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TPS3620-50DGK Fiches technique(PDF) 10 Page - Texas Instruments |
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TPS3620-50DGK Fiches technique(HTML) 10 Page - Texas Instruments |
10 / 18 page www.ti.com DETAILED DESCRIPTION Battery Freshness Seal (TPS3619) Power-Fail Comparator (PFI and PFO) Backup-Battery Switchover TPS3619-33 ,, TPS3619-50 TPS3620-33, TPS3620-50 SLVS387G – APRIL 2001 – REVISED DECEMBER 2006 The battery freshness seal of the TPS3619 family disconnects the backup-battery from internal circuitry until it is needed. This function prevents the backup-battery from being discharged unitl the final product is put to use. The following steps explain how to enable the freshness seal mode. 1. Connect VBAT (VBAT > VBAT min) 2. Ground PFO 3. Connect PFI to VDD (PFI = VDD) 4. Connect VDD to power supply (VDD > VIT) and keep connected for 5 ms < t < 35 ms The battery freshness seal mode is automatically removed by the positive-going edge of RESET when VDD is applied. An additional comparator is provided to monitor voltages other than the nominal supply voltage. The power-fail-input (PFI) is compared with an internal voltage reference of 1.15 V. If the input voltage falls below the power-fail threshold VIT(PFI) of typical 1.15 V, the power-fail output (PFO) goes low. If VIT(PFI) goes above V(PFI), plus about 12-mV hysteresis, the output returns to high. By connecting two external resistors, it is possible to supervise any voltages above V(PFI). The sum of both resistors should be about 1 MΩ, to minimize power consumption and also to assure that the current in the PFI pin can be ignored compared with the current through the resistor network. The tolerance of the external resistors should be not more than 1% to ensure minimal variation of sensed voltage. If the power-fail comparator is unused, PFI should be connected to ground and PFO left unconnected. In case of a brownout or power failure, it may be necessary to preserve the contents of RAM. If a backup battery is installed at VBAT, the device automatically switches the connected RAM to backup power when VDD fails. In order to allow the backup battery (e.g., a 3.6-V lithium cell) to have a higher voltage than VDD, these supervisors do not connect VBAT to VOUT when VBAT is greater than VDD. VBAT only connects to VOUT (through a 15-Ω switch) when VDD falls below VIT and VBAT is greater than VDD. When VDD recovers, switchover is deferred either until VDD crosses VBAT, or until VDD rises above the reset threshold VIT. VOUT connects to VDD through a 1-Ω (max) PMOS switch when VDD crosses the reset threshold. FUNCTION TABLE VDD > VBAT VDD > VIT VOUT 1 1 VDD 1 0 VDD 0 1 VDD 0 0 VBAT 10 Submit Documentation Feedback |
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