REV. 0

ADP3408

–11–

THEORY OF OPERATION

The ADP3408 is a power management chip optimized for use

with GSM baseband chipsets in handset applications. Figure 1

shows a block diagram of the ADP3408.

The ADP3408 contains several blocks:

• Six Low Dropout Regulators (SIM, Core, Analog, Crystal

Oscillator, Memory, Real-Time Clock)

• Reset Generator

• Buffered Precision Reference

• Lithium Ion Charge Controller and Processor Interface

• Power-On/-Off Logic

• Undervoltage Lockout

• Deep Discharge Lockout

These functions have traditionally been done either as a discrete

implementation or as a custom ASIC design. The ADP3408

combines the benefits of both worlds by providing an integrated

standard product where every block is optimized to operate in a

GSM environment while maintaining a cost competitive solution.

Figure 3 shows the external circuitry associated with the ADP3408.

Only a minimal number of support components are required.

Input Voltage

The input voltage range of the ADP3408 is 3 V to 5.5 V and is

optimized for a single Li-Ion cell or three NiMH cells. The

thermal impedance of the ADP3408 is 68

°C/W for four-layer

boards. The end-of-charge voltage for high capacity NiMH cells

can be as high as 5.5 V. Power dissipation should be calculated

at maximum ambient temperatures and battery voltage in order

not to exceed the 125

°C maximum allowable junction temperature.

Figure 4 shows the maximum power dissipation as a function of

ambient temperature.

However, high battery voltages normally occur only when the

battery is being charged and the handset is not in conversation

mode. In this mode there is a relatively light load on the LDOs.

A fully charged Li-Ion battery is 4.25 V, where the ADP3408

can deliver the maximum power (0.56W) up to 85

°C ambient

temperature.

AMBIENT TEMPERATURE – C

1.2

0.0

–20

100

0

20

40

60

80

1.0

0.8

0.6

0.4

0.2

Figure 4. Power Dissipation vs. Temperature

Low Dropout Regulators (LDOs)

The ADP3408 high-performance LDOs are optimized for their

given functions by balancing quiescent current, dropout voltage,

regulation, ripple rejection, and output noise. 2.2

µF tantalum

or MLCC ceramic capacitors are recommended for use with the

core, memory, SIM, and analog LDOs. A 0.22

µF capacitor is

recommended for the TCXO LDO.

PWRONIN

PWRONKEY

ROWX

SIMEN

VRTCIN

VRTC

BATSNS

MVBAT

CHRDET

CHRIN

GATEIN

GATEDR

DGND

ISENSE

TCXOEN

AGND

REFOUT

VTCXO

VAN

VBAT

VCORE

VMEM

VBAT2

VSIM

RESET

RESCAP

CHGEN

EOC

U1

ADP3408

C1

0.1 F

CAPACITOR

TYPE BACKUP

COIN CELL

C2, 10nF

R1

0.33

Q1

SI3441DY

D1

LI OR NIMH

BATTERY

PWRON

PWRONKEY

KEYPADROW

GPIO

VRTC

AUXADC

GPIO

CHARGER IN

GPIO

C3, 10 F

R2

10

C4

0.1 F

C5

2.2 F

C6

2.2 F

C7

2.2 F

C8

2.2 F

C9

0.22 F

C10

0.1 F

CLKON

REF

VTCXO

VAN

VCORE

VMEM

VSIM

RESET

GPIO

GPIO

Figure 3. Typical Application Circuit