LTC2500-32 can't work with 7.5V Vref voltage appear

When I was using ltc2500-32, the ADC was able to work normally. After a while, the circuit board was connected with + -20v to supply power to the amplifier, and then the busy signal of ADC disappeared and no longer worked. The VREF voltage measured by Voltmeter was 7.5V abnormal, VDD was 2.5V normal (in my design circuit, the power supply of the chip was Vdd=2.5v, Ovdd = 5V, VREF = 5V, where Ovdd and VREF are connected directly to 5V. Will problems within ADC lead to VREF with 5V + 2.5V = 7.5V? Or is the 7.5V voltage introduced by the peripheral circuit?

Thank you!

ShadowJie