When selecting resistors, in addition to the conventional parameters, the following parameters cannot be ignored.

1. Rated power

1/16W, the current blocked by the resistor turns into heat. A small resistor, if the heat cannot be dissipated in time, it will overheat and burn out.

When designing the hardware, it is necessary to calculate the current passing through the resistor, power = current square x resistance, and the power cannot be overrun.

2. Operating temperature and high temperature power constraints

Operating Temperature Range -55°C to +155°C, operating temperature -55 to +115°C, but in actual use, there is a power limit at high temperatures.

There is a curve of power and temperature at the back of the specification. After +70 degrees, the power needs to be reduced. When the extreme temperature of +155 degrees is reached, the power must be reduced to almost 0.

The reason is very simple, if it is still running at full power at high temperature, the temperature will rise higher and higher, and soon exceed the maximum temperature, and it will be burned.

3. Maximum working voltage

Maximum Working Voltage 50V, Maximum Overload Voltage 100V. They are the maximum working voltage and the maximum overload voltage respectively.

These two parameters are for the instantaneous peak voltage. If it continues at 50V, the rated power of the resistor has already been exceeded.

During normal design, the voltage should be controlled according to the actual working power so that it does not exceed the budget. If the circuit has glitches, you need to consider whether the peak is overrun.

4. Temperature drift

Temperature Coefficient, 10 Ω < R ≤ 10 MΩ ±100 ppm/°C.

The conversion is that for every degree of temperature change, the resistance value changes by one ten-thousandth. One ten-thousandth is not much, but if the operating temperature rises from -50°C to +50°C, the resistance value will change by 1%, which is equivalent to the 1% error of fine resistors.

If you need to use fine resistors in scenes with large temperature changes, you need to pay attention to this.

5. Taping method

When some engineers design, they will write the material code in a very specific way, accurate to the weaving method. Although there are three taping methods for 0402 resistors, the most commonly used ones are 7-inch disks, with 10k pieces per disk.

If it is written in a large volume, it may not be easy to buy, and it may not fit in the feeder of some chip factories.

6. Zero ohm resistor resistance

A 0 ohm resistor is not an absolute 0 ohm. The number 0 cannot be calculated, so the error and power are different from ordinary resistors.

The error is <0.05Ω, the power is not calculated, only the passing current is calculated. The 0402's 0 ohm resistor is rated at 1A.

When designing hardware, if a 0-ohm resistor is connected in series on the power line, be sure to calculate the current clearly.