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©2021 Renesas Electronics Corporation

R31DS0073EU0200 July 30, 2021

831742I Datasheet

Power Considerations

This section provides information on power dissipation and junction temperature for the 831742I.

Equations and example calculations are also provided.

1.Power Dissipation.

The total power dissipation for the 831742I is the sum of the core power plus the power dissipated in the load(s).

The following is the power dissipation for VDD = 3.3V + 0.3V = 3.6V, which gives worst case results.

NOTE: Please refer to Section 3 for details on calculating power dissipated in the load.

•

Power (core)MAX = VDD_MAX * IDD_MAX= 3.6V * 26mA = 93.6mW

•

Power (outputs)MAX = 46.8mW/Loaded Output pair

If all outputs are loaded, the total power is 2 * 46.8mW =

93.6mW

Total Power_MAX = 93.6mW + 93.6mW = 187.2mW

2. Junction Temperature.

Junction temperature, Tj, is the temperature at the junction of the bond wire and bond pad and directly affects the reliability of the device. The

maximum recommended junction temperature for devices is 125°C.

The equation for Tj is as follows: Tj = JA * Pd_total + TA

Tj = Junction Temperature

JA = Junction-to-Ambient Thermal Resistance

Pd_total = Total Device Power Dissipation (example calculation is in section 1 above)

TA = Ambient Temperature

In order to calculate junction temperature, the appropriate junction-to-ambient thermal resistance JA must be used. Assuming no air flow and

a multi-layer board, the appropriate value is 87.8°C/W per Table 6 below.

Therefore, Tj for an ambient temperature of 85°C with all outputs switching is:

85°C + 0.187W * 87.8°C/W = 101.4°C. This is below the limit of 125°C.

This calculation is only an example. Tj will obviously vary depending on the number of loaded outputs, supply voltage, air flow and the type of

board (single layer or multi-layer).

Table 6. Thermal Resistance JA for 24 Lead TSSOP, Forced Convection

JA vs. Air Flow

Meters per Second

0

1

2.5

Multi-Layer PCB, JEDEC Standard Test Boards

87.8°C/W

83.5°C/W

81.3°C/W