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Alternative device for LTC6906

Shotaro Sakai
Expert 3420 points
Other Parts Discussed in Thread: LM555, LMC555, TLC555

Hello team,

Do we have competitive device for LTC6906HS6#PBF or LTC6906IS6#PBF?

The device is used as a 400kHz oscillator by resistor set.

Best regards,

Shotaro

  • +1
    TI__Mastermind 33950 points

    Hello Shotaro,

    Would something like a TLC555 work? This is a lower-power version of the well-known LM555 timer circuit, and can be configured for monostable operation with close to 50% duty cycle. The stability and frequency accuracy will be worse compared to LTC6906; if better stability or frequency accuracy is required we don't have competitive comparable offerings.

    Regards,

    Derek Payne

  • 0 in reply to Derek Payne
    TI__Expert 3420 points

    Hello Derek,

    Thank you for the suggestion. I will check if 555 timer works in their system.

    Best regards,

    Shotaro

  • 0 in reply to Derek Payne
    TI__Expert 3420 points

    Hello Derek,

    Can you prepare the data of "frequency vs current supply" and "power supply vs current supply" with LMC555 which is the lowest power consumption device?

    The customer concerns is that power consumption because LTC6906 is used during backup with battery.

    Note that LTC6906 is set to 400kHz, and power supply is 3.0V

    Best regards,

    Shotaro

  • 0 in reply to Shotaro Sakai
    TI__Mastermind 33950 points

    Shotaro,

    I said monostable but I meant astable earlier, my mistake...

    TLC555 has about 250µA quiescent current consumption. I used the TLC555 astable design calculator to compute an approximately 55% duty cycle waveform with 3.0V supply at nominal 400kHz, using a 10pF capacitor. I achieved nominal 57% duty cycle with typical capacitor tolerance of 10%, though there's some frequency variation between 450kHz and 325kHz depending on component tolerance and TLC555 process variation. The power calculations are sort of complex for this case, since the actual voltage at the capacitor is constantly changing, but simplifying to assume the 10pF capacitor is charged and discharged suggests an additional current consumption of around 13µA (I = C*V*F = 450kHz * 3V * 10pF = 13.5µA). R1 also drops to 0V at the discharge pin roughly 40% of the time, and was computed as about 32.4kΩ; this adds 0.4 * 3V / 32.4kΩ = about 37.5µA. There may also be losses in the device switching circuitry that are difficult to model, and whatever load is being driven by the 400kHz oscillator output. I would predict about 0.5mA total current consumption worst case for this oscillator. I wouldn't consider this a good alternative for the LTC6906 with well over 10x typical current consumption from our solution, but maybe the customer feels differently.

    TI clocks and timing products don't have a comparable low-power alternative to LTC6906.

    Regards,

    Derek Payne

  • +1 in reply to Derek Payne
    TI__Mastermind 33950 points

    Follow-up after noticing you referred to LMC555: it does have lower quiescent current, but no comparable astable design calculator to give a good approximation for astable operation component values at 400kHz. I would still anticipate >100µA total supply current, and probably at least 3x LTC6906 supply current, just by assuming the circuits are comparable: about somewhere between 50µA and 100µA quiescent current, and maybe 50µA additional supply current due to the external RC oscillator.

    Keep in mind that, even if this gets close to the appropriate current consumption expected for this circuit, the frequency accuracy is still only about ±20%. This may be a bigger disadvantage than the difference in current consumption.