Data Sheet

LT3073

analog.com

Rev 0.

29 of 37

Figure 74. EVAL-LT3073-AZ Evaluation Board

Protection Features

The LT3073 has an internal current limit that clamps output current to 4.5A. In addition, the LT3073 has a ±3%

accurate programmable precision current limit. The die junction temperature can exceed the 125°C maximum

operating temperature if the ambient temperature is high enough. If this occurs, the LT3073 relies on an internal

thermal safety feature. Typically at 168°C, the LT3073 thermal shutdown engages and the output is shut down until

the IC temperature falls below its thermal hysteresis limit.

Current Monitor and Externally Programmable Current Limit

The IMON pin’s current limit threshold is 1V. Connecting a resistor from IMON to GND sets the maximum current

flowing out of the IMON pin, which in turn, programs LT3073’s current limit. With a 3A•kΩ programming scale factor,

the current limit can be calculated as follows:

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For example, a 1kΩ resistor programs the current limit to 3A, and a 2kΩ resistor programs the current limit to 1.5A.

Kelvin connect this resistor to the LT3073’s GND pin for good accuracy.

As shown in the electrical characteristic table (Table 1), the IMON pin sources current proportional (1:3000) to output

current; if the external current limit is not used, connect IMON to GND, which sets the Internal current limit to 4.5A.

Thermal Considerations

For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the

LT3073. The IN and OUT pins on the bottom of the package should be soldered to IN and OUT planes accordingly. In

addition, the IN and OUT must be connected to large copper layers below with thermal vias; these layers will spread

heat dissipated by the LT3073. Placing additional vias can reduce thermal resistance further. The die temperature is

calculated by multiplying the LT3073 power dissipation by the thermal resistance from the junction to the ambient.

The internal overtemperature protection monitors the junction temperature of the LT3073. If the junction

temperature reaches approximately 168°C, the LT3073 output is shut down until the temperature drops about 7°C.