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RES60A-Q1: Rated power or allowable dissipation clarification

Conor
Guru 15090 points

Part Number: RES60A-Q1

Hi,

We are currently evaluating RES60A (and RES60A-Q1) as a high-voltage resistor divider in our design.

After reviewing the datasheet, we could not find an explicit specification for rated power or allowable power dissipation (W) for the device.
We understand that RES60A is a precision resistor divider and that voltage rating and thermal considerations are the primary limits, however our customer is asking for clarification from TI regarding power dissipation.

Is there an official rated power / maximum allowable power dissipation specification for RES60A (or per internal resistor element)? If no explicit power rating is defined, what is the recommended method to evaluate allowable dissipation, for example based on maximum junction temperature or self-heating limits?

Best regards,

Conor

  • 0
    TI__Expert 6030 points

    Hi Conor,

    There isn't an official rated power specification for the part, as this is dependent on the self-heating of the device, which changes with the applied voltage. As you mentioned, the thermals of the package are the upper limit for the power dissipation of the RES60, as the junction temperature cannot exceed 150°C. 

    The maximum allowable power dissipation of the package itself is set by the junction temperature maximum (150°C) and thermal resistance of the package (110.4°C/W), which is a function of the ambient temperature. See AN-336 Understanding Integrated Circuit Package Power Capabilities for more details.

    • Power limit at 25°C: (150°C - 25°C) / 110.4°C/W = 1.13W
    • Power limit at 125°C: (150°C - 125°C) / 110.4°C/W = 0.226W

    The highest power dissipation for the RES60 is a function of the DC voltage applied (max = 1400V) and the minimum total resistance of the divider (RHV+RLV)*(1-tabs). This is a very conservative estimate, as this assumes the total resistance of the divider is the lowest it can be while being within the 15% tabs specification.

    P_max = V^2 / R_total_min 
    R_total_min = (RHV+RLV)*(1-tabs) = (12.5M + RLV)*(0.85)
    For each ratio, the below table shows the resulting power dissipation at 1400V:
    Part Number RHV (MΩ) RLV (kΩ) Rtotal_min (MΩ) Pmax (W)
    RES60A145 12.5 86.2 10.698 0.183
    RES60A210 12.5 59.5 10.676 0.184
    RES60A315 12.5 39.7 10.659 0.184
    RES60A410 12.5 30.5 10.651 0.184
    RES60A500 12.5 25.0 10.646 0.184
    RES60A610 12.5 20.5 10.642 0.184
    RES60A100 12.5 12.5 10.636 0.184
     
    The power dissipated by the divider multiplied by RθJA gives an estimate of the self-heating. The temperature rise from self-heating plus the ambient temperature gives the estimated junction temperature.
    TJ = TA + PD (θJA)
    For each ratio: 
    Part Number RHV (MΩ) RLV (kΩ) Rtotal_min (MΩ) Pmax (W) TJ at 25°C TJ at 125°C
    RES60A145 12.5 86.2 10.698 0.183 45.23 145.23
    RES60A210 12.5 59.5 10.676 0.184 45.27 145.27
    RES60A315 12.5 39.7 10.659 0.184 45.30 145.30
    RES60A410 12.5 30.5 10.651 0.184 45.32 145.32
    RES60A500 12.5 25 10.646 0.184 45.32 145.32
    RES60A610 12.5 20.5 10.642 0.184 45.33 145.33
    RES60A100 12.5 12.5 10.636 0.184 45.35 145.35

    To summarize, as long as the heat dissipation of the board is adequate, the junction temperature of the RES60 won't exceed 150C, even when operating at the maximum ambient temperature of 125C, the highest recommended DC operating voltage, and the lowest possible total resistance. The most important limiting factors will be staying within the recommended operating voltage of the part, and following best practices for the PCB layout to ensure good heat dissipation through the board.

    Best Regards,

    Alex Curtis