LDO Can Disperse PCB Heat Without Radiator

- Aug 04, 2018-

The problem of local hot spots on PCB is difficult to solve.Switching voltage stabilizer and charging pump generate less heat because of the switching topology.On the other hand, LDO generates more heat depending on the input to output voltage difference, output current, and packaging thermal characteristics.The design of surface mounted circuit boards evolved with more sophisticated manufacturing methods, multilayer PCB, smaller and thinner vertical components, and thinner IC packaging.Traditionally, linear or switching voltage regulators with power packs and radiators have been used in such systems when large currents are required.Unfortunately, the use of radiators makes the circuit boards more complex, expensive and difficult to assemble than the full-surface mount solution.Until now, the power consumption of LDO has been limited to about 2W due to the heat dissipation limitation of IC on the circuit board.Typical problems with using linear voltage regulators in such applications include:
• large output current cannot be obtained in the surface mount system.Parallel connection allows for greater output current and dissipation of power to a larger area in a surface mount system.Otherwise, when the voltage regulator is attached to the PC board surface, the high peak temperature will limit the power consumption to a maximum of 2W.
• cannot adjust the output voltage below 1.2v.The new high performance digital circuit requires a voltage below 1.2v.
• it is not possible to achieve optimal use in all surface mount systems.Surface mount assemblies and high density circuit boards preclude the possibility of radiators (height limits, etc.) for older linear regulators.
High performance switching voltage stabilizers fill these gaps, providing low output voltage and minimal heat accumulation.The drawback is the increased cost and complexity.Now, however, the improved design approach has given the low-voltage differential stabilizer a significant and growing share of this application.
A new architectural ━ ━ can parallel 3 a NPN"
The LT3083 is a 3A LDO that can be easily connected in parallel to disperse heat and provide a large output current.The device adopts current source reference and high power voltage follower.The following input of the voltage regulator is connected together (SET pin). Only a small section of PC wire is used as the ballast to realize equal output current and disperse heat between multiple voltage regulators, so that the output current of several amperes can be realized in the whole surface mounting system without radiators.
LT3083 can achieve unparalleled in any output voltage of the stability of plus or minus 2 mv. This device has a 1.2 V TO 18 V (DD - Pak and the TO - 220 encapsulation) wide input voltage ability, when using a separate bias power supply, the full load current differential pressure is 310 mv. Only the output voltage can be a single resistor adjustment and programming, ranging from 0 V TO 17.5 V voltage range wide,And has fine tune the built-in 50 (including A current benchmark reached the high accuracy of plus or minus 1%. Because this device adopts A unity-gain follower voltage architecture, so the stability and the output noise (40 (including VRMS) is not affected by the output voltage. The output of the big electric current, the width of the input and output voltage range, the voltage and the load regulation strictly, high ripple suppression, few external components and parallel ability make LT3083 multi-track system is very suitable for modern large current.

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Optional to meet minimum load current requirements of 1mA
LT3083 USES a variety of heat resistant and enhanced surface mount compatible packaging, including flat (0.75mm) 12 lead 4mm x 4mm DFN and 16 lead heat resistant and enhanced TSSOP.In surface mount applications, these two packages allow 2W dissipation without a radiator.The device also USES a 5-lead TO-220 and DD-Pak power pack TO install on the radiator, allowing greater power dissipation.
Advantages of large reference current
The SET pin current of LT3083 is 50uA (the former is 10uA) compared with the similar devices introduced before it (LT3080 / LT3082 / LT3085), so it is not sensitive to circuit board leakage current that affects the actual output voltage.For the given leakage current from SET to GND caused by improper circuit board cleaning and/or contamination, a small percentage error will be presented: 50uA to 10uA.In addition, for a given output voltage, the RSET resistor has a small resistance value (it is a low impedance node that makes it difficult for stray signals to be coupled in), thus producing a more stable output.The SET pin current of the device is also highly accurate (an initial accuracy of 1%) and stable throughout the temperature range

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This new generation of NPN LDO series is suitable for various innovative circuit schemes, two of which are current source and parallel configuration.

Compared with other analog circuits, current source design seems relatively easy on the surface, but it is actually more complex.Although high quality voltage sources are common, they were not seen as component current sources until LRT introduced LT3092.Configuring LT3083 as a current source provides many of the capabilities that LT3092 provides, and the current source also provides much higher power currents (3A over 200mA), as shown in figure 3 for more information.In addition, this current source eliminates many problems in the traditional vertical scheme, especially when it is expected to have high accuracy and stability with temperature change.

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Direct parallel IC dispersion heat

Compared with a single IC, a voltage regulator in parallel on a PC board can disperse heat to help keep the peak temperature of the circuit board within an acceptable range and increase the maximum output current.Traditionally, this has required an external operational amplifier and several resistors to achieve the best balanced current parity.The LT3083, on the other hand, can be easily and directly connected in parallel (that is, without an external operational amplifier) to disperse heat and provide a large output current, and its output can still be regulated by a single resistor.This allows full surface mount solutions to be implemented using LT3083, whereas previously in such solutions switching voltage regulators were used or decided to use linear regulators with radiators due to noise requirements.Until recently, the ability of the surface mounted IC to dissipate the associated 2W power has limited large current output.The heat generated can now be dispersed over several voltage regulators, providing a large output current.By adopting the innovative current reference and follower architecture and using only a small section of PC wire as the ballast, accurate current equalization can be achieved between multiple voltage regulators, so as to realize the linear regulation of several amperes in the whole surface mounting system without radiators, as shown in figure 4.So that the collector of the channel transistor is available, the heat dissipation option can be further increased.Power consumption can be spread over several voltage regulators to keep hot spots off the system board.External resistors can be used to further disperse heat at a very low cost.This ability to equalize current and power consumption makes the voltage regulator ideal for circuit board power sources who do not want to use a switch voltage regulator.

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conclusion

Traditionally, a multi-track, surface mounted PCB system for high-current applications has been filled with linear voltage regulators using power packs and radiators, increasing size, complexity and cost, or with switching voltage regulators.Now, a new linear low voltage differential voltage regulator is on the market, which continues to carry forward the excellent tradition of the trident LT3080 series, namely the 3A LT3083.The LT3083, with its current based reference architecture and large output current, solves a variety of problems commonly associated with such designs, including excessive local heat, radiators and excessive conductors, and a large number of passive components.This innovative IC provides almost unlimited output current through direct parallel connection, thus dispersing the PCB's heat without the need for a radiator, stabilizing the VOUT with a single resistor and adjusting the output voltage to 0V, all of which are achieved with low output noise.