ZHCSFY8B January 2017 – September 2021 TPS3850-Q1
PRODUCTION DATA
The TPS3850-Q1 uses a CRST pin charging current (ICRST) of 375 nA. When using an external capacitor, the rising RESET delay time can be set to any value between 700 µs (CCRST = 100 pF) and 3.2 seconds (CCRST = 1 µF). The typical ideal capacitor value needed for a given delay time can be calculated using Equation 3, where CCRST is in microfarads and tRST is in seconds:
To calculate the minimum and maximum-reset delay time use Equation 4 and Equation 5, respectively.
The slope of Equation 3 is determined by the time the CRST charging current (ICRST) takes to charge the external capacitor up to the CRST comparator threshold voltage (VCRST). When RESET is asserted, the capacitor is discharged through the internal CRST pulldown resistor. When the RESET conditions are cleared, the internal precision current source is enabled and begins to charge the external capacitor; when VCRST = 1.21 V, RESET is unasserted. Note that to minimize the difference between the calculated RESET delay time and the actual RESET delay time, use a use a high-quality ceramic dielectric COG, X5R, or X7R capacitor and minimize parasitic board capacitance around this pin. Table 8-2 lists the reset delay time ideal capacitor values for CCRST.
CCRST | RESET DELAY TIME (tRST) | UNIT | ||
---|---|---|---|---|
MIN(1) | TYP | MAX(1) | ||
100 pF | 0.61 | 0.70 | 0.80 | ms |
1 nF | 3.21 | 3.61 | 4.08 | ms |
10 nF | 29.2 | 32.6 | 36.8 | ms |
100 nF | 289 | 323 | 364 | ms |
1 μF | 2886 | 3227 | 3644 | ms |