LT1994 Linear Technology, LT1994 Datasheet - Page 15

• Manufacturer Part Number: LT1994
• Description: Low Noise - Low Distortion Fully Differential Input/Output Amplifier/Driver
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
The power dissipation in the IC is a function of the supply
voltage, the output voltage, and the load resistance. For
fully differential output amplifi ers at a given supply voltage
(±V
case power dissipation P
quiescent current (I
current is given by the expression:
The worst case power dissipation in the LT1994 at
Example: A LT1994 is mounted on a circuit board in a
MSOP-8 package (θ
±5V supplies driving an equivalent load (external load plus
feedback network) of 75Ω. The worst-case power that
would be dissipated in the device occurs when:
The maximum ambient temperature the 8-lead MSOP is
allowed to operate under these conditions is:
I
LOAD
T
(140°C/W) = 75°C
I
P
R
P
75
LOAD
5
CC
A
D MAX
D MAX
LOAD
V
(
(
= T
), and a given differential load (R
Ω
=
2
+
R
JMAX
=
)
V
)
=
LOAD
2 5
R
CC
=
=
•
R
V
LOAD
V
R
2
LOAD
CC
– P
V
CC
V
LOAD
•
CC
is:
V
• •
2
D
CC
2
17 5
U
• θ
Q(MAX)
+
JA
+
.
•
2
(
JA
2
MA
= 140°C/W), and is running off of
I
•
LOAD
•
V
D(MAX)
= 150°C – (0.54W) •
U
V
CC
=
= 20.5mA) and when the load
CC
0 54
•
+
.
•
I
Q MAX
I
I
Q MAX
Q MAX
occurs at the worst case
(
(
(
W
W
)
)
)
)
LOAD
=
–
I
LOAD
), the worst-
U
2
•
To operate the device at higher ambient temperature,
connect more copper to the V
resistance of the package as indicated in Table 1. Note that
T
150°C for the 8-lead MSOP), and the data for the equation
above should be altered accordingly.
Table 1. LT1994 MSOP and DD Package Thermal Resistivity
LT1994 8-LEAD MSOP PACKAGE
Layout Considerations
Because the LT1994 is a high speed amplifi er, it is sensitive
to both stray capacitance and stray inductance. Compo-
nents connected to the LT1994 should be connected with
as short and direct connections as possible. A low noise,
low impedance ground plane is critical for the highest
performance. In single supply applications, high quality
surface mount 1μF and 0.1μF ceramic bypass capacitors
with minimum PCB trace should be used directly across
the power supplies V
high quality surface mount 1μF and 0.1μF ceramic bypass
capacitors should be placed across the power supplies
V
bypass caps should be used from each supply to ground
with direct (short) connections.
Copper Area
JMAX
+
Topside
(mm
to V
100
100
540
30
0
for the 8-lead DD package is 125°C (as opposed to
2
–
)
, and individual high quality surface mount 0.1μF
Copper Area
Backside
(mm
100
540
0
0
0
2
)
+
(Junction to
to V
Resistance
Ambient)
Thermal
140
135
130
120
110
–
. In split supply applications,
–
pin to reduce the thermal
www.DataSheet4U.com
LT1994 8-LEAD DD PACKAGE
Copper Area
Topside
(mm
130
16
32
64
4
2
)
LT1994
(Junction to
Resistance
Ambient)
Thermal
15
160
135
110
95
70
1994fa