[introduction]The article will discuss the action of laden switch, its are basic function, add function and high-quality character, be these functions make they not just relatively simple, and can undertake to power source course the electron leaves / pass control. The article will use Toshiba Electronic Devices&IC of 3 in the TCK12xBG series of Storage Corporation (Toshiba) new-style and laden switch will describe these points, show the need that how applies them to satisfy newest products plan.

The article will discuss the action of laden switch, its are basic function, add function and high-quality character, be these functions make they not just relatively simple, and can undertake to power source course the electron leaves / pass control. The article will use Toshiba Electronic Devices&IC of 3 in the TCK12xBG series of Storage Corporation (Toshiba) new-style and laden switch will describe these points, show the need that how applies them to satisfy newest products plan.

Be in almost in all systematic designs, course of administrative direct current source and protecting them to avoid the effect that suffers all sorts of interior and exterior breakdown mode is crucial. When having course of many power source, the challenge becomes complex. In today’s system, use small-sized, low power comsumption and batteries power supply design such circumstance is increasing.

The challenge that power source course manages

The management of power source course only then manage integrated circuit at a power source (PMIC) , it appoints open and the electric current that close path of flow direction power source according to need. PMIC still is in charge of administering the time between course of many power source and order. However, it is the task of laden switch to the control of the actual physics level of power source course, this is a kind of arrangement that is based on MOSFET, can accept the directive that allow electric current to pass or prevents electric current.

Besides such as surge voltaic pressing is placed outside leading the main demand such as control and overheating protection, ask laden switch offers other function and character increasingly now, be like controlled drop report, fast output discharge and block of true retrorse electric current are broken etc, but all these use the design that is based on schism type FET very hard to come true.

To bypass this is planted complexity, the cost that reduces schism type to realize means place to need at the same time is mixed circuit board space, design personnel can choose laden switch IC, the function that wants place and switch are compositive enclose in in. The problem of power source course that switch solves these compositive type load or avoided a lot of operation sexes, also conduce to satisfy requirement of a lot of shift or batteries power supply design.

Laden switch ABC

Basic model laden switch cites a base 4 times only: Input voltage, output voltage, make can be mixed ground connection (graph 1) . When signal of logistic n control brings to bear on to its ON/OFF control cites a base (can be tall n effective or low n is effective) when, this parts of an apparatus is enabled namely, next direct FET is opened. This allows electric current to bring crural VIN to flow to output to bring crural VOUT from the input, provide electric energy to laden circuit thereby.

Laden switch is an enclosed direct FET not just. Still include to control effect of logistic, field to run shift of driver, n at least implement protect a function with all sorts of circuit, if flow to protect and prevent circumfluence too (also call retrorse electric current) , and flow to be able to damage with circumfluence the system reachs its component too. They still can realize other and useful function, if be when open of power source course,undertake control and overheating are protected pressing placing leading.

In its simplest application, laden switch is used between power source and individual and laden power source course, so that PMIC is passed to undertake open when need, or enter static state in order to save electric power (graph 2) .

Laden switch parameter

Laden switch has a few crucial parameter, design personnel must be evaluated. Among them 3 the most important parameter are the biggest input respectively electric current of the voltage, biggest output and ” guide ” resistor. Other parameter may be very crucial also, specific depend on applied need, include:

. Static electric current (IQ) : For the electricity that place of laden switch power supply needs, its output end to do not have any electric current.

. Close (bide one’s time) electric current (ISD) : The electric current of VIN is flowed into when parts of an apparatus is banned to use.

. ON brings a foot to input leak electric current (ION) : ON/OFF is flowed into to control the electricity that makes a base when parts of an apparatus is enabled.

Electric current of small static state and it is more and more important in batteries power supply application to involve electric current, if can apparel equipment, smartphone and module of content couplet net, they have very big effect to battery life and run time.

Shed protection too

Of laden switch shedding protective function too is to protect clear breakdown not just, be in like load temporarily or permanent short circuit. Need possibly also to alleviate the result that output voltage drops, below certain circumstance, when course of a power source is a few laden power supply, with respect to meeting occurrence output voltage drops, and a laden open speed is met faster (graph 3) . Increase the output that can cause power supply suddenly of voltaic demand to drop for an instant to its rating is the following. This defer or convalescence are decided by the function of laden transient state of power source and laden particular case.

Conversely, this kind drops to be brought about possibly the 2nd load cannot be started normally or behavior is deviant. As a result of these reasons, the current limliting function of laden switch is useful, because it can alleviate,the first load increases the output tension that causes to drop to voltaic demand.

A lot of systems need to ensure its many load with specific ordinal electrify, enter an activity in course of every power source there is affirmatory time between condition. Below these circumstances, many laden switch can be used below PMIC control, the order that administers them and opposite time (graph 4) .

Block of retrorse electric current is broken

The retrorse report flow resistance of laden switch breaks what its name place narrates no less than in that way: When the voltage prep above that outputs side inputs side, it can flow reversely with preventing electric current.

Because two kinds of common circumstances are caused,this may be. Above all, brushed batteries terminal as a result of disconnecting cable accident, make mistake when joining afresh even, power source (be like car batteries) the likelihood is received to turn over inadvertently. It may be to resemble average user inserting batteries even returned such basic error.

The 2nd kind of circumstance some are not quite apparent. The power source that considers two different voltage by answer the case that is used to a load (graph 5) . The tension that shares output side can become higher than the voltage of side of input of low voltage power source. Below this kind of circumstance, electric current can flow to low voltage side from tall voltage side, damage thereby low voltage source.

3 kinds of methods will handle block of retrorse electric current to decide an issue:

The simplest method is in output end establishs ties a diode. But the voltage drop on diode (standard silicon detector comes for 0.6 bend over 0.8 bend over) reduced tension of power supply course, and diode must have enough rated power to come the quantity of heat with corresponding dissipation.

The 2nd kind of method is to use a MOSFET and series connection of power source course, but its guide electrify block (RON) also can cause voltage drop, and its heat up dissipation to ask that its must get satisfaction.

The 3rd kind of choice is the laden switch that makes appliance has block of retrorse electric current to break a function, it can realize what what need to prevent flow backwards countermeasure, and do not need to undertake eclectic.

Discharge function

Normally the circumstance falls, when power source multichannel answer is used implement when shutting, automatic discharge function can join VOUT and GND. Have function of discharge of this kind of fast output to have a lot of profit:

Output is not floating, always be in a foregone condition.

Downstream module always is shut completely.

However, below some circumstances, fast output discharge cannot be taken.

If the output of laden switch receives batteries to go up repeatedly, when laden switch brings a foot to be banned to use through ON, fast output discharge can cause cell extinct.

If be in the multichannel of a two inputs, one output answer with implement in use two laden switch (output is bound together) , can waste power ceaselessly through outputting discharge quickly so, because want laden switch to bring a foot to be banned to use through ON only, electric current reachs the ground via internal resistance with respect to meeting shedding.

Accordingly, in configuration power answer is used implement with laden switch IC when, be necessary to choose not to have the laden switch of discharge function. The laden switch function that needs to call block of truly retrorse electric current to break at this moment. It can prevent carry flow direction to input the retrorse electric current of end from output, and without giving thought to the ON/OFF condition of laden switch how.

The output voltage VOUT in having the laden switch of this kind of function to will input voltage VIN and IC undertakes comparative, when VOUT>VIN, prevent galvanic Lu Qi to move (graph 6) .

With true retrorse electric current block is broken and the delicate place related automatic discharge function still has more; Explain in Toshiba application ” of laden switch IC shed protective function and retrorse electric current to prevent a function too ” in delicate to these place undertook more detailed discussion.

New-style IC is aimed at fast growth application

Laden switch is not new, but they want increasingly to ask to undertake according to what specific applying custom-built. Switch of load of the generation below Toshiba TCK12xBG series proved this explicitly, this series includes 3 parts of an apparatus or appliance: TCK126BG, TCK127BG and TCK128BG (graph 7) .

The rated job voltage of these 3 IC is 1 to 5.5 bend over, electric current is 1 A, they are very similar, but some places have a bit different, so that its match the priority of specific application and demand with optimal way. A lot of their norms excel takes the place of before its product and existing competitive equipment.

The most outstanding is static electric current (of IQ) decrease, install from 110 accept (NA) falls to only 0.8 NA, decreased 99.9% , promotion exceeds two amounts level. In addition, wait for machine electric current to be 13 NA only. The model guides electrify block RON is 46 M Ω when 5 bend over, 58 M Ω is when 3.3 bend over, 106 M Ω is when 1.8 bend over, 210 M Ω is when 1.2 bend over.

The other property of these laden switch all realized electric norms to surmount. The identical voltage that they also are less than Toshiba and other vendor to offer far / the other and usable parts of an apparatus of voltaic grade. They use 4 down-lead WCSP4G to enclose, dimension is 0.645 × of 0.645 × 0.465 Mm, solder ball span is 0.35 Mm. The 0.55 Mm of × of 0.79 of 0.79 × that span takes the place of to be 0.4 Mm before this means photograph comparing is enclosed, this load switch reduced 34% spaces to need (graph 8) .

This kind of small size saved very big circuit to design staff board space, and this to can appareling equipment exceed small-sized applying for crucial. In addition, this contain a 25 micron (the rear coating of μ M) , can reduce physical concussion and damage, prevent to burst apart.

3 laden switch in this series are had inside buy pressing places rate control drive, when 3.3 bend over rise time is 363 small seconds (μ S) . The distinction between these switch depends on whether having function of fast output discharge, and the effective condition that ON/OFF cites a base (graph 9) .

Epilogue

If design personnel to want to satisfy small-sized batteries power supply equipment (if can apparel equipment and smartphone) and equipment of content couplet network is right the demand of feebleminded bad news, small size and low cost, have high collect to appear crucial into laden switch of the function. As above, the switch of TCK12xBG series load of Toshiba has static electricity low with dimension smaller dominant position, contain contented function and the compositive element that protect a requirement, simplified to design.

(author: Bill Schweber, origin: Get nimble electron DigiKey)

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