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DAC7750: Alarm detection

Masayoshi Takahashi
Intellectual 1530 points

Part Number: DAC7750

Hi team,

I got 2 question from the customer. Could you support this?

1. When the alarm detection is working, what is the status of the IOUT? Keep output value?

2. If DAC7750's die temperature goes higher than 142C, the Alarm will work. Could you tell me the example of the event to increase the die temperature?

Regards,

Yoshi

  • 0
    TI__Guru 56943 points

    Hi Yoshi-san,

    We will get back to you tomorrow.

    Thanks,

    Paul

  • 0
    TI__Mastermind 46290 points

    Hello,

    I have responded to each of your questions below.

    Masayoshi Takahashi said:
    1. When the alarm detection is working, what is the status of the IOUT? Keep output value?

    Nothing about the outputs change on this device. Other later generation products have the capability to autonomously respond to alarm conditions.

    Masayoshi Takahashi said:
    2. If DAC7750's die temperature goes higher than 142C, the Alarm will work. Could you tell me the example of the event to increase the die temperature?

    The thermal impedance of the device, depending on package, is specified as 32.9C/W and 32.3C/W for the VQFN and HTSSOP, respectively. The primary concern for heat is with respect to the current outputs and is load dependent as well as supply dependent. It is possible to dissipate significant heat with nominal 24V AVDD supplies and low impedance loads. Additionally, if there were any failure which allowed significant current to flow the die temperature could increase.

    For the most part, this is a concern for applications which will operate at high ambient temperatures. Given that the device is rated to 125C - it is a reasonable concern to reach 142C.

  • 0 in reply to Kevin Duke
    TI__Intellectual 1530 points

    Hi Kevin, 

    Thanks for your reply.

    Regarding question 1

    After alarm detection is working, the device may keep heat up. So the customer should disable the DAC from MCU. Is it correct?

    Regarding question 2

    Do we have the threshold of the load?

    Regards,

    Yoshi

  • 0 in reply to Masayoshi Takahashi
    TI__Mastermind 46290 points

    Hello,

    Masayoshi Takahashi said:
    After alarm detection is working, the device may keep heat up. So the customer should disable the DAC from MCU. Is it correct?

    Only one of the alarm conditions is related to heat. The others do not directly suggest that the device would be heating up. However, it is fairly common for customers to be interested in placing the device in some kind of fail-safe state in the event of any suggested malfunction of the system.

    Masayoshi Takahashi said:

    Do we have the threshold of the load?

    The die temperature is a function of multiple factors including output current value, load impedance value, ambient temperature, and the integrity of the thermal pad connection. Typically the worst case is when the output load is 0ohms because in this case all of the output current is dissipated in the output PMOS.

    From what I've seen in the past you can anticipate 30-35C delta over ambient with 24V high-side supply and 24mA into a 1ohm load. This was with a proper thermal pad connection on a 4-layer PCB with one dedicated ground plane.