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Original question:

PGA280: Input switch leakage

PGA280: Will PGA280 have a Iq > 3mA?

Marsh Cai
Intellectual 2715 points
Part Number: PGA280

Hi Teams,

I noticed that with VCP-VSN, the max Iq is 3mA( see pic ). Whether there will be some operating condition in which PGA280 pulls a current > 3mA?

BRs,

Marsh

  • 0
    TI__Guru 54306 points

    HI Marsh,

    In general, the quiescent current, or IQ specification for instrumentation amplifiers specifies the current consumption of the device when the device is on a quiescent state, in other words, the device is turned on, but the device is provided zero volt differential input and placed in a light load or quiescent condition.  For the PGA280, the conditions are described at the top of the datasheet: input stage voltage supplies VSP = 15 V, VSN = –15, Gain = 1 V/V, with internal current  buffer (BUF) inactive, VCM = 0 V; and input common-mode, differential close to zero.

    Yes, the device can be placed in conditions where the VSP / VSN supplies will consume more current:

    - The PGA280 uses internal resistors to set the gain.  The quiescent current is increased by the current that passes through these resistors as the differential input signal voltage increases as the signal flows through these gain resistors. Under normal conditions, when the amplifier is not overloaded, the largest amplitude could increase the supply current by roughly ~±0.4 mA.

    - In overload conditions, the current through the supplies and inputs can increase:

    In a maximum overload condition, with gain of 128 V/V,  and each or the inputs connected to the opposite supply voltage -- essentially a large differential input voltage where the amplifier is overdriven well outside of the linear range -- a large current can be flow through the inputs. This is described on the datasheet on page 18.   As explained on the datasheet, external resistors in series with the input pins can help limit this current...

    - When the internal current buffers (BUF) are activated, for example, when providing the switching command of the multiplexer or internal switching of the multiplexer. 

    - In conditions where a fast input signal is applied, or a fast channel switching transient due to multiplexer switching is present.

    Please review in detail section 7 of the PGA280 datasheet, pages 15-22 may be of interest, where the datasheet provides an overview of overload conditions.

    Thank you and Regards,

    Luis