RT6211A/B
Shut-Down, Start-Up and Enable (EN)
The enable input (EN) has a logic-low level. When V
EN
is below this level the IC enters shutdown mode and
supply current drops to less than 6A. When V
EN
exceeds its logic-high level the IC is fully operational.
External Bootstrap Capacitor
Connect a 0.1F low ESR ceramic capacitor between
BOOT and LX. This bootstrap capacitor provides the
gate driver supply voltage for the high side N-channel
MOSFET switch.
Soft-Start (SS)
The RT6211A/B provides an internal soft-start feature
for inrush control. At power up, the internal capacitor is
charged by an internal current source I
SS
to generate a
soft-start ramp voltage as a reference voltage to the
PWM comparator. The device will initiate switching and
the output voltage will smoothly ramp up to its targeted
regulation voltage only after this ramp voltage is
greater than the feedback voltage V
FB
to ensure the
converters have a smooth start-up. The output voltage
starts to rise in 70s from EN rising, and the soft-start
ramp-up time (V
FB
from 0V to 0.8V) is 0.85ms.
VIN
V
IN
= 12V
operation. For continuous operation, provide adequate
cooling so that the junction temperature does not
exceed 150C.
Output Under-Voltage Protection and Hiccup Mode
The RT6211A/B includes output
protection (UVP) against over-load or
condition by constantly monitoring
voltage V
FB
. If V
FB
drops below the
under-voltage
short-circuited
the feedback
under-voltage
protection trip threshold (typically 50% of the internal
feedback reference voltage), the UV comparator will go
high to turn off both the internal high-side and low-side
MOSFET switches.
If the output under-voltage condition continues for a
period of time, the RT6211A/B will enter output
under-voltage protection with hiccup mode. During
hiccup mode, the IC will shut down for t
HICCUP_OFF
(3.6ms), and then attempt to recover automatically for
t
HICCUP_ON
(1.2ms). Upon completion of the soft-start
sequence, if the fault condition is removed, the
converter will resume normal operation; otherwise,
such cycle for auto-recovery will be repeated until the
fault condition is cleared. Hiccup mode allows the
circuit to operate safely with low input current and
power dissipation, and then resume normal operation
EN
70μs
850μs
as soon as the over-load or short-circuit condition is
removed.
VOUT
Abnormal case t
HICCUP_ON
=
detected (UV) 1.2ms t
HICCUP_OFF
=
3.6ms
Resume normal
operation
Fault condition
removed
t
VOUT
Over-Temperature Protection
The
RT6211A/B
includes
an
over-temperature
LX
0.85ms
protection (OTP) circuitry to prevent overheating due to
excessive power dissipation. The OTP will shut down
switching operation when the junction temperature
exceeds 150C. Once the junction temperature cools
down by approximately 20C the IC will resume normal
t
Copyright © 2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6211A/B-07
September 2018
www.richtek.com
5
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
