RT8239B datasheet(20/24 Pages) RICHTEK

20 / 24 page

RT8239A/B/C

DS8239A/B/C-06 October 2012

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is a registered trademark of Richtek Technology Corporation.

Output Over Voltage Protection (OVP)

The output voltage can be continuously monitored for over

voltage. If the output voltage exceeds 12% of its set voltage

threshold, the over voltage protection is triggered and the

LGATEx low side gate drivers are forced high. This

activates the low side MOSFET switch, which rapidly

discharges the output capacitor and pulls the input voltage

downward.

The RT8239A/B/C is latched once OVP is triggered and

can only be released by either toggling ENLDO, ENTRIPx

or cycling VIN. There is a 5

μs delay built into the over

voltage protection circuit to prevent false transition.

Note that latching LGATEx high will cause the output

voltage to dip slightly negative due to previously stored

energy in the LC tank circuit. For loads that cannot tolerate

a negative voltage, place a power Schottky diode across

the output to act as a reverse polarity clamp.

If the over voltage condition is caused by a short in high

side switch, turning the low side MOSFET on 100% will

create an electrical short between the battery and GND,

hence blowing the fuse and disconnecting the battery from

the output.

Output Under Voltage Protection (UVP)

The output voltage can be continuously monitored for under

voltage. If the output is less than 58% of its set voltage

threshold, the under voltage protection will be triggered

and then both UGATEx and LGATEx gate drivers will be

forced low. The UVP is ignored for at least 5ms (typ.)

after a start up or a rising edge on ENTRIPx. Toggle

ENTRIPx or cycle VIN to reset the UVP fault latch and

restart the controller.

Thermal Protection

The RT8239A/B/C features thermal shutdown to prevent

damage from excessive heat dissipation. Thermal

shutdown occurs when the die temperature exceeds

150

°C. All internal circuitry is inactive during thermal

shutdown. The RT8239A/B/C triggers thermal shutdown

if LDOx is not supplied from VOUTx, while input voltage on

VIN and drawing current from LDOx are too high.

Nevertheless, even if LDOx is supplied from VOUTx,

overloading LDOx can cause large power dissipation on

automatic switches, which may still result in thermal

shutdown.

Discharge Mode (Soft Discharge)

When ENTRIPx is low and a transition to standby or

shutdown mode occurs, or 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.

Shutdown Mode

SMPS1, SMPS2, LDO3 and LDO5 all have independent

enabling control. Drive ENLDO, ENTRIP1 and ENTRIP2

below the precise input falling edge trip level to place the

RT8239A/B/C in its low power shutdown state. The

RT8239A/B/C consumes only 20

μA of input current while

in shutdown. When shutdown mode is activated, the

reference turns off. The accurate 0.95V falling edge

threshold on ENLDO 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.

Power Up Sequencing and On/Off Controls

(ENTRIPx, ENM)

ENTRIP1 and ENTRIP2 control SMPS power up

sequencing. When the RT8239A/B/C is applied in the

single channel mode, ENTRIPx disables the respective

output when ENTRIPx voltage rises above 4.5V.

Furthermore, when the RT8239A is applied in the dual

channel mode, the outputs are enabled when ENM voltage

rises above 2.3V.

RT8239B Datasheet(PDF) 20 Page - Richtek Technology Corporation

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