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OPA330: OPA330AIDBVR max differential voltage

Part Number: OPA330
Other Parts Discussed in Thread: OPA376, OPA191

Hi All, 

can anyone please let me know, what is the absolute max differential voltage for the part OPA330AIDBVR .

As per the Figure 17 of the datasheet it appears the anti parallel diodes conduct 30uA at 0.8v but its not clear whether that is a stress ful condition?

thanks 

  • SIDDHARTH,

    Since OPA330 includes internal 10k input resistors (see Fig 19 on page 16), which will limit the input current to less than +/-10mA, the maximum differential voltage between the input terminals is the same as the supply voltage, (V+)-(V-). However, please be aware that the exposure to the absolute maximum-rated conditions for extended periods of time may effect the device reliability.

  • thanks for the reply Marek but referring to figure 17 of the datasheet , it appears that the parasitic clamp diodes between the input terminals start conducting only when the differential voltage exceeds 0.6v , what is your opinion on this.
  • also can the parasitic clamp diodes between the input terminals be assumed to conduct 30uA at 0.8v ?
  • SIDDHARTH,

    The OPA330 parasitic diodes between the input terminals start conducting the moment forward-bias voltage is greater than 0V but its magnitude is very small (in fA) until Vbe>0.6V so you see zero on uA scale shown in Fig 17; Id= Is*e^(Vbe/KT/q). Also notice, that Id current is an inverse function of temperature with Vbe changing at -2mV/deg C for constant current.

    However, be aware that as you increase the voltage between the input terminals, most voltage drop will occur across the 10k input resistor and not the diode. If for 0.8V differential voltage, Vbe=~0.5V and 0.3V voltage drop occurs across the 10k resistor (0.3V/10k=30uA), this means that in case of 5V differential voltage, Vbe=~0.57V and ~4.43V voltage drop occurs across the resistor resulting in 443uA input current and thus far below the absolute maximum rating of 10mA.

    Having said that, you should not drive both inputs independently but instead allow the negative feedback to drive the inverting input within a virtual short of positive so both inputs are within max Vos of +/-50uV. Therefore, do NOT contamplate using OPA330 as a comparator because its back-to-back input diodes thru current conduction will cause corruption of the trashold voltage resulting in a wrong tripping point. For comparator function you may use only op amps with no such diodes - see OPA376 (5V) or OPA191 (36V).

  • thanks Marek, this is very valuable input. So from you your reply it appears that the diodes conduct 30uA current when 0.5v is applied across them??

    i am checking that the input differential voltage does not exceed the limits. So having an input differential voltage of 0.8v or above a stress condition ?

  • also i think that VBE should be 0.2v for 30uA when the input differential voltage is 0.8v. I feel this because there will be 30uA current through each of the 10K resistors (both on the positive & negative terminal) reulting in total of 0.6v drop across both these resistors.

    so the internal diode across the inputs conducts 30uA at 0.2v across it kindly confirm
  • Even if Vbe=0, with 0.8V input differential voltage and two 10k resistors, the largest current that could flow is I=0.8/20k=40uA, thus far below the Absolute Maximum rating of 10 mA.  Therefore, it would take at least 10mA*20k=200V between the input terminals to exceed the max rated current limit.  But in reality, for 0.8V input differential voltage, the voltage split would be closer to Vbe=0.5V and 150mV across each 10k resistor resulting in about 15uA current flow.  BTW, Vbe diode drop of 0.2V would result in current in 1nA range.  

    All and all, regardless of the actual Vbe, you do not need to worry about exceeding the max rated current limit of 10mA unless the differential voltage is above 200V.

  • thanks for the reply Marek,

    so for 150mV across the resistors we have 15uA through the diode but the Fig17 indicates 30uA when the input differential voltage is 0.8v so how to reconcile these?
  • There is an error in the horizontal axis of Fig 17 in being shifted to the right by 100mV.  This results in the 30uA current at Vbe of 0.8V but -30uA current at Vbe of -1V instead of  correct value of +/-30uA at Vbe of +/-0.9V

  • Thanks for the reply Marek, so can i assume the diode to conduct 15uA at 0.5v across itself ?
  • A short answer is no. Since the current thru a diode is an exponential function of Vbe, the current will double every 18mV change in Vbe. Considering that Vbe changes at -2mV/C, any change of ambient temperature or increase in junction temperature due to power dissipation will effect the diode current itself.
    I am not sure what are you trying to determine with the series of never ending questions regarding non-linear operation of OPA330. Therefore, if you have any other question, please explain to me what are you trying to do because the part is not designed to operate in the manner you're attempting to use it.