JAJSIB3D August 2017 – February 2021 THS4561
The power down ( PD) pin must be asserted to the desired voltage for proper power-down mode operation. A physical internal pullup resistor is not provided on the PD pin so that if the pin is floated, the device defaults to an ON state. Tie the PD pin to the positive supply voltage for applications that simply require the device to power on when the supplies are present. For single-supply operation, a minimum of 0.5 V within the positive supply is required for operation.
The disable operation is referenced from the positive supply. For an OFF state condition, the disable control pin must be 1.8 V below the positive supply. The THS4561 has a unique power-down circuit that requires overcoming the specified peak PD pulldown current when the PD voltage is pulled low. When this current threshold is overcome, the PD current drops to a very small value. The benefit of the circuit is that the device stays disabled without having to use an active pullup resistor that wastes crucial power to keep the amplifier disabled in power-sensitive applications.