RT8205L RICHTEK [Richtek Technology Corporation], RT8205L Datasheet - Page 21

• Manufacturer Part Number: RT8205L
• Description: High Efficiency, Main Power Supply Controller for Notebook Computer
• Manufacturer: RICHTEK [Richtek Technology Corporation]

standby, and shutdown. It is released when both output
voltages are above 91% of the nominal regulation point.
The PGOOD goes low if either output turns off or is 15%
below its nominal regulator point.
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 RT8205L/M is latched once OVP is triggered and can
only be released by toggling EN, ENTRIPx or cycling V
There is a 5μs delay built into the over voltage protection
circuit to prevent false alarm.
Note that the latching LGATEx 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 the
high side switch, completely turning on the low side
MOSFET can create an electrical short between the
battery and GND, which will blow the fuse and disconnect
the battery from the output.
Output Under Voltage Protection (UVP)
The output voltage can be continuously monitored for under
voltage protection. If the output is less than 52% of its set
voltage threshold, under voltage protection will be triggered,
and then both UGATEx and LGATEx gate drivers will be
forced low. The UVP will be ignored for at least 5ms (typ.)
after start up or a rising edge on ENTRIPx. Toggle ENTRIPx
or cycle V
controller.
Thermal Protection
The RT8205L/M features thermal shutdown protection to
prevent overheat damage to the device. Thermal shutdown
occurs when the die temperature exceeds 150°C. All
internal circuitry is inactive during thermal shutdown. The
RT8205L/M triggers thermal shutdown if VREGx is not
DS8205L/M-05 June 2011
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to reset the UVP fault latch and restart the
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supplied from VOUTx, while the input voltage on V
the drawing current from VREGx are too high. Even if
VREGx is supplied from VOUTx, large power dissipation
on automatic switches caused by overloading VREGx,
which may also 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, the output capacitors' residual
charge will be discharge to GND through an internal switch.
Shutdown Mode
The RT8205L/M 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 RT8205L/M in its low power shutdown state.
The RT8205L/M consumes only 20μA of input current while
in shutdown. When shutdown mode is activated, the
reference turns off. The accurate 0.4V falling edge threshold
on the EN pin can be used to detect a specific analog
voltage level as well as to shutdown the device. Once in
shutdown, the 1V rising edge threshold activates, providing
sufficient hysteresis for most applications.
Power Up Sequencing and On/Off Controls
(ENTRIPx)
ENTRIP1 and ENTRIP2 control the SMPS power up
sequencing. When the RT8205L/M is in single channel
mode, ENTRIP1 or ENTRIP2 enables the respective
outputs when ENTRIPx voltage rises above 0.515V.
Since current source form ENTRIPx has 4700ppm/°C
temperature slope, please make sure that ENTRIPx voltage
is high enough to enable the respective output in low
temperature application.
If ENTRIPx pin becomes higher than the enable threshold
voltage while another channel is starting up, soft-start is
postponed until the other channel's soft-start has
completed. If both ENTRIP1 and ENTRIP2 become higher
than the enable threshold voltage simultaneously (within
60μs), both channels will be start up simultaneously. The
timing diagrams of the power sequence is shown below
(Figure 5).
RT8205L/M
www.richtek.com
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