THS3491 Datasheet, PDF (11/28 Pages) Texas Instruments – 900-MHz, High-Power Output, Current Feedback Amplifier

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THS3491
SBOS875 – AUGUST 2017
Feature Description (continued)
8.3.2 Power-Down Reference (REF) Pin
In addition to the power-down pin, the DDA package features a reference pin (REF) that allows control over the
enable or disable power-down voltage levels applied to the PD pin. This reference pin is explicitly pinned out on
the DDA package as the REF pin. However, on the RGT package, the reference pin refers to pin 5 (GND), which
must be connected to GND. In most split-supply applications, the reference pin is connected to ground. In either
case, be aware of voltage-level thresholds that apply to the power-down pin. Table 1 shows examples and
illustrates the relationship between the reference voltage and the power-down thresholds. In Table 1, the
threshold levels are derived by these conditions:
• PD ≤ REF + 0.8 V for disable
• PD ≥ REF + 1.3 V for enable
where the usable range at the REF pin is:
• V_S– ≤ V_REF ≤ (V_S+ – 5 V)
Table 1. Example Power-Down Threshold Voltage Levels
SUPPLY
VOLTAGE (V)
±15, ±7
±15
±15
±7
±7
30
14
REFERENCE PIN
VOLTAGE (V)
0
2
–2
1
–1
15
7
ENABLE
LEVEL (V)
1.3
3.3
–0.7
2.3
0.3
16.3
8.3
DISABLE
LEVEL (V)
0.8
2.8
–1.2
1.8
–0.2
15.8
7.8
The recommended mode of operation is to tie the REF pin to ground for both single and split-supply operation,
thus setting the enable and disable thresholds to 1.3 V and 0.8 V, respectively.
If the REF pin is left unterminated, the pin floats to about 1 V below the positive rail and falls outside of the
recommended operating range (–V_S ≤ V_(REF) ≤ +V_S – 5 V). As a result, the REF pin no longer serves as a reliable
reference for the PD pin ,and the enable and disable thresholds given previously no longer apply. If the PD pin is
also left unterminated, the PD pin also floats to 2 V below the positive rail. The internal disable circuitry is
actually off when both REF and PD pin are floated, but the device remains enabled. As a result, the THS3491
DDA package can be a drop-in replacement for the THS3091 DDA pinout and operate if pins 1 and 8 are floated.
If balanced, split supplies are used (±V_S) and the REF and PD pins are grounded, the device is disabled.
8.3.3 Internal Junction Temperature Sense (Tj_Sense) Pin
The RGT package includes an internal, junction-temperature sense pin, Tj_Sense. This pin is a temperature-
dependent current source from the positive supply into one side of the internal resistor, where the other side of
the internal resistor is connected to pin 5 (GND), the PD logic reference pin on the die. For simplicity, and to
keep the Tj_Sense output ground referenced, tie pin 5 to ground (internally, the PD logic reference pin). If pin 5
is tied to a voltage in the same range as the REF pin voltage for the DDA package, the output of the Tj_sense
voltage and input threshold voltages of the PD pin are level shifted.
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