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TS321: Low Headroom Current Sink

Antonio Fadhel
Genius 9410 points
Part Number: TS321
Other Parts Discussed in Thread: LMC8101, TINA-TI, LM321

Hi Team,

I am looking for a low cost linear single-LED driver for the following requirements:

- Vin: 3.5V-8V

- LED Vf: 3.2V

- Iled: 40mA-300mA - resistor programmable

- Iled accuracy: +/-5% 

- As low cost and small as possible but no BGA/CSP packages

Do you have a recommended circuit for this? Would the TS321 be the best fit? I tried the below on Tina which seems to work fine (PNs are just for illustration - I used different devices and adjusted parameters), but want to make sure I'm not missing anything. Any low-cost way to generate the 200mV reference (or a smaller/lower cost LM10-type device)?

Thanks,

Antonio

  • 0
    TI__Mastermind 22825 points

    Hi Antonio,

    The lowest cost BGA / CSP device would be the LMC8101 that would fit this application and can run the entire supply voltage range (3.5V - 8V).

    TINA-TI simulation looks fine and the MOSFET seems to stay in the Saturation region, where you want it to be, for all voltages. Some devices I tried led to instability which I could not remedy! These could have been older devices with less-than-optimal models. But I don't see any issues with using the LMC8101, shown below.

    TINA-TI Simulation File here (I've edited the MOSFET model for lower threshold voltage to match the device you're using):

    LMC8101 LED driver Hooman 4_4_17.TSC

    Regards,

    Hooman

  • 0 in reply to Hooman Hashemi
    TI__Genius 9410 points
    Hi Hooman,

    Thanks for the detailed response. Sorry if I wasn't clear, but the customer cannot use BGA/CSP packages. Do you have a similar device that would work but is smaller than the VSSOP (a SOT-23, for example)? Any low-cost recommendations to generate the 200mV reference?

    Thanks,
    Antonio
  • 0 in reply to Antonio Fadhel
    TI__Mastermind 22825 points

    Hi Antonio,
    The only small package (SOT23 or smaller) OPA device that can cover the supply voltage range is the LM321. I've not simulated with this device to see the result.

    For the 0.2V reference, I'd just use a zener biased off the supply voltage, or a 1.2V common shunt reference and then divide the voltage down (voltage divider using 2 R's) to 0.2V with adequate noise / shunt-cap decoupling to remove noise.

    Regards,
    Hooman