Choosing a voltage regulator chip (IC) requires consideration of a series of key parameters, which directly determine whether it can operate reliably and efficiently in your circuit. Here are some core parameters for you to consider when selecting:
1、 Basic input/output parameters
Input voltage range:
Meaning: The input voltage range that an IC can withstand and operate normally.
Importance: It is necessary to ensure that the voltage provided by your power source (such as battery, adapter, front-end power source), including its fluctuation range (such as voltage drop during battery discharge, adapter ripple), falls completely within this range. Exceeding the range may result in chip damage or abnormal operation.
Output voltage:
Meaning: The stable voltage value that an IC can provide.
Importance:
Fixed output: Select a chip with a nominal value that perfectly matches the voltage you need (such as 3.3V, 5V, 12V).
Adjustable output: Check if its adjustable range can cover the voltage you need (such as 1.2V-15V). At the same time, attention should be paid to the adjustment method (external resistance voltage division).
Output voltage accuracy: The allowable deviation between the nominal output voltage and the actual output voltage (such as ± 1%, ± 2%, ± 3%). Applications that require high precision, such as precision sensors and ADC references, require the selection of high-precision models.
Output current capability:
Meaning: The maximum load current that an IC can continuously provide.
Importance: It is crucial! It must meet the maximum demand of your circuit load and leave a certain margin (usually 20% -50%). Not only should we consider the nominal continuous current, but also pay attention to:
Peak current capability: Does the load have an instantaneous high current demand (such as when the motor starts or the LED lights up)? Can the chip withstand brief peak currents without triggering protection or damage.
Heat dissipation limitation: The actual maximum output current is limited by the packaging and heat dissipation conditions of the chip (see "thermal parameters" below).
2、 Performance and efficiency parameters
Pressure difference:
Meaning: For linear regulators (especially LDOs), it refers to the minimum input-output voltage difference required to maintain a stable output voltage.
Importance: This is particularly crucial in applications where the input voltage is close to the output voltage (such as battery powered devices, where the battery voltage gradually decreases). Choose an LDO with a sufficiently low voltage difference to ensure stable output of the required voltage even at the lowest input voltage. For example, if the output is 3.3V and the input may be as low as 3.6V, an LDO with a voltage difference<0.3V needs to be selected.
Efficiency:
Meaning: Output power/Input power 100%.
Importance:
Switching regulator: High efficiency is its core advantage (usually 70% -95%+), which can significantly reduce heat generation and extend battery life. The efficiency value usually varies with the input voltage, output voltage, and load current, and it is necessary to refer to the efficiency curve chart in the data manual.
Linear regulator: Efficiency ≈ (Vout/Vin) 100%, low efficiency when there is a large input/output voltage difference (such as Vin=12V, Vout=3.3V, efficiency ≈ 27.5%), and most of the power is dissipated in the form of heat. The efficiency is higher when the pressure difference is small and Vin is close to Vout.
Static current/turn off current:
Static current: The current consumed by a chip during its own operation under no-load or light load conditions.
Turn off current: The current consumed when the chip is disabled (Enable pin pulled low).
Importance: Extremely important for battery powered equipment, directly affecting standby time. Choosing models with low static current (especially for LDO) and ultra-low turn off current can significantly reduce the standby power consumption of the system.
Load adjustment rate:
Meaning: The change in output voltage (usually expressed as a percentage or millivolt) when the load current changes while the input voltage and ambient temperature remain constant.
Importance: Reflecting the stability of the voltage regulator in response to load changes. The smaller the value, the better, indicating that load changes have little impact on the output voltage.
Linear adjustment rate:
Meaning: The change in output voltage (usually expressed as a percentage or millivolt) when the input voltage changes while the load current and ambient temperature remain constant.
Importance: Reflects the ability of a voltage regulator to suppress input voltage fluctuations. The smaller the value, the better, indicating that changes in input voltage have little impact on output voltage.
Output voltage noise&ripple suppression ratio:
Output voltage noise: The output noise generated by the chip itself (usually high-frequency noise, measured in uV RMS).
Ripple suppression ratio: The ability of linear regulators (especially LDOs) to suppress specific frequency ripples in the input voltage (in dB, the larger the value, the better).
Importance: It is crucial for noise sensitive circuits such as RF modules, high-precision ADC/DAC, and audio circuits. Low noise, high PSRR LDO needs to be selected. The switching regulator itself generates significant switching noise, requiring post LDO filtering or careful PCB layout.
3、 Protection and reliability parameters
Overcurrent protection:
Meaning: When the output current exceeds the safety threshold, the chip limits the current or shuts off the output to protect itself and the circuit.
Importance: To prevent permanent damage to the chip caused by load short circuit or overload. Common types of flow patterns include Fold, Constant Current, and Latch off.
Overheating protection:
Meaning: When the junction temperature of the chip exceeds the safety threshold, the output will be automatically turned off.
Importance: To prevent the chip from burning out due to overload or poor heat dissipation. After the chip cools down, it usually automatically recovers (Hiccup mode) or requires a restart.
Reverse input protection:
Meaning: To prevent damage to the chip caused by connecting the positive and negative poles of the power supply.
Importance: Provide additional protection in applications where misoperation may occur. Some chips are built-in and sometimes require external circuits to implement.
Working temperature range:
Meaning: The temperature range within which the silicon wafer (junction) inside the chip can operate normally.
Importance: It is necessary to ensure that the chip junction temperature does not exceed this range in your application environment, especially in high-temperature environments. The actual junction temperature is determined by the ambient temperature, power consumption, and thermal resistance.
4、 Physical and Interface Parameters
Encapsulation type:
Meaning: The physical appearance and pin arrangement of the chip (such as SOT-23, SOT-223, TO-220, DFN, QFN, BGA).
Importance:
PCB space: Small size applications (such as wearable devices) require the selection of small packages (SOT-23, DFN).
Heat dissipation capability: For high current applications, it is necessary to choose a package with strong heat dissipation capability (SOT-223 with heat sink, TO-220, DFN/QFN with heat dissipation pads at the bottom).
Production process: Confirm if the packaging is suitable for your soldering process (such as hand soldering, reflow soldering).
Thermal resistance:
Meaning: Refers to the resistance (in ℃/W) of heat transfer from the junction to the environment or case of the chip. Common parameters: Connected to the environment (θ JA), Connected to the shell (θ JC).
Importance: It is crucial for high-power linear regulators and switching regulators! Calculate whether the chip can operate safely without triggering overheating protection by combining the maximum allowable junction temperature (Tj max), ambient temperature (Ta), and chip power consumption (Pd):
`Tj = Ta + (Pd θJA)`。 It is necessary to ensure that Tj<Tj max. The θ JA value is highly dependent on PCB design and heat dissipation measures (copper foil area, heat sink).
Enable pins:
Meaning: The pin that controls the opening or closing of the chip (usually labeled as EN, SHDN).
Importance: Used for power timing control and low-power standby mode. Check if its logic level (high-level enable or low-level enable) is compatible with your control signal.
5、 Other considerations
Cost: While meeting all technical indicators, cost is certainly an important factor.
Usability: Does it require complex external compensation circuits? Is it easy to choose external components (inductors, capacitors)? Switching regulators are typically more complex in design than linear regulators.
Supplier and Supply: Choose mainstream suppliers and models with stable supply to avoid production downtime risks.
Application notes and reference designs: Supplier provided reference designs and application notes can greatly simplify the design process.
Summarize the selection logic
Clear requirements: Determine your input voltage range, required output voltage, maximum load current, working environment temperature, space limitations, power consumption requirements (especially battery powered), noise requirements, and cost budget.
Preliminary selection of voltage regulator types: Based on efficiency requirements (large voltage difference, high efficiency requirements, switch regulator; small voltage difference, high noise requirements, simple circuit, LDO) and current size, preliminary selection of voltage regulator types.
Parameter screening: In the initial selection of types, based on the requirements of step 1, focus on checking the input range, output voltage, output current capability (considering heat dissipation), voltage difference (LDO), efficiency (switch), static current, protection function, packaging thermal resistance, noise/PSRR (if necessary).
Detail confirmation: Refer to the data manual to confirm whether key parameters (such as load/linear adjustment rate, temperature range, enable logic, external component requirements) meet the requirements, and review typical application circuits and layout guidelines.
Simulation/Evaluation: If possible, use simulation tools provided by suppliers or purchase evaluation boards for actual testing and verification.
Remember: there is no "best" voltage regulator chip, only the one that is "most suitable" for your specific application needs. Carefully weighing various parameters and performing necessary calculations (especially power consumption and temperature rise) is the key to successfully designing a power supply.