The OPAx863 includes a power-down mode for low-power standby operation with a quiescent current of only 1.5 μA (maximum) with a 3-V supply and high output impedance. Many low-power systems are active for only a small time interval when the parameters of interest are measured and remain in low-power standby mode for a majority of the time for an overall small average power consumption. The OPAx863 enables such a low-power operation with quick turn-on within less than 6.5 μsec. Refer to the electrical characteristics tables for power-down pin control thresholds.
The PD pin always needs to be driven to avoid false triggering and oscillations. If use of power-down mode is not necessary, the PD pin should be connected to VS+. For applications which need the power-down mode, an external pull-up resistor from PD pin to VS+, driven with an open-collector power-down control logic may be used.
The choice of value of the pull-up resistor RPU in Figure 8-2 impacts the current consumption in power-down mode. Using a large RPU reduces the power consumption, but increases the noise at the PD pin which could cause the amplifier to power-down. A 1 nF capacitor may be used in parallel with RPU to avoid couping of external noise and false triggering. For the case of PD pin driven to VS-, the current IPU through RPU is given as,