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LM7332 Absolute Maximum Vin Differential Clarification needed

Other Parts Discussed in Thread: LM7332

Greetings,


With reference to the LM7332 data sheet [SNOSAV4A-April 2008 - Rev March 2013], the stated Absolute Maximum Vin Differential is +/-10V. 

What is driving this requirement and is this true for all Supply Voltages? 

Does this mean that if I power the component with +/-12V and my Vin+ = +12V then Vin- must be no lower than +2V? 

How does this effect +/-5V operation?

Thanks in advance!

Bill

  • Hello WIlliam,

    The two inputs should not have more than 10V between them.

    The input stage base-emitter junctions have a reverse breakdown limit of around 5-7V. Differential voltages of just a few volts can cause damage to the input stage.

    To prevent damage, internal diode clamps are placed across the input pins to limit the differential voltage between the bases. To limit the current into these clamps during high differential voltages, there are series resistors added in series with each input pin. These resistors absorb the clamping current through the diodes. Otherwise, the max differential spec would be less than a volt if these resistors were not included (some precision devices have differential limit specs less than ±1V).

    Under "normal" op-amp feedback conditions, where the inputs move with the output, the differential voltage is in the millivolts, with some spikes during fast output slewing. So these clamps do not affect the "normal" circuit operation.

    Since there is a finite limit to how big these series resistors can be before degrading specifications, the maximum voltage across the inputs must be limited. This is the reason for the ±10V spec.

    But there is always someone who wants to use an op-amp for non-op-amp applications, such as a comparator, so we need to include these specs (we do NOT recommend op-amps as comparators..).

    The ±10V limit is for all supply voltages, but you would run into the ESD clamps to the supplies if the differential voltage was greater than the total supply voltage.

    So if you are operating at ±5V supplies, the differential voltage could be ±10V (either +10 or -10V differentially, since the total supply voltage is +10V). 

    Remember that the differential voltage has no "ground" reference - it is just the voltage between the input pins. But if the "common mode" voltage (the voltage from one pin to ground) exceeds the supplies, it will be clamped by the ESD diode. So if you have a ±5V supply, and the inputs voltages are +10V and 0V, the 10V will hard-clamp to +5.7V - even though differentially it is 10V and within spec.

    In short...you should never push the differential voltage spec...under normal conditions it should not even be an issue.

    Regards,

  • Paul,


    Thank you for your response.  Your answer was perfect!

    Thanks Again and Best Regards,

    Bill