How much current can an opamp source

Started by panfilero in sci.electronics.design8 years ago 2 replies

Hello, How do you figure out how much current an opamp can source from the datashe= et? I'm looking at this instrumentation amplifier...

Hello, How do you figure out how much current an opamp can source from the datashe= et? I'm looking at this instrumentation amplifier (datasheet link below) an= d the only things I find that relate to current is=20 link: http://www.ti.com/lit/ds/symlink/ina210.pdf Maximum Input Current to any pin is 5mA - which makes me think "any" includ= es power pins, which means this thing can't ...


opamp thermal errors

Started by John Larkin in sci.electronics.design6 years ago 26 replies

Opamps usually have specs for Vos, Vos tempco, Theta-ja, and max power dissipation. But nobody seems to talk about input offset as a...

Opamps usually have specs for Vos, Vos tempco, Theta-ja, and max power dissipation. But nobody seems to talk about input offset as a function of power dissipation. The concern here is thermoelectrics driven by temperature gradients, both inside the chip and on the PC board. We plan to use an ADA4638 opamp in a situation where we need to keep the max drift down around a few microvolts...


4quad supply

Started by John Larkin in sci.electronics.design6 years ago 71 replies

I'm designing a gadget that will need a bunch of 4-quadrant (+- voltage, source/sink) power supplies, DAC controlled, well bypassed on the...

I'm designing a gadget that will need a bunch of 4-quadrant (+- voltage, source/sink) power supplies, DAC controlled, well bypassed on the output. Range is roughly +-12 volts, 100 mA or so. So I need a power opamp that doesn't mind a capacitive load. We have TCA0372 in stock, a dual 40-volt, 1 amp opamp that costs 45 cents. Great part. I set one up. It really, really doesn't like cap...


nice fA opamp

Started by John Larkin in sci.electronics.design5 years ago 21 replies

http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overv iew Input current is typically 0.1 fA at...

http://www.analog.com/en/products/amplifiers/operational-amplifiers/ada4530-1.html#product-overv iew Input current is typically 0.1 fA at room temp. Noise and offset specs are impressive for a fA opamp. 0.1 fA is 625 electrons per second. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http:/


Yet Another Jellybean Opamp

Started by Allan Herriman in sci.electronics.design6 years ago 19 replies

Hi, I'm looking for a single supply jellybean opamp to meet the following requirements: V supply = 5.0V Vin (e.g. Vicm) 0V to 4V. Iin...

Hi, I'm looking for a single supply jellybean opamp to meet the following requirements: V supply = 5.0V Vin (e.g. Vicm) 0V to 4V. Iin +/- 100pA max. (prefer < 10pA) Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C, up to $2 for a dual, etc.. Here's the hard part: I want the Iin spec to apply over the Vin range *even when the supply voltage is zero*. Th


op-amp-controlled MOSFET cucrrent-source

Started by Winfield Hill in sci.electronics.design2 years ago 23 replies

Have you seen an analysis of the classic op-amp-controlled MOSFET current-source? I needed this for a design, plus I'd like to squeeze it...

Have you seen an analysis of the classic op-amp-controlled MOSFET current-source? I needed this for a design, plus I'd like to squeeze it into the x-Chapters, before the mid-August printing deadline. https://www.dropbox.com/s/nednxac2bykld8q/opamp-MOSFET_current-source.pdf?dl=1 In the formulas, I assume the opamp's output signal is controlled by Vin-Vs and R2 C2. I'm still ch...


cooling a SOT23 opamp

Started by John Larkin in sci.electronics.design6 years ago 7 replies

I'm designing this RTD/resistor simulator and it's convenient to use an LM8261 opamp in the output stage. The 8261 doesn't really current or...

I'm designing this RTD/resistor simulator and it's convenient to use an LM8261 opamp in the output stage. The 8261 doesn't really current or thermal limit (that's part of its charm) but I can limit power dissipation by adding a resistor in series with the output. We have the SOT23-5 parts in stock. But the SOT23 8261 is spec'd at 325 K/w, and I'd like to push it as much as possible. So...


Interfacing an OpAmp to a differential VCA

Started by Fibo in sci.electronics.design6 years ago 5 replies

Greeting, I'm having trouble interfacing an OpAmp (OPA378) to a Voltage Controlled Amplifier IC (VCA822). My signal coming out of the OPA378 is...

Greeting, I'm having trouble interfacing an OpAmp (OPA378) to a Voltage Controlled Amplifier IC (VCA822). My signal coming out of the OPA378 is riding on a 2.5V DC bias. I have a 22uF cap to cancel the 2.5V bias but with the cap there the input of the VCA822 floated to -3.3V. I then added a 12.7k resistor to ground after the cap which helped remove the -3.3V offset, but my output si


Using reverse biased zeners to correct for mosfett turnon voltage in a push pull stage

Started by Adrian Nievergelt in sci.electronics.design9 years ago 75 replies

Hi I'm trying to use mosfets for a push pull current gain stage on a dc coupled amplifier with opamp feedback. The feedback is supposed to...

Hi I'm trying to use mosfets for a push pull current gain stage on a dc coupled amplifier with opamp feedback. The feedback is supposed to operate in the high MHz range, so I'm looking for ways to statically reduce crossover distortion even before feedback to alleviate the load on the opamp and get a better THD. After looking around for a way which does not involve a lot of components...


OpAmp Output DeadBand

Started by Jim Thompson in sci.electronics.design5 years ago 2 replies

Turns out I was making things too difficult with my nice LOG(COSH(x)) "smoother" when it comes to modeling OpAmp Output DeadBand. Examination...

Turns out I was making things too difficult with my nice LOG(COSH(x)) "smoother" when it comes to modeling OpAmp Output DeadBand. Examination of the LOG(COSH(x)) solution puzzled me, exhibiting some unexpected instability. Last night, as I tossed and tumbled, fearing a Clinton Supreme Court disaster when I awoke, one nightmare suggested this downright trivial solution...


Stiff osc source on the reflective properties of an ultrasonic transducer

Started by Dirk Bruere at NeoPax in sci.electronics.design7 years ago 8 replies

I have an ultrasonic transducer that I am driving in pulsed mode from a fai= rly stiff opamp source. The result being that when V=3DGND after...

I have an ultrasonic transducer that I am driving in pulsed mode from a fai= rly stiff opamp source. The result being that when V=3DGND after transmitti= ng the pulse there is almost no trace of ringing on the transducers Tx circ= uit as the opamp feedback suppresses it. The question becomes whether the face of the transducer will still efficien= tly reflect other ultrasound pulse impinging...


PSpice worst case simulation

Started by Joerg in sci.electronics.design11 years ago 36 replies

Hi Folks, Reached an end of a rope here: How do you make a worst case simulation in PSpice (or even Monte Carlo for that matter) properly find...

Hi Folks, Reached an end of a rope here: How do you make a worst case simulation in PSpice (or even Monte Carlo for that matter) properly find the extremes for an opamp offset voltage and input bias current? For example, for the opamp we have: VOS: Offset voltage VOS_DIST: Distribution, I assume VOS_NTOL: What gets entered here? VOS_PTOL: ... and here? If I enter 7mV or whatever f...


OpAmp input protection against ringing

Started by Nils in sci.electronics.design7 years ago 15 replies

Say I have a high impedance signal that is connected to an OpAmp input. My signal will on occasion go above the rails due to ringing. I...

Say I have a high impedance signal that is connected to an OpAmp input. My signal will on occasion go above the rails due to ringing. I expect 10V spikes against a 5V rails voltage worst case. I will leave the common mode input range of the amp, but I an okay with that. The voltage at the input also does not really go above the rail because it will get clamped by the ESD protection diodes. ...


Virtual ground topology

Started by bitrex in sci.electronics.design7 years ago 4 replies

I recently saw a single supply opamp circuit that had what looked like an interesting virtual ground topology. The incoming signal needed...

I recently saw a single supply opamp circuit that had what looked like an interesting virtual ground topology. The incoming signal needed to be differential for the rest of the circuit, so there's an opamp phase splitter arranged with a voltage divider on one of the noninvering inputs such that the outputs of the phase splitter center at half the supply at quiescense. Equal value...


new (to me) all-pass circuit

Started by John Larkin in sci.electronics.design3 years ago 27 replies

It occurred to me that, in the conventional opamp all-pass 90 degree phase shifter...

It occurred to me that, in the conventional opamp all-pass 90 degree phase shifter circuit, https://www.dropbox.com/s/nfwd32p3z61g15y/90_degree.JPG?raw=1 a fast signal passes through all the opamp stages, so all the amps have to be fast. In this one, https://www.dropbox.com/s/rulyvlt072k49cp/New_All-Pass_1.jpg?raw=1 the fast signals just rip through the big caps in the slow stage...


DDR3L vref opamp

Started by acd in sci.electronics.design10 years ago 2 replies

I need to generate the reference voltage for a DDR3 design separately, i.e. I cannot use an integrated solution for VDDQ/VTT/Vref. Following...

I need to generate the reference voltage for a DDR3 design separately, i.e. I cannot use an integrated solution for VDDQ/VTT/Vref. Following the recommendations in the EE-Times article "Powering DDR memory and SSTL logic" by Peter James > http://www.eetimes.com/design/memory-design/4216279/Powering-DDR-memory-and-SSTL-logic it is advisable to use an OpAmp for Vref generation. In my


AN: Basic OpAmp Output Stage Spice Model Posted to my Website

Started by Jim Thompson in sci.electronics.design6 years ago 6 replies

Basic OpAmp Output Stage Spice Model... Passes load current to proper Voltage Rail... No Voltage Bounds, No Current Limit, Yet ;-) See... ...

Basic OpAmp Output Stage Spice Model... Passes load current to proper Voltage Rail... No Voltage Bounds, No Current Limit, Yet ;-) See... BasicOpAmpOutputStage.png on the Device Models & Subcircuits Page of my website. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations ...


how to tell if opamp is unity gain stable

Started by panfilero in sci.electronics.design9 years ago 19 replies

hello, does anyone know how to tell if an opamp is unity gain stable? My guess is= to check out the open loop phase margin and make sure...

hello, does anyone know how to tell if an opamp is unity gain stable? My guess is= to check out the open loop phase margin and make sure it's over... I dunno= ... about 30 degrees... is this it? Don't most opamps have decent open loo= p phase margin? Should I be saying open loop phase margin or does just say= ing phase margin imply that you are talking about the open loop phase margi= ...


opamp clamp

Started by John Larkin in sci.electronics.design7 years ago 127 replies

How's this? ftp://66.117.156.8/Clamp.JPG I need clean clipping, and can't overdrive some downstream mux's that run off +5 and...

How's this? ftp://66.117.156.8/Clamp.JPG I need clean clipping, and can't overdrive some downstream mux's that run off +5 and ground. John


Power supply games

Started by George Herold in sci.electronics.design9 years ago 15 replies

Hi guys, Doing a simple circuit. V(+)------+------+ 20-30V _ | ^ LED|\| +----|+\ | | >...

Hi guys, Doing a simple circuit. V(+)------+------+ 20-30V _ | ^ LED|\| +----|+\ | | > -+--out R +-|-/ | | | |/| | | +---)--+ GND | Vminus The LED is a GaP one that avalanches at ~25V* R is 100k I need V minus to be 3 or so volts below ground. (V+ to the opamp will get the us