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Posted on 01 June 2019

Intelligent Power Switch

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Applications are the proximity detectors and industrial automation

In the fields of factory automation and process control several output devices are used to drive different types of actuators. Depending on the market and application, the output drivers can be configured in high-side configuration (load to ground) or in low-side configuration (load to supply). Embedded protection and diagnostic are always requested.

By Giuseppe Distefano and Michelangelo Marchese, Marketing Industrial and Power Conversion Division, STMicroelectronics

 

These devices are required to switch ON-OFF with very large inductive loads (more than 1 henry), for thousands of cycles during their life. In addition to IEC specification compliance for Electro Magnetic Compatibility (EMC) such as the 2.5 kV burst test, the devices must also fit in very small cases (< 5 mm), so very tiny packages are required.

STMicroelectronics’ TDE1708DFT device belonging to the Intelligent Power Switch (IPS) family provides a solution to the above requirements. An IPS integrates a control part (logic, interface, drivers and protection) with a power stage. The TDE1708DFT can work as a high-side driver as well as a low-side driver, offering maximum flexibility in the configuration of the loads.

High-Side Driver Configuration

Low-Side Driver Configuration

The chip integrates several blocks for protection against abnormal electrical conditions or faults. It has a pin for output status indication and is housed in the tiny leadless DFN 8-lead with exposed pad package.

Micro lead package DFN 4x4 8-lead

Device Description

Figure 4 clearly identifies the main protection blocks of the device: junction over-temperature, current limitation (0.3A typical), auxiliary voltage regulator, and the clamping voltage.

TDE1708DFT block diagram

Junction over-temperature protection and current limit protect the device against overload and short circuit of the load to ground. Turn- ON time during short circuit and/or overload is set by an external capacitor, thus minimizing the power dissipation on the device during these tough electrical conditions.

The clamping voltage protects the final stage against voltage spikes and also performs fast demagnetization of inductive loads (-55V minimum demagnetization voltage).

Although not visible in Figure 4, the device is also protected against reverse supply (-Vcc), reverse output (up to -50V), loss of ground and loss of Vcc. In case of loss of ground or Vcc, the power stage is switched OFF. In this condition the internal +5V voltage regulator will not work properly. The internal voltage regulator supplies all the logic blocks. It can also be used to supply an external circuit. The status of the output is visible by connecting an LED to the LED driver pin of the device. Other features of the device include a maximum supply voltage up to 50V and high impedance differential input which ensures high noise immunity.

Application

Often the TDE1708DFT is connected to proximity detectors to drive actuators in factory automation, process control and building automation.

Proximity detector

Figure 6 provides a typical application circuit for proximity detectors. The proximity detector is directly connected to the input of the device. The schematic is optimized to accept detectors with the body connected to ground or with an independent ground (by properly using J1 and J2). Any type of proximity detector can be used thanks to an adjustable input hysteresis through R1. To avoid over-voltages or disturbances caused by serial inductance of the long connection wires between the device and power supply, filtering capacitors on pins Vreg and Vs are adopted. A delay capacitor assures proper behavior during short circuit of the output. Figure 7 reports the Vcc and output current waveforms during short circuit.

Application circuit

The TDE1708DFT complies with the international standards of Programmable Logic Controllers (PLCs) and with the typical industrial Electro Magnetic Compatibility (EMC) standards. One of the tough EMC tests for an industrial device is the fast transient (burst) immunity test. This test is described in the international rule IEC 61000-4.

Short circuit protection

A burst exceeding the tolerance level causes the output transistor to switch OFF even if the input has not changed its high state. A burst test performed on the TDE1708DFT, with a delay capacitor of 10nF, provided noise immunity up to +2500V/-2500V burst voltage.

Spurious transition of the output transistor due to burst pulse

Conclusions

An Intelligent Power Switch for proximity detectors, and industrial automation in general, has been presented. The device allows reduction of external component count, optimized application performance and provides a high quality and low cost system solution.

References:

1) “Intelligent Power Switch”, TDE1708DFT Datasheet, www.st.com
2) “Effective Filtering of TDE1707”, AN495, www.st.com
3) “TDE1707 Noise immunity, short circuit and reverse output protection characterization”,  AN1213, www.st.com

 

 

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