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LM2594: LM2594 OCP behavior

Mark Chen52
Expert 5755 points
Part Number: LM2594

Hi Expert,

my customer found a strange phenomenon on LM2594 OCP test.

According to difference output current to trigger the OCP point, the drop of output voltage is difference, please refer attached waveform.

when load current 0.8A, the output voltage pull down to 1.5V then discharge to zero.---figure 1

when load current 0.9A, the output voltage pull down to 0.8V then discharge to zero.---figure 2

when load current 1.0A or above, the output voltage pull down to zero.---figure 3

Could you help to explain this saturation? And what’s device behavior as triggered current limit? i didn't found any description for current limit protection.

Figure1: 0.8A

figure 2:

figure 3:

Best Regards,

Mark

  • 0
    TI__Mastermind 27045 points

    Hi Mark,

    The switch current peak is 0.8A typical. the maximum output current is below 0.8A if considering inductor current ripple, the output voltage will drop with heavy load biased.

    B R

    Andy 

  • 0 in reply to Andy Chen
    TI__Expert 5755 points

    Hi Andy,

    So this is normal phenomenon on this device, right? 

    if the vout drop under the heavy load condition, why the output voltage drop to 1.2V stop then discharge output cap to zero as the output current 0.8A instead of drop down to zero directly? 

    Best Regards,

    Mark 

  • 0 in reply to Mark Chen52
    TI__Mastermind 27045 points

    Hi Mark,

    This is quite normal behavior at heavy load condition.

    For fixed Vin, Fsw, inductor value and peak current limit, the output voltage will change the inductor current ripple which limit the maximum output current capability, the higher load current, the lower output voltage.

    B R

    Andy