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ZHCSJ38C December 2018 – August 2019 TPS3840

PRODUCTION DATA.

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机械数据 (封装 | 引脚)

DBV|5
- MPDS018T

散热焊盘机械数据 (封装 | 引脚)

订购信息

8.3.2 User-Programmable Reset Time Delay

The reset time delay can be set to a minimum value of 50 µs by leaving the CT pin floating, or a maximum value of approximately 6.2 seconds by connecting 10 µF delay capacitor. The reset time delay (t_D) can be programmed by connecting a capacitor no larger than 10 µF between CT pin and GND.

The relationship between external capacitor (C_{CT_EXT}) in µF at CT pin and the time delay (t_D) in seconds is given by Equation 2.

Equation 2. t_D = -ln (0.29) x R_CT x C_{CT_EXT} + t_D (no cap)

Equation 2 is simplified to Equation 3 by plugging R_CT and t_{D(no cap)} given in Electrical Characteristics section:

Equation 3. t_D = 618937 x C_{CT_EXT} + 50 µs

Equation 4 solves for external capacitor value (C_{CT_EXT}) in units of µF where t_D is in units of seconds

Equation 4. C_{CT_EXT} = (t_D- 50 µs) ÷ 618937

The reset delay varies according to three variables: the external capacitor variance (C_CT), CT pin internal resistance (R_CT) provided in the Electrical Characteristics table, and a constant. The minimum and maximum variance due to the constant is shown in Equation 5 and Equation 6.

Equation 5. t_{D (minimum)} = -ln (0.36) x R_{CT (min)} x C_{CT (min)} + t_{D (no cap, min)}

Equation 6. t_{D (maximum)} = -ln (0.26) x R_{CT (max)} x C_{CT (max)} + t_{D (no cap, max)}

The recommended maximum delay capacitor for the TPS3840 is limited to 10 µF as this ensures there is enough time for the capacitor to fully discharge when the reset condition occurs. When a voltage fault occurs, the previously charged up capacitor discharges, and if the monitored voltage returns from the fault condition before the delay capacitor discharges completely, the delay capacitor will begin charging from a voltage above zero and the reset delay will be shorter than expected. Larger delay capacitors can be used so long as the capacitor has enough time to fully discharge during the duration of the voltage fault.