RT9941 datasheet(30/33 Pages) RICHTEK

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RT9941

DS9941-01 April 2011

www.richtek.com

The RT9941 compares the voltage on the TS pin against the internal VTS thresholds to determine if charging is allowed.

When the temperature outside the VTS thresholds is detected, the device immediately stops the charger. Charging is

resumed when the VTS is recovered to the operation range. However, the user may modify thresholds by adding external

resistors to change biasing voltage.

Timer

As a safety mechanism, the charger has a user programmable timer that monitors the pre-charge and fast charge time.

This timer (charge safety timer) is started at the beginning of the pre-charge and fast charge period. The safety charge

timeout value is set by the value of an external capacitor connected to the TIMR pin (CTIMR), if pin TIMR is short to GND,

the charge safety timer is disabled.

As CTIMR = 0.1

μF, TFAULT is CTIMR (F) x 1.97 x 1011 secs = 19700 secs and TPRECH = TFAULT /8

As timer fault, re-plug-in power or I2C ON/OFF charger again can release the fault condition.

SYS Output

The RT9941 contains a SYS output which can be regulated up to 5V. Bypass SYS to GND with a 22

μF or larger ceramic

capacitor to improve the transient droops. When charging a battery, the load on SYS is serviced first and the remaining

available current goes to charge the battery.

Battery PRE-CHARGE

During a charge cycle, if the battery voltage is below the VPRECH threshold and the RT9941 applies a pre-charge mode to

the battery. This feature revives deeply discharged cells and protects battery life. The RT9941 internally determines the

pre-charge rate as 10% of the fast charge current.

Thermal Regulation

The RT9941 features a thermal limit that reduces the charge current when the die temperature exceeds +125

°C. As the

temperature increases, the RT9941 features a junction temperature regulation loop. If the power dissipation of the IC

results in a junction temperature greater than the thermal regulation threshold (125

°C), the RT9941 throttles back on the

charge current in order to maintain a junction temperature around the thermal regulation threshold (125

°C). The RT9941

monitors the junction temperature, TJ, of the die and disconnects the battery from the input if TJ exceeds 125°C. This

operation continues until junction temperature falls below the thermal regulation threshold (125

°C) by the hysteresis

level. This feature prevents the maximum power dissipation from exceeding typical design conditions.

Figure 21. Connection of Battery Temperature Monitor

With Divider

NTC

R(R

)

×+

=×

Temperature

Sense

ITS

0.1uF to 10uF

NTC

VBATT

Battery

RT1

RT2

Figure 20. Connection of Battery Temperature Monitor

100uA

=×

Temperature

Sense

ITS

0.1uF to 10uF

NTC

VBATT

Battery

RT9941 Datasheet(PDF) 30 Page - Richtek Technology Corporation

RT9941 Datasheet(HTML) 30 Page - Richtek Technology Corporation

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