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Circuit Breaker IC Does Just That and Much More

Much like the IC eFuse, which introduces additional functions and features to a traditional passive overcurrent and safety device, the LTC4249 does a similar enhancement for the time-honored electromagnetic or thermal circuit breaker. The classic circuit breaker, also known as a resettable overcurrent cutoff device, has been in existence since the 1920s and is renowned for its consistent and dependable performance, as well as its uncomplicated schematic representation (as seen in Figure 1). Whether the breaker is designed to trigger due to a current overload detected through thermal or electromagnetic means (both methods are employed), the primary objective and subsequent execution are meticulously centered on excelling in a singular task. (It’s worth noting that circuit breakers and fuses are not the sole types of circuits and overcurrent protection devices, but that’s a topic for another discussion.)
1- The conventional standard circuit breaker, with its straightforward schematic symbol, is triggered by either thermal or electromagnetic energy and serves a singular purpose: delivering consistent and dependable overcurrent protection (Photo credit: Wikipedia).While this single-minded focus is commendable, it can sometimes limit the flexibility and range of options in system design. In such scenarios, an electronic circuit breaker (ECB), exemplified by Analog Devices’ LTC4249 as shown in Figure 2, proves to be invaluable. This dual ECB offers capabilities, functionalities, and adaptability that surpass those of a conventional circuit breaker.

2- The LTC4249, a dual electronic circuit breaker (ECB), carries a rating of 65 V/1.2 A and boasts capabilities and functions that go beyond those of a typical circuit breaker. Its primary purpose is to supply bias for a 1-A servo function in a sequenced GaN power amplifier, while also providing 1.2-A protection.With its relatively high voltage rating and a current capacity of 1.2 A, this device can offer current monitoring and protection across a broad spectrum of applications. These applications encompass safeguarding power amplifier arrays, ensuring industrial safety, monitoring equipment conditions, replacing relays, and managing load switching.

The LTC4249 dual ECB furnishes overcurrent protection for two loads. Each channel features a precision enable input, current-monitor output, and ready status output, with a single resistor determining the ECB threshold. If an overcurrent condition arises in either channel, the associated breaker disconnects the input from the load.

It’s worth noting that the relationship between a traditional circuit breaker and an electronic circuit breaker parallels that of a traditional fusible-link device (fuse) and an electronic fuse (eFuse). The former focuses on a single function but lacks flexibility, which may be viewed as either an advantage or limitation, while the latter offers increased sophistication and introduces additional features, functions, and design options.

The open-drain RDY status output drops to a low state following any circuit-breaker “event,” and the ECB latches into the off state. After a one-second cool-off period, the user can reactivate the ECB by toggling the enable input. The circuit breakers incorporate a cool-off timer, overtemperature sensor, short-circuit detector, and inrush controller to ensure operation within a safe working range.

The LTC4249 simplifies voltage sequencing and closed-loop-bias current-control applications through its precision enable inputs, ready outputs, and analog current-monitor outputs. It also offers a 5 percent accurate analog current-monitor output, a filtered (50 s) main overcurrent threshold, a fast (2 s) secondary overcurrent threshold, and integrated 75-m switches.

The LTC4249, with an operating temperature range spanning from -40 to +125°C, is priced at $2.39 per 1,000 pieces. It comes in a 16-lead, 3-mm LQFN package. For applications requiring compliance with creepage and clearance specifications up to 65 V, a 12-lead “skipped leading” 3-4 mm LQFN package is also available.


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