RT5002 datasheet(31/40 Pages) RICHTEK

31 / 40 page

RT5002

DS5002-00

November 2011

www.richtek.com

The Control Temperature Used in JEITA Operation :

The above calculation gives R1 and R2. JEITA control

thresholds for full charging current and 4.2V regulation

voltage are at TS/VP ratio = 40% and 54% (for TSSEL =

H), 35% and 64% (for TSSEL = L). With the ratio, the

corresponding NTC thermistor resistances from the

resistors in the voltage divider circuit can be obtained.

According to the NTC resistances, the corresponding

temperatures can be found. The two temperatures are the

control temperatures used in JEITA operation.

Power Switch

For the charger, there are three power scenarios :

(1) When a battery and an external power supply (USB or

adapter) are connected simultaneously :

If the system load requirements exceed that of the input

current limit, the battery will be used to supplement the

current to the load. Howev er, if the system load

requirements are less than that of the input current limit,

the excess power from the external power supply will be

used to charge the battery.

(2) When only the battery is connected to the system :

The battery provides the power to the system.

(3) When only an external power supply is connected to

the system :

The external power supply provides the power to the

system.

Input DPM Mode

For the charger, the input voltage is monitored when

USB100 or USB500 is selected. If the input voltage is

lower than VDPM, the input current limit will be reduced

to stop the input voltage from dropping any further. This

can prevent the IC from damaging improperly configured

or inadequately designed USB sources.

APPM Mode

Once the sum of the charging and system load currents

becomes higher than the maximum input current limit,

the SYS pin voltage will be reduced. When the SYS pin

v oltage is reduced to VAPPM, the RT5002 will

automatically operate in APPM mode. In this mode, the

charging current is reduced while the SYS current is

increased to maintain system output. In APPM mode,

the battery termination function is disabled.

Battery Supplement Mode Short Circuit Protect

In APPM mode, the SYS voltage will continue to drop if

the charge current is zero and the system load increases

beyond the input current limit. When the SYS voltage

decreases below the battery voltage, the battery will kick

in to supplement the system load until the SYS voltage

rises above the battery voltage.

While in supplement mode, there is no battery supplement

current regulation. However, a built-in short circuit

protection feature is available to prevent any abnormal

current situations. While the battery is supplementing the

load, if the difference between the battery and SYS voltage

becomes more than the short circuit threshold voltage,

SYS will be disabled. After a short circuit recovery time,

tSHORT_R, the counter will be restarted. In supplement

mode, the battery termination function is disabled. Note

that for the battery supply mode exit condition, VBAT-

VSYS < 0V.

Thermal Regulation and Thermal Shutdown

The charger provides a thermal regulation loop function to

monitor the device temperature. If the die temperature rises

above the regulation temperature, TREG, the charge

current will automatically be reduced to lower the die

temperature. However, in certain circumstances (such as

high VIN, heavy system load, etc.) even with the thermal

loop in place, the die temperature may still continue to

increase. In this case, if the temperature rises above the

thermal shutdown threshold, TSD, the internal switch

between VIN and SYS will be turned off. The switch

between the battery and SYS will remain on, however, to

allow continuous battery power to the load. Once the die

temperature decreases by

∆TSD, the internal switch

between VIN and SYS will be turned on again and the

device returns to normal thermal regulation.

The internal thermal feedback circuitry regulates the die

temperature to optimize the charge rate for all ambient

temperatures.

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