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About TL7702B reference voltage 2 and CT pin

Other Parts Discussed in Thread: TL7702B

Dear Sirs

I use TL7702B for my new project. My schematic is shown as follow (figure 1).

I measure VCC, Reset_N and CT pin (the following fugure 2).

Q1: Is the reference voltage 2 2.53V?

Q2: If  the reference voltage 2 is 2.53V,

Why When CT voltage up to 1.9V=> trigger Reset_N , (CT voltage should up to 2.53V then Reset_N )

From datasheet block diagram (fugure 3)

BRS

Nat

  • Hello Nat,

    While we don't specify the Reference voltage 2, we do say that the td = 2.6*10^4 *Ct.
    Given that td = 2.6^4 *Ct and the charge current is approximately 70uA as shown in the block diagram we can actually calculate the voltage of the internal Reference 2.

    After a quick calculation using C = Q/V and Q = I*t and given t = 26000 *C we find that the Reference voltage 2 is approximately 1.82V. This would seem to correlate pretty well with the 1.9V that you are seeing as the trip point for the RESET pins.

    I am sure there is some variation between devices in the exact current that the internal current source provides, but in general it would seem its close to 1.8 to 1.9V.

    I hope this helps! Let me know if you have additional questions.

    Best,
    Michael
  • Dear Michael
    Thank you very much.

    BRS
    Nat
  • Nat,

    Very happy to help!

    Best,
    Michael