a modded R7 with the extra n-mosfet and 10k resistor (left of the LDO):


Feedback and more discussion is welcome and if someone does find a way to reproduce this I am curious to find out !

[DonpK]

I recall seeing higher consumption on MoteinoUSBs some years ago (10-20uA?) and I attributed it to the FTDI chip at that time without doing further optimization, now I cannot reproduce that same scenario,

A while ago, I thought I noticed the same thing - higher current consumption on a USB Moteino with no USB cable connected and the board powered with an external supply. I figured it might be the on-board FTDI chip drawing some additional current, but, like  you, I haven't been able to  reproduce it. Both the regular Moteino and the Moteino USB draw ca. 6µA to 7µA in the sleep mode.

[perky]

This is curious. The OP seems to have shown there was some leakage into the RX of the FT231X. The datasheet however has this as a 5V tolerant input, with no dependence on any power net. So technically the FT232X could be powered down and there would be no leakage.

However the FT231X datasheet says there are 200k pull-ups on the UART control signals to VCCIO, "When the FT231X is in reset, the UART interface I/O pins are tri-stated. Input pins have internal 200kΩ pull-up resistors to VCCIO, so they will gently pull high unless driven by some external logic"

So, this could explain why a high on the RX pin when the FT231X is powered down could possible cause leakage. The question is why do you now see something different? I'm wondering whether there has been a silicon revision to fix this such that the pull-ups are disabled when it is powered down. It's not mentioned in any errata though. Maybe the leakage isn't sufficient to turn on some logic in the device in some devices but is on others.

It would be interesting to measure what the VCCIO voltage is on a Moteino-USB (with a high impedance probe obviously).

Mark.

[akstudios]

Update on this: I have to add that I've only ever seen this leakage on custom DIY Moteinos I've made on my own and one MoteinoUSB R4 I had lying around that I extensively messed around with. All Moteino products I've used R4 onward, including the latest boards have the advertised current draw of 6-7uA out of the box, MoteinoUSBs included.

Somehow, my DIY Moteinos always have some leak into FT231X RX pin unless I do the isolation/mosfet mod, at which point it goes down to ~6.5uA. I've even tried using Arduino UNO bootloader (optiboot) and DualOptiboot, but still the same results. I've also tried other packages of the chips (i.e., QFN package for both: ATmega328P-MU and FT231XQ) and there's still some 100-120uA in power down mode which goes away after the isolation/mosfet mod.

Not sure what I'm doing wrong, but here are the files on git if anyone wants to take a look at point out the obvious that I may be missing: https://github.com/AKstudios/FSK_USB_Gateway
(Note that I don't populate the 10K pull-up on radio SS pin as I have a socket to program the bootloader on chips, so it's not leakage via the pull-up)

So just to reiterate: Moteino and MoteinoUSBs are able to achieve 6-7uA in its lowest power state out of the box. LowPowerLab FTW!

P.S. My apologies to Felix for making him spend time to do the mod, but maybe it'll help later on in case it's not the boards, but some batch of FTDI chips with some specific firmware.

[perky]

I've had a quick look, it seems you have not wired up the diode between VBUS and VIN around the FT231X on the schematic. The PCB does though appear to have the diode. Are you using two versions of the PCB?

I'm not sure if its a valid thing to do to have the VIN high impedance and drive the Vout of the LDO with 3V3, this I think would tend to drive VIN up towards 3V3 which might cause excessive quiescent current in the LDO. There is an A version of the MCP1703that might be a little different.

Mark.

[DonpK]

When I thought I was seeing a higher sleep mode current with the Moteino USB, I also looked at the schematic. It appears to show a resistor of unspecified value between Vin and Vbus. The Shottky diode doesn't appear to be connected to anything. BTW, the reverse current on the diode is "Max 0.001mA" according to the spec sheet.

[akstudios]

perky, DonpK - the diode is the resistor labelled "SHOTTKY" in the schematic. Since it's the same footprint as an 0805 resistor, I just reused a resistor symbol but physically placed a diode there on the actual board. The grey diode symbol underneath the "resistor" is just that - a symbol showing the polarity of the actual diode. Moteino schematic has it setup the same way btw, just uses an 0603 diode. Attaching the Moteino schematic for reference.

[akstudios]

Actually -- very good point about the diode reverse current. I was using this diode  (SD0805S040S0R5), but it appears to have 0.1mA as leakage! Never realized that. I switched over to a SD103AW and now the reverse current seems almost negligible.

I assembled a fresh board, burned bootloader and tested a sleep sketch with latest libraries -- getting the 6-7uA without mosfet mod now. Still not sure how the mosfet on RX is able to remove this on other boards if the FTDI was being back-powered by the diode leakage current.

Using the Moteino schematic and BOM as recommended by LPL will definitely give you the low power as advertised.

This forum rocks

[Felix]

Using the Moteino schematic and BOM as recommended by LPL will definitely give you the low power as advertised.

Great to see this come to a conclusion, now I remember it was indeed a different diode that I observed caused higher consumption on an old MoteinoUSB (probably on the first revision).

[perky]

Well done!

I noted earlier that the FT231X has 200k pull-ups on the inputs on the UART signals to VCCIO. Maybe the combination of that current plus the leakage through the diode was enough to parasitically power the chip, but remove one of them (i.e. use a low leakage diode, or stop the RX pin leakage via the 200k resistor by isolation) and the problem goes away?

Mark.

[DonpK]

Felix,
Just out of curiosity, at what date did you start shipping Moteino USB with the lower current consumption? I'm wondering whether I have any of the older units with the higher consumption.

PS. As I was typing this message on the Forum I got a Warning that a new reply had just been posted that I might want to look at before posting mine. Cool feature!

[Felix]

Felix,
Just out of curiosity, at what date did you start shipping Moteino USB with the lower current consumption? I'm wondering whether I have any of the older units with the higher consumption.

PS. As I was typing this message on the Forum I got a Warning that a new reply had just been posted that I might want to look at before posting mine. Cool feature!

I can't quite be sure of this. It must have been pretty early on, but I could be wrong. I have been using this current diode for years though.

It is not really an issue on most boards and to be honest in most use cases - the reason being that MoteinoUSB and MoteinoMEGA-USB was generally speaking designed to be USB powered/connected (I think that's how it even became a product - after people asking, for convenience purposes), and in most cases (even talking to customers) it appears to be used as such.
It can certainly be battery connected instead. So maybe I was not completely concerned with this from the beginning, although once I found the higher MoteinoUSB consumption I now recall that I made it a priority and traced down the issue to the diode and replaced it on all my designs at that point.