THS3091 Datasheet, PDF (26/45 Pages) Texas Instruments – HIGH-VOLTAGE, LOW-DISTORTION, CURRENT-FEEDBACK OPERATIONAL AMPLIFIERS

THS3091, THS3095
SLOS423H – SEPTEMBER 2003 – REVISED DECEMBER 2015
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Feature Description (continued)
The time delays associated with turning the device on and off are specified as the time it takes for the amplifier to
reach either 10% or 90% of the final output voltage. The time delays are in the order of microseconds because
the amplifier moves in and out of the linear mode of operation in these transitions.
7.2.2 Power-Down Reference Pin Operation
In addition to the power-down pin, the THS3095 features a reference pin (REF) which allows the user to control
the enable or disable power-down voltage levels applied to the PD pin. In most split-supply applications, the
reference pin is connected to ground. In either case, the user needs to be aware of voltage-level thresholds that
apply to the power-down pin. The tables below show examples and illustrate the relationship between the
reference voltage and the power-down thresholds. In the table, the threshold levels are derived by the following
equations:
PD ≤ REF + 0.8 V for disable
(1)
PD ≥ REF + 2.0 V for enable
(2)
where the usable range at the REF pin is:
V_S– ≤ V_REF ≤ (V_S+ – 4 V).
(3)
The recommended mode of operation is to tie the REF pin to midrail, thus setting the enable/disable thresholds
to V_midrail + 2 V and V_midrail + 0.8 V respectively.
SUPPLY
VOLTAGE (V)
±15, ±5
±15
±15
±5
±5
30
10
Table 3. Power-Down Threshold Voltage Levels
REFERENCE PIN
VOLTAGE (V)
0
2
–2
1
–1
15
5
ENABLE
LEVEL (V)
2
4
0
3
1
17
7
DISABLE
LEVEL (V)
0.8
2.8
–1.2
1.8
–0.2
15.8
5.8
Note that if the REF pin is left unterminated, it will float to the positive rail and will fall outside of the
recommended operating range given above (V_S– ≤ VREF ≤ V_S+ – 4 V). As a result, it will no longer serve as a
reliable reference for the PD pin and the enable/disable thresholds given above will no longer apply. If the PD pin
is also left unterminated, it will also float to the positive rail and the device will be enabled. If balanced, split
supplies are used (±Vs) and the REF and PD pins are grounded, the device will be disabled.
7.3 Device Functional Modes
7.3.1 Wideband, Noninverting Operation
The THS309x are unity gain stable 235-MHz current-feedback operational amplifiers, designed to operate from a
±5-V to ±15-V power supply.
Figure 60 shows the THS3091 in a noninverting gain of 2-V/V configuration typically used to generate the
performance curves. Most of the curves were characterized using signal sources with 50-Ω source impedance,
and with measurement equipment presenting a 50-Ω load impedance.
26
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