TINA/Spice/LMV761: Input Bias Current Above Common Mode Input Range

Doran Akutagawa

Part Number: LMV761
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

I am using an LMV761 Spice model provided by TI and I am seeing something in the simulation I don't understand. My application uses a 5V supply for the device and I have a situation where the (+) input is within the -03 to 3.8V common mode input range, while the (-) input goes to 5V at the input of a 1K series resitor. The simulation shows the LMV761 input bias current increases greatly when the 3.8V common mode input voltage is exceeded, and I am seeing a 1.15V drop across the 1K series resistor, or 1.15 mA bias current with 5V applied to it. This is in direct conflict with Figure 4. "Input Bias vs Common Mode at 25°C" of the data sheet.

Is there something wrong with the Spice model. I'm assuming the actual device bias currents meet the 50pA limit as long as the supply voltage is not exceeded. Is this correct.

Thanks,

Doran Akutagawa

over 7 years ago

0 John Miller - Sensing over 7 years ago

TI__Mastermind 40295 points

Doran,

Would you please provide a schematic of the circuit you are simulating?

Regards,
John

0 Doran Akutagawa over 7 years ago in reply to John Miller - Sensing

Prodigy 50 points

Fuel_Flow_Sensor_Input_Schematic.pdfHi John. Here is my schematic.

0 John Miller - Sensing over 7 years ago in reply to Doran Akutagawa

TI__Mastermind 40295 points

Thank you Doran.
I will look at the model's behavior per your description.
I will try to give some feedback before the beginning of next week.
Regards,
John

0 John Miller - Sensing over 7 years ago in reply to John Miller - Sensing

TI__Mastermind 40295 points

Doran,

You can usually find the specs and features the model supports in the netlist text header.
Part of the LMV761 model's header appears below.

* THIS COMPARATOR MODEL FEATURES :
* LOW AND HIGH LEVEL OUTPUT VOLTAGE, QUIESCENT CURRENT VARIATION WITH POWER-SUPPLY,
* INPUT COMMON MODE RANGE, INPUT OFFSET VOLTAGE, PROPAGATION, DELAY TIME
* CHARACTERISTICS FOR OVERDRIVE VOLTAGE EQUAL TO 100mV, RISING AND FALLING TIME

The header doesn't mention IIB as one of the supported parameters, so the model may not have been designed to meet that spec.

As you noted, the recommended input common-mode range for normal operation is 0V to VCC-1.3V, so the 5V input is outside of normal operating range. The model is not usually designed to mimic the device outside of this range.

Regards,
John

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TINA/Spice/LMV761: Input Bias Current Above Common Mode Input Range