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TPS25947EVM: current limit

GARETH OU
Guru 11595 points
Part Number: TPS25947EVM


Hi

he customer tested the EVB TPS259474L and encountered several problems. The resistance value calculated by the ILM resistance formula There is a big gap with the actual 3334/2.5A=1.333K Actual 2.12A Shutdown 3334/3A=1.111K Actual 2.4A Shutdown Resistance on EVB 1.65K 3334/2A=1.667K Actual 1.81A Shutdown And it is powered by a power supply, the power supply is very stable Connect the EVB input 12V, the output end is connected to the load The output current will float, no matter how high the current is adjusted, it will float Take 2.12A as an example, the lowest to 2A, the highest to 2.3A will keep jumping

  • 0
    TI__Guru* 79181 points

    Hi Gareth,

    Sorry but I was not able to clearly understand your issue. You mean that what current limit is set by formula you are seeing deviation from that?

    Please tell one example of RILIM you chose and at what current level did device break the circuit?

    Also can you tell one test result from the default resistor of 549 already on EVM(J19,7-8,R23)?

    What type of load are you using for testing?

    Also accuracy of current limit can vary due to PVT:

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Guru 11595 points

    Hi Kunal

    1.)Also can you tell one test result from the default resistor of 549 already on EVM(J19,7-8,R23)?

    TPS259472A RILM setting 1.65K test result 2.5A suhtdown (The current is stable before Suhtdown)

    TPS259474L RILM setting 1.65K test result 1.81A suhtdown (The current will be unstable before Suhtdown)

    2.)What type of load are you using for testing?

    LCD backlight

  • 0 in reply to GARETH OU
    TI__Guru* 79181 points

    Hi Gareth,

    Reading through multimeter can be inaccurate. Please use a oscilloscope to measure. Use a current probe to measure current through device from input side of device. Please probe VIN,VOUT,IIN. Slowly increase current , set trigger to VOUT falling and then see.

    You can see EVM user guide result , for 6A setting device is turning off at 6.1A.

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Guru 11595 points

    Hi Kunal

    The loading test done by the customer using the LCM Backlight module, Because Backlight Control Curren uses PWM method, Therefore, the Power Loading square wave causes the differential output voltage and current to be unstable And our LCM module Inrush Current is too large to cause the IC Current limit to activate the protection circuit, so Ilimit will be wrong The figure below is the Input voltage waveform

  • 0 in reply to GARETH OU
    TI__Guru* 79181 points

    Hi Gareth,

    eFuse input is PWM? eFuse output is LCM backlight module? Since input is a square wave so output current is not stable?

    Regards

    Kunal Goel

  • 0 in reply to Kunal Goel
    Guru 11595 points

    Hi Kunal

    eFuse input is PWM? is DC12v

    eFuse output is LCM backlight module? Yes, because the Backlight Control Curren uses the PWM method, the Power Loading square wave causes the differential output voltage and current to be unstable In this way,

    Control Curren uses PWM mode. Should customers not be suitable to use efuse? It is more suitable for traditional fuse?

  • 0 in reply to GARETH OU
    TI__Guru* 79181 points

    Hi Gareth,

    Can you show me a block diagram of your system and how does signal look at important nodes ,that will be easy to understand .

    Is this waveform at eFuse input?

    Regards

    Kunal Goel