Latch up AD8646

Question

Hello, 
 i am using AD8646 for voltage follower as illustrated in following schematic. the output of AD8646 shall be connected to 12Bit ADC for voltage measurement UDC (range 0 to 820V). The supply of AD8646 is V2 (4,5V), which can be manually turned off and on; or permanently off. This is my issue because during the power cycle of V2, the UDC could still present and with the voltage divider, 3V is present at the (+) input of ADC8646. The sum of current (flows on R1) is relatively low at 300uA. 
 Could this condition triggers latch up on AD8646? is there any other damage that could occurs? 
 many thx and best regards, 
 M.Brata

harrynsc · Answer

MB, 
 Without knowing the exact design of the input stage, it's hard to say, but a general solution is to increase R5 to 10k-100k?? 
 and add reverse biased Shottky diodes from pin 1 to the supply rails. Also add a matching (R5) resistor in the feedback, 
 45 to 2. 
 BTW, in Spiceland, voltage sources are perfect and have no noise, so C2 does nothing. 
 In real life, on your pcb, put 0.1uF next to the part, and a 1uF to 10uF bulk cap farther away. 
 Harry