Toshiba Introduces Its First Family of Reusable eFuse ICsNovember 21, 2019 by Gary Elinoff
The TCKE8xx series instantly shuts off when extreme overheating, overcurrent, or a short circuit is detected.
Many designers currently use the venerable glass fuse, which has a link that burns up after stopping a current surge. Toshiba has designed it's first electronic fuse, the TCKE8xx series, as a reusable solution to current surges.
The new family of eFuse ICs can be used repeatedly. Image from Toshiba
Like a glass fuse and an electrical circuit breaker, members of the new series of electronic fuses can shut off the power in the event of a severe current overload. But that’s where the resemblances to these common devices end.
Toshiba claims that the eFuse ICs can save board space, cut weight, and reduce the BOM.
Protection Against Overcurrent and Overvoltage
Members of this family of eFuse ICs are surprisingly complicated devices, perhaps because they offer more functions than typical fuses. They provide protection against over and under voltages, as well as excess heat and current.
Users can control the level of current that members of the TCKE8xx series pass through before shutdown. The eFuse ICs also feature current clamp and voltage clamp functions to protect against overcurrent and overvoltage.
Example of application circuit. Image from Toshiba
This enables them to maintain the supply of power while still providing protection by clamping voltage and current at specified values, even when excess over current or over voltage is present. Over-temperature and short circuit capabilities serve to protect circuits by instantly shutting off when extreme overheating, or a short circuit, is detected.
Features of the TCKE8xx Series
There are a total of six members of this series planned and two of those six—the TCKE805NA and TCKE805NL—are currently in production. Both of the available devices have an input voltage of 4.4V to 18V and a fixed over-voltage clamping of 6.04V.
The output current limit is user selectable from 0 to 5.0 amps and the overcurrent limit accuracy is within ±11%. The eFuse ICs' fast-trip comparator delay is 150 nanoseconds.
For inrush current protection, the slew rate is controlled through the choice of an external capacitance.
Block diagram of the TCKE8xx series. Image from Toshiba
The under voltage lockout (UVLO) is controlled by an external resistor. Reverse current blocking is provided through a built-in MOSFET driver.
Auto Retry vs. Latching
The TCKE805NA features auto-retry, while the TCKE805NL is latched. This means that the TCKE805NA will attempt to restart on its own, while the TCKE805NL needs outside intervention through the EN/UVLO pin to return to normal operation.
Timing chart of overcurrent protection operation (auto-retry type). Image from Toshiba
The diagram above illustrates the sequence of the latched TCKE805NL detecting over current and restarting to provide overcurrent protection.
While the two available members of the new eFuse family feature overvoltage clamping at 6.04V, the two TCKE812x members, under development, will feature overvoltage clamping at 15V. The last two under development, the TCKE800x, will feature no over-voltage protection at all.
Overvoltage characteristics of TCKE800/805/812. Image from Toshiba
The two series members now available come in a 3.0mm by 3.0mm x 0.75mm WSON10B package, as will the other four now in development. All members of the series are designed to operate over a -40°C to 85°C temperature range.
Toshiba is actively seeking IEC 62368-1 safety standard certification for all members of the TCKE8xx series.