Datasheet

TPS65022

www.ti.com

SLVS667A –JULY 2006– REVISED SEPTEMBER 2011

DETAILED DESCRIPTION

VRTC OUTPUT AND OPERATION WITH OR WITHOUT BACKUP BATTERY

The VRTC pin is an always-on output, intended to supply up to 30 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 TPS65022

VBACKUP pin if a Li-Ion cell is used, or via a boost converter (e.g. 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 TPS65022 asserts

the RESPWRON signal if VRTC drops below 2.4 V. This, together with 375 mV at 30 mA drop out for the PMOS

switch means that the voltage applied at VBACKUP must be greater than 2.775 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 30 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 TPS65022 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

The main 1.5-MHz oscillator, and the I

C™ interface are only powered from V

Product Folder Link(s) : TPS65022