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LM3697 questions

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: LM3697

Hello,

I have some questions of LM3697.

(1) Power Up sequence
Is attached power up sequence of LM3697 correct?

20150219_power up sequence of lm3697.pdf

(2) tHWEN
I couldn't understand the meaning of 5us(typ) tHWEN parameter at the POR reset complete , Ta=25°C.
Is this parameter at the condition of 2.1V≤Vin<2.7V?

(3)PWM zero detection
Could you please let me know the behavior when LM3697 detect the PWM neare zero pulse?

(4) Start-up/Shutdown Ramp
Could you please let me know the determination method of Start-up / Shutdown Ramp time?

(5) LED off
Could you please let me know the recommendation method of LED off?
Showld we use HWEN ?
If  we use Control bank enables register for LED off, is supply current  larger than ISHDN?


Best Regards,
Ryuji Asaka

  • 0
    TI__Intellectual 2090 points
    1) You should wait at least 20 us before transitioning SDA (VIH level instead of VIL), otherwise your diagram is correct.
    2) No, this is the time for HWEN enable after POR reset complete. If HWEN is connected to VIN then only the 20 us POR release time matters.
    3) This feature would be used to ensure no flicker in LED brightness if the PWM min pulse is less than 0.75 us
    4) That is a choice for your application, most customers use the default value.
    5) Using the control bank enable results in IQ current > ISHDN when the LED is off however, the device retains all register values. If you use HWEN you will have to repeat initialization of the device configuration.