RT8205CGQW datasheet(23/28 Pages) RICHTEK

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RT8205A/B/C

DS8205A/B/C-06 July 2012

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

LGATEx gate drivers are forced low while entering soft-

discharge mode. During soft-start, the UVP will be blanked

around 3ms.

Thermal Protection

The RT8205A/B/C have 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 RT8205A/B/C triggers

thermal shutdown if VREGx is not supplied from VOUTx,

while input voltage on VINand drawing current form 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.

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 outputs discharge mode will be triggered.

During discharge mode, there is one path to discharge

the outputs capacitor residual charge. That is output

capacitor discharge to GND through an internal switch.

Shutdown Mode

The RT8205A/B/C SMPS1, SMPS2, VREG3 and VREG5

have independent enabling control. Drive EN, ENTRIP1

and ENTRIP2 below the precise input falling-edge trip level

to place the RT8205A/B/C in its low-power shutdown

state. The RT8205A/B/C consumes only 20uA of input

current while in shutdown.

Power-Up Sequencing and On/Off Controls

(ENTRIPx)

ENTRIP1 and ENTRIP2 control SMPS power-up

sequencing. When the RT8205A/B/C applies in the single

channel mode, ENTRIP1 or ENTRIP2 enables the

respective outputs when ENTRIPx voltage rising above

0.4V.

If both of ENTRIP1 and ENTRIP2 become higher than the

enable threshold voltage at a different time (without 60us),

one can force the latter one output starts after the former

one regulates.

UVLO Protection

The RT8205A/B/C 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 are also shut off. This

is 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 is released when both outputs

voltage above than 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 exceeded 11% 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.

RT8205A/B/C is latched once OVP is triggered and can

only be released by EN power-on reset. There is 10us

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. When under voltage protection is enabled, if the

output is less than 70% of its set voltage threshold, under

voltage protection is triggered, then both UGATEx and

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