This example shows how to calculate IC power dissipation for a configuration with separate V_CC and V_CCO supplies and unused outputs. Because some outputs are not used, the I_{CCO_PECL} value specified in Electrical Characteristics cannot be used directly, and output bank current (I_{CCO_BANK}) should be calculated to accurately estimate the IC power dissipation.

• V_CC = 3.3 V, V_CCOA = 3.3 V, V_CCOB = 2.5 V. Typical I_CC and I_CCO values.
• CLKin0/CLKin0* input is selected.
• Bank A is configured for LVPECL: 4 pairs used with R_T = 50 Ω to V_T = V_CCO – 2 V (1 pair unused).
• Bank B is configured for LVDS: 3 pairs used with R_L = 100 Ω differential (2 pairs unused).
• REFout is disabled.
• T_A = 85°C

Using the current and power calculations from the previous section, we can compute P_TOTAL and P_DEVICE.

• From Equation 6: I_{CC_TOTAL} = 8.5 mA + 20 mA + 26 mA + 0 mA = 54.5 mA
• From Table 11-1: I_{OUT_LOAD} (LVPECL) = (1.6 V – 0.5 V) 50 Ω + (0.75 V – 0.5 V)/50 Ω = 27 mA
• From Equation 7: I_{CCO_BANK_A} = 33 mA + (4 × 27 mA) = 141 mA
• From Equation 8: P_TOTAL = (3.3 V × 54.5 mA) + (3.3 V × 141 mA) + (2.5 V × 34 mA)] = 730 mW
• From Equation 9: P_{RT_PECL} = ((2.4 V – 1.3 V)²/50 Ω) + ((1.55 V – 1.3 V)²/50 Ω) = 25.5 mW (per output pair)
• From Equation 10: P_{VTT_PECL} = 0.5 V × [ ((2.4 V – 1.3 V) / 50 Ω) + ((1.55 V – 1.3 V) / 50 Ω) ] = 13.5 mW (per output pair)
• From Equation 11: P_{RT_HCSL} = 0 mW (no HCSL outputs)
• From Equation 12: P_DEVICE = 730 mW – (4 × (25.5 mW + 13.5 mW)) – 0 mW = 574 mW

In this example, the IC device will dissipate about 574 mW or 79% of the total power (730 mW), while the remaining 21% will be dissipated in the emitter resistors (102 mW for 4 pairs) and termination voltage (54 mW into V_CCO – 2 V).

Based on the thermal resistance junction-to-case (R_θJA) of 28.5°C/W, the estimated die junction temperature would be about 16.4°C above ambient, or 101.4°C when T_A = 85°C.