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TPS92612: Can the PWM pin be held low for blinking an LED?

John Griffith
Mastermind 21811 points
Part Number: TPS92612
Other Parts Discussed in Thread: LP5522, , TPS92610EVM,

Tool/software:

Hello,

My customer would like to blink and LED at 0.5Hz (1 second on and one second off). They do not want to use I2C, and would prefer a resistor for setting current and another pin for controlling PWM / on-off status. They were using the LP5522 device but had an issue where the drive signal was being interpreted by the 1-wire interface and getting stuck in an undesirable state. 

Could they use the PWM pin as just constant low (completely off), and constant high (full output current) to blink the LED at 0.5Hz? Ibeleive this is okay, but want to double check. None of the graphs or parametric tables talk about 0% duty cycle, but there is one line in the datasheet that says "PWM input can be adopted for LED brightness adjust and LED ON/OFF control."

Please confirm, and thanks!
John

  • +1
    TI__Prodigy 540 points

    Hello John,

    The TPS92612 will function properly like that. Section 7.3.3 of the data sheet says "When the voltage applied on the PWM pin is higher than VIH(PWM), the output current is enabled. When the voltage applied on PWM pin is lower than V_IL(PWM), the output current is disabled." This is also how the EVM for the device is configured so a shunt can enable and disable the output. If you have any more questions about the device, please let me know.

    Kind Regards,

    Nicholas Alexander

  • 0 in reply to Nicholas Alexander
    TI__Mastermind 21811 points

    Hi Nicholas,

    My customer wants an LED current of 1-2mA, and the datasheet shows a minimum output current at 100% duty cycle of 4mA. In SW today, they only blink the LED and do not utilize PWMing to drive a lower average current. Would using a higher RSNS resistance be possible? Is the concern just around accuracy or do we think there could be other issues? They are trying to only make HW changes and not have to update SW as this causes an additional validation effort. 

    If not, are there any other devices that could be used the same way (0.5Hz for blinking, no PWM, and RSNS with an output current in the range of 1-2mA)?

    John

  • 0 in reply to John Griffith
    TI__Prodigy 540 points

    Hello John,

    Why do you need to support such a small current? This might not be the best part for that, but I tested it today.

    I do not believe that the current will be accurate below 4 mA and the short circuit function might not work.

    I did not have a TPS92612EVM but I do have a TPS92610EVM and these chips have similar designs. The 10 also has a device output-current range minimum of 4 mA. I changed the value of R_SNS to 53.8 Ohms and was able to control a drive current of 1.8 mA on and off with the PWM pin. I swept the supply voltage from 4.5 V to 12 V and was able to output  I do not recommend this function as it is outside of the data sheets specs and did not validate it over temperature.

    Otherwise, I support the automotive linear LED drivers and did not find one that officially supports such a low current. I'll talk to my team and see if we have another device that can support this.

    Best,

    Nicholas Alexander