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Original question:

OPA548: Does output current limit drift with aging?

OPA548: Current limit settings in OPA548

Ambili R
Prodigy 10 points
Part Number: OPA548

We are using OPA548 in our design with the following requirement-

“The output current of OPA548 must be limited to 171mA.”

 

For this, we have used a 402k Ohm resistor as the current limit resistor (RCL). Can you suggest if there is any way in which we can avoid using a big value resistor like 402k Ohm and achieve the 171mA current limit?

 

 

Also, there is a 4.75V source internal to the OPA548 connected to a 13750 Ohm resistor as shown from the snippet attached below (from the datasheet) –

 

 

Formula for RCL shown below (from the datasheet)-

 

 

Could you also let us know how the value “15000” is derived in the formula?

  • 0
    TI__Mastermind 49405 points

    HI Ambili,

    The OPA548 output current drive is as high as 5-A, so the current limit resistor will need to be very high to limit the current to only 171mA; this current is only~3% of 5-A drive capability; therefore, as you have mentioned, the 402-kOhm resistor will be required to set a ~171.3mA current limit. 

    A second option, the datasheet shows on Figure 41, p.26 that applying a voltage referred to (V-) at pin(3) can be used to set the current limit as well, where setting pin (3) to V(-) sets the limit to 5A and setting pin 3 to a potential of (V-) + 4.75V sets the current limit to 0-A.  By adjusting/trimming this voltage, the current limit can be adjusted.

    A third option to set the current limit may be to place a reference voltage of +4.096-V referred to the V- supply, and add a series resistor of around 80.6-kOhm connected to pin (3) to set the current limit to approximately ~100mA.  See TINA simulation below.

     

    The 15,000 is a function of the gain of the internal circuit / current mirror setting the current limit; and therefore it is not show in the datasheet derivation.

    Thank you and Best Regards,

    Luis