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TPS92515: TPS92515: Operation current

Christian Bach
Prodigy 30 points
Part Number: TPS92515

Hello there
I have to design a standby power consumption optimized design with the TPS92515.
The LEDs are turned off: Vadj is directly tied to Vcc. PWM input is controlled by uC and has a logic level of 0.
So everything is switched off.

My measurements show a power consumption of 4.9mA @24VDC and I can measure a leakage voltage at pin sw= 0.069V
From the datasheet 7.5 -> Electrical characteristics -> System currents
Icq operating current not switching VIADJ=VCC 0.85mA (typ) / 1.5mA (max)
How I can reach a 1.5mA operating current? Do I misunderstand operating current?

Thanks and regards,

Christian

  • 0
    TI__Mastermind 28655 points
    Hello Christian,

    Do you have a schematic you can share? Where are you measuring 4.9 mA @ 24 VDC input? What is connected to VCC? What is connected to Vadj, is it just tied to VCC? What is connected to PWM? Have you verified that the output is not switching?

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 30 points

    Hello Irwin,

    thank you for your quick reply.

    Yes I can share you the schematic.

    I measure the 4.9mA at the 24V lab power unit with a Fluke179 as amp meter. I can disconnect the TPS92515 part which is on a seperate pcb with a connector. When I do this there is a difference of 4.9mA which is for sure from the TPS92515.

    Connected to the VCC from the TPS92515 is Vadj (Iadj Pin 10) and D4 with the boot pin (pin 4). I also tried as mentioned in the datasheet to supply the boot pin (pin4) from a external 5V source to safe some power but this didn't changed anything.

    Connected to pwm is my uC, direct to pwm pin over R6. C33 is not connected. Logic level is 0 and is also 0V measured also the uC software is programmed to put pwm to 0. I tried to quick tie pwm to gnd to be sure it is off - no change.

    Best regards,

    Christian

  • 0 in reply to Christian Bach
    TI__Mastermind 28655 points
    Hello Christian,

    I just took the TPS92515 EVM in the lab. Removed R14, R12 and R11 leaving 100K pull ups on the Vadj pin from VCC (basically pulling it up to VCC) and I removed R5 to reduce the current for testing. I have a function generator providing PWM from 0-4 VDC. I set it to 0.1 Hz at 1% duty to see what the PWM low input current is. I measure 89.5 mV across a 100 ohm resistor resulting in 895 uA or 0.895 mA. This is very close to the 0.85 mA for the typical value stand-by current and below the maximum of 1.5 mA. I looked at your schematic and don't see anything that would pull the extra current you are seeing. Is this the entire circuit? Is it possible you have a test equipment path that could be drawing some current from the circuit? If you take the separate PCB and just power it from +24V and measure the input current is it still off?

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 30 points

    Hello Irwin

    Thank you very much for testing. I found the cause of the higher power consumption.

    So I was suspicious after your reply and changed the amp meter and the cables. And now I can measure 0.922 mA current consumption per TPS92515.

    Time for new equipment.

    Best regards,

    Christian