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TPS65020 Datasheet(PDF) 22 Page - Texas Instruments |
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TPS65020 Datasheet(HTML) 22 Page - Texas Instruments |
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22 / 53 page  TPS65020 SLVS607D – SEPTEMBER 2005 – REVISED JANUARY 2016 www.ti.com 8.3 Feature Description 8.3.1 VRTC Output and Operation With or Without Backup Battery The VRTC pin is an always-on output, intended to supply up to 20 mA to a permanently required rail. This is the VCC_BATT rail of the Intel PXA270 Bulverde processor for example. In applications using a backup battery, the backup voltage can be either directly connected to the TPS65020 VBACKUP pin if a Li-Ion cell is used, or through a boost converter (for example, TPS61070) if a single NiMH battery is used. The voltage applied to the VBACKUP pin is fed through a PMOS switch to the VRTC pin. The TPS65020 asserts the RESPWRON signal if VRTC drops below 2.4 V. This, together with 250 mV at 20-mA dropout for the PMOS switch means that the voltage applied at VBACKUP must be greater than 2.65 V for normal system operation. When the voltage at the VSYSIN pin exceeds 2.65 V, the path from VBACKUP to VRTC is cut, and VRTC is supplied by a similar PMOS switch from the voltage source connected to the VSYSIN input. Typically this is the VDCDC1 converter but can be any voltage source within the appropriate range. In systems where no backup battery is used, the VBACKUP pin is connected to GND. In this case, a low power LDO is enabled, supplied from VCC and capable of delivering 20 mA to the 3-V output. This LDO is disabled if the voltage at the VSYSIN input exceeds 2.65 V. VRTC is then supplied from the external source connected to this pin as previously described. Inside TPS65020 there is a switch (Vmax switch) which selects the higher voltage between VCC and VBACKUP. This is used as the supply voltage for some basic functions. The functions powered from the output of the Vmax switch are: • INT output • RESPWRON output • HOT_RESET input • LOW_BATT output • PWRFAIL output • Enable pins for DC-DC converters, LDO1 and LDO2 • Undervoltage lockout comparator (UVLO) • Reference system with low frequency timing oscillators • LOW_BATT and PWRFAIL comparators PB-IN, PB-OUT, the main 1.5-MHz oscillator, and the I2C interface are only powered from VCC. 22 Submit Documentation Feedback Copyright © 2005–2016, Texas Instruments Incorporated Product Folder Links: TPS65020 |
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