Datasheet

Power-Down Reference Operation—THS4275EVM Only

3-4

Figure 3-4. Power-Down Reference Operation

THS4275

4 1

Vin+

249

Vs+

Vs-

Vin-

Power Down

Vout

249 

0.1 F

453 

49.9 

0.1 F

49.9 

Power-Down Ref

Note: This schematic reflects the default THS4275EVM configuration.

The reference pin allows the user the ability to control the logic levels of the

power-down pin. The reference pin is mainly designed for systems with supply

voltages higher than 5 V; however, it works with any voltage within the

amplifier’s voltage range. In most cases, the reference pin is connected to a

digital ground or to ground. For example, a customer is using a 3-V

microcontroller to control the power-down pin of an amplifier that is operating

from a ±5 V power supply. Using the traditional power-down circuit, the

customer has to buffer/boost the 3-V signal from the microcontroller to a higher

level to ensure the proper voltage level for the amplifier to toggle between

enable and disable. With the reference circuit, the customer can connect the

3-V signal directly to the power-down pin.

When the reference pin is connected to ground, the power-down voltage

applied to the power-down pin must be greater than Ref +1.8 V (GND +1.8 V)

for the amplifier to be active (enable). To place the device into power-down

mode (disable) the voltage applied to the power-down pin must be less than

Ref +1 V (GND+1 V).

Now, when the reference pin is connected to the positive supply or allowed to

float, the power-down logic levels are referenced to the positive supply.

Therefore, if a system is operating on a split supply of 5 V and the reference

pin is left floating (not connected), the power-down pin voltage must be greater

than Ref –1 V (5 V–1; V = 4 V) for the amplifier to be active (enable). To place

the device into power-down mode (disable) the voltage applied to the

power-down pin must be less than Ref –1.5 V (5 V–1.5; V = 3.5 V).