Conventional fuses and poly switches, which use heat generation to shut down or limit overcurrent, are susceptible to ambient temperature and operating conditions, and it is difficult to set the operating current with high accuracy. Therefore, they may operate at an unintentional current to cause abnormal system operation. In the case of a fuse that uses blowing, there is also the disadvantage that parts need to be replaced.
On the other hand, electronic fuses (eFuse IC) are a solution to these issues. eFuse IC utilizes semiconductor-based integrated circuits to provide not only a simple shut down function but also a variety of built-in protective functions. Main features are short-circuit protection, overvoltage clamping (OVP) [Note 1], overcurrent clamping (OCP) [Note 1], overheat protection, inrush current suppression, reverse current prevention, etc., and conformity to the component standards of the safety standard IEC62368-1 for IT/AV equipment.
This article introduces the current setting of short-circuit as basic function of fuse and overcurrent clamping.
[Note 1] OCP : Over Current Protection OVP : Over Voltage Protection
Electronic fuse Toshiba eFuse IC |
Resettable fuse (poly switch) |
Chip fuse |
Glass fuse |
|
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Protection method |
Shut down by MOSFET switch |
Current limit by resistance increase |
Blown conductive part |
Blown conductive part |
Protection speed |
150ns (Typ.) |
Several hundred ms to several seconds |
Several seconds |
Several seconds |
Repeated use |
Possible |
Possible |
Not possible |
Not possible |
The figure below shows a simulated waveform when TCKE812 is supplying power of 12V and the output voltage is shorted steeply. Since the short-circuit detection current of eFuse IC is set by an external resistor, the detection current can be set with higher accuracy than a conventional fuse that uses heat generation.
When current flow reach at the short-circuit detection value, eFuse IC judges the short-circuit state (this state is also called as Fast Trip or Short Trip) and shut down the output current.
The overcurrent clamping function clamps (holds) the output current so as not to exceed the clamping limit value when the output current increases due to a load abnormality or short-circuit, etc., and protects against deterioration or destruction caused by heat generation of the device itself as well as preventing instantaneous power-off.
The clamping limit value is 62.5% of the short-circuit detection value. The optimum settings can be set according to the system. A robust design can be achieved by having a double overcurrent protection function in conjunction with a short-circuit protection function that operates when the output current exceeds the limit value significantly in a very short period of time.
TCKE8xx series can be clamped from low temperature to high temperature with high accuracy, and its accuracy is ±11%. This accuracy improves the degree of freedom in designing/selecting the components to be mounted. In addition, when the load at the subsequent stage fluctuates, the normal overcurrent protection function (circuit break) stops the output current immediately when the current reaches overcurrent limit value, and the output voltage drops.
On the other hand, eFuse IC clamps the current so that the current does not exceed the limit, so that a more stable power supply can be configured by keeping the output voltage within the withstand voltage of the subsequent IC while keeping the output voltage.
Product Number |
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Data sheet |
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Stock check |
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Over voltage clamp VOVC Typ. (V) |
- |
6.04 |
15.1 |
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Recovery operation type |
Auto-retry |
Latch |
Auto-retry |
Latch |
Auto-retry |
Latch |
|
Package |
Name |
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Size Typ. (mm) |
3.00×3.00, t=0.75 Max |
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Operating ranges |
Input voltage VIN (V) |
4.4 to 18 |
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Output current IOUT (A) |
0 to 5.0 |
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Over current limit accuracy (%) |
±11 @Ta= -40 to 85℃、ILIM=4.38A |
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On-resistance RON Typ. (mΩ) |
28 |