ZHCSH72I September 2011 – December 2017 LMK00301
The current consumption values specified in Electrical Characteristics can be used to calculate the total power dissipation and IC power dissipation for any device configuration. The total VCC core supply current (ICC_TOTAL) can be calculated using Equation 5:
Since the output supplies (VCCOA, VCCOB, VCCOC) can be powered from 3 independent voltages, the respective output supply currents (ICCO_BANK_A, ICCO_BANK_B, ICCO_CMOS) should be calculated separately.
ICCO_BANK for either Bank A or B can be directly taken from the corresponding output supply current specification (ICCO_PECL, ICCO_LVDS, or ICCO_HCSL) provided the output loading matches the specified conditions. Otherwise, ICCO_BANK should be calculated as follows:
Table 6 shows the typical IBANK_BIAS values and IOUT_LOAD expressions for the 3 differential output types.
For LVPECL, it is possible to use a larger termination resistor (RT) to ground instead of terminating with 50 Ω to VTT = Vcco - 2 V; this technique is commonly used to eliminate the extra termination voltage supply (VTT) and potentially reduce device power dissipation at the expense of lower output swing. For example, when Vcco is 3.3 V, a RT value of 160 Ω to ground will eliminate the 1.3 V termination supply without sacrificing much output swing. In this case, the typical IOUT_LOAD is 25 mA, so ICCO_PECL for a fully-loaded bank reduces to 158 mA (vs. 165 mA with 50 Ω resistors to Vcco - 2 V).
|IBANK_BIAS||33 mA||34 mA||6 mA|
|IOUT_LOAD||(VOH - VTT)/RT + (VOL - VTT)/RT||0 mA (No DC load current)||VOH/RT|
Once the current consumption is calculated or known for each supply, the total power dissipation (PTOTAL) can be calculated as:
If the device configuration has LVPECL or HCSL outputs, then it is also necessary to calculate the power dissipated in any termination resistors (PRT_ PECL and PRT_HCSL) and in any termination voltages (PVTT). The external power dissipation values can be calculated as follows:
Finally, the IC power dissipation (PDEVICE) can be computed by subtracting the external power dissipation values from PTOTAL as follows: