This document introduces the power-on reset circuit of the AD7416/AD7417/AD7418 circuit, which can ensure that the correct power-on reset is achieved when the power-off, power-on time is short.
This document addresses the issue where the Vpp line takes too long to discharge to 0 V when power is switched off, potentially causing the AD7416/AD7417/AD7418 to reset into an unknown state if power is reapplied too quickly. The text explains that using large decoupling capacitors on the Vpp line can result in residual voltage as high as 0.5 V after power-off.
Applying power before the Vpp line has fully discharged to 0 V can cause the internal circuitry to not fully switch off.
The PNP transistor in the recommended circuit starts switching off when the main Vpp line falls below approximately 1 V.