DS6550A Datasheet, PDF (12/16 Pages) Richtek Technology Corporation – Synchronous DC-DC Step-Down Controller with 5V LDO

RT6550A
UVLO Protection
The RT6550A has LDO5 under-voltage lock out protection
(UVLO). When the LDO5 voltage is lower than 3.9V (typ.),
both switch power supply is shut off. This is a non-latch
protection.
Output Over-Voltage Protection (OVP)
The output voltage can be continuously monitored for over-
voltage condition. If the output voltage exceeds 13% of
its set voltage threshold, the over-voltage protection is
triggered and the LGATE low-side gate drivers is forced
high. This activates the low-side MOSFET switch, which
rapidly discharges the output capacitor and pulls the output
voltage downward.
The RT6550A is latched once OVP is triggered and can
only be released by either toggling EN or cycling VIN.
There is a 1μs delay built into the over-voltage protection
circuit to prevent false transition.
Note that latching LGATE high will cause the output voltage
to dip slightly negative due to previously stored energy 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 shorted in
high-side switch, turning the low-side MOSFET on 100%
will create an electrical shorted circuit between the battery
and GND to blow the fuse and disconnecting the battery
from the output.
Output Under-Voltage Protection (UVP)
The output voltage can be continuously monitored for under-
voltage condition. If the output is less than 52% (typ.) of
its set voltage threshold, the under-voltage protection will
be triggered and then both UGATE and LGATE gate drivers
will be forced low. The UVP is ignored for at least 1.3ms
(typ.) after a start-up or a rising edge on EN. Toggle EN or
cycle VIN to reset the UVP fault latch and restart the
controller.
Thermal Protection
The RT6550A features thermal shutdown to prevent
damage from excessive heat dissipation. Thermal
shutdown occurs when the die temperature exceeds
150°C. All internal circuitries are turned off during thermal
shutdown. The RT6550A triggers thermal shutdown while
input voltage on VIN and drawing current from LDO5 are
too high.
Discharge Mode (Soft Discharge)
When EN is low the output under-voltage fault latch is
set, the output discharge mode will be triggered. During
discharge mode, an internal switch creates a path for
discharging the output capacitors' residual charge to GND.
Shutdown Mode
When VIN exceeds POR threshold and EN < 0.4V, the
RT6550A operate in shutdown mode, and PWM contoller
is OFF state. For the RT6550A, LDO5 is OFF and
approximately consumes 17μA of input current.
Power-Up Sequencing and On/Off Controls (EN)
EN controls the power-up sequencing of the Buck
converter. The 0.4V falling edge threshold on EN can be
used to detect a specific analog voltage level and to
shutdown the device. Once in shutdown, the 1.6V rising
edge threshold activates, providing sufficient hysteresis
for most applications.
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
DS6550A-00 September 2016