Zero-ohm resistors, also known as jumper resistors, are a kind of special-purpose resistors. The zero-ohm resistor is not a real resistance value of zero (that is what superconductors do). The chip resistance also has the index of error accuracy. Fenghua Hi-Tech has three accuracy levels for 0Ω chip resistors, namely F file (≤10mΩ), G file (≤20mΩ), and J file (≤50mΩ). That is to say, the resistance value of 0 ohm is less than or equal to 50mΩ.
We often see a resistance of 0 ohms in the circuit. For novices, they are often confused: since it is a resistance of 0 ohms, that is a wire, why should it be installed? Is there such a resistor on the market In fact, a resistance of 0 ohms is quite useful. There are probably the following functions:
①Use as a jumper. This is both beautiful and easy to install.
②In mixed circuits such as digital and analog, two grounds are often required to be separated and connected at a single point. We can connect these two grounds with a 0 ohm resistor instead of directly connecting them together. The advantage of this is that the ground wire is divided into two networks, which will be much more convenient when processing copper and other large areas. As a side note, in such cases, inductance or magnetic beads are sometimes used for connection.
③Used as a fuse. Due to the large fusing current of the traces on the PCB, it is difficult to fuse if faults such as short-circuit and over-current occur, which may lead to greater accidents. Because the current resistance capability of the 0 ohm resistor is relatively weak (in fact, the 0 ohm resistor also has a certain resistance, but it is only very small), the 0 ohm resistor is fused first when overcurrent, thereby disconnecting the circuit and preventing a larger accident happened. Sometimes small resistors with a resistance of a few tenths or a few ohms are used as fuses. However, it is not recommended to use it in this way, but some manufacturers will use it in order to save costs.
④The place reserved for debugging. You can decide whether to install or other values according to your needs. Sometimes it will be marked with *, which means that it is determined by debugging.
⑤Used as a configuration circuit. This function is similar to the jumper or DIP switch, but fixed by welding, so as to avoid ordinary users from modifying the configuration at will. By installing resistors in different locations, you can change the function of the circuit or set the address.
The specifications of 0 ohm resistors are generally divided by power, such as 1/8 watt, 1/4 watt and so on.
(Different package 0Ω resistance flow capacity)
Package, rated current (maximum overload current)
0201, 0.5A (1A)
0402, 1A (2A)
0603, 1A (3A)
0805, 2A (5A)
1206, 2A (5A)
1210, 2A (5A)
1812, 2A (5A)
2010, 2A (5A)
2512, 2A (5A)
Single point grounding of analog ground and digital ground
As long as it is the ground, it will eventually be received together and then into the earth. If it is not connected, it is “floating ground”, there is a pressure difference, and it is easy to accumulate charge and cause static electricity. The ground is referenced to the zero potential, and all voltages are derived from the reference ground. The ground standards must be consistent, so the various grounds should be shorted together. It is believed that the earth can absorb all electric charges and maintain stability at all times, which is the ultimate reference point of the earth. Although some boards are not connected to the ground, the power plant is connected to the ground, and the power on the board will eventually return to the power plant and enter the ground. If the analog ground and digital ground are directly connected in a large area, it will cause mutual interference. The reason is not short-circuiting and wrong. If we use the following four methods to solve this problem:
- Connect with magnetic beads;
- Connect with a capacitor;
- Connect with inductance;
- Connect with 0 ohm resistor.
Can we achieve our desired effect?
The equivalent circuit of the magnetic bead is equivalent to a band stop wave limiter, which only has a significant effect on suppressing the noise at a certain frequency point. It is necessary to estimate the noise frequency in advance in order to select the appropriate model. The magnetic beads are not suitable for situations where the frequency is uncertain or unpredictable.
Capacitors are connected directly, causing floating ground.
The inductor has a large volume, many stray parameters, and is unstable.
0 ohm resistor connection, impedance controllable range, impedance is low enough, there will be no problems such as resonance frequency.