SLOS382E September 2001 – May 2015 THS3122 , THS3125
PRODUCTION DATA.
Achieving optimum performance with high-frequency amplifiers such as the THS3125 and THS3122 requires careful attention to board layout parasitic and external component types. Recommendations that optimize performance include:
The THS3125 and THS3122 are available in a thermally-enhanced PowerPAD family of packages. These packages are constructed using a downset leadframe upon which the die is mounted [see Figure 48(a) and Figure 48(b)]. This arrangement results in the lead frame being exposed as a thermal pad on the underside of the package [see Figure 48(c)]. Because this thermal pad has direct thermal contact with the die, excellent thermal performance can be achieved by providing a good thermal path away from the thermal pad. Note that devices such as the THS312x have no electrical connection between the PowerPAD and the die.
The PowerPAD package allows for both assembly and thermal management in one manufacturing operation. During the surface-mount solder operation (when the leads are being soldered), the thermal pad can also be soldered to a copper area underneath the package. Through the use of thermal paths within this copper area, heat can be conducted away from the package into either a ground plane or other heat dissipating device.
The PowerPAD package represents a breakthrough in combining the small area and ease of assembly of surface mount with the, heretofore, awkward mechanical methods of heatsinking.
NOINDENT:
Dimensions are in inches (millimeters).Although there are many ways to properly heatsink the PowerPAD package, the following steps illustrate the recommended approach.
The THS3125 and THS3122 incorporate 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. However, for maximum performance and reliability, the designer must take care to 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 PCB. Maximum power dissipation for a given package can be calculated using the following formula.
where
where
For systems where heat dissipation is more critical, the THS3125 and THS3122 are also available in an 8-pin MSOP with PowerPAD package that offers even better thermal performance. The thermal coefficient for the PowerPAD packages are substantially improved over the traditional SOIC. Maximum power dissipation levels are depicted in Figure 50 for the available packages. The data for the PowerPAD packages assume a board layout that follows the PowerPAD layout guidelines discussed above and detailed in the PowerPAD application note (literature number SLMA002). Figure 50 also illustrates the effect of not soldering the PowerPAD to a PCB. The thermal impedance increases substantially, which may cause serious heat and performance issues. Always solder the PowerPAD to the PCB for optimum performance.
NOINDENT:
Results shown are with no air flow and PCB size of 3 in × 3 in (76,2 mm × 76,2 mm).When determining whether or not the device satisfies the maximum power dissipation requirement, it is important to not only consider quiescent power dissipation, but also dynamic power dissipation. Often times, this type of dissipation 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.