Majority of system design engineer possibly can agree that the linear voltage regulator is one kind which in the numerous manostats is easiest to use, moreover as a result of this reason, also most receives system design engineer to welcome. But new generation’s system request is extremely strict, will therefore only use the linear constant voltage technology the high performance system to receive many restrictions, so that very difficult to display its performance fully. This trend of development carries over the following several questions: System design engineer forms in one’s mind when the new product can obtain which, on the one hand technical support? What good and bad points uses the linear constant voltage technology the direct-current/cocurrent power conversion system to have? Whether to use other line layout the power conversion system to be more superior than? What in the technology also has to limit? If by identical should serve as the comparison, which kind of low pressure drop manostat does have the high efficiency? Whether the different manufacturer’s linear voltage regulator does have difference the high under fit and unfit quality?
Looks like these questions probably to be simple, actually the question answer imagines complex compared to us, because needs to consider the important attribute and the technical parameter are many, in addition the related factor’s importance is neglected frequently by the human, therefore system design engineer makes time the choices must be careful. Because the new product’s power supply request more hastens strictly, the circuit wafer area also unceasingly reduces, in addition the system must guarantee that can display the most basic performance, therefore we must for the new product choice appropriate low pressure drop manostat. The good low pressure drop manostat may solve in many application problems; If manostat’s choice is improper, the entire design is unable to carry out the execution radically.
Radiation, efficiency and seal
Linear voltage regulator’s power input can definitely output by no means from the output port, both’s phase difference can transfer the heat energy diffusion to fall. Wattage dissipation (Pd) may according to the following formula to estimate sketchily:
Pd = (Vin - Vout) * Iout
If the more precise rated output diffusion, we must Vin * Iq this variable computation. Below the wattage dissipation total amount may according to the formula to calculate:
Pd = (Vin - Vout) * Iout Vin * Iq
If according to the above two formulas, lowers 5 volt (V) voltages to 1.5 volts (quiescent current is again 300mA), then the linear voltage regulator diffusion will not be short for the heat energy power in:
(5 - 1.5) * 0.35 = 1.225W
Actually should this power loss quantity regard as high low? Concerns this question we not to be possible premature to make the judgment, we must according to the chip seal as well as the circuit wafer type and the area (, if uses surface to paste installs seal), discovers these variable with the temperature rise scope between functional relations, will thus calculate 1.225W the wattage dissipation actually make temperature rise how many. Like this we only then may make a more comprehensive judgment, determined that 1.225W the wattage dissipation is high or low. System design engineer likes using the most exquisite seal generally, but this kind of seal’s thermal resistance value is high, therefore radiation ability is also worst.
Standard SOT-23 and SC-70 and so on exquisite seal (the JA value is situated between 200 (C/W and 400 (between C/W. Volume not too big nor too small SOT-223, TO-252 (DPAK) and other not concealed welding bead SMD seal (including PSOP and ETSSOP) (the JA value is situated between 50 (C/W and 90 (between C/W. Generally speaking, only then the big seal (e.g. TO-220 and TO-263) only then have ideally (the JA value, its value is situated between 40 (C/W and 60 (between C/W. Roughly, this is seals the size and between the temperature rise scope change rule, is suitable in except LLP (beside all seals. Because LLP (the seal internal structure is more special, under for example the chip by facing on, the bottom faces the way to put in the metal surface, but the metal surface supposes in seals the base, and does not have any concealed, therefore this kind of subminiature seal’s thermal resistance is extremely low, even may compare favorably with the big seal, is the present only one thermal resistance value such low subminiature seal.
What does the above digit have to the system temperature to affect? If the wattage dissipation is Pd = 1.225W, theoretically the 2.85mm x 3mm SOT-23 seal’s temperature will rise 300 (C at least. the 6.6mm x 9.7mm DPAK seal’s heating temperature compared to the ambient temperature high 80 (C, only then the 10.4mm x 14.35mm TO-263 seal or the 2.9mm x 3.3mm LLP seal will only then have small temperature rise (50(C). If system design engineer understood how to choose the appropriate linear voltage regulator seal, then may know approximately whether needs to change to the switch manostat.
Quiescent current (Iq) and supplementary metal oxidation semiconductor (CMOS) low pressure drop manostat
Quiescent current (Iq) is also called the operating current or the earth current, is the design low power, the low operating current and by when the battery power supply electronic products needs to consider an important attribute. When we refer to 1A, 2A or the 3A constant flow load, can we neglect the influential role which the quiescent current displays? System design engineer are many when neglects this question - to disregard the quiescent current the importance possibly to actually pay the very great price. System’s quiescent current along with the load current will possibly increase, but will rise largely, the rise will be decided the processing technology which truly will use in the low pressure drop manostat. As regularly said take the double-pole low pressure drop manostat that the 3A load current’s quiescent current possibly surpasses 200mA. In addition, the CMOS low pressure drop manostat’s quiescent current is extremely low, moreover not load size influence, if the full load current is 3A, quiescent current generally only then 3mA to 15mA; If the load current is 1A/2A, the quiescent current is situated between 100 (between A and 6mA. (refers to Figure 1 to carry closes supply current and load current function relational graph, two section of 150mA low pressure drop manostat which in chart compares uses CMOS and bipolar technology technology manufacture separately.)
If the output current is 3A, the quiescent current is 200mA or the 6mA question like this to be actually whether important? Just like the preceding text said that the wattage dissipation total amount judges the low pressure drop manostat solution is feasible or not the decisive target, although in the rated output diffusion’s formula, first variable will change (i.e. this along with the different application to be decided variable by input voltage and output voltage), but second variable completely will be decided by the quiescent current size, will possibly be about a wattage dissipation actual size important attribute. As regularly said take 3.3 volt input voltages that the 200mA quiescent current will enhance the wattage dissipation 660mW, by the so high wattage dissipation, the related design possibly needs to change to the switch manostat. If the quiescent current lowers to only then 6mA, the wattage dissipation only will increase approximately 20mW, this increased range may say not worthy of mentioning, therefore wattage dissipation total amount nearly not any influence. By the so low quiescent current, the linear voltage regulator still might play its role, so long as therefore the quiescent current sufficed lowly, system design engineer still might select the CMOS linear voltage regulator.
Which quiescent current value before the decision does select, should better consult the full load value which first in the data sheet the page institute carries. At present the entrepreneurs will like being lowest or the non-load quiescent current value are listed in a fence which in the data sheet will most go against, engineer will be many when thought that this is the full load value, very easily by this fence digit misleading.
Pressure drop and low input voltage low pressure drop manostat
Low pressure drop manostat’s pressure drop whether is really very low? We should ponder this question over and over. In although the product standards document marks needs the pressure drop is 100mV, but this value is only suitable for certain application situation, for example, input voltage, if is bigger than the manostat chip’s lowest input voltage, pressure drop then possible only then 100mV, but system, if needs 1.2 volt or the lower output voltage (the present many applications must use such low output voltage), but the manostat needs many in 2.5 volt input voltage operation, for example the input voltage is situated between 2.5 volts then to need 2.5 with 5.5 volt between typical manostats to respectively consider that on the input voltage, in this case, the true pressure drop is:
2.5V - 1.2V = 1.3V
Theoretically, the above system should be possible to carry out the normal function, but the diffusion will account for the very great proportion for the heat energy power.
If system’s input voltage may change 1.5 volts or 1.8 volts, when uses indicates the 100mV pressure drop the low pressure drop manostat to be possible the large lifting efficiency, as well as reduced temperature increase rate and diffusion quantity of heat. As regularly said take 2.5 volt lowest input voltage’s low pressure drop manostat, if uses 500mA the load:
Wattage dissipation = (2.5 - 1.2) * 0.5 = 0.65W
But if the same system changes to 1.5 volt lowest input voltages the low pressure drop manostat:
Wattage dissipation = (1.5 - 1.2) * 0.5 = 0.15W
Both’s wattage dissipation differs 500mW, this value may not be small, can we ignore?
Summary
Because the new generation electron system request is strict, therefore used the low pressure drop chip design high performance the solution to look like by no means so was formerly simple easily. But so long as system design engineer understood that the choice appropriate manostat, and uses fully many frequently the parameter which neglects, or the full use only then the new generation low pressure drop manostat only then has the function, then may use has the linear constant voltage structure which extremely the cost benefit and easy to design, with the aim of using this kind of structure fully the brand-new function and the characteristic like advanced radiates an ability stronger subminiature seal, the low quiescent current (, regardless of load current height), ultra low input voltage, as well as advanced CMOS low pressure drop manostat processing technology.
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