Datasheet

Power-Down Reference Operation—THS4215EVM Only

3-4

Figure 3-4. Power-Down Reference Operation

THS4215

4 1

Vin+

Vs+

Vs-

Vin-

Power Down

Vout

392 

0.1 F

453 

49.9 

0.1 F

49.9 

Power-Down Ref

Note: This schematic reflects the default THS4215EVM configuration.

392 

0 

The reference pin allows the user 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).