In the age of the IC, transistors usually are not considered particularily interesting. However, some MOSFETs stand in the center of attention – let us be your guide to some cool components.
Crees C3M0065090J is not particularily impressive from a purely technical point of view – its main secret, instead, lays in the land layout shown in figure 1.
…Smart land layouts lead to reduced creepage current potential
Cree forgoes the dedicated drain pin, and instead exposes this part of the semiconductor crystal using the tab normally used as a heatsink. When combined with the rest of the circuit layout, a spacing of more than 7mm is achieved – this helps reduce creeping currents, which can be a problem at high voltages or in precision designs.
CREE furthermore promises a Drain – Source Voltage of 900V, which also makes the part well-suited to “rectifier” type activities.
Better Be Mindful
Part number two is IR’s irlml5203pbf – a classic which has been on the market for some time, but keeps generating significant spikes of search interest. When first introduced, the idea of packing a full HEXFET module into a SOT23 module was considered odd.
By now, the concept established itself. This does not, however, mean that the parts are not recommended for new designs: the on-resistance values shown in the figure still are respectable.
…If power is at a premium, reducing losses can help
IR recommends that parts such as the irlml5203pbf or its sister part irlml6402pbf should be used in PCMCIA cards and similarly space-constrained settings. One classic application would be “low drop diodes” and similar polarity protection – in this case, however, take care to not exceed reverse voltage limits.
Finally, allow us to point you at here and here in case you never thought of using a FET as a reverse polarity protection component. Their extremely low voltage drop makes them effective in “corner cases” such as an automotive cold crank; losing 0.7V can make a world of difference…
Through-Hole Connectors Going Strong
SMD inductors are a common culprit for TMI failures – if a HP 34401A croaks, checking input coils is a great idea. Nevertheless, engineers keep using SMD parts in this area. An interesting question is how developers think about SMD connectors.
Having analysed search trends for both SMD and THT connector searches, the trend is clear – throughhole comes out on top.
This is valid all over the block. A “conventional” candidate would be the USB3145-30-1-A by GCT; it implements traditional USB, but comes with a neat twist of being rectangular. This means that insertion forces do not bend the connector – removal can, of course, strain the solder joints.
Of course, the automotive market and its high vibration and high reliability demands come with their own caveats. While SMD usually is better for cars as the lower mass lowers stress cracking, connectors such as the DT13-08PA are THT as they can dissipate connection and disconnection stresses more efficiently.
Finally, friends of odd connectors can feast their eyes on the nf2d-b-2 by Neutrik. It is an RCA connector which has to be soldered in; an interesting approach which was used to great success on systems such as the SolarTron 7150. Mechanical mounting must then be done with a set of screws, as seen in the figure.
…Physical and electrical positioning are two different problems
THT and SMD connectors usually do not give one another much in terms of price. The extra price for the drill holes usually is insignificant, PCB layouts can even become smaller in one plane. However, word on the street has it that reflow soldering machines gravely dislike headers and similar elements – touching base with your manufacturing partner is very recommended.
While engineering usually is not a black and white subject matter, the voice of the people seems clear when connectors are concerned. Going THT might increase prices slightly; the increased reliability makes it worth your while most of the time…
Precision colour sensing made easy
Austrian MicroSemi recently divested itself of its transceiver portfolio, leaving standards such as AS-I stranded. Sensors were selected as the new main field of business, leading to the introduction of a few extremely interesting products such as the JENCOLOR colour sensor ICs.
In principle, the sensor is laid out according to the schemes shown in the two figures accompanying the screen. The main priority is that the part contains but three photo-diodes, all three of which are conveniently located behind a filter to eliminate unwanted spectral components.
The three diodes are located in seperate areas of the main die…
…AMS provides a relatively complex set of signal conditioning circuits
To clarify a few aspects: first of all, the AS73211 is strictly an one-pixel color detector – it has nothing to do with the traditional linear or two-dimensional CCD chips which are well-known from digital cameras. Secondarily, the chip’s intended usage is processes – think about quality control, sorting of goods and similar tasks where accurate color sampling is required.
Finally, the AS73211 is intended to reach extreme high accuracies – its internal DACs can work at 24bit if required.
When compared to a homebrew solution, benefits pop up. ADC linearity and temperature issues are handled by AMS – the chip contains various bits of logic which ensure that issues affecting resolution adversely are handled effectively.
Getting data out of the part is accomplished via an insutry standard I2C connection. In the first step, both CREG1:GAIN and CREG1:TIME must be programmed to set up ADC gain and the time spent on the individual conversion cycles. In the next step, the remaining hardware must be configured – when done, actual measuring processes can be triggered. More information on this is readily available in the excellent datasheet, which is waiting for you here.
On development kits
Like most other optical systems, the AS73211 also puts demands on the accompanying optics. Developers working on sensor software are well-advised to start out by buying the (somewhat pricey) AS73211-AB5 SET DK development kit rather than the basic PCB version – the former comes with a complete optical assembly, thereby taking one bit of hassle off your neck.
… Be careful when selecting your development kit – not all are created equal
A Very Brainy Diode
Jack Ganssle, publisher of the legendary EmbeddedMuse newsletter, once stated that the embedded space is ideal as things permanently improve. When looking at diodes, the reverse is true – silicon-based diodes have had a drop of 0.7V for ages. Analog Devices now brings a workaround for power supply ORring circuits.
In principle, ORring is simple; two diodes are used to allow one power supply to perform a “soft takeover” against the second one. As long as both power supplies get their energy from an unlimited source, diode losses are insignificant – once a battery is involved, things get less funny.
A FET, obviously, is a better solution; when switched on, its resistance is very low and usually causes less loss than when a diode is involved. Figure one shows how Analog Devices wants to solve the problem.
…Replacing a diode reduces voltage losses
Who Controls the MOSFET
The LTC4412 does its magic via a dedicated sensing pin, which allows the system to find out if external power is present – if this is the case, the MOSFET is enabled. The part makes good use of FETs in that it is strong enough to drive both large and small transistors, thereby ensuring that both large and small loads can be supplied efficiently.
Circuit functionality becomes clearer in the block diagram…
Another interesting aspect of the part is the low quiescent current, which flows in all modes of operation. With a typical value of 11yA, very little energy is lost on management of the backup circuitry.
Analog Devices apparently foresaw the current MLCC capacitor crisis – the LT4412B is one of very few parts which prefer to be decoupled with traditional capacitors or an electrolytic part.
Finally, the zener diode shown in the “basic” version of the circuit can also be substituted with a secondary MOSFET via the STAT output.
…A second MOSFET decreases power consumption
To build or to buy?
Power supply design has always been a bit of a topic – long-term followers of the OEMsecrets article series know that repairing TMI usually starts out with power supply trouble. Due to that, buying an off-the-shelf module can be attractive. Here are a few parts which caught our eye recently.
From Germany with love…
One part which caught lots of attention recently comes from Weidmüller – the company is usually known for its easy-to-insert connectors commonly found on 3D printers. The designation 1469530000 reveals a relatively uncommon part – feast yourself on figure A.
…Not cheap, but a real stress-saver
While three-phase current systems might not be an electrical engineer’s everyday fare, one still meets them quite often – designing a power supply for them is an especially hairy affair due to the tremendous amounts of power which can be set free if something does go wrong. Weidmüller offers the part in various output modes – the example we picked here provides a neat 5A and 24V.
…and in a compact form factor
Should you ever feel bad about your DC-DC converter design skills, fret not. Traco Power’s TMR 1212 family is a series of SIP modules which act as buck or boost converters – impressively, they can also be used to split up a single supply into multiple different rails.
All of this is accomplished with an efficiency ranging from 75 to 85% – dedicated converter designs might be a bit more efficient, but also headaches when sourcing coils and other parts. Furthermore, the SIP module “stands” on your PCB – you need to give up but 2 square centimeters of space if one of these modules happens to find its way into your circuit.
Was it worth it?
Before leaving you with these parts, allow us to impart some stranger thoughts. CUI – the company is well known for all kind of mechanical gadgetry – published an excellent whitepaper comparing bought and self-developed solutions. It can be accessed at by clicking here – simply scroll to the bottom and download the full PDF if you want to find out more…