Calculating Power Supply Resistance for Chips

When calculating the power supply resistance for chips, multiple factors need to be considered, including the resistance value, power, package form, as well as specific circuit requirements and chip specifications. Here are some basic steps and precautions for calculating the power supply resistance of chips:

Determining the Resistance Value

1. Consult the Chip Datasheet:
   • The datasheet of the chip usually provides specific requirements or recommended values for the power supply resistance.
   • Carefully read the datasheet and find the section related to the power supply resistance to understand the required resistance range.
2. Use Formulas for Calculation:
   • If the datasheet provides a calculation formula, such as the adjustable LDO output voltage formula Vout = Vref × (1 + R2/R1), the required resistance values can be calculated using this formula.
   • In this formula, Vout is the output voltage, Vref is the reference voltage, and R1 and R2 are the power supply resistances. By adjusting the resistance values of R1 and R2, the desired output voltage can be obtained.
3. Consider Current and Voltage Requirements:
   • Select an appropriate resistance value based on the chip's power supply current and voltage requirements to ensure circuit stability and reliability.
   • The resistance value should be small enough to provide sufficient current to the chip, but large enough to avoid excessive power consumption and heating.

Determining Power and Package Form of the Resistance

1. Calculate Power:
   • According to Ohm's law, the power P of the resistance is P = I²R, where I is the current flowing through the resistance and R is the resistance value.
   • Ensure that the power of the selected resistance is greater than or equal to the calculated power to prevent overheating and damage to the resistance.
2. Select Package Form:
   • Choose an appropriate resistance package form based on the layout and size requirements of the circuit board.
   • Common resistance package forms include 0402, 0603, 0805, etc. The smaller the package, the less space it occupies on the circuit board.

Precautions

1. Accuracy and Stability:
   • Select resistors with high accuracy and stability to ensure circuit stability and accuracy.
   • Especially for circuits that require precise control of voltage and current, high-precision and low-temperature coefficient resistors should be selected.
2. Heat Dissipation:
   • If the power consumption of the resistance is large, heat dissipation issues need to be considered.
   • Heat sinks or fans can be used as heat dissipation measures to reduce the temperature of the resistance and improve its reliability.
3. Safety Margin:
   • When selecting resistors, a certain safety margin should be considered to account for uncertainties and changes in the circuit.
   • Typically, the resistance value, power, and package form of the resistor should have a certain margin to ensure circuit stability and reliability.