Datasheet

Power-Down Functionality Saves Power
3-4
3.3 Power-Down Functionality Saves Power
The THS4225 EVM features a power-down pin (PD) which lowers the
quiescent current from 14 mA down to 700 µA, ideal for reducing system
power. The power-down pin of the amplifier defaults to the positive supply
voltage in the absence of an applied voltage, putting the amplifier in the
power-on mode of operation. To turn off the amplifier and conserve power, the
power-down pin can be driven towards the negative rail. The threshold
voltages for power-on and power-down are relative to the supply rails and
given in the specification tables in the data sheets. Above the Enable
Threshold Voltage, the device is on. Below the Disable Threshold Voltage, the
device is off. Behavior in between these threshold voltages is not specified.
Note that this power-down functionality is just that; the amplifier consumes
less power in power-down mode. The power-down mode is not intended to
provide a high impedance output. In other words, the power-down functionality
is not intended to allow use as a 3-state bus driver. When in power-down mode,
the impedance looking back into the output of the amplifier is dominated by the
feedback and gain setting resistors, but the output impedance of the device
itself varies, depending on the voltage applied to the outputs.
The time delays associated with turning the device on and off are specified as
the time it takes for the amplifier to reach 50% of the nominal quiescent current.
The time delays are on the order of microseconds, because the amplifier
moves in and out of the linear mode of operation in these transitions.