BUF16821-Q1 I2C writing problem

Tachibana-san,

We are not aware of any condition in the I2C communication, or register setting that can cause issues as described.

To better assist you, can you please provide more details such as

1. How many units exhibited this problem, have you swapped the problematic device with a new one?

2. What is the circuit configuration/schematic?

3. You mentioned 50mA nominal quiescent current. Is this expected? Under this condition, what is the output voltage at each channel and what is the load at each channel? Do the numbers add up?

4. Although it may not matter - the outputs can be programed in two ways, through the OTP or the registers. Which one are you referring to?

VS supply has to be present. The logic requires high voltage derived from VS supply to work properly.

Regards,

Guang-Apps CS Products

Dear Guang-san,

Thank for your support and I'm sorry for the late reply.
I’ll answer your question below.

1. I heard that such a phenomenon is occurring with at least two units.
The customer said that he changed the defective IC to a new one, so it worked normally.

2. The peripheral circuit diagram of the device is below.

    The data of the register being written is as follows.
        VCOM2     0x3BF
        OUT1      0x3CD
        OUT2      0x340
        OUT3      0x30E
        OUT4      0x2CC
        OUT5      0x295
        OUT6      0x26B
        OUT7      0x214
        OUT8      0x208
        OUT9      0x1E5
        OUT10     0x1D7
        OUT11     0x182
        OUT12     0x159
        OUT13     0x121
        OUT14     0x0E1
        OUT15     0x0AE
        OUT16     0x020
        VCOM1     0x030

3. The value of 50 mA may not be accurate.
It is not quiescent current but operating current.
It may be expected one.
The LCD driver which is as load of BUF16821-Q1 is connected to all 18 channels of OUT 1 - 16 and VCOM 1 - 2.

4. The customer is using both reading from the OTP and setting via registers.
Problem seems to be occurring when setting the output voltage via the registers.

Thanks and best regards,
M. Tachibana

Tachibana-san,

Thank you for the additional information. It would be helpful to figure out where the current is going. We can isolate the output channels by uninstalling the ‘0’ Ohm resistors. By doing this, we should not (finger crossed) see the same problem again. Then putting back the resistors one at a time while performing the same test may help identify the problem location.

On the other hand, if the problem persists even with no loads, then we are probably looking at some damaged devices; we can take further actions to find out the root cause.

Regards,

Guang-Apps CS Products

Dear Guang-san,

I'm sorry for the late reply.

The customer says the abnormal current seems to flow from Vs (analog power supply) to GND.
Even if all loads are removed, abnormal current flows.

It does not occur at the time of turning on or off the power supply.
He also says that the digital power supply is turned on first, and then the analog power supply is turns on.
And, after turning off the analog power supply, the digital power supply is turned off.

Can you think of any cause?

Best regards,
M. Tachibana

Tachibana-san,

Can you confirm the output voltages under both normal and abnormal conditions? One experiment is to program one channel at a time to see if you can find out which channel is causing the problem while leaving other channels alone.

If one or more problematic channels can be located, it most likely is due to physical damage to the device, not because of the logic block. Identifying failure area will help with future FA because we’ll know where to look.

Regards,

Guang-Apps CS Products

Dear Guang-san,

Thank so much for your advice.

Customer says as follows.
Under normal condition, the voltage corresponding to the register setting is seen at each of output pins.
Vs is about 12.3 V.

On the other hand, under abnormal condition, the voltage of all output pins is almost 0 V.
The customer recognizes that the device is destroyed.

Best regards,
M. Tachibana

Tachibana-san,

Most likely some of the outputs are shorted to ground as a result of some kind of overstress event. The customer can measure the resistance to confirm.

Regards,

Guang-Apps CS Products