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RT8223AGQW

High Efficiency, Main Power Supply Controller for Notebook Computers

Richtek Technology 

RT8223A/B

that drives LGATEx low is robust, with a 0.6Ω typical on-

resistance. A 5V bias voltage is delivered from VREG5

supply. The instantaneous drive current is supplied by an

input capacitor connected between VREG5 and GND.

For high current applications, some combinations of high

and low side MOSFETs might be encountered that will

cause excessive gate-drain coupling, which can lead to

efficiency-killing, EMI-producing shoot-through currents.

This is often remedied by adding a resistor in series with

BOOTx, which increases the turn-on time of the high side

MOSFET without degrading the turn-off time (Figure 3).

VIN

10

BOOTx

UGATEx

PHASEx

Figure 3. Reducing the UGATEx Rise Time

Soft-Start

A build-in soft-start is used to prevent surge current from

power supply input after ENTRIPx is enabled. The typical

soft-start duration is 2ms period. Furthermore, the

maximum allowed current limit is segmented in 5 steps:

20%, 40%, 60%, 80% and 100% during the 2ms period.

UVLO Protection

The RT8223A/B has VREG5 under voltage lock out

protection (UVLO). When the VREG5 voltage is lower than

4.2V (typ.) and the VREG3 voltage is lower than 2.5V

(typ.), both switch power supplies will be shut off. This is

a non-latch protection.

Power Good Output (PGOOD)

The PGOOD is an open-drain type output and requires a

pull-up resistor. PGOOD is actively held low in soft-start,

standby, and shutdown. It will be released when both

output voltage are above 92.5% of nominal regulation point.

The PGOOD goes low if either output turns off or is 10%

below its nominal regulator point.

Output Over Voltage Protection (OVP)

The output voltage can be continuously monitored for over

voltage. When over voltage protection is enabled, if the

output voltage exceeds 11% of its set voltage threshold,

the over voltage protection will be triggered and the LGATEx

low-side gate drivers will be forced high. This activates

the low side MOSFET switch, which rapidly discharges

the output capacitor and pulls the input voltage downward.

RT8223A/B will be latched once OVP is triggered and

can only be released by EN power-on reset. There is a

10μs delay built into the over voltage protection circuit to

prevent false transition.

Note that LGATEx latching high causes the output voltage

to dip slightly negative when energy has been previously

stored 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%

creates an electrical short between the battery and GND,

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 protection. When under voltage protection is

enabled, if the output is less than 70% of its set voltage

threshold, under voltage protection will be triggered, then

both UGATEx and LGATEx gate drivers are forced low

while entering soft-discharge mode. During soft-start, the

UVP will be blanked around 3ms.

Thermal Protection

The RT8223A/B provides thermal shutdown to prevent the

overheat damage. Thermal shutdown occurs when the die

temperature exceeds +150°C. All internal circuitry shuts

down during thermal shutdown. The RT8223A/B triggers

thermal shutdown if VREGx is not supplied from VOUTx,

while input voltage on VIN and drawing current from VREGx

are too high. Even if VREGx is supplied from VOUTx,

overloading the VREGx causes large power dissipation

on automatic switches, which may result in thermal

shutdown.

DS8223A/B-04 April 2011

www.richtek.com

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