THS6022_16 Datasheet, PDF (23/44 Pages) Texas Instruments – 250-mA DUAL DIFFERENTIAL LINE DRIVER

THS6022
www.ti.com
SLOS225D – SEPTEMBER 1998 – REVISED JULY 2007
APPLICATION INFORMATION (continued)
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. This
is discussed in more detail in the PCB Design Considerations section of this document.
The PowerPAD package represents a design breakthrough, combining the small area and ease of the surface
mount assembly method to eliminate the previously difficult mechanical methods of heatsinking.
DIE
Side View (a)
Thermal
Pad
DIE
End View (b)
Bottom View (c)
M0088-01
The thermal pad is electrically isolated from all terminals in the package.
Figure 49. Views of Thermally Enhanced PWP Package
Recommended Feedback and Gain Resistor Values
As with all current feedback amplifiers, the bandwidth of the THS6022 is an inversely proportional function of the
value of the feedback resistor. This can be seen from Figure 19 through Figure 32. The recommended resistors
for the optimum frequency response are shown in Table 1. These should be used as a starting point and once
optimum values are found, 1% tolerance resistors should be used to maintain frequency response
characteristics. Because there is a finite amount of output resistance of the operational amplifier, load resistance
can play a major part in frequency response. This is especially true with these drivers, which tend to drive
low-impedance loads. This can be seen in Figure 10 and Figure 25 through Figure 28. As the load resistance
increases, the output resistance of the amplifier becomes less dominant at high frequencies. To compensate for
this, the feedback resistor should change. For most applications, a feedback resistor value of 1 kΩ is
recommended, which is a good compromise between bandwidth and phase margin that yields a very stable
amplifier.
GAIN
1
2
–1
Table 1. Recommended Feedback (R_F) Values for Optimum Frequency Response
V_CC = ±15 V
R_L = 50 Ω
R_L = 100 Ω
787 Ω
750 Ω
R_L = 25 Ω
1 kΩ
V_CC = ±15 V
R_L = 50 Ω
910 Ω
R_L = 100 Ω
820 Ω
590 Ω
590 Ω
820 Ω
715 Ω
680 Ω
560 Ω
–
–
680 Ω
–
Consistent with current-feedback amplifiers, increasing the gain is best accomplished by changing the gain
resistor, not the feedback resistor. This is because the bandwidth of the amplifier is dominated by the feedback
resistor value and internal dominant-pole capacitor. The ability to control the amplifier gain independently of the
bandwidth constitutes a major advantage of current-feedback amplifiers over conventional voltage feedback
amplifiers. Therefore, once a frequency response is found suitable to a particular application, adjust the value of
the gain resistor to increase or decrease the overall amplifier gain.
Finally, it is important to realize the effects of the feedback resistance on distortion. Increasing the resistance
decreases the loop gain and increases the distortion. It is also important to know that decreasing load
impedance increases total harmonic distortion (THD). Typically, the third-order harmonic distortion increases
more than the second-order harmonic distortion. This is illustrated in Figure 40.
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