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LM5021: Current limit value

Kuramochi Tadahiko
Guru 28715 points
Part Number: LM5021

Hi,

I received the following question from my customer.

They are evaluating the LM5021-1.

How can we estimate the current limit value?

The datasheet is described that If the CS pin voltage plus the slope compensation voltage exceeds 500 mV, the OUT pin output pulse will be immediately terminated. 

How should we calculate the slope compensation voltage?

Best Regards,

Kuramochi 

  • 0
    TI__Genius 9130 points
    Kuramochi-san,

    As shown in the block diagram on page 10 of the datasheet, there is 0-50 uA ramp current source that pulls up on the CS pin. So the pk-pk slope comp voltage will depend on the external resistor value that the user puts in series with the CS pin, together with the internal 1.8 k resistor shown in the block diagram.

    The electrical table shows the peak slope comp voltage is 90 mV (min 70 mV, max 110 mV), and this accounts for the tolerance of both the current source and resistor. This is the minimum amount of slope comp ramp that can be achieved with the CS pin shorted directly to the shunt resistor.

    If extra resistance is inserted between the CS shunt and the shunt, more slope comp voltage can be generated, if required. E.g. if an external 1 k resistor is used on the CS pin, slope comp pk-pk ramp ~ [90 mV + (50 uA * 1 k)] = ~140 mV pp.


    I hope this helps to answer your question, if so please click the "verify answer" button.

    Thanks,
    Bernard