Background: I'm using the Smoke Analysis tool with its "Standard Derating" option enabled—i.e., AMS Advanced Analysis [Smoke] > ANALYSIS menu > Smoke > Derating > Standard Derating.
Question: I'd like to know how the Smoke Analysis tool calculates the values under the "% Derating" column in Fig. 1—i.e., what formulas does the Smoke Analysis tool use to calculate the values in the "% Derating" column.
In this particular example, the Smoke Analysis tool derates resistor R1's PDM parameter to 0%, and I'd like to understand how the Smoke Analysis tool arrives at (calculates) the value 0%.
Miscellaneous: Table 1 shows the applicable values for resistor R1. The circuit under test is shown in Fig. 2. The transient analysis simulation runs for 10 ms.
The PSpice Advanced Analysis User Guide does not, as far as I can tell, provide the formulas the Smoke Analysis tool uses to calculate the values under the "% Derating" column when the tool's "Standard Derating" option is enabled.
Figure 1. Smoke Analysis results for resistor R1.
Table 1. Resistor R1's relevent properties.
| PARAMETER | VALUE |
|---|---|
| Resistor Value | 5.6 kΩ |
| RTMAX | 200 W |
| RMAX | 0.25 W |
| RSMAX | 0.0125 W/°C |
| RVMAX | 100 V |
| I(R1) | 5.178 mADC |
| V(R1) | 29 VDC |
| T_amb | 27 °C |
Figure 3. The circuit under test.
Copyright © 2020 Cadence Design Systems, Inc. All rights reserved.
Hi,
In PSpice AA Smoke, when we move from "No Derating" option to "Standard Derating", for this particular example, PDM for resistor will get derated to 55% of rated value. This will mean that its rated power RMAX = 0.25W will get derated to 55% of 0.25W = 0.1375W.
Since the simulation result for power dissipation of R1 under "Measured Value" column is 0.148W, which is higher than 0.137W, thus "% Derating" is shown as 0%.
% Derating for PDM of Resistor is dependent on resistor temperature along with other limits. If PDM for component is measured more than its rated, % Derating will be 0.