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Part Number: OPA4188
Hi, application team,
A customer has a question regarding the absolute maximum rating of the OPA4188 input terminal.
From the maximum rating in the data sheet, when +/- power supply is used, the maximum power supply voltage rating is ± 20V, and the input terminal rating is "+ power supply voltage + 0.5V" on the upper side and "-power supply voltage -0.5V" on the lower side.
- Does this mean that if the power supply voltage is not supplied (= + /-0V) and the voltage is applied to the input terminal, the input terminal must always keep within 0V ± 0.5V?
- Or, Note (2) in absolute maximum rating table states that “Input terminals are diode-clamped to the power-supply rails. Input signals that can swing more than 0.5-V beyond the supply rails should be current-limited to 10 mA or less.”
If this protection diode current is kept within 10mA, is it okay to understand that the voltage rating (+/- 0.5V) of the input terminal is no longer a problem?
Regarding your OPA4188 Questions:
The OPA4188 power supply voltage range is (V+) - (V–), is 4 V (±2 V) to 36 V (±18 V). The Signal input terminals Voltage listed in the 7.1, Absolute Maximum Ratings table, of (V–) – 0.5 and (V+) + 0.5 V are applicable to that power supply range. If the OPA4188 supplies are off and appear as a high impedance applying a voltage to an input pin could forward bias an input ESD diode between the input and a supply rail. The diode would then provide a current path to the V+ or V- terminal and some level of current would flow. Since this is an abnormal condition just exactly how much current would flow and how the internal OPA4188 become biased is not stated. Since the datasheet makes no claims or assurances about the OPA4188 behaviors with voltage applied to the inputs and the supplies turned off the user assumes responsibility for any outcome.
First, the absolute maximum input and supply voltage ratings must not be exceeded. Second, the input current must be limited to +/-10 mA to avoid damaging the input circuitry, or ESD clamps. The 10 mA is the key specification. When I have evaluated the forward characteristics of ESD diodes on the bench I find that they must be forward biased greater than 0.5 V to get 10 mA to flow. That is why the specification is written limiting the forward voltage to a maximum of 0.5 V beyond the supply rails.
If and ESD diode to the supply does become forward biased it will have to source/sink the current to the corresponding supply rail. That current will end up being sunk/sourced by the OPA4188 supply pin, or something else connected to the particular supply rail.
Precision Amplifiers Applications Engineering
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In reply to Thomas Kuehl:
Did my response to your OPA4188 input absolute maximum ratings answer your questions? If so, please close this e2e inquiry.
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