34675 datasheet(18/24 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34675

TYPICAL APPLICATIONS

APPLICATION INFORMATION

TYPICAL APPLICATIONS

APPLICATION INFORMATION

INPUT CAPACITOR

The input capacitor is used to reduce the input voltage

transient, which may cause instability when the input voltage

is near VBAT+VOS. A 1.0μF, X5R, 16V rated ceramic

capacitor is recommended for most applications.

OUTPUT CAPACITOR

For stable operation, an X5R ceramic capacitor with a

minimum 2.2

μF nominal value is recommended at the

charger output. Depending on the load transient current, a

larger capacitance may be required.

The linear regulator is designed to be stable with a ceramic

capacitor of 0.1

μF through 1.0μF. An X5R ceramic capacitor

of 0.22

μF is recommended for the application.

CC MODE CURRENT SETTING

The CC mode current can be programmed by the external

resistor, RISET. A 1% accuracy resistor is recommended to

guarantee 6% current accuracy.

DROPOUT VOLTAGE

If the DC input voltage is too low, it may not maintain the

programmed charge current due to the voltage dropout over

the power MOSFET. The worst case of the RDS(ON) is

475m

Ω. The input voltage should be at least higher than

VBAT + ICHG x 475mΩ, to guarantee the programmed CC

mode current.

USE DET AS POWER PRESENCE INTERRUPT

Some cell phone designs require an active-high power

presence indication signal, to turn on an originally-off phone,

when an ac/dc adapter is plugged in. The DET output can be

used for such a purpose, instead of the PPR pin.

THERMAL CONSIDERATIONS

The 34675 is available in a tiny 2x3 thermally-enhanced

UDFN package. A careful thermal design must be

considered. The exposed pad needs to be well soldered to a

large copper ground plane on the component layer. If the

component layer is space limited and does not allow for a

large copper plane, the thermal pad must be connected to

other ground layers through a via array. This allows the

34675 to charge the battery with the maximum current, while

minimizing the die temperature.

TYPICAL APPLICATIONS

CHARGER IN THE HANDHELD SYSTEM

When the charger is used in handheld systems with MCU

control, the 34675 uses PPR to report the DC input status to

the MCU. After the MCU pulls the EN pin to a low logic level

to start charging, the 34675 reports the charge status through

the CHG pin to the MCU. The MCU can also monitor the

charge current by measuring the voltage at the ISET pin. The

linear regulator powers subsystems, such as a USB

transceiver, that require a voltage higher than 4.5V.

Figure 30 is the typical application circuit.

Figure 30. Li+ Battery Charger in Handheld System

VIN

GND

ISET

BAT

VIO

DET

OFF

Input

MCU

Li+

1.0µF

2.2µF

8.06K

100K

MC34675

100K

USB

Xcvr

0.22µF

CHG

PPR

34675 Datasheet(PDF) 18 Page - Freescale Semiconductor, Inc

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