ON-Off circuit design using ADP198
The on-off circuit is designed to allow the battery supply to the DSP system to be detached from the circuit when the device is in off state. The circuit contains a push-button switch and ADP198 load switch. The input voltage comes from the Li-ion battery. The EN pin of the load switch allows electronic control of the switch, which is connected to the push-button and a GPIO from the DSP for firmware control of the load switch.
When the user pushes the button and hold for some time, the circuit is closed and the DC/DC converter start supplying the DSP and firmware is loaded. The firmware sets the GPIO high so that even when the push-button is not pressed, the EN keeps active. The push-button switch out put is also connected to the DSP interrupt pin so as to generate an interrupt(low-to-high) when the device is ON state. This interrupt sets the GPIO low and the load switch cuts the supply to the DC/DC converter to shut hte device off.
Desgin works well for basic turining ON and OFF. However when the device is turned off and presses the button again when the out put of the load switch(ADP198) is between 0.01V and 0V, the switch failes to turn fully on and goes in to a loop. This is observed to vary with the slew rate change of ADP198 chip.
The Oscilloscope out put at VOUT is given below. VIN =4.18
Please help us find and rectify the issue.