I2C SDA PIN input current

RE: I2C SDA PIN input current

AD1170 — Thu, 13 Aug 2020 12:24:28 GMT

Yes, the communication works perfect now. Thanks again.

RE: I2C SDA PIN input current

haakonsh — Thu, 13 Aug 2020 11:53:51 GMT

Did the issue disappear after you removed this macro?

RE: I2C SDA PIN input current

AD1170 — Wed, 12 Aug 2020 14:22:52 GMT

Many thanks, i have seen that register was changed to disconnect and S0S1 drive after the 1st initialization. This was done in a macro related to control the I2C level shifter. The macro was a left over from a former state of development.

RE: I2C SDA PIN input current

haakonsh — Wed, 12 Aug 2020 13:42:12 GMT

I need you to halt the cpu after a transfer has started and read out the PIN_CNF[n] register for p0.20.

This will tell us if the GPIO configuration is overridden somewhere else in the SW.

RE: I2C SDA PIN input current

AD1170 — Wed, 12 Aug 2020 09:55:42 GMT

I'm sure the the SDA Pin (P0.20) is only initialized on start up, before the I2C peripheral is initialized and only controlled by the I2C peripheral.

Here are the I2C related initialization code.

//! GPIO pin for TWI
#define GPIO_PIN_IN_TWI 	((GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos) | \
                       	 	 (GPIO_PIN_CNF_DRIVE_S0D1 << GPIO_PIN_CNF_DRIVE_Pos) | \
                         	 (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos) | \
                         	 (GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos) | \
                         	 (GPIO_PIN_CNF_DIR_Input << GPIO_PIN_CNF_DIR_Pos))


// GPIO initialization

  //
  // I2C
  //
  NRF_P0->OUTSET = BitP0_SCL;
  NRF_P0->PIN_CNF[PinP0_SCL] = GPIO_PIN_IN_TWI; // GPIO_PIN_OUT;
  NRF_P0->PIN_CNF[PinP0_SDA] = GPIO_PIN_IN_TWI; // GPIO_PIN_IN_DISCON;

// I2C Initialization (later in the code)

  I2C_IF->PSEL.SCL = PinP0_SCL;
  I2C_IF->PSEL.SDA = PinP0_SDA;

  I2C_IF->ADDRESS = 0;
  I2C_IF->FREQUENCY = TWIM_FREQUENCY_FREQUENCY_K390 << TWIM_FREQUENCY_FREQUENCY_Pos; // see Errata 219
  I2C_IF->SHORTS = 0;

  I2C_IF->INTENSET = TWIM_INTENSET_STOPPED_Msk | TWIM_INTENSET_ERROR_Msk;

  sd_nvic_SetPriority(TWIM0_IRQ, APP_IRQ_PRIORITY_HIGH);
  sd_nvic_ClearPendingIRQ(TWIM0_IRQ);
  sd_nvic_EnableIRQ(TWIM0_IRQ);

  I2C_IF->ENABLE = TWIM_ENABLE_ENABLE_Enabled << TWIM_ENABLE_ENABLE_Pos;

  nrf_mtx_init(&I2C_mtx);

Please note, there are 4 more I2C devices on the custom board. The communication with devices works w/o issues. Perhaps, this is because the devices can sink at least 10mA.

RE: I2C SDA PIN input current

haakonsh — Wed, 12 Aug 2020 09:40:47 GMT

Thanks, it's clear to me now that p0.20 likely sources the excessive current. There are two options, either the GPIO is in the output-high state or the GPIO's ESD protection diode is blown due to over-voltage (short-circuit). Since you can reproduce this issue on the DK it's likely not an over-voltage issue.

Does any of your code, other than TWI related, try to control p0.20?

Can you share your code?

RE: I2C SDA PIN input current

AD1170 — Wed, 12 Aug 2020 09:00:49 GMT

No, the voltage drop is every time when the sensor try to pull the SDA line LOW. In this case to ACK the I2C device address (9th clock).

RE: I2C SDA PIN input current

haakonsh — Wed, 12 Aug 2020 08:54:53 GMT

Then it's definitely not the level shifter.

I'm struggling to understand your circuit as the voltage drop over the series resistor only seem to be present at certain times when the SDA line should not be sinked.

Can you draw a schematic of the SDA line with the nRF pin, series resistor, external pull-up resistor, probe, and sensor pin?

RE: I2C SDA PIN input current

AD1170 — Wed, 12 Aug 2020 06:40:54 GMT

I have tested the sensor with the PCA10100 with 1.8V Vcc. As you can see in the picture below, the current is still around 5mA.

RE: I2C SDA PIN input current

AD1170 — Tue, 11 Aug 2020 11:41:51 GMT

I can not test this scenario because the custom board does not run on 1.8V.

However, i can use the PCA10100 and a separate sensor breakout board, but it will take some time.

RE: I2C SDA PIN input current

haakonsh — Tue, 11 Aug 2020 11:33:12 GMT

Also, what happens if you power the nRF at 1.8V and bypass the level shifter?

RE: I2C SDA PIN input current

AD1170 — Tue, 11 Aug 2020 10:18:01 GMT

Sure, i can do that but i think i will see the same. Because I've already tested with a simple pass gate level shifter (2 FET's, mostly the same as the used TCA9406).

RE: I2C SDA PIN input current

haakonsh — Tue, 11 Aug 2020 09:53:35 GMT

I suggest you try the same with a 100R between the nRF52 and the level shifter

RE: I2C SDA PIN input current

AD1170 — Tue, 11 Aug 2020 09:46:08 GMT

As mentioned above, it seems that the current is came from the nRF52833. I have no other idea.

I have inserted a 100R resistor between the Sensor SDA and the Level Shifter. Scope Ch 1 and Scope Ch 2 in the picture above show the signal on both side of the resistor. The red signal is the difference, around 970mV (the voltage drop over 100R).

RE: I2C SDA PIN input current

haakonsh — Tue, 11 Aug 2020 09:01:09 GMT

Then how are you able to sink 2mA? Where does this current come from?

With 10k pull-ups at 3V, you should sink 300µA.

RE: I2C SDA PIN input current

AD1170 — Tue, 11 Aug 2020 08:32:47 GMT

The pull-up resistors are 10k on both sides of the level shifter.

RE: I2C SDA PIN input current

haakonsh — Tue, 11 Aug 2020 08:29:21 GMT

What resistance do your pull-up resistors have?