THS3091 Datasheet, PDF (42/45 Pages) Texas Instruments – HIGH-VOLTAGE, LOW-DISTORTION, CURRENT-FEEDBACK OPERATIONAL AMPLIFIERS

THS3091, THS3095
SLOS423H – SEPTEMBER 2003 – REVISED DECEMBER 2015
www.ti.com
PowerPAD Design Considerations (continued)
4. Connect all holes to the internal ground plane. Note that the PowerPAD is electrically isolated from the
silicon and all leads. Connecting the PowerPAD to any potential voltage such as V_S– is acceptable as there
is no electrical connection to the silicon.
5. When connecting these holes to the ground plane, do not use the typical web or spoke via connection
methodology. Web connections have a high thermal resistance connection that is useful for slowing the heat
transfer during soldering operations. This makes the soldering of vias that have plane connections easier. In
this application, however, low thermal resistance is desired for the most efficient heat transfer. Therefore, the
holes under the THS309x PowerPAD package should make their connection to the internal ground plane
with a complete connection around the entire circumference of the plated-through hole.
6. The top-side solder mask should leave the terminals of the package and the thermal pad area with its 13
holes exposed. The bottom-side solder mask should cover the 13 holes of the thermal pad area. This
prevents solder from being pulled away from the thermal pad area during the reflow process.
7. Apply solder paste to the exposed thermal pad area and all of the IC terminals.
8. With these preparatory steps in place, the IC is simply placed in position and run through the solder reflow
operation as any standard surface-mount component. This results in a part that is properly installed.
10.3.2 Power Dissipation and Thermal Considerations
The THS309x incorporates automatic thermal shutoff protection. This protection circuitry shuts down the amplifier
if the junction temperature exceeds approximately 160°C. When the junction temperature reduces to
approximately 140°C, the amplifier turns on again. But, for maximum performance and reliability, the designer
must ensure that the design does not exceed a junction temperature of 125°C. Between 125°C and 150°C,
damage does not occur, but the performance of the amplifier begins to degrade and long-term reliability suffers.
The thermal characteristics of the device are dictated by the package and the PC board. Maximum power
dissipation for a given package can be calculated using the following formula.
P _Dmax
+
T_max *
q_JA
T_A
where:
P_Dmax is the maximum power dissipation in the amplifier (W).
T_max is the absolute maximum junction temperature (°C).
T_A is the ambient temperature (°C).
θ_JA = θ_JC + θ_CA
θ_JC is the thermal coefficient from the silicon junctions to the
case (°C/W).
θ_CA is the thermal coefficient from the case to ambient air
(°C/W).
(4)
For systems where heat dissipation is more critical, the THS3091 and THS3095 are offered in an 8-pin SOIC
(DDA) with PowerPAD package. The thermal coefficient for the PowerPAD packages are substantially improved
over the traditional SOIC. Maximum power dissipation levels are depicted in the graph for the available
packages. The data for the PowerPAD packages assume a board layout that follows the PowerPAD layout
guidelines referenced above and detailed in the PowerPAD application note (SLMA002). If the PowerPAD is not
soldered to the PCB, the thermal impedance will increase substantially which may cause serious heat and
performance issues. Be sure to always solder the PowerPAD to the PCB for optimum performance.
When determining whether or not the device satisfies the maximum power dissipation requirement, it is important
to consider not only quiescent power dissipation, but also dynamic power dissipation. Often times, this is difficult
to quantify because the signal pattern is inconsistent, but an estimate of the RMS power dissipation can provide
visibility into a possible problem.
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