Voltage leak on ADG1406BCPZ

Question

Hi, 
 I am using an ADG1406 (12Vdc) to multiplex voltages to the ADC of a Cypress Psoc5 microcontroller (5Vdc permanent). The 5V is also connected to the ADG1406 on S8. 
 The problem appears when the 12V is down (so when the ADG is OFF), the 5V (which is permanent) connected to S8 is found on the VDD pin of the multiplexer. The 5V is therefore connected to the 12V line of the card. How to explain this? 
 Thank you, 
 Vincent.

Davidforde · Accepted Answer

HI Vincent, 
 Is the 12 Vdc the supply for the ADG1406? 
 
 If so it sounds like you might be violating the max ratings of the ADG1406.

The source inputs must be kept within the supply voltages. 
 The source inputs of the ADG1406 have internal esd protection diodes to the supply, therefore when the supply is removed and 5 V is on S8 this forward biases the internal diode and the 5 V will show up on the supply pin. 
 
 To solve this you could have a look at our fault protection multiplexers such as the ADG5208F . These can stand off voltages up to +/-55 V in the power off condition. 
 
 Regards, 
 David)

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Voltage leak on ADG1406BCPZ