ICS8525 Datasheet, PDF (9/12 Pages) Integrated Circuit Systems – LOW SKEW, 1-TO-4 LVCMOS-TO-LVHSTL FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
ICS8525
LOW SKEW, 1-TO-4
LVCMOS-TO-LVHSTL FANOUT BUFFER
3. Calculations and Equations.
The purpose of this section is to derive the power dissipated into the load.
LVHSTL output driver circuit and termination are shown in Figure 8.
V_DDO
Q1
V_OUT
RL
50
V_DDO - 2V
FIGURE 8 - LVHSTL 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 V - 2V.
DD
Pd_H is power dissipation when the output drives high.
Pd_L is the power dissipation when the output drives low.
Pd_H = (V
/R ) * (V
-V
)
OH_MAX L
DD_MAX OH_MAX
Pd_L = (V /R ) * (V - V )
OL_MAX L
DD_MAX OL_MAX
• For logic high, V = V
=V
– 1.2V
OUT
OH_MAX
DD_MAX
• For logic low, V = V
=V
– 0.4V
OUT
OL_MAX
DD_MAX
Pd_H = (1.2V/50Ω) * (2V - 1.2V) = 19.2mW
Pd_L = (0.4V/50Ω) * (2V - 0.4V) = 12.8mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 32mW
8525BG
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9
REV. B JULY 27, 2001