ICS8430002 datasheet(22/27 Pages) IDT

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ICS8430002AY REVISION C NOVEMBER 12, 2009

ICS8430002 Data Sheet

HIGH-PERFORMANCE FRACTIONAL-N FREQUENCY SYNTHESIZER

3. Calculations and Equations.

The purpose of this section is to calculate the power dissipation for the LVPECL output pair.

LVPECL output driver circuit and termination are shown in Figure 10.

Figure 10. LVPECL Driver Circuit and Termination

To calculate worst case power dissipation into the load, use the following equations which assume a 50Ω load, and a termination voltage of

VCCO – 2V.

•

For logic high, VOUT = VOH_MAX = VCCO_MAX – 0.9V

(VCCO_MAX – VOH_MAX) = 0.9V

•

For logic low, VOUT = VOL_MAX = VCCO_MAX – 1.7V

(VCCO_MAX – VOL_MAX) = 1.7V

Pd_H is power dissipation when the output drives high.

Pd_L is the power dissipation when the output drives low.

Pd_H = [(VOH_MAX – (VCCO_MAX – 2V))/RL] * (VCCO_MAX – VOH_MAX) = [(2V – (VCCO_MAX – VOH_MAX))/RL] * (VCCO_MAX – VOH_MAX) =

[(2V – 0.9V)/50

Ω] * 0.9V = 19.8mW

Pd_L = [(VOL_MAX – (VCCO_MAX – 2V))/RL] * (VCCO_MAX – VOL_MAX) = [(2V – (VCCO_MAX – VOL_MAX))/RL] * (VCCO_MAX – VOL_MAX) =

[(2V – 1.7V)/50

Ω] * 1.7V = 10.2mW

Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW

OUT

CCO

CCO - 2V

Ω

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