The fuse electronization changes the design?

High precision current setting of shut down improves design flexibility

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

Comparison of various fuses

 

Electronic fuse

Toshiba eFuse IC

Resettable fuse

(poly switch)

Chip fuse

Glass fuse

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

Providing high-precision short-circuit protection

Providing high-precision short-circuit protection

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.

High-precision overcurrent clamping function

High-precision overcurrent clamping function

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

TCKE800NA

TCKE800NL

TCKE805NA

TCKE805NL

TCKE812NA

TCKE812NL

Data sheet

PDF (1725 KB)

Stock check

StockChecking

StockChecking

StockChecking

StockChecking

StockChecking

StockChecking

Over voltage clamp

VOVC Typ. (V)

-

6.04

15.1

Recovery operation type

Auto-retry

Latch

Auto-retry

Latch

Auto-retry

Latch

Package

Name

WSON10B

Size

Typ. (mm)

3.00×3.00, t=0.75 Max

Operating

ranges

Input voltage

VIN (V)

4.4 to 18

Output current

IOUT (A)

0 to 5.0

Over current limit accuracy (%)

±11 @Ta= -40 to 85℃、ILIM=4.38A

On-resistance

RON Typ. (mΩ)

28

Other protection functions and safety standards

Application

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