Datasheet

Power-Down Functionality Saves Power
3-3
THS4226EVM Applications
3.4 Power-Down Functionality Saves Power
The THS4226 EVM features a power-down pin (PD) for each channel, which
lowers the quiescent current from 14 mA/channel down to 700 µA/channel,
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 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.