Basic Knowledge of Voltage Regulator（4/4）
Types and Application Examples
Increasing Power Dissipation Capacity by a Package
The power dissipation of a linear regulator is determined by the relationship among input voltage, output voltage, and output current.
Power Dissipation (Pd) = (Input Voltage – Output Voltage) x Output Current
It is important how effectively the package can release heat and prevent from heating in actual devices. USP package is one of the packages that can effectively release heat. On the backside of the package, the metal die which the ICs silicon is on is exposed, and heat is released to the PC board through the die. [Picture 2]
[Picture 2] Heat Dissipation Pad on the Backside of USP-6C
[Figure 6] PC Board used for the Evaluation of Heat Dissipation
[Graph 14] Heat Dissipation Characteristics: USP-6C Package
The output voltage is fixed in the most of CMOS linear regulators, and is not adjustable by external components such as a resistor [Figure 7].
Instead, in most cases, the output voltages are set in 0.1 or 0.05V increments precisely by laser-trimming technology. This is because CMOS process cannot generate a stable reference voltage source in its structure like a bandgap reference for bipolar transistors [See Note 1]. Voltage is set freely and voltage accuracy is stabilized by trimming off tolerance of the internal reference voltage source and the output voltage preset resistor [Figure 7]. The output voltage accuracy is generally ±2%, and ±1% for high-precision versions. There are also products of which output voltage accuracy within their operating temperature range is strictly defined.
[Note 1] Bandgap Reference
The circuit to obtain stable voltage in certain temperature by using energy bandgaps and resistance of a bipolar transistor, utilizing the antithetic nature of the voltage temperature coefficient relative to the rated temperature.
[Figure 7] The Image of Tolerance Compensation by Lazar Trimming Technology
Trimming size is determined based on the measured value of each chip to improve accuracy.
Which Voltage Is Accessible When Small Quantity Is Needed?
Since most CMOS regulators cannot adjust their output voltage externally, you need to check stock availability before buying it. Popular output voltages such as 5.0V, 3.3V, 3.0V, 2.8V, 1.8V should be more accessible than other.
The Trend of Development in Future
The miniaturization of CMOS process LSI is evolving year by year, and recently even 22nm rule is about to be mass produced. Extreme miniaturization is not always effective for power ICs like linear regulators, as a certain level of input power source voltage is necessary. Still, miniaturization is what CMOS is good at. Utilizing the technology, for instance, a new regulator that can output 1.2V/2A with the input voltage of 1.7V using 0.25μm or 0.35μm should be available in near future. Further improvements of high voltage regulators using various CMOS technologies are also expected. Such positive prediction is possible because CMOS process have a large accumulation of technologies and experiences in the development of LSI and memories. In future, CMOS linear regulators are expected to be used in a wider range of fields including automotives.