Trimming method for current sense amplifiers

A method for adjusting a current sense (CS) amplifier, increasing a Common Mode Rejection Ratio (CMRR) and reducing a gain error of the CS amplifier as compared to an unadjusted CS amplifier, the method comprising:

• computing a first slope as a difference of a first set of two measured referred to input (RTI) offset voltages divided by the difference of two different CM input voltages at which each RTI offset voltage of the first set was measured;
• adding one of a plurality of selectable trim resistors to an adjustable feedback resistor chain coupling an output of a differential amplifier within the CS amplifier to an inverting input of the differential amplifier;
• computing a second slope as a difference of a second set of two measured RTI offset voltages divided by the difference of the two CM input voltages at which each RTI offset voltage of the second set was measured;
• calculating a line equation for slope versus trim resistance values and determining a target trim resistance value corresponding to a slope value of zero;
• identifying selectable trim resistors producing a trim resistance value as close as possible to the target trim resistance value, given the selectable trim resistors available in the feedback resistor chain;
• and
• adding the identified selectable trim resistors to the feedback resistor chain.

A method for adjusting a current sense (CS) amplifier, increasing a common mode rejection ratio (CMRR) and reducing a gain error of the CS amplifier as compared to an unadjusted CS amplifier, the CS amplifier comprising a differential amplifier, and the method comprising:

• setting a non-inverting CS amplifier input node and an inverting CS amplifier input node to a same common mode voltage;
• measuring a first input voltage across a first input resistor coupled between an inverting differential amplifier input node and the inverting CS amplifier input node;
• computing a target feedback trim voltage across a plurality of programmable feedback resistors within a feedback resistor chain based on a target CS amplifier gain and the first input voltage, said feedback resistor chain coupled between the inverting differential amplifier input node and a differential amplifier output node;
• computing a voltage across each of the plurality of programmable feedback resistors based on a resistance value ratio of each corresponding programmable feedback resistor and a first fixed feedback resistor within the feedback resistor chain;
• identifying a first combination comprising one or more programmable feedback resistors that produces a voltage drop closest to the target feedback trim voltage as compared to other combinations, said identifying based on the computed programmable feedback resistor voltages;
• and
• selecting the one or more programmable feedback resistors identified within the first combination for inclusion in an electrical path of the feedback resistor chain.

A method for adjusting a current sense (CS) amplifier, increasing a common mode rejection ratio (CMRR) and reducing a gain error of the CS amplifier as compared to an unadjusted CS amplifier, the CS amplifier comprising a differential amplifier and the method comprising:

• connecting a short across at least part of a programmable feedback resistor chain, said programmable feedback resistor chain coupled between an inverting differential amplifier input node and a differential amplifier output node;
• measuring a first set of output voltages of the differential amplifier at each of two different common mode (CM) voltages, each of the CM voltages being applied at both a non-inverting CS amplifier input node and an inverting CS amplifier input node;
• removing the short and measuring a correction resistor within the programmable feedback resistor chain;
• measuring a second set of output voltages of the differential amplifier at each of said CM voltages, each of the CM voltages being applied at both a non-inverting CS amplifier input node and an inverting CS amplifier input node;
• computing a line equation based at least in part on output voltage differences for the first and second set of output voltages and on resistance values of at least part of the programmable feedback resistor chain with and without the short;
• determining a target feedback resistance value to add to the programmable feedback resistor chain based at least in part on the computed line equation;
• identifying a first combination of programmable feedback resistors that produces a resistance closest to the target feedback resistance value as compared to other combinations;
• selecting one or more programmable feedback resistors identified within the first combination for inclusion in an electrical path of the programmable feedback resistor chain.