ADR34xx Micro-Power, High-Accuracy Voltage References
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To introduce ADR34xx high accuracy voltage references, their key features and application circuits.
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ADR34xx Micro-Power, High-Accuracy Voltage References
- 10. Basic Voltage Reference Connection Improving transient response Improving stability and help filter out high frequency noise Reducing high frequency supply noise
- 11. Product Offerings Part Number Vout Initial Accuracy (%) Ref Out TC (ppm/C) 0.1-10 Hz Noise (µV p-p) Ref Output Current (mA) Supply Voltage Range (V) ADR3412 1.2 0.1 8 8 10 2.5 to 5.5 ADR3420 2.048 0.1 8 15 10 2.3 to 5.5 ADR3425 2.5 0.1 2.5 18 10 +2.7 to +5.5 ADR3430 3 0.1 2.5 22 10 +3.2 to +5.5 ADR3433 3.3 0.1 8 25 10 - ADR3440 4.096 0.1 2.5 29 10 +4.3 to +5.5 ADR3450 5 0.1 2.5 35 10 +5.2 to +5.5
- 12. Application Example 1 – Negative Reference Virtual GND
- 13. Application Example 2 – Bipolar Output Reference
- 14. Application Example 3 – Boosted Output Current Reference
Editor's Notes
- Welcome to the training module on ADR34xx Micro-Power, High-Accuracy Voltage References.
- This training module will To introduce ADR34xx high accuracy voltage references, their key features and application circuits.
- Although they are not new technologies, voltage references have a major impact on the performance and accuracy of analog systems. They are used as a precise analog meter stick against which the incoming analog signal is compared or the outgoing analog signal is generated. The standard reference ICs are often available in series, or three terminal form - VIN, Common, and Vout. The series types have the potential advantages of lower and more stable quiescent current, standard pre-trimmed output voltages, and relatively high output current without accuracy loss. However, shunt, or two-terminal references, like diode references, has more flexible regarding operating polarity, but more restrictive as to loading.
- Here we discuss some key performance parameters. Tolerance indicates the accuracy of the reference. It is a percent of the nominal value, which is not even a unit. Temperature drift or drift due to aging may be an even greater problem than absolute accuracy. The initial error can always be trimmed, but compensating for drift is difficult. Noise in voltage references is often overlooked, but it can be very important in system design. Load sensitivity (or output impedance) is usually specified in μV/mA of load current, or mΩ, or ppm/mA. It is a measure of the change in output voltage due to a change in input voltage. Noise is an instantaneous change in the reference voltage. It is generally specified on data sheets, but system designers frequently ignore the specification and assume that voltage references do not contribute to system noise.
- The ADR34xx series of voltage references are low cost, low power, high precision CMOS voltage references, featuring ±0.1% initial accuracy, low operating current, and low output noise in a small SOT-23 package. For high accuracy, output voltage and temperature coefficient are trimmed digitally during final assembly using Analog Devices, patented DigiTrim® technology. Stability and system reliability are further improved by the low output voltage hysteresis of the device and low long-term output voltage drift. Furthermore, the low operating current of the device (100 μA maximum) facilitates usage in low power devices, and its low output noise helps maintain signal integrity in critical signal processing systems. These CMOS are available in a wide range of output voltages, all of which are specified over the industrial temperature range of −40°C to +125°C.
- Like all bandgap references, the ADR34xx references combine two voltages of opposite temperature coefficients (TC) to create an output voltage that is nearly independent of ambient temperature. However, unlike traditional bandgap voltage references, the temperature-independent voltage of the references are arranged to be the base-emitter voltage, V BE , of a bipolar transistor at room temperature rather than the V BE extrapolated to 0 K (the V BE of bipolar transistor at 0 K is approximately V G0 , the bandgap voltage of silicon). A corresponding positive-TC voltage is then added to the V BE voltage to compensate for its negative TC. The band gap voltage (VBG) is then buffered and amplified to produce stable output voltages.
- The TC relates the change in output voltage to the change in ambient temperature of the device, as normalized by the output voltage at 25°C. The ADR34xx family leverages Analog Devices patented DigiTrim technology to achieve low temperature coefficient (TC). Normally the reference circuit maintains an internal voltage source that has a positive temperature coefficient and another internal voltage source that has a negative temperature coefficient. By summing the two together, the temperature dependence can be canceled. In ADR34xx devices, the temperature-independent voltage of the references are arranged to be the base-emitter voltage at the room temperature and a corresponding positive-TC voltage is then added to the VBE voltage to compensate for its negative TC.
- One of the key parameters of the ADR34xx references is long-term stability. Regardless of output voltage, internal testing during development showed a typical drift of approximately 30ppm after 1000 hours of continuous, non-loaded operation in a 50°C environment. It is important to understand that long-term stability is not guaranteed by design and that the output from the device may shift beyond the typical 30 ppm specification at any time, especially during the first 200 hours of operation. For systems that require highly stable output voltages over long periods of time, the designer should consider burning in the devices prior to use to minimize the amount of output drift exhibited by the reference over time.
- Load regulation refers to the change in output voltage in response to a given change in load current and is expressed in μV per mA, ppm per mA, or ohms of dc output resistance. This parameter is important if the reference load current changes while the reference is operating. The parameter is a DC parameter and is specified typically at DC. It accounts for the effects of self-heating. In general, load regulation deteriorates inversely with the rate at which the load current changes. Output capacitors are recommended to stabilize the output voltage in applications subject to load-current transients.
- The circuit shown in the figure illustrates the basic configuration for the ADR34xx references. A 1 μF to 10 μF electrolytic or ceramic capacitor can be connected to the input to improve transient response in applications where the supply voltage may fluctuate. An additional 0.1 μF ceramic capacitor should be connected in parallel to reduce high frequency supply noise. A ceramic capacitor of at least a 0.1 μF must be connected to the output to improve stability and help filter out high frequency noise.
- Here we list all product offerings under ADR34xx family. This series references are available in seven fixed-output-voltage options, from 1.2 V to 5.0 V, feature 0.1% max initial error and 8-ppm/°C max drift. Able to source 10 mA and sink 3 mA, they specify 250-mV max dropout voltage with a 2-mA load. Operating from a 2.3-V to 5.5-V supply, the ADR34xx draw 85 μA max when enabled and 5 μA max in shutdown mode.
- This diagram shows how to connect the ADR3450 and a standard CMOS op amp, such as the AD8663, to provide a negative reference voltage. This configuration provides two main advantages: first, it only requires two devices and, therefore, does not require excessive board space; second, and more importantly, it does not require any external resistors, meaning that the performance of this circuit does not rely on choosing expensive parts with low temperature coefficients to ensure accuracy. In this configuration, the VOUT pins of the reference sit at virtual ground, and the negative reference voltage and load current are taken directly from the output of the operational amplifier.
- This figure shows a bipolar reference configuration. By connecting the output of the ADR3450 to the inverting terminal of an operational amplifier, it is possible to obtain both positive and negative reference voltages. R1 and R2 must be matched as closely as possible to ensure minimal difference between the negative and positive outputs. Resistors with low temperature coefficients must also be used if the circuit is used in environments with large temperature swings; otherwise, a voltage difference develops between the two outputs as the ambient temperature changes.
- The figure shows a configuration for obtaining higher current drive capability from the ADR34xx references without sacrificing accuracy. The op amp regulates the current flow through the MOSFET until VOUT equals the output voltage of the reference; current is then drawn directly from VIN instead of from the reference itself, allowing increased current drive capability.
- Thank you for taking the time to view this presentation on “ ADR34xx Micro-Power, High-Accuracy Voltage References” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link right beside the play button on the TechCast portal, or simply call our sales hotline. For more technical information you may either visit the Analog Devices site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit element14 e-community to post your questions.