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Original question:

TPS55285: TPS55285

TPS55285: Halogen bulb application suitability

Minh Vu
Prodigy 10 points
Part Number: TPS55285
Other Parts Discussed in Thread: TPS55289

Tool/software:

Hi TI Engineers, 

I am in the development phase for a broadband Near-Infrared (NIR) light source intended for a portable spectroscopy device.

The light source will consist of mini halogen indicator bulbs. I am considering two types of bulbs as viable candidates:

  • Type 1: 6.5V, 250mA

  • Type 2: 10-15V, 110mA

The expected input power will come from a 2-cell (2S) battery pack, providing a voltage range of approximately 6V to 8.2V. The output voltage to the bulbs would ideally be programmable to allow for dimming and spectral tuning. I anticipate powering between 2 and 8 bulbs simultaneously, hopefully I will know the exact number after the first prototype is created.


I am currently evaluating two of your synchronous buck-boost converters with integrated MOSFETs: the TPS55285 and the TPS55289. As far as I can tell, the only difference is the MOSFET Rds_on and the input voltage range. Since the lights do not need to be independently switched, I was planning to drive them directly from the output voltage.

My primary concern, especially when driving multiple halogen bulbs, is managing the high inrush current that occurs when the cold filaments are first energised. Assuming a 10x factor, 8 of the 6.5V/250mA ones could draw up to 20A. I am planning on doing some measurements to find the exact figure on the inrush current over the next few days.

Given these requirements and my inrush current concerns, which would you recommend?

Thank you for your time and assistance.

Best regards,
Minh

  • +1
    TI__Genius 14960 points

    Hi Minh,

    Thank you for reaching out. Both TPS55285 and TPS55289 has output current limit function. TPS55289 needs external sense resistor  for output current limit function.

    Even though the output current limit function are not used, both ICs cannot support 20A output current. It will be limited by 8A average inductor current limit. When the limit is triggered, Vout may drop. 

    I have a question that, if current is limited and Vout cannot reach the target, can the first energize be completed? If no problem, I recommend TPS55285 for low cost, small size and simple external circuit.

    Regards,

    Mulin

  • 0 in reply to Mulin Yuan
    Prodigy 10 points

    Hi Mulin, 

    Thank you, I had not realised that the TPS55285 does not need a sense resistor. Although I would still need to add one for current monitoring.

    The current inrush is due to the cold filament so it should still turn on but just slower, should still be fine for our application at this stage. 

    Thank you for the recommendation, I will proceed with the TPS55285.

    Best wishes,
    Minh