ATR0621P_08 Datasheet, PDF (22/31 Pages) ATMEL Corporation – GPS Baseband GPS Baseband

The baseband IC contains a built in low dropout voltage regulator LDO18. This regulator can be
used if the host system does not provide the core voltage VDD18 of 1.8V nominal. In such case,
LDO18 will provide a 1.8V supply voltage from any input voltage VDD between 2.3V and 3.6V. It
will also allow supplying external components such as FLASH memory with 1.8V. The LDO_EN
input can be used to shut down VDD18 if the system is in standby mode.
If the host system does however supply a 1.8V core voltage directly, this voltage has to be con-
nected to the VDD18 supply pins of the baseband IC. LDO_EN must be connected to GND.
LDO_IN can be connected to GND. LDO_OUT must not be connected.
A second built in low dropout voltage regulator LDOBAT provides the supply voltage for the RTC
and backup SRAM from any input voltage VBAT between 1.5V and 3.6V. The backup battery is
only discharged if VDD - supplied via pin LDOBAT_IN - is shut down.
Only after VDD18 has been supplied to ATR0621 the RTC section will be initialized properly. If
only VBAT is applied first, the current consumption of the RTC and backup SRAM is
undetermined.
Figure 4-2. External Wiring Example Using 1.8V from Host System and Backup Power
Supply
ATR0621P internal
LDO_IN
LDO_EN
LDO_OUT
ldoin
ldoen
ldoout
LDO18
1.65V to 1.95V
VDD18
Core
2.3V to 3.6V
1.5V to 3.6V
1 µF
(X7R)
VDDIO
1 µF
(X7R)
LDOBAT_IN
VBAT
VBAT18
1.8V to 3.3V
variable IO Domain
ldobat_in
vbat
vbat18
LDOBAT
vdd
RTC
Backup Memory
0V or 3V to 3.6V
VDDUSB
USB SM and
Transceiver
22 ATR0621P
4890H–GPS–08/08