MPM54304 return no ACK at the first IIC contact since power up

DC-DC Power Converters
1

There are 9 MPM54304s on my board, and some of the devices will fail to respond to the first IIC communication when powered on, but the following communication will succeed. The positions of the components which fail are random and vary with each power-on.

It seems that the power-on initialization process is improper, causing the IIC state machine to be abnormal.

Can you provide some Debug methods?

2

Hello hongyuc,

Is it possible for you to check if the startup input and pull up voltages proper?
Is there any droop that causes the devices to go in UVLO during startup?
Can you check what the first initial i2c communication data is?
Does our Virtual Bench Pro 4.0 show any faults?

Regards,
Vinh Tran

3

Hi vinh.tran，

Please check the results as follows.
Since I can only attach one picture to each reply, I have to reply separately.

Is it possible for you to check if the startup input and pull up voltages proper?

Vin_Vpull-up
Vin_Vpull-up1280×534 36.2 KB

Is there any droop that causes the devices to go in UVLO during startup?
The input voltage stays stable before the first IIC commucation.

4

Can you check what the first initial i2c communication data is?
Power up overview:

image
image1664×654 320 KB

Does our Virtual Bench Pro 4.0 show any faults?
Sorry，we don’t have the USB Cable

5

Hello hongyuc,

I2c startup looks fine to me.

You can see the PMBus message format on page 27 figure 7. The initial connection looks to be Start, Address, Write, NACK, then Stop. This looks to be just the acknowledge process upon i2c startup. It looks to be not acknowledge. Please check if you have the correct device address in the firmware.

Regards,
Vinh Tran

6

Hi vinh.tran

  1. We use the default address 0x68 which is mentioned in datasheet.
  2. This fault occurs sporadically on different MPM54304 devices, which does not look like a device address problem.
  3. Please check the following diagram, the first and second IIC communication, using the same device address, and the time interval is very short. But the device returns NACK the first time and ACK the second time.
    image
    image1315×512 139 KB
  4. MPM54304 does not seem to follow the PMbus protocol, it seems to follow the IIC protocol designed by MPS itself. What are the initialization factors that would put the IIC’s state machine into an abnormal state?
7

Hello Hongyuc,

You are correct, I was looking at wrong information. MPM54304 does not have PMBus. Only i2c.

Can you confirm that the VCC is above 2V for all device when the i2c communication starts? It is possible that the the internal circuitry is not working properly because Vcc is not >2V yet.

Does this i2c communication failure occur during operation too? Or just at startup? Is this the only device on the i2c lines?

Regards,
Vinh Tran

8

Hi vinh.tran

I added Vcc to the test:
Yellow: Vin (12V)
Red: Vcc (3.3V)
Blue: SCL
Green: SDA

image
image1250×1212 556 KB

The failure only occurs at startup, and MPM54304 is the only slaver on the I2C bus.