June Birth Magoncia

user Electronics Engineer

city Innovuze Solutions, Inc.

  • 24V/1A eFuse Input Protection Circuit for Industrial PLC CPU

  • Created: Dec 08, 2016

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The TPS26600 is a device that acts as an industrial eFuse. It has a wide operating voltage (4.2V-55V), which allows the device to protect different industrial applications with different DC bus voltages. The device can endure up to 60V supply and it can also protect loads from reverse polarity inputs up to -60V. It has an integrated back to back MOSFETs with 150mΩ ON resistance that provide reverse current blocking feature, making the device suitable for systems with output voltage holdup requirements during power fail and brownout conditions. The TPS26600 has an adjustable current limit from 0.1A to 2.23A. It is available in a 5-mm×4.4-mm 16-pin HTSSOP as well as 5-mmx4-mm 24-pin VQFN package and are specified over a –40°C to +125°C temperature range.

This reference design shows a typical application for the TPS26600 device. The circuit serves as an eFuse input protection for industrial PLC CPU, which operates in a 24V/1A power supply. The design of the circuit typically requires a 24V supply input for normal operation. The undervoltage lockout and overvoltage trip point are set at 18V and 30V, respectively. They are adjusted through an external voltage divider network composed of R1-R3, connected between the IN, UVLO, OVP and RTN pins of the device. The 1A current limit output of the circuit is set through the resistance of R5, which is connected between ILIM pin and ground. The voltage at IMON pin represents the voltage proportional to the load current. This can be connected to an ADC of the downstream system for health monitoring of the system. The resistor R6 serves as a current monitoring resistor. Its resistance is based on the maximum current limit (1A) and an ADC with a 2.5V maximum input voltage. The capacitor C3 serves as an output capacitor while C2 serves as a ramp-up capacitor that sets the start-up time and in-rush current limit to avoid thermal shutdown during start-up with and without load. The resistor R4 serves as pull-up for the open-drain fault output, while capacitor C1 acts as a bypass capacitor to suppress noise at the input.

The TPS26600 can be disabled through an external device or a microcontroller. By pulling the /SHDN pin to ground or below the 0.76V threshold, the internal FETs and hence the load current can be switched off. A thermal shutdown circuitry is also included in the device design to protect the internal FETs, if the junction temperature exceeds 157ºC. In this design, since the MODE pin is shorted to RTN pin, overload fault response is set to active current limiting with auto-retry. The TPS26600 device is not only limited to PLC applications. It can be also used in distributed control system, control and automation, redundant supply ORing, and industrial surge protection.



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