The AD8541 /AD8542/AD8544 are single, dual and quad rail-to-rail input and output, single-supply amplifiers. Low supply current and 1 MHz bandwidth. All are guaranteed to operate from a single 2.7 V supply and a 5 V supply. These devices provide 1MHz bandwidth with low current consumption of 45µA per amplifier

The AD8541/AD8542/AD8544 have very low input bias currents.

Used in integrators, photodiode amplifiers, piezoelectric sensors and other applications with high source impedance. Supply current is only 45µA per amplifier, making it ideal for battery-powered operation. Rail-to-rail inputs and outputs are useful for designers of buffering ASICs in single-supply systems. The AD8541/AD8542/AD8544 are optimized to maintain high gain at lower supply voltages making them useful for active filters and gain stages.

The AD8541/AD8542/AD8544 are specified over the industrial temperature range (-40°C to + 125 °C). The AD8541 is available in 5-lead SOT-23 , 5-lead SC70 and 8-lead SOIC packages. The AD8542 is available in 8-lead SOIC, 8-lead MSOP, and 8-lead TSSOP surface mount packages. The AD8544 is available in 14-lead narrow SOIC and 14-lead TSSOP surface mount packages. All MSOP, SC70 and SOT versions are available on tape and reel only.

feature

Single supply operation: 2.7 V to 5.5 V.

Low Supply Current: 45μA/Amplifier

Wide bandwidth: 1 MHz

no phase reversal

Low input current: 4 pA

unity and stability

Rail-to-rail input and output

Suitable for automotive applications

application

ASIC input or output amplifier

sensor interface

Piezo Transducer Amplifier

Medical equipment

mobile communication

Audio output

Portable System

Theory of Operation

The AD8541/AD8542/AD8544 amplifiers are general purpose operational amplifiers with improved performance. Performance has improved over previous amplifiers in several ways, including lower supply current bandwidth with 1MHz gain, higher output current and lower voltage for better performance. The lower supply current AD854x family of 1MHz gain bandwidth typically uses 45μA per amplifier, which is much lower than the 200 μA to 700 μA previously used to generate parts with similar performance. This makes the AD854x family a good choice for upgrading portable designs to extend battery life. Alternatively, additional functionality and performance can be added at the same current consumption. Higher output currents are typically 60µA short-circuit current at a single 5 V supply. The AD854x amplifiers can provide a 30 mA output current, source or sink, even at 1 V on the supply rail. Sampling and sinking are strong at lower voltages, giving 2.7 V for 15 mA and 18 mA for 3.0 V. Output higher currents, see the AD8531/AD8532/AD8534 devices have an output current of 250 mA. Information on these components is available from Analog Devices representatives and data sheets are available on .

Better Performance at Lower Voltage The AD854x family of devices are designed to provide better AC performance at 3.0 V and 2.7 V, higher than previously available parts. The typical gain-bandwidth product is close to 1 MHz at 2.7 V. Voltage gains of 2.7 V and 3.0 V are typically 500,000 . Phase margins typically exceed 60°C, making the part easy to work with.

The AD854x has a very high open-loop gain (especially for supply voltages below 4 V), which makes it suitable for all types of active filters. The figure below shows the classic dual-T notch filter design in the AD8542. Dual T notch is required for simplicity, low output impedance and minimal operating ampere usage. In fact, this notch filter can only be designed with one op amp if no Q adjustment is required. Just delete U2 as shown in Figure 2 below. However, this is a major disadvantage. The circuit topology ensures that all R and Cs are closely matched. Components must be closely matched or the notch frequency offset and drift cause the circuit to no longer attenuate at the ideal notch frequency. To achieve ideal performance, 1% or higher is usually required for component tolerances or special component screens. One way to desensitize a circuit to a component mismatch is to increase R2 relative to R1, which reduces Q. Lower Q increases attenuation over a wider frequency range but reduces attenuation at peak notch frequencies.

The figure below is an example of the AD8544 in a notch filter circuit. This Frequency Dependent Negative Resistance (FDNR) notch filter has fewer critical matching requirements than a double T notch because the Q of the FDNR is proportional to a single resistor R1. While matching component values are still important, it is also easier and/or cheaper to complete circuits in FDNR. For example, a double T notch uses three capacitors with two unique values, while an FDNR circuit uses only two capacitors, possibly with the same value. U3 is simply an addition of a buffer to reduce the output impedance of the circuit.

The comparator function is a common application for alternate operation of amplifiers in a four-in-one package. The figure below shows the comparator in a quarter standard overload detection application of the AD8544. Unlike many op amps, the AD854x family can double as a comparator because this op amp family has a rail-to-rail differential input range, rail-to-rail output, and an extremely high speed-to-power ratio. R2 is used to introduce hysteresis. The AD854x are used as time comparators with a 5µs propagation delay overload recovery time at 5 V and 5µs.

The AD854x family has very high impedance and input bias current is typically around 4 pA. This feature allows the AD854x op amps to be used in photodiode applications and other applications that require high input impedance. Note that the AD854x has a significant voltage offset that can be removed

Calibration via capacitive coupling or software. The figure below shows a photodiode or current measurement application. The feedback resistor is limited to 10MΩ to avoid excessive output offset. Furthermore, no resistor non-inverting input is required to cancel the bias current offset, since the bias current dependent output offset is not significant when comparing the contribution to the voltage offset. For best performance, follow standard high-impedance layout techniques.