RT8249 datasheet(19/23 Pages) RICHTEK

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RT8249A/B/C

DS8249A/B/C-02

June 2014

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Thermal Protection

The RT8249A/B/C features thermal shutdown to prevent

damage from excessive heat dissipation. Thermal

shutdown occurs when the die temperature exceeds

150

°C. All internal circuitries are turned off during thermal

shutdown. The RT8249A/B/C triggers thermal shutdown

if LDO5 is not supplied from VOUT1, while input voltage on

VIN and drawing current from LDO5 are too high.

Nevertheless, even if LDO5 is supplied from VOUT1,

overloading LDO5 can cause large power dissipation on

automatic switches, which may still result in thermal

shutdown.

Discharge Mode (Soft Discharge)

When ENx is low the output under-voltage fault latch is

set, the output discharge mode will be triggered. During

discharge mode, an internal switch creates a path for

discharging the output capacitors' residual charge to GND.

Standby Mode

When VIN rises POR threshold and ENx < 0.4V, RT8249A/

B/C operate in standby mode, CH1 and CH2 is OFF state.

For RT8249A/C, LDO5 is OFF and LDO3 is ON state and

approximately consumes 17

μA of input current. For

RT8249B, LDO5 and LDO3 are ON state and approximately

consumes 30

μA while in standby mode.

Power-Up Sequencing and On/Off Controls (ENx)

EN1 and EN2 control the power-up sequencing of the two

channels of the Buck converter. The 0.4V falling edge

threshold on ENx can be used to detect a specific analog

voltage level and to shutdown the device. Once in

shutdown, the 1.6V rising edge threshold activates,

providing sufficient hysteresis for most applications.

Table 1. Operation Mode Truth Table

Mode

Condition

Comment

LDO Over

Current Limit

LDOx < UVLO threshold

Transitions to discharge mode after VIN POR. LDO5

and LDO3 remain active.

Run

ENx = high, VOUT1 or VOUT2 are enabled

Normal Operation.

Over-Voltage

Protection

Either output >113% of the nominal level.

LGATEx is forced high. LDO3 and LDO5 are active.

Exit by VIN POR or by toggling ENx.

Under-Voltage

Protection

Either output < 52% of the nominal level

after 1.3ms time-out expires and output is

enabled

Both UGATEx and LGATEx are forced low and enter

discharge mode. LDO3 and LDO5 are active. Exit by

VIN POR or by toggling ENx.

Discharge

Either output is still high in standby mode

During discharge mode, there is one path to

discharge the output capacitors’ residual charge to

GND via an internal switch.

Standby

VIN > POR

ENx < 0.4V

For RT8249A/B : LDO3 is active

For RT8249C : LDO3, LDO5 are active

Thermal

Shutdown

TJ > 150C

All circuitries are off. Exit by VIN POR.

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