THS3491 Datasheet, PDF (15/28 Pages) Texas Instruments – 900-MHz, High-Power Output, Current Feedback Amplifier

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THS3491
SBOS875 – AUGUST 2017
Application Information (continued)
Placing a small series resistor, R_ISO, between the amplifier output and the capacitive load, as shown in Figure 11,
is an easy way of isolating the load capacitance.
Figure 12 is shown using two amplifiers in parallel to double the output drive current to larger capacitive loads.
This technique is used when more output current is needed to charge and discharge the load faster like when
driving large FET transistors.
1 kΩ
249 Ω
24.9 Ω
V_S
_
+
−V_S
1 kΩ
5.11 Ω
V_S
V_S
1 nF
249 Ω
_
5.11 Ω
+
24.9 Ω
−V_S
Figure 12. Driving a Large Capacitive Load Using Two Parallel Amplifier Channels
Figure 13 shows a push-pull FET driver circuit typical of ultrasound applications with isolation resistors to isolate
the gate capacitance from the amplifier.
V_S
V_S
+
5.11 Ω
_
−V_S
866 Ω
191 Ω
866 Ω
V_S
_
5.11 Ω
+
−V_S
−V_S
Figure 13. PowerFET Drive Circuit
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