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THS3491

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SBOS875 – AUGUST 2017

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Copyright © 2017, Texas Instruments Incorporated

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:

•

Table 1. Example Power-Down Threshold Voltage Levels

SUPPLY

VOLTAGE (V)

REFERENCE PIN

VOLTAGE (V)

ENABLE

LEVEL (V)

DISABLE

LEVEL (V)

±15, ±7

0

1.3

0.8

±15

2

3.3

2.8

±15

–2

–0.7

–1.2

±7

1

2.3

1.8

±7

–1

0.3

–0.2

30

15

16.3

15.8

14

7

8.3

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

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.

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.