®
RT6278A/B
23V, 8A, 500kHz ACOT
TM
Synchronous Step-Down Converter
General Description
The RT6278A/B is a simple, easy-to-use, 8A synchronous
step-down DC-DC converter with an input supply voltage
range of 4.5V to 23V. The device build-in an accurate 0.6V
reference voltage and integrates low R
DS(ON)
power
MOSFETs to achieve high efficiency in a UQFN-12HL 3x3
package. The RT6278A/B adopts Advanced Constant On-
Time (ACOT
TM
) control architecture to provide an ultrafast
transient response with few external components and to
operate in nearly constant switching frequency over the
line, load, and output voltage range. The RT6278A operates
in automatic PSM that maintains high efficiency during
light load operation. The RT6278B operates in Forced
PWM that helps meet tight voltage regulation accuracy
requirements. The RT6278A/B senses both FETs current
for a robust over-current protection. It features cycle-by-
cycle current limit protection and prevent the device from
the catastrophic damage in output short circuit, over current
or inductor saturation. A built-in soft-start function prevents
inrush current during start-up. The device also includes
input under-voltage lockout, output under-voltage
protection, over-voltage protection, and over-temperature
protection (thermal shutdown) to provide safe and smooth
operation in all operating conditions. The RT6278A/B is
offered in a UQFN-12HL 3x3(FC) package.
Features
Ω
Ω
8A Converter With Built-In 24mΩ/12mΩ Low R
DS(ON)
Power FETs
Input Supply Voltage Range : 4.5V to 23V
Output Voltage Range : 0.6V to 6V
Advanced Constant On-Time (ACOT
TM
) Control
½
Ultrafast Transient Response
No Needs For External Compensations
½
Optimized for Low-ESR Ceramic Output Capacitors
0.6V
±
1% High-Accuracy Feedback Reference
½
Voltage
Optional for Operation Modes :
½
Power Saving Mode (PSM) (RT6278A)
½
Forced PWM Mode (RT6278B)
Fixed Switching Frequency : 500kHz
Built-In Internally Fixed Soft-Start (Typ. 0.4ms)
Input Under-Voltage Lockout (UVLO)
Output Under-Voltage Protection (UVP) with Hiccup
Mode
Output Over-Voltage Protection (OVP) with Auto-
Recovery Mode
Ultrasonic Mode (USM) for RT6278A
Available In UQFN-12HL 3x3 (FC) (U-Type) Package
Ordering Information
RT6278A/B
Package Type
QUF : UQFN-12HL 3x3 (FC) (U-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
UVP Option
H : Hiccup
PWM Operation Mode
A : Automatic PSM
B: Forced PWM
Note :
Richtek products are :
½
Applications
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
Networking Communication
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
½
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6278A/B-01 May 2018
www.richtek.com
1
RT6278A/B
Pin Configuration
(TOP VIEW)
AGND
PGOOD
ILMT
VCC
BYP
FB
Marking Information
RT6278AHGQUF
M8= : Product Code
YMDNN : Date Code
12 11 10
9
8
7
6
5
M8=YM
DNN
EN
VIN
PGND
BOOT
LX
LX
1
2
4
3
RT6278BHGQUF
M7= : Product Code
UQFN-12HL 3x3
M7=YM
DNN
YMDNN : Date Code
Functional Pin Description
Pin No.
1
2, 3
4
5
Pin Name
BOOT
LX
PGND
VIN
Pin Function
Boot-strap pin. Supply high-side gate driver. Decouple this pin to LX pin with
0.1F ceramic cap.
Inductor pin. Connect this pin to the switching node of inductor.
Power ground.
Input pin. Decouple this pin to GND pin with at least 10F ceramic cap.
Enable control. Pull this pin high to turn on the Buck. Do not leave this pin
floating. EN pin will also be used to set USM mode for RT6278A, when EN
pin voltage is between 2.3V and 23V, it will enter USM mode, if EN pin
voltage is between 0.8V and 1.7V, then it is normal mode.
Power good indicator. Open drain output when the output voltage is within
90% to 120% of regulation point.
Analog ground. Connect AGND to a clean inner GND point with separate
trace.
5V linear regulator output for internal control circuit. A capacitor (typical 1F)
should be connected to PGND. Don’t connect to external Load.
Output feedback pin. Connect this pin to the center point of the output
resistor divider to program the output voltage.
Bypass input for the internal LDO. BYP is externally connected to the output
of switching regulator. When the BYP voltage rises above the bypass switch
turn-on threshold, the LDO regulator shuts down and the VCC pin is
connected to the BYP pin through an internal switch. But when BYP pin is
not used, it should be connected to ground.
Current limit setting pin. The current limit is set to 8A, 10A or 12A when this
pin is pull low, floating or pull high respectively.
6
EN
7
8
9
10
PGOOD
AGND
VCC
FB
11
BYP
12
ILMT
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS6278A/B-01 May 2018
RT6278A/B
Functional Block Diagram
VIN
Input UVLO
4.2V
BOOT
LX
ILMT
EN
Internal
SST
Thermal
Protection
0.6V
FB
+
-
-
PWM
Control
&
Protect
Logic
+
Current Sense
PGND
PGOOD
AGND
EN
VIN
5V
LDO
4.7V
+
-
VCC
BYP
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6278A/B-01 May 2018
www.richtek.com
3
RT6278A/B
Operation
The RT6278A/B is a high-efficiency, synchronous step-
down DC-DC converter that can deliver up to 8A output
current from a 4.5V to 23V input supply. The RT6278A/B
adopts ACOT
TM
control mode, which can reduce the output
capacitance and provide ultrafast transient responses, and
allow minimal component sizes without any additional
external compensation network.
Input Under-Voltage Lockout
In addition to the EN pin, the RT6278A/B also provides
enable control through the VIN pin. It features an under-
voltage lockout (UVLO) function that monitors the internal
linear regulator (VCC). If V
EN
rises above V
ENH
first,
switching will still be inhibited until the VIN voltage rises
above V
UVLO
. It is to ensure that the internal regulator is
ready so that operation with not-fully-enhanced internal
MOSFET switches can be prevented. After the device is
powered up, if the input voltage VIN goes below the UVLO
falling threshold voltage (V
UVLO
− ΔV
UVLO
), this switching
will be inhibited; if VIN rises above the UVLO rising
threshold (V
UVLO
), the device will resume switching.
Soft-Start
The soft-start function is used to prevent large inrush
currents while the converter is being powered up. The
RT6278A/B provides an internal soft-start feature for inrush
control. During the start-up sequence, 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 typical soft-start time is
0.4ms.
Over-Current Limit
The RT6278A/B current limit is (8A, 10A, 12A) it is a cycle-
by-cycle
“valley”
type, measuring the inductor current
through the synchronous rectifier during the off-time while
the inductor current ramps down. If output voltage drops
below the output under-voltage protection level, the
RT6278A/B will stop switching to avoid excessive heat.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
Output Over-Voltage Protection (OVP) and Under-
Voltage Protection (UVP)
The RT6278A/B includes output under-voltage protection
(UVP) against over-load or short-circuited condition by
constantly monitoring the feedback voltage V
FB
. If V
FB
drops below the under-voltage protection trip threshold
(typically 60% of the internal reference voltage), the UV
comparator will go high to turn off both the internal high-
side and low-side MOSFET switches.
Power Good
The PGOOD pin is an open-drain output and is connected
to an external pull-up resistor. It is controlled by a
comparator, which the feedback signal V
FB
is fed to. If
V
FB
is above 90% of the internal reference voltage, the
PGOOD pin will be in high impedance and VPGOOD will
be held high. Otherwise, the PGOOD output will be pulled
low.
Over-Temperature Protection (Thermal Shutdown)
The RT6278A/B includes an over-temperature protection
(OTP) circuitry to prevent overheating due to excessive
power dissipation. The OTP will shut down switching
operation when junction temperature exceeds a thermal
shutdown threshold T
SD
. Once the junction temperature
cools down by a thermal shutdown hysteresis (ΔT
SD
), the
IC will resume normal operation with a complete soft-start.
www.richtek.com
4
DS6278A/B-01 May 2018
RT6278A/B
Absolute Maximum Ratings
(Note 1)
−0.3V
to 27V
−0.3V
to 27V
−0.3V
to 4.5V
−0.3V
to (V
IN
+ 0.3V)
−5V
to 28V
(V
LX
−
0.3V) to (V
LX
+ 6V)
−0.3V
to 6V
Supply Voltage, VIN --------------------------------------------------------------------------------------------
Enable Pin Voltage, EN ---------------------------------------------------------------------------------------
FB Pin Voltage, FB --------------------------------------------------------------------------------------------
Switch Voltage, LX ---------------------------------------------------------------------------------------------
<30ns -------------------------------------------------------------------------------------------------------------
Boot Voltage, V
BS
----------------------------------------------------------------------------------------------
Other I/O Pin Voltages ----------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
UQFN-12HL 3x3 (FC) ----------------------------------------------------------------------------------------- 2.5W
Package Thermal Resistance (Note 2)
UQFN-12HL 3x3 (FC),
θ
JA
------------------------------------------------------------------------------------ 40°C/W
Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------- 260°C
Junction Temperature ------------------------------------------------------------------------------------------ 150°C
Junction Temperature Range ---------------------------------------------------------------------------------
−40°C
to 125°C
Storage Temperature Range ----------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, VIN ------------------------------------------------------------------------------------ 4.5V to 23V
Ambient Temperature Range ---------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25°C, unless otherwise specified)
Parameter
Input Voltage Range
Supply Current
Supply Current (Shutdown)
Supply Current (Quiescent)
Logic Threshold
EN Input Low Voltage
EN Input High Voltage
Ultra-Sonic Mode
Normal Mode
Output Voltage
VCC Regulator Voltage
Feedback Voltage
Feedback Reference Voltage
Feedback Current
Symbol
V
IN
Test Conditions
Min
4.5
Typ
--
Max
23
Unit
V
A
A
V
V
V
V
V
V
nA
I
SHDN
I
Q
V
ENL
V
ENH
V
EN
V
EN
V
CC
V
REF
I
FB
V
EN
= 0
I
OUT
= 0, V
FB
= V
REF
x 105%
--
--
0.4
0.45
2.3
--
--
0.594
50
5
130
0.54
0.625
--
--
5
0.6
--
10
--
0.68
0.8
--
1.7
--
0.606
50
V
FB
= 4V
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6278A/B-01 May 2018
www.richtek.com
5
嵌入式系统
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
