RK818 datasheet(31/93 Pages) ROCKCHIP

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RK818 Datasheet

Rev 1.0

Function Description

4.1 Function overview

4.1.1 POWER UP/POWER DOWN

The RK818 can be powered by either a battery, or an external power supply through the

USB port. When the PMIC is powered by a battery only, pressing the PWRON key powers up

the PMIC. All the power channels start up at the default output voltages with a preset power

up sequence, which has 2mS intervals between the channels. When the power up process is

done, the NRESPWRON turns to high logic level to inform the processor that all the power

rails are up and stable. And now the processor can communicate with the PMIC to re-

configure the output voltage of each power channel if needed.

To power down the PMIC, the processor needs to issue a “power down” signal through the

I2C interface. Upon receiving the power down signal, the PMIC first saves all the information

on the existing states, and then switches the NRESPWRON to low logic level. At this point, the

power channels start to be turned off one after another with the power down sequence. If for

any reason the processor fails to issue the power down signal, the PMIC can be powered off

by “pressing and holding” the PWRON key.

In a case where a battery is the sole power supply and the PMIC is in off state, when an

external power supply is plugged into the USB, the PMIC will first check to see if this is a valid

power supply. If the power supply from the USB is valid, then the power channels are turned

on and the battery is charged.

4.1.2 SWITCHING CHARGER

The RK818 has integrated a switch mode charger, which provides the functions like trickle

current charging, constant current charging, constant voltage charging, charging termination,

automatic recharging, battery temperature monitoring, charging timer and thermal feedback

protection. The values of constant current and constant voltage charging can be set through

I2C interface.

The input average current limit function allows as large as possible a charging current to

be used without having to worry about the input current exceeding the maximum current

allowed by the USB port. The input current limits can be configured through I2C interface. For

example, when an USB port is used as the input, the input current limit can be configured to

either 450mA, or 850mA, to meet the requirements of USB2.0 and USB3.0 respectively.

The charger also has a timer function which sets the maximum charging time for trickle,

constant current and constant voltage charging, respectively. If the charging does not

complete when a preset maximum charging time is reached, the charging is terminated.

The battery temperature can be monitored through the TS1 pin. A battery typically has a

thermistor inside. The RK818 sinks a constant current into the thermistor and senses the

voltage across the thermistor through an internal ADC. A safe charging temperature range is

preset in the PMIC. The charging can proceed normally if the battery temperature falls within

the preset range. If, however, the battery temperature goes either above the upper limit or

below the lower limit of the preset range, the charging will pause until the battery

temperature goes back in the preset range. If the value of the available thermistor is either

too large or too small, a normal resistor can be connected in series or in parallel with the

thermistor so that the sensed voltage fits the ADC’s input range.

During Charging, Vsys will be set to 3.6V when the battery voltage is below 3.6V. This

design is to guarantee that when an external power supply is plugged into the USB port to

charge the battery while the battery voltage is low, the Vsys is already at 3.6V, which allows

the PMIC to start up quickly without having to wait for the Vsys ramping up.

RK818 Datasheet(PDF) 31 Page - Rockchip Electronics Co., Ltd

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