MAX44211 Output Protection

MAX44211-Output-Protection.jpg

Unwanted transients emanating from the power line back to the line-driver’s output and back-EMF generated by the coupling circuit when the load is disconnected and connected, and vice versa, create undesirable over-voltage conditions. Back-EMF is also generated when the line driver outputs are toggled from high to low impedance state, if significant current was flowing at the disconnect time. The MAX44211 power line communications driver most often is placed facing the power line with an isolating stage between them. In case of such over-stress conditions, external protection is required to protect the MAX44211 and downstream circuits.

The internal ESD clamping structure is present inside MAX44211 (see Figure) to protect the part from ESD or sub-microsecond events. When the application has hazards where these events can occur frequently and for comparatively longer time, it is recommended to have external protection circuitry. Failure to accommodate an output protection can result in over-stressing the outputs (OUT+/ OUT-) and eventually damage the part.

This application note provides insights and information on how to add external protection circuitry at the outputs of the MAX44211. A circuit using VAVDD = 15V is used in this application note.

The figure shows the internal ESD clamping protection structure.

Download PDF: MAX44211-Output-Protection

Source: Maxim Integrated

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High-Speed Over-current Detection

High-Speed-Overcurrent-Detection

This high-speed, low-side over-current detection solution is implemented with a single zero-drift fast-settling amplifier (OPA388) and one high-speed comparator (TLV3201). This circuit is designed for applications that monitor fast current signals and over-current events, such as current detection in motors and power supply units.

The OPA388 is selected for its widest bandwidth with ultra-low offset and fast slew rate. These parameters allow the circuit to be a well-balanced, high-speed solution in order to accurately detect high frequency current components. In applications that only require average current detection, devices with less bandwidth can be used like the LPV821. In applications that require faster response time, devices with larger bandwidth can be used like the THS4521.

The TLV3201 is selected for its fast response due to its small propagation delay of 40 ns and rise time of 4.8 ns. This allows the comparator to quickly respond and alert the system of an over-current event all within the transient response time requirement. The push-pull output stage also allows the comparator to directly interface with the logic levels of the micro-controller. The TLV3201 also has low power consumption with a quiescent current of 40 µA.

Typically for low-side current detection, the amplifier across the sense resistor can be used in a non-inverting configuration. The application circuit shown, however, uses the OPA388 as a differential amplifier across the sense resistor. This provides a true differential measurement across the shunt resistor and can be beneficial in cases where the supply ground and load ground are not necessarily the same.

Dedicated current sense amplifiers can also be an option for high-speed current detection. The trade-offs for each option should be taken into account when deciding on a current sense solution. Integrated solutions can provide larger bandwidth and savings on board space, but can be more costly and offer limited customization. Discrete solutions can be lower cost and easily customizable, but could require precision resistors to increase measurement precision.

Download PDF: High-Speed-Overcurrent-Detection

Source: Texas Instrument

Portable Variable Power Supply

Portable Variable Power Supply.jpg
Photo taken from http://www.Instructables.com website

In many of the project applications and testing applications, Variable DC Power supplies are used. Sometimes it happens that one can not find an AC power socket nearby testing circuit. Also, Power supplies are usually AC powered and are bulky, because of their voltage transformers, to bring anywhere near testing circuit or equipment. Hence, Portable Variable DC Power Supply is required which helps people become mobile in doing electronic projects that will need power supplies.

This project uses a voltage regulator and a potentiometer that allows the user to change the output voltage between 2 volts to 25 volts. It is also equipped with a small seven segment display which acts a voltage meter which lets the user to know how much voltage is being supplied by the regulator. Powered by a 9V battery, this project gives mobility in making circuit projects. It also includes a banana jack that accommodates plugs that can help attach it to different applications.

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Source: Portable Variable Power Supply