A resettable fuse is a polymeric positive temperature coefficient (PPTC) device that is a passive electronic component used to protect against overcurrent faults in electronic circuits. The device is also known as a multifuse or polyfuse or polyswitch. . Beam deflection tube · Charactron · Iconoscope · Magic eye tube. Read about ‘F1/F2 polyfuses gone’ on elementcom. are made to the Raspberry Pi’s hardware in the future and how they are justified by. Isoloop magnetic couplers 6) Working 7) Digital isolators 8) Advantages 9) Applications 10) Future scope 11) conclusion 12) References; 3.

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The problem is that USB power is dead. Both polysilicon and aluminum fuses are difficult to program after encapsulation. Sometimes a resistor becomes so narrow that contacts cannot reside inside it without violating design rules.

They provide a convenient means of obtaining small currents for startup circuits, but their inherent variability and nonlinearity usually preclude their application elsewhere. As long as a few kilohms of resistance lie between the zaps and the remainder of the circuit, programming will generally cause no harm.

Each material possesses a characteristic resistivity, usually measured in 1 The International System of Units,or Systeme Internationale SIis more commonly called the metricsystem.

power – Raspberry Pi 3 Model B (not B+) USB polyfuse location – Raspberry Pi Stack Exchange

Assuming that transistor Q 1 always conducts, the tank of R5 will be biased one base-emitter drop above the positive terminal of the resistor. If available, these should be used when calculating resistor values.

An NBL overlap of 5 to 8um will usually suffice. Not only does this impair polyfus blowing of the fuses, but it also makes them prone to regrowth because conductive material remains near them. Their effective sheet resistance is typically 2 to allowing very compact layouts. It is a fuse that after it has blown will self heal; that is after several days, it will almost behave as if nothing has happened.


The design of remotely programmed trim networks is beyond the scope of this text, but the foregoing comments should convey the general concept.

Resettable fuse

If CMOS transistors are scopr, then these can be used as switches to reconfigure the resistor network. This layout theoretically consumes less space, but since the tanks can extend underneath the adjacent trimpads, the two layouts actually consume similar amounts of area.

Lay out a 30kR HSR resistor with a width of 8um. Linewidth control of submicron features depends quite strongly on the precise dimensions of the geometry, but submicron resistors are rarely employed.

Electronic eye is the electronic device that continuously watches if anyone is visiting your home. Streetman, Solid State Electronic Devices, 2nd ed. If the parasitic capacitance of the field oxide is still too large for a given application, consider using a second poly layer if available since the interlevel oxide will further reduce the parasitic capacitance.

Each square corner adds approximately 0. After sample wafers have been evaluated, a new mask can be made incorporating corrected resistor values. For example, N-well resistors are often more compact than poly resistors in processes with a polysilicon sheet resistance of Thus, diffused resistors still see occasional use even in processes that offer poyfuse resistors. An approximate value can be obtained by assuming that the resistor consists of two sections in series: The latter is quite expensive so the RPI uses polyfuses.

The additional trimpads required for differential trim make this technique uneconomic for all but the smallest resistors.

Long leads are required to connect fuses at the edge of the die to resistors in the middle. Diffused resistors have larger volumes and arc in intimate contact with the silicon die, which serves to provide additional heat-sinking.

The resistor is surrounded on all sides by oxide, an excellent insulator that exhibits virtually no leakage. Polysilicon fuses are more difficult to program. The value of the resistor equals where Rs is the sheet resistance of the HSR implant, Wb is the width bias, and Lb is the length bias.


The device can be said to have latching functionality. Care must be taken to ensure that the CMOS transistors have small on-resistances compared with the trim resistors. Experimental fabrication of Zener zaps on a process using refractory barrier metal demonstrated that the Zeners could be zapped, but only with difficulty. This pinching effect becomes more pronounced as the voltage across the resistor increases.

If a silicide block is used, the heads of the sccope must remain silicided’to ensure proper contact. Metal resistors are still used for very low-value resistors, and well resistors are sometimes used t o obtain large values of resistance when high-sheet poly is unavailable.

Mark 16 October Resistors shorter than L min can be constructed, but their resistance will increase at high voltages.

The use of separate current-carrying and voltage-sensing leads is called a Kelvin connection Section The current must crowd inward as it approaches the contacts, making the actual value of the resistor slightly larger than that estimated by width and length.

If necessary, diodes or Zeners can be used to clamp the voltage seen by delicate circuitry. Medical devices are classified and these classifications became Somewhat The majority of these sections are connected in series to form the final resistor, but several sections are left unconnected as spares.

Keep metal a minimum of 2um away from the openings in opening in the protective overcoat. The equation assumes that the resistor is long enough to ignore length variations. If the effective width were increased to 10um, then the variability would be reduced to Since the emitter pinch plate connects to the tank, each segment of the resistor must occupy a separate tank.