RT5021 datasheet(44/67 Pages) RICHTEK

44 / 67 page

RT5021

DS5021-01 April 2013

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

ISYS

VSYS

IUSB

IBAT

T1, T7

SYS Regulation Voltage

CHG_MAX

T2, T6

< IVIN_OC (USB) − CHG_MAX

SYS Regulation Voltage

ISYS + CHG_MAX

CHG_MAX

T3, T5

> IVIN_OC (USB) − CHG_MAX

< IVIN_OC (USB)

Auto Charge Voltage

Threshold

IVIN_OC (USB)

IVIN_OC (USB) − ISYS

> IVIN_OC (USB)

VBAT − IBAT x RDS(ON)

IVIN_OC (USB)

ISYS − IVIN_OC (USB)

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 situation. While the battery is supplementing the load, if the difference

between the battery and SYS voltage exceeds 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 the battery supply mode exiting condition is 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

ΔTSD, 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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