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TLC04: how to generate Low pass filter with single power supply ?

kamlesh
Prodigy 20 points
Part Number: TLC04


Hi Dear All

i have LTC04 fourth order low pass filter.i have to need use this in my project with single positive power supply and 8khz frequency low pass filter.

ic have to need generate Fclock=400khz  for pass Fc=8khz(cutoff) signal input.

i have use equation for generate fclock = 1/(1.69*RC).

as per equation i get value of R=15R and C=0.1uf. but it only pass 128Hz.

Please suggest me how to use TLC04 for 8khz LPF with +5v(VCC+) and 0v(VCC-) power supply.

thanks in advance.

   

  • 0
    TI__Guru* 93105 points

    Hello Kamlesh,

    I believe the TLC04 is now supported by TI's SAR team, but I have some familarity with it from when we used to support it here from the Precision Amplifiers team. If you need more help beyond what I am providing please post an inquiry to their E2E forum.

    I reviewed your 8 kHz cutoff and +5 V single supply requirements, and have the following conclusions and recommendations:

    • Use the circuit shown on Figure 7 of the TLC04 datasheet
    • fclock = 1 / RC ln 5.444 = 1 / 1.695 RC, for V+ = 5 V
    • fclock = 50 x fc = 50 (8 kHz) = 400 kHz
    • Reduce the value of C from 100 nF to a much lower value for an fclock = 400 kHz, 1 nF is suggested
    • Then, R = 1 / [1.695 (fclock) C] = 1 / [1.695 (400 kHz) (1nF)] = 1.475 k-ohm
    • When using a single supply the "FILTER IN" pin must be biased to mid-supply (+2.5 V), or AC coupled using a coupling capacitor
    • The source impedance driving the filter must be less than 2 k-ohms

    This should get you moving in the right direction.

    Regards, Thomas

    Precision Amplifiers Applications Engineering