ADP3402

–10–

REV. 0

AMBIENT TEMPERATURE – C

300

0

20

0

20

40

60

80

250

200

150

100

50

85

VBAT = 5.5V

VBAT = 7V

VBAT = 6V

VBAT = 5V

4-LAYER BOARD

Figure 16. Total LDO Load Current vs. Temperature and VBAT

Low Dropout Regulators (LDOs)

The ADP3402 high-performance LDOs are optimized for their

given functions by balancing quiescent current, dropout voltage,

line/load regulation, ripple rejection, and output noise. 2.2

µF

tantalum or MLCC ceramic capacitors are recommended for

use with the digital and analog LDOs, and 0.22

µF for the

TCXO LDO.

Digital LDO (VCC)

The digital LDO (VCC) supplies all the digital circuitry in the

handset (baseband processor, baseband converter, external

memory, display, etc). The LDO has been optimized for very

low quiescent current (30

µA maximum) at light loads as this

LDO is on at all times.

Analog LDO (VCCA)

This LDO has the same features as the digital LDO. It has further-

more been optimized for good low frequency ripple rejection for use

with analog sections in order to reject the ripple coming from the RF

power amplifier. VCCA is rated to 130 mA load which is sufficient

to supply the complete analog section of a baseband converter such

as the AD6421/AD6425, including a 32

Ω earpiece.

TCXO LDO (VTCXO)

The TCXO LDO is intended as a supply for temperature com-

pensated crystal oscillator, which needs its own ultralow noise

supply. The output current is rated to 5 mA for the TCXO LDO.

RTC LDO (VRTC)

The RTC LDO charges a capacitor-type backup coin cell to run

the real-time clock module. It has been targeted to charge elec-

tric double layer capacitors such as the PAS621 from Kanebo.

The PAS621 has a small physical size (6.8 mm diameter) and a

nominal capacity of 0.3 F, giving many hours of backup time.

ADP3402

GSM PROCESSOR

VRTC

PWRON

PWRONIN

COIN

CELL

VRTC

RTC

MODULE

Figure 17. Connecting VRTC and POWERONIN to the Chipset

The ADP3402 supplies current both for charging the coin cell and

for the RTC module when the digital supply is off. The nominal

charging voltage is 2.45 V, which ensures long cell life while obtain-

ing in excess of 90% of the nominal capacity. In addition, it features

a very low quiescent current (10

µA) since this LDO is running all

the time, even when the handset is switched off. It also has reverse

current protection with low leakage which is needed when the main

battery is removed and the coin cell supplies the RTC module.

Reference Output (REFOUT)

The reference output is a low noise, high precision reference with a

guaranteed accuracy of 1.5% over temperature. The reference can

be fed to the baseband converter, such as the AD6425, improving

the absolute accuracy of the converters from 5% to 1.5%. This

significantly reduces calibration time needed for the baseband

converter during production.

SIM Interface

The SIM interface generates the needed SIM voltage—either 3 V

or 5 V, dependent on SIM type, and also performs the needed

logic level translation. Quiescent current is low, as the SIM card

will be powered all the time. Note that DATAIO and I/O have

integrated pull-up resistors as shown in Figure 18. See Table II for

the control logic of the charge pump output, VSIM.

RESETIN

CLKIN

DATAIO

RST

CLK

I/O

LEVEL

SHIFT

VCC

VSIM

ADP3402

LEVEL

SHIFT

VCC

VCC

VSIM

VSIM

Figure 18. Schematic for Level Translators

Power-On/-Off

ADP3402 handles all issues regarding power-on/-off of the hand-

set. It is possible to turn on the ADP3402 in three different ways:

• Pulling PWRONKEY Low

• Pulling PWRONIN High

• CHRON exceeds threshold

Pulling PWRONKEY key low is the normal way of turning on the

handset. This will turn on all the LDOs as long as PWRONKEY is

held low. The microprocessor then starts and pulls PWRONIN

high after which PWRONKEY can be released. PWRONIN going

high will also turn on the handset. This is the case when the alarm

in the RTC module expires.

An external charger can also turn on the phone. The turn-on

threshold and hysteresis can be programmed via external resistors

to allow full flexibility with any external charger and battery chem-

istry. These resistors are referred to as R1 and R2 in Figure 15.

Undervoltage Lockout (ULVO)

The UVLO function in the ADP3402 prevents startup when the

initial voltage of the main battery is below the 3.2 V threshold.

If the battery is this low with no load, there will be little or no

capacity left. When the battery is greater than 3.2 V, as with the

insertion of a fresh battery, the UVLO comparator trips, the