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TPS92638-Q1: Regarding selection of the Led Driver and components for the application

Vishaal S
Prodigy 50 points
Part Number: TPS92638-Q1
Other Parts Discussed in Thread: TPS92638EVM, DRV5056

Tool/software:

Hi sir, 

This is Vishaal working as an Hardware Engineer. We are planning to use TPS92638-Q1 for our Automotive application where the main working is the 6 LEDs each will be connected in 6 Channels (1 LED per channel) and LEDs will turn on/ off based on the magnetic sensor. For interior Lighting we are planning to use PWMs which will be controlled by Magnetic sensor. As we are not using the REFHI Pin so, we are planning to Pull it down with a 100kOhm Resistor at STOP Pin.  REF resistor value as per datasheet is calculated for our Output current 11mA we are planning to use 22k Ohm resistor with 1% Tolerance for R(REF) and the unused PWM we are planning to ground with a 100k Ohm resistor. Please confirm this as soon as possible so that we can start with our design.

Thanks, 

Vishaal S

  • +1
    TI__Intellectual 1400 points

    Hello Vishaal,

    A 100k Ohm pull down resistor for the STOP pin is acceptable.

    A 22k Ohm will result in an output current of 11.11mA so this calculation is correct.

    100k Ohm pull down resistors for the unused PWM pins is acceptable.

    If you have any questions, please let me know

    Kind Regards,

    Nicholas Alexander

  • 0 in reply to Nicholas Alexander
    Prodigy 50 points

    Hi Nicholas, 

    Thank you for your quick response and support. Additionally for the TEMP Pin we have calculated for the Temperature at which IC is going to have (100 degree Celsius) and in Evaluation board it is instructed to connect a 100pF in schematic but in BOM its 0.1uF which is 100000pF and for R9 we are planning to use 100k Ohm Resistor to pull down. Same for C1 its 0.1uF in schematic and in BOM its 0.01uF. Please do confirm the value to be used for the Capacitor - C4, C1 and R9 in the Evaluation board TPS92638EVM. 

    Thank you, 

    Vishaal S

  • +1 in reply to Vishaal S
    TI__Intellectual 1400 points

    Hello Vishaal,

    I believe that C4 in the EVM is only to help with decoupling noise across the TEMP pin and potentiometer. This is not necessary if you are going to have a static voltage from a pull down resistor or voltage divider attached to it. 

    C1 is also to minimize input noise. I would recommend using 0.1uF for this value.

    Can I get more information for the TEMP pin? Is 100 degrees C your goal for the foldback temperature?  A 100k Ohm resistor will work but this will move your T(th) to about 115C then your 50% output limit would be at 135C. Please refer to the figure for how the pulldown resistor will change T(th).

    Here is another TI design that uses the TPS92638-Q1 for your reference. https://www.ti.com/tool/TIDA-01007

    Kind Regards,

    Nicholas Alexander

  • 0 in reply to Nicholas Alexander
    Prodigy 50 points

    Hi Nicholas,

    Thank you for clearing the above doubt. We do not want PWM dimming. So we are planning to connect PWM channel input pins to battery voltage VIN line itself. So our query is :- with our  battery voltage range of 8V to 16V, will there be any dimming when battery voltage starts dropping towards 8V from 16V? 

    we will have to enable / shutdown the LED driver IC TPS92638-Q1 based on the magnetic sensor output. we are planning to use DRV5056A1 as its voltage output is 0.6V at 0 magnetic field and it suits the Vil level of EN pin of LED driver which is 0.7V. However, this DRV5056 is unipolar, so can you please recommend any bipolar magnetic sensor output compatible with logic low (0.7V max) and high levels(2V min) of EN pin of LED driver TPS92638-Q1.

    Thanks, 

    Vishaal S

  • 0 in reply to Vishaal S
    TI__Intellectual 1400 points

    Hello Vishaal,

    As long as your input voltage is greater than the forward voltage of the LEDs and the dropout voltage across the device, there should be no dimming. The dropout voltage at 35 mA is typically 0.28V with a maximum of 0.45V. There should be no dimming as long as your forward voltage of the LEDs are less than 7.55V.

    I am not an expert on magnetic sensors that TI provides so I do not know the best device for your application. Please create a new thread with the magnetic sensor as the topic to contact an expert. 

    Here is the list of TI's bipolar hall effect sensors: https://www.ti.com/product-category/sensors/magnetic/linear-hall-effect/products.html#1241=Bipolar%3BRatiometric%20bipolar&sort=1241;desc&

    Here is the list of TI's omnipolar hall effect latches: https://www.ti.com/product-category/sensors/magnetic/hall-effect-latches-switches/products.html#1241=Omnipolar%20switch&

    Best,

    Nicholas Alexander

  • 0 in reply to Nicholas Alexander
    Prodigy 50 points

    Hi Nicholas, 

    Our LEDs Forward Voltage is around 3V and we are connecting 6 LEDs in parallel with our Battery voltage varies between 8-16V. As i understand from the above comments i hope for this spec the LED Driver will work without dimming. 

    Thanks, 

    Vishaal S

  • 0 in reply to Vishaal S
    TI__Intellectual 1400 points

    Hello Vishaal,

    This is correct. There should be no dimming.

    Best,

    Nicholas Alexander