OPA4872-EP_12 Datasheet, PDF (18/25 Pages) Texas Instruments – 4:1 HIGH-SPEED MULTIPLEXER

OPA4872-EP
SBOS444 – DECEMBER 2008........................................................................................................................................................................................... www.ti.com
THERMAL ANALYSIS
Heatsinking or forced airflow may be required under
extreme operating conditions. Maximum desired
junction temperature sets the maximum allowed
internal power dissipation as discussed in this
document. In no case should the maximum junction
temperature be allowed to exceed +150°C.
Operating junction temperature (T_J) is given by T_A +
P_D × θ_JA. The total internal power dissipation (P_D) is
the sum of quiescent power (P_DQ) and additional
power dissipated in the output stage (P_DL) to deliver
load power. Quiescent power is simply the specified
no-load supply current times the total supply voltage
across the part. P_DL depends on the required output
signal and load; for a grounded resistive load, P_DL is
at a maximum when the output is fixed at a voltage
equal to 1/2 of either supply voltage (for equal bipolar
supplies). Under this condition P_DL = V_S2/(4 × R_L),
where R_L includes feedback network loading.
Note that it is the power in the output stage and not in
the load that determines internal power dissipation.
e_n
OPA4872
-20
4kT = 1.6 x 10 J
at 290K
R_S
i_ni
V_RS = Ö4kTR_S
e_o
R_F
V_RF = Ö4kTR_F
i_in
R_G
Ö^iRG
4kT
R_G
Figure 35. OPA4872 Noise Analysis Model
18
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