DVCC
AUXVCC1
AUX
2
VCC
VDSYS
VASYS
AUX
3
VCC
PMM->Core Logic
Backup Subsystem
V
DSYS
V
BAK
AVCC
Analog Modules
V
ASYS
Charger
Charger
Auxiliary Supply Operation
135
SLAU208Q – June 2008 – Revised March 2018
Copyright © 2008–2018, Texas Instruments Incorporated
Auxiliary Supply System (AUX)
Figure 4-1. Auxiliary Supply Switch Overview
4.2.1 Start-up
The device starts whenever a supply is connected to DVCC or AUXVCC1. If both supplies are connected,
AUX uses whichever voltage is higher to supply the digital and analog system voltages, V
DSYS
and V
ASYS
. If
the supplies (DVCC/AVCC and AUXVCC1) differ by less than 100 mV, the selected supply can be either
DVCC/AVCC or AUXVCC1. The supply with the higher voltage is selected only if the difference is greater
than 100 mV.
After start-up from any condition that causes a BOR event (including connection of power or wake from
LPMx.5), the AUX module is automatically locked. To configure the behavior of the auxiliary supply
system, write AUXKEY = 0xA5 in the AUXCTL0 register to enable access to the AUXCTL1 and AUXCTL2
registers (see
). After configuration is completed, the AUX module switches between the
input supplies as defined during configuration.
NOTE:
The AUXKEY field can be written only when LOCKAUX bit is clear. AUXKEY and LOCKAUX
can be updated in the same CPU instruction.
If the LOCKAUX bit remains set, the device continues to be supplied by DVCC or AUXVCC1 (whichever
was selected at start-up).
describes additional considerations for setting the power supply before entering LPMx.5.
NOTE:
Highest supply voltage
To ensure reliable operation, the selected supply voltage (by default, the highest voltage in
the system) must always supply at least 0.5 µA to critical circuitry.