THS3091 Datasheet, PDF (25/45 Pages) Texas Instruments – HIGH-VOLTAGE, LOW-DISTORTION, CURRENT-FEEDBACK OPERATIONAL AMPLIFIERS

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7 Detailed Description
THS3091, THS3095
SLOS423H – SEPTEMBER 2003 – REVISED DECEMBER 2015
7.1 Overview
The THS3091 and THS3095 are high-voltage, low-distortion , high-speed, current feedback amplifiers designed
to operate over a wide supply range of ± V to ±15 V for applications requiring large, linear output swings such as
Arbitrary Waveform Generators.
The THS3095 features a power-down pin that puts the amplifier in low power standby mode, and lowers the
quiescent current from 9.5 mA to 500 uA
7.2 Feature Description
7.2.1 Saving Power With Power-Down Functionality and Setting Threshold Levels With the Reference
Pin
The THS3095 features a power-down pin (PD) which lowers the quiescent current from 9.5 mA down to 500 μA,
ideal for reducing system power.
The power-down pin of the amplifier defaults to the positive supply voltage in the absence of an applied voltage,
putting the amplifier in the power-on mode of operation. To turn off the amplifier in an effort to conserve power,
the power-down pin can be driven towards the negative rail. The threshold voltages for power on and power
down are relative to the supply rails and are given Typical Characteristics (±15 V) and Typical Characteristics (±5
V) tables. Above the Enable Threshold Voltage, the device is on. Below the Disable Threshold Voltage, the
device is off. Behavior in between these threshold voltages is not specified.
Note that this power-down functionality is just that; the amplifier consumes less power in power-down mode. The
power-down mode is not intended to provide a high-impedance output. In other words, the power-down
functionality is not intended to allow use as a 3-state bus driver. When in power-down mode, the impedance
looking back into the output of the amplifier is dominated by the feedback and gain-setting resistors, but the
output impedance of the device itself varies depending on the voltage applied to the outputs.
Figure 59 shows the total system output impedance which includes the amplifier output impedance in parallel
with the feedback plus gain resistors, which cumulate to 2380 Ω. Figure 60 shows this circuit configuration for
reference.
2500
V_S = ±15 V and ±5 V
2000
1500
1000
1.21 kΩ 1.21 kΩ
500
−
50 Ω ^VO
+
0
100 k
1M
10 M
100 M 1 G
f − Frequency − Hz
Figure 59. Power-Down Output Impedance vs Frequency
As with most current feedback amplifiers, the internal architecture places some limitations on the system when in
power-down mode. Most notably is the fact that the amplifier actually turns ON if there is a ±0.7 V or greater
difference between the two input nodes (V+ and V–) of the amplifier. If this difference exceeds ±0.7 V, the output
of the amplifier creates an output voltage equal to approximately [(V+ – V–) –0.7 V] × Gain. This also implies that
if a voltage is applied to the output while in power-down mode, the V– node voltage is equal to V_O(applied) ×
R_G/(R_F + R_G). For low gain configurations and a large applied voltage at the output, the amplifier may actually
turn ON due to the aforementioned behavior.
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Product Folder Links: THS3091 THS3095
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