RT8206L RICHTEK [Richtek Technology Corporation], RT8206L Datasheet - Page 22

• Manufacturer Part Number: RT8206L
• Description: High Efficiency, Main Power Supply Controller for Notebook Computers
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8206L/M
capacitor between BOOTx and PHASEx pins. A dead time
to prevent shoot through is internally generated between
high side MOSFET off to low side MOSFET on, and low
side MOSFET off to high side MOSFET on.
The low side driver is designed to drive high current low
R
that drives LGATEx low is robust, with a 0.6Ω typical on-
resistance. A 5V bias voltage is typically delivered from
PVCC through LDO supply. The instantaneous drive
current is supplied by an input capacitor connected
between PVCC 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 5).
Soft-Start
The RT8206L/M provides an internal soft-start function to
prevent large inrush current and output voltage overshoot
when the converter starts up. The soft-start (SS)
automatically begins once the chip is enabled. During
soft-start period, the internal current limit circuit gradually
ramps up the inductor current from zero. The maximum
current limit value is set externally as described in previous
section. The soft-star time is determined by the current
limit and output capacitor value. The current limit threshold
ramp up time is typically 2ms from zero to 200mV after
ENx is enabled. A unique PWM duty limit control that
prevents output over voltage during soft-start period is
designed specifically for FBx floating.
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DS(ON)
Figure 5. Reducing the UGATEx Rise Time
©
N-MOSFET(s). The internal pulldown transistor
2012 Richtek Technology Corporation. All rights reserved.
UGATEx
PHASEx
BOOTx
V
IN
POR and UVLO
Power On Reset (POR) occurs when VIN rises above
approximately 5V (typ.), resetting the fault latches. PVCC
Under Voltage Lockout (UVLO) circuitry inhibits switching
by keeping UGATEx and LGATEx low when PVCC is
below 4.05V. The PWM outputs begin to ramp up once
PVCC exceeds its UVLO threshold and ENx is enabled.
Power Good Output (PGOODx)
The PGOODx is an open-drain type output. PGOODx is
actively held low in soft-start, standby, and shutdown. It is
released when the VOUTx voltage is above 90% of the
nominal regulation point. The PGOODx goes low if it is
10% below its nominal regulator point.
Output Over Voltage Protection (OVP)
The output voltage can be continuously monitored for over
voltage protection. When the output voltage of the VOUTx
is 12% above the set voltage, over voltage protection will
be enabled. If the output exceeds the over voltage
threshold, over voltage fault protection will be 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 reduces the output
voltage. Once an over voltage fault condition is set, it can
only be reset by toggling ENLDO, ENx, or cycling VIN
(POR.)
Output Under Voltage Protection (UVP)
The output voltage can be continuously monitored for under
voltage protection. If the output is less than 55% of the
error-amplifier trip voltage, 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 after a rising edge on ENx.
Toggle ENx or cycle VIN (POR) to clear the under voltage
fault latch and restart the controller. The UVP only applies
to the PWM outputs.
Thermal Protection
The RT8206L/M has a thermal shutdown protection
function to prevent it from overheating. Thermal shutdown
occurs when the die temperature exceeds +150°C. All
is a registered trademark of Richtek Technology Corporation.
DS8206L/M-07 June 2012