RT8205A RICHTEK [Richtek Technology Corporation], RT8205A Datasheet - Page 23

• Manufacturer Part Number: RT8205A
• Description: High Efficiency, Main Power Supply Controllers for Notebook Computers
• Manufacturer: RICHTEK [Richtek Technology Corporation]

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
Copyright
DS8205A/B/C-06 July 2012
©
2012 Richtek Technology Corporation. All rights reserved.
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 VIN and 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.
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RT8205A/B/C
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