DPA423-426 External Current Limit design
Posted by: rossiking
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In DPA423-426 datasheet figure 16,External Current Limit design:Ilimit=100%@36VDC,64V@72V,why?Can you tell me how I can calculate the Ilimit at other voltage and the relationship with RLS,RIL?Besides,how X work as a voltage source?
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I measure the vlotage of X with multimeter,it is 1.2V,sometimes 1.14V,but the limit of X in our tester-FCT is 2.15V-27V.Sometimes when the common mode inductor of the input voltage is abnormal,the X pin voltage is 3.017V,I don't know why,can you tell me what affect the voltage of X and how,thanks a lot.
sorry the limit is 2.15v-2.7v
You can calculate the x-pin current (positive when flowing into the chip) as follows:
Ix = (Vin-Vx)/RLS-Vx/RIL
@36V input, Ix = (36-1.3)/363-1.3/4.2 = -0.213 mA --> 100% current limit
@72V input, Ix = (36-1.3)/363-1.3/4.2 = -0.114 mA --> 64% current limit by the curve shown in Figure 34.