RT9481 datasheet(13/41 Pages) RICHTEK

13 / 41 page

RT9481

is a registered trademark of Richtek Technology Corporation.

DS9481-00 June 2015

www.richtek.com

Application Information

Switching Charger

The switching charger integrates a synchronous PWM

controller with power MOSFETs to provide Minimum

Input

Voltage Regulation (MIVR),

Average Input

Current Regulation (AICR), high accuracy current and

voltage regulation, and charge termination.

In charge mode, the switching charger supports a

precision charging system for single cell. In boost

mode, the switching charger works as the boost

converter. And in high impedance mode, the switching

charger stops charging or boosting and operates in a

mode with low current from battery to reduce the

power consumption when the portable device is in

standby mode.

Notice that the switching charger does not integrate

input power source (AC adapter or USB input)

charging detection. Thus, the switching charger does

not set the charge current automatically. The charge

current needs to be set via I2C interface by the host.

The switching charger application mechanism and I2C

compatible interface are introduced in later sections.

Charge Mode Operation

Minimum Input Voltage Regulation (MIVR)

The switching charger features Minimum Input Voltage

Regulation function to prevent input voltage drop due

to insufficient current provided by the adaptor or USB

input. If MIVR function is enabled, the input voltage

decreases when the over current of the input power

source occurs. VBUS is regulated at a predetermined

voltage level which can be set as 4.2V to 4.8V per

0.1V by I2C interface. At this time, the current drawn by

the switching charger equals to the maximum current

value that the input power can provide at the

predetermined voltage level, instead of the set value.

Table 1. MIVR Register Setting Table

MIVR[2:0]

VMIVR

000

Disable

001

4.2V

010

4.3V

011

4.4V

100

4.5V

101

4.6V

110

4.7V (default)

111

4.8V

Charge Profile

The switching charger provides a precision Li-ion or Li-

polymer charging solution for single-cell applications.

Input current limit, charge current, termination current,

charge voltage and input voltage MIVR are all

programmable via the I2C interface. In charge mode,

the switching charger has five control loops to regulate

input current, charge current, charge voltage, input

voltage MIVR and device junction temperature. During

the charging process, all five loops (if MIVR is enabled)

are enabled and the dominant one will take over the

control.

For normal charging process, the Li-ion or Li-polymer

battery is charged in three charging modes depending

on the battery voltage. At the beginning of the charging

process, the switching charger is in pre-charge mode.

When the battery voltage rises above pre-charge

threshold voltage (VPREC), the switching charger

enters fast-charge mode. Once the battery voltage is

the

regulation

voltage

(VBATREG),

the

switching charger enters constant voltage mode.

Pre-Charge Mode

For life-cycle consideration, the battery cannot be

charged with large current under low battery condition.

When the ISENSN pin voltage is below pre-charge

threshold voltage (VPREC), the charger is in pre-charge

mode with a weak charge current witch equals to the

pre-charge current (IPREC). In pre-charge mode, the

charger basically works as a Linear Charger. The pre-

charge current also acts as the current limit when the

ISENSN pin is shorted.

The Pre-Charge current levels are 200mA to 500mA

programmed by I2C per 100mA.

RT9481 Datasheet(PDF) 13 Page - Richtek Technology Corporation

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