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TPS1663: current limit accuracy

Gene Qiu
Intellectual 1720 points
Part Number: TPS1663

Hi Team,

We tested TPS16630PWPR and used a 5.6k resistor （1% accuracy）to connect it to the Ilim pin. According to the specification, the current limit should be 18/5.6k= 3.2A. we used electric load with CC mode, and then slowly increase/decrease the load current to test the protection. During the actual test, the data are shown below.

Vin Electric load with CC mode, slowly increase load current till protection Electric load with CC mode, slowly decrease load current till retry V(IMON), R(IMON=27k ohm)
5V 4.12A 3.04A 2.809V/2.078V
9V 4.30A 2.84A 2.939V/1.945V
12V 4.30A 2.85A 2.933V/1.945V
15V 3.41A 2.98A 2.312V/2.031V
20V 3.67A 3.35A 2.502V/2.291V

We hope that the current point is relatively stable. For example, if we set the current point at 3.2A, it should be protected if it is higher than 3.2A, and it should be restored if it is lower than 3.2A. There may be errors +-6% as shown in datasheet, but here test with more than ± 20%.

We also tested the voltage on the IMON pin, which is relatively accurate. We want to use the voltage of this pin to give the ADC pin of MCU to detect the current. If it exceeds 2.2V, turn off the current limiting IC.

I hope to ask below two questions

1: Why is the current protection point of the current limiting IC different from that of the rising and falling protection points? Different voltage values? What is the cause? It is better if you could help to explain the working principle of current limiting of this IC.

2: Is the voltage feedback current value of IMON pin accurate? I think the error in the specification is very small. Is it appropriate to use this foot as the judgment of over-current protection?

Rilim=5.6k ohm， 1% accuracy Electric load with CC mode, increase load current till protection Electric load with CC mode, decrease load current till retry V(IMON), R(IMON=27k ohm)
5V 4.12A 3.04A 2.809V/2.078V
9V 4.30A 2.84A 2.939V/1.945V
12V 4.30A 2.85A 2.933V/1.945V
15V 3.41A 2.98A 2.312V/2.031V
20V 3.67A 3.35A 2.502V/2.291V
  • 0
    TI__Guru** 105611 points

    Hi Gene,

    The issue is due to e-load in cc mode. Always use resistive loads or e-load in CR mode to evaluate eFuse devices. 

    With resistive loads, the output operating point will be decided by the eFuse in current limit mode of operation. In case of active loads (e-load), the output voltage & current will be decided by both the e-load characteristics and eFuse characteristics in current limit mode. So, load current cannot be limited by the set current limit of the eFuse. You will observe current limiting at different value than the programmed current limit value.

     Alternate explanation: When the eFuse device reaches current limit, the device acts as a current source. If an electronic load is used for testing in CC mode, which turns out to be placing two current sources in series in the network. When the electronic CC load exceeds set current limit of eFuse device, the electronic load tries to pull down the output voltage and shifts the operating current other than the current limit value.

    Can you retest again.

    Best Regards, Rakesh