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How an open-load condition can be detected by PROFET™ +2 12V devices?

How an open-load condition can be detected by PROFET™ +2 12V devices?

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Open-loads in PROFET™ +2 12V devices can be detected by using the integrated diagnosis feature and external components.

For some loads, it may be necessary to check their availability without powering them up. For example, it may be necessary to check if loads, bulbs or LEDs (or the cable they are connected to) are intact or broken, without creating a flash light by switching them on.

Examples of the open load detection at "OFF" for a single output and for multiple device or outputs are shown in Figure 1 and Figure 2.

Note:              These are very simplified examples of an application circuit. The function must be verified in the real application.

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Figure 1       Application diagram with open load detection circuitry

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Figure 2       Application diagram with open load detection circuitry for multiple outputs and devices

In the example circuitry in Figure 1, a small current (few milliamperes) is injected into the output, powerful enough to pull up the output if there is no load connected, but not powerful enough to activate the load in a disturbing manner. If DEN = "high" while IN = "low" and the output voltage of a PROFET™ +2 12V increases close to VS, drain-source voltage will be lower than VDS(OLOFF) and the PROFET™ +2 12V will provide an open load signal IIS(OLOFF). To avoid continuous power losses in "OFF" state in open-load condition, and to be able to distinguish open load from short-to-battery in "off" state, the pull-up circuitry must be switchable.

The value of the output voltage depending on different conditions can be seen in Table 1. 

Table 1: VDS voltage with fixed pull-down and switchable pull-up

Channel OFF

Load OK

Open-load

Short circuit to battery

Pull-Up activated

VDS ~ VS

VDS ~ 0V

VDS ~ 0V

Pull-Up deactivated

VDS ~ VS

VDS ~ VS

VDS ~ 0V

Figure 3 shows a possible software strategy using the circuitries in Figure 1 and Figure 2.

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Figure 3       Example code for open-load or short-to-battery detection

The limits of the pull-up currents have to be below the maximum allowed load current, which does not activate the load. That depends strongly on the load, and has to be adapted accordingly. To compensate leakage currents from battery to output (e.g. output leakage current IL(OFF)) and from output to GND, pull-up and pull-down resistors might be needed.

More information   

Application note: https://www.infineon.com/dgdl/Infineon-Z8F65048819_PROFET_2_FAQ-ApplicationNotes-v01_20-EN.pdf?fileI...

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