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4979D–GPS–06/08

ATR0635P1

Figure 4-1.

Connecting Example: Separate Power Supplies for RF and Digital Part Using the Internal LDOs

The ATR0635P1 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.

The LDO_EN input can be used to shut down VDD18 if the system is in standby mode.

If the host system does supply a 1.8V core voltage directly, this voltage has to be connected to

the VDD18 supply pins of the Core. LDO_EN must be connected to GND. LDO_IN can be con-

nected 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

delivers the supply current if LDOBAT_IN is not powered.

ATR0635P1 internal

VDDUSB

0V or 3V to 3.6V

1.5V to 3.6V

1 µF

(X7R)

ldoout

ldoen

ldoin

LDO18

LDO_IN

1 µF

(X7R)

VDDIO

2.3V to 3.6V

LDO_EN

NSHDN

VDD18

LDO_OUT

USB SM and

transceiver

1.8V to 3.3V

variable I/O domain

RTC

backup memory

Core

vbat18

vbat

VDD

ldobat_in

LDOBAT

LDOBAT_IN

VBAT

VBAT18

RF

VCC1

VCC2

VBP

VDIG

2.7V to 3.3V