Datasheet

TPS65023, TPS65023B

www.ti.com

SLVS670J –JUNE 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 (i.e. for a

Real Time Clock). The TPS65023, TPS65023B asserts the RESPWRON signal if VRTC drops below 2.4 V.

VRTC is selected from a priority scheme based on the VSYSIN and VBACKUP inputs.

When the voltage at the VSYSIN pin exceeds 2.65 V, VRTC connects to the VSYSIN input via a PMOS switch

and all other paths to VRTC are disabled. The PMOS switch drops a maximum of 375 mV at 30 mA, which

should be considered when using VRTC. VSYSIN can be connected to any voltage source with the appropriate

input voltage, including VCC or, if set to 3.3 V output, DCDC2 or DCDC3. When VSYSIN falls below 2.65 V or

shorts to ground, the PMOS switch connecting VRTC and VSYSIN opens and VRTC then connects to either

VBACKUP or the output of a dedicated 3V/30mA LDO. Texas Instruments recommends connecting VSYSIN to

VCC or ground - VCC if a non-replaceable primary cell is connected to VBACKUP and ground if the VRTC

output will float.

If the PMOS switch between VSYSIN and VRTC is open and VBACKUP exceeds 2.65 V, VRTC connects to

VBACKUP via a PMOS switch. The PMOS switch drops a maximum of 375 mV at 30 mA, which should be

considered if using VRTC. A typical application may connect VBACKUP to a primary Li button cell, but any

battery that provides a voltage between 2.65 V and 6 V (i.e. a single Li-Ion cell or a single boosted NiMH battery)

is acceptable, to supply the VRTC output. In systems with no backup battery, the VBACKUP pin should be

connected to GND.

If the switches between VRTC and VSYSIN or VBACKUP are open, the dedicated 3-V/30-mA LDO, driven from

VCC, connects to VRTC. This LDO is disabled if the voltage at the VSYSIN input exceeds 2.65 V.

Inside TPS65023, TPS65023B 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 2.25-MHz oscillator, and the I

C™ interface are only powered from V

Product Folder Link(s) :TPS65023 TPS65023B