LMK00308 Datasheet, PDF (21/25 Pages) Texas Instruments – 3-GHz 8-Output Differential Clock Buffer/Level Translator

14.4.1.1 Power Dissipation Example: Worst-Case Dissipation
This example shows how to calculate IC power dissipation for a configuration to estimate worst-case power dissipation. In this
case, the maximum supply voltage and supply current values specified in Section 11.0 Electrical Characteristics are used.
• V_CC = V_CCO = 3.465 V. Max I_CC and I_CCO values.
• CLKin0/CLKin0* input is selected.
• Banks A and B are configured for LVPECL: all outputs terminated with 50 Ω to V_T = Vcco - 2 V.
• REFout is enabled with 5 pF load.
• T_A = 85 °C
Using the power calculations from the previous section and maximum supply current specifications, we can compute P_TOTAL and
P_DEVICE.
• From Equation 5: I_{CC_TOTAL} = 10.5 mA + 20 mA + 20 mA + 5.5 mA = 56 mA
• From I_{CCO_PECL} max spec: I_{CCO_BANK_A} = I_{CCO_BANK_B} = 160 mA
• From Equation 7: P_TOTAL = 3.465 V * (56 mA + 160 mA + 160 mA + 10 mA) = 1337 mW
• From Equation 8: P_{RT_PECL} = ((2.57 V - 1.47 V)²/50 Ω) + ((1.72 V - 1.47 V)²/50 Ω) = 25.5 mW (per output pair)
• From Equation 9: P_{VTT_PECL} = 1.47 V * [ ((2.57 V - 1.47 V) / 50 Ω) + ((1.72 V - 1.47 V) / 50 Ω) ] = 39.5 mW (per output pair)
• From Equation 10: P_{RT_HCSL} = 0 mW (no HCSL outputs)
• From Equation 11: P_DEVICE = 1337 mW - (8 * (25.5 mW + 39.5 mW)) – 0 mW = 817 mW
In this worst-case example, the IC device will dissipate about 817 mW or 61% of the total power (1337 mW), while the remaining
39% will be dissipated in the LVPECL emitter resistors (204 mW for 8 pairs) and termination voltage (316 mW into Vcco - 2 V).
Based on θ_JA of 31.4 °C/W, the estimated die junction temperature would be about 26 °C above ambient, or 111 °C when T_A = 85
°C.
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