The truth table difference of ADUM2401 and ADUM241E1

Question

Hi 
 I am FAE in Japanese distributor. 
 Our customer is comparing ADUM2401BRWZ with ADuM241E1BRWZ. 
 Table 11 of ADUM2401BRWZ datasheet shows Vox =H at Vix= X , Vex=H or NC, VDDi=Unpowered and VDDo=Powered conditions. 
 In case of Vix=H, Vex=H or NC, VDDi=Unpowered and VDDo=Powered conditions, would the conditions 
 violate the Abs Max table which limits the voltage to VDDi + 0.5V? 
 
 On the other hand, Table 20 of ADuM241E1BRWZ datasheet shows Vox = H (Fail-safe condition) at Vix=L, Vex=H or NC, VDDi=Unpowered and VDDo=Powered conditions. 
 Why do ADUM2401BRWZ and ADuM241E1BRWZ have different expressions? 
 
 Best regards 
 N.Kokubo

jnaso · Accepted Answer

Hi Kokubo-san, 
 Both the ADuM241E1BRWZ and the ADUM2401BRWZ have ESD diodes between input pins and local VDD pin. With either isolator, a voltage on the input pins greater than a diode drop above the supply voltage is going to cause current to flow from the input signal. 
 I'm not sure why the truth tables are expressed differently between the isolator generations. In theory, the input state does not matter when the supply pin is undervoltage. So in theory, the ADUM2401BRWZ is correct. In practice however, if there is a signal with a valid high level, and the supply pin is undervoltage, the signal will power the isolator (maybe other components on the VDDi rail) and may cause odd circuit behavior. That is a condition that should be avoided. 
 Regards, 
 Jason)

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The truth table difference of ADUM2401 and ADUM241E1

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