SBOS875B August 2017 – July 2018 THS3491
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 shows the relationship between the reference voltage and the power-down thresholds. In Table 1, the threshold levels are derived by these conditions:
|±15, ±7, 30||0||1.5||0.8|
The recommended operating mode is to tie the REF pin to ground for single and split-supply operations, which sets the enable and disable thresholds to 1.5 V and 0.8 V, respectively.
The REF pin must be tied to a valid potential within the recommended operating range of (–VS ≤ V(REF) ≤ +VS – 5 V). Although the PD pin can be floated, TI does not recommend floating the PD pin in case stray signals couple into the pin and cause unintended turnon or turnoff device behavior. However, if the PD pin is left unterminated, the PD pin floats to 2 V below the positive rail and the device remains enabled. As a result, the THS3491 DDA package is a drop-in replacement for the THS3091 DDA pinout if the REF pin (pin 1) is tied to a valid potential. If balanced, split supplies are used (±VS) and the REF and PD pins are grounded, the device is disabled.