This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

High Iq for OPA 4241

Other Parts Discussed in Thread: OPA4241

I am using OPA 4241 on a low power battery operated application.

When I connect VCC = 5 volts and VEE = 0 volt or -5 Volt I measure a DC current of 800uA  which is much more than expected.

According to the datasheet Iq=~25uA so for 4 amplifiers it should be around 100uA.

The current remains high either when the inputs are floating or tied to ground .

There is no load at the output of the amplifiers.

Is there an explanation for the high current ? 

  • Nir,

    What circuit configuration are you using and what is your input voltage? Do you have any loads? You may not use OPA4241 in open-loop configuration or let the inputs floating since this would result in them rising toward a positive rail thus violating the input common-mode voltage range of (V-)-0.2V<Vcm<(V+)-0.8V as well as exceeding the allowable output swing - see PDS table below.  Such conditions would also result in the saturation of the output stage as thus significant increase in the quiescent current.

  • Hi,
    Thanks for your reply.
    Regarding the un-connected inputs - I understand.
    I have no load at all.

    My "grounded" configuration is : Pins 2,4,5,6,9,10,12,13 : GND
    Pin 4 : Vcc = 5 Volts
    Pin 11 : VEE = 0 Volt.
    Is there a VCM violation when I use it this way? Is there another violation ?
  • Nir,

    I assume you meant to say 2,3,5,6,9,10,12,13 are at GND (since pin 4 is at 5V).  Shorting the inputs of any amplifier forces the internal input offset voltage, Vos, to be gained up by the open-loop gain, AOL, of the amplifier driving the output to one of the rails.

    For example, since OPA4241 typical Vos is +/-50uV (0.00005V) and typical AOL is 120dB or equivalent of G=1,000,000 (see below), shorting the input together drives the output to: Vout=AOL*Vos=1,0000,000*(+/-0.00005V)=+/-50V; thus depending on the polarity of the offset voltage this attempts to drive the output to either a positive or negative rail (in your case to 0V or 5V); such condition in bipolar transistor output stages like the one used in OPA4241 results in a sharp decrease in the output transistor β gain and thus a large increase in the quiescent current, IQ.

    Therefore, in your configuration you violate the output voltage linear swing, Vout, which is defined in the OPA4241 datasheet AOL condition column (see below) in case of 0V to 5V supplies to be:  100mV<Vout<4.9V for RL=100K and 0.2V<Vout<4.8V for RL=10k.

    A broader point here is that Op Amps are NOT meant to be used in an open-loop configuration like what you attempt to do in your application since this almost always result in the output being driven beyond its rails - thus you should always use a negative feedback to set the close-loop gain to a desired value and by doing so control the output voltage.

    What you need to do in you circuit is to place each of the op amps in a close-loop configuration (for example a follower, G=1, configuration shown below) and make sure to drive the input (by choosing R1 and R2) in such a way so the input common-mode AND output voltage range are not violated.