LT6604-5
13
66045fa
TYPICAL APPLICATIONS
Junction temperature, T
J
, is calculated from the ambient
temperature, T
A
, and power dissipation, P
D
. The power
dissipation is the product of supply voltage, V
S
, and total
supply current, I
S
. Therefore, the junction temperature is
given by:
T
J
= T
A
+ (P
D
• θ
JA
) = T
A
+ (V
S
• I
S
• θ
JA
)
where the supply current, I
S
, is a function of signal level,
load impedance, temperature and common mode volt-
ages. For a given supply voltage, the worst-case power
dissipation occurs when the differential input signal is
maximum, the common mode currents are maximum (see
the Applications Information section regarding Common
Mode DC Currents), the load impedance is small and
the ambient temperature is maximum. To compute the
junction temperature, measure the supply current under
these worst-case conditions, use 43°C/W as the package
thermal resistance, then apply the equation for T
J
. For
example, using the circuit in Figure 3 with DC differential
input voltage of 250mV, a differential output voltage of 1V,
1k load resistance and an ambient temperature of 85°C,
the supply current (current into V
+
) measures 32.2mA per
channel. The resulting junction temperature is: T
J
= T
A
+
(P
D
• θ
JA
) = 85 + (5 • 2 • 0.0322 • 43) = 99°C. The thermal
resistance can be affected by the amount of copper on the
PCB that is connected to V
–
. The thermal resistance of the
circuit can increase if the exposed pad is not connected
to a large ground plane with a number of vias.
–
–
+
+
–
–
+
+
3V
3V
R
IN
V
OCM
(1V-1.5V)
I
IN
Q
IN
Q
OUT
I
OUT
R
IN
R
IN
R
IN
0.1μF
0.01μF
0.01μF
0.1μF
GAIN =
806Ω
R
IN
5MHz PHASE (DEG)
PERCENTAGE OF UNITS (%)
66045 TA02
30
25
20
15
10
5
0
–134.5 –134 –133.5 –133 –132.5 –132
25
27
29
7
34
4
6
2
17
19
21
24
8
12
14
10
1/2
LT6604-5
1/2
LT6604-5
Dual, Matched, 5MHz Lowpass Filter 5MHz Phase Distribution
(50 Units)
APPLICATIONS INFORMATION
