Why is the reference voltage source far less accurate than the data sheet? In many cases it is due to improper use. If the reference is used improperly, it will cause trouble. There are three common misuses that can cause such problems: insufficient margin, incorrect load, and reverse output current. The first two items are generally mentioned in the data sheet and are easy to avoid; the third item is rarely mentioned and may lead to problems that are difficult to diagnose. Most reference sources have input, output, and ground terminals—the output terminals maintain precise voltage above ground over a wide range of input voltages and load currents. However, if the difference between the input and output voltages is too small, the accuracy of the output voltage decreases. While some devices do work at slightly lower voltages (but have poor performance), they are not safe. Working within full precision is important to get the specified accuracy. Most voltage references have a current-limited output and are therefore not subject to short-circuit damage. If used to supply too much current, the output voltage will drop—the effect will occur from well below this point, causing the device to enter full current limit mode. Check the maximum load current and output current in the data sheet to see where the accuracy begins to drop (usually on the graph). Another cause of incorrectly loading a reference is the use of an incorrect capacitive load—many (or even most) of the reference can be stabilized under any capacitive load, especially some low dropout (LDO1) types. Oscillate with too much or too little load capacitance, even in two cases! If this happens, the output voltage will not be adjusted correctly. The RTFDS2 or experiment ensures that the capacitance range encountered by the reference in the application does not cause this oscillation - remember that in a complex system, multiple subsystems may share a single reference, but you are not responsible for all subsystems. design. A few weeks ago, I encountered a third problem myself. At the time, I was designing two very simple low-power battery management systems. It was also simple to define the resistance equation for the voltage detection part, but both systems could not work as long as they were close to the correct voltage. It took me a few days to discover that the reference voltage source in these devices drives the non-inverting input of the op amp, while the positive feedback configuration is comparator 3 with a defined hysteresis. When the op amp outputs a high level, the feedback resistor drives approximately 6 μA of current back to the reference output. I am using the ADR291 and ADR292 voltage references, and the “Simplified Schematic†display output in these device data sheets is driven by a similar op amp structure. The op amp can perform source current and sink current operation at the output, and I subconsciously think that these reference voltage sources are the same. But in fact, it's not! A reverse current of around 5 μA is sufficient to increase the output voltage. The data sheet does not alert this question at all. Load regulation is defined over the 0 mA to 5 mA output current range, which means that large reverse currents (tens or hundreds of μA!) can cause problems, but this does not mean that very small reverse currents are not safe. Flow through resistor chains R1, R2, and R3 (as shown in the simplified schematic). Once you understand this problem, it is very easy to avoid. Many references have the ability to sink current and source current. If the data sheet defines the output voltage for the ±X mA output current, this is the case. Alternatively, if it is known that current will flow to the output of the reference, the output can be grounded through a small enough resistor to sink all current. This ensures that the current in the reference output always flows out of the device and the problem is solved. references 1 The low dropout reference (or linear regulator) uses an output stage that allows the input voltage to be very close (several hundred mV or even closer) to regulate the output voltage without loss of output voltage accuracy. 2 RTFDS = Read easy-to-understand data sheets. 3 Be cautious when using an op amp as a comparator, as there may be problems in Answer 11 and this problem is expanding. The op amps I used in these two designs have been carefully chosen to avoid such problems. Face Mask,Medical Face Mask,Disposable Face Mask,Disposable Protective Mask Ningbo Anbo United Electric Appliance Co.,ltd , https://www.airfryerfactory.com