®
RT7291A/B
6A, 23V, 500kHz, ACOT
TM
Synchronous Buck Converter
with LDO for System 5V
General Description
The RT7291A/B is a synchronous Buck converter with
Advanced Constant On-Time (ACOT
TM
) mode control. The
main control loop of the RT7291A/B uses an ACOT
TM
mode control which provides a very fast transient response
with no external compensators. The RT7291A/B operates
from 5V to 23V input voltage, provides a 5V LDO and a
300kHz CLK to drive an external charge pump. OCP, UVP
and OVP are included in the RT7291A/B. This IC also
provides a 1.5ms internal soft-start function and an open-
drain power good indicator.
Features
5V to 23V Input Voltage Range
Up to 98% Duty for 2S Battery Application
PWM Frequency Fixed 500kHz
ACOT
TM
Mode Performs Fast Transient Response
Integrated MOSFETs
Ω
½
31mΩ of High-Side MOSFET
½
20mΩ of Low-Side MOSFET
Ω
Support Output MLCC Stable
Internal Soft-Start (1.5ms typ)
Built-in OVP/UVP/OCP
Power Good Indicator
Fixed 300kHz VCLK to Support Charge Pump
Individual EN for PWM and LDO
Thermal Shutdown
Applications
Laptop Computers
Tablet PCs
Networking Systems
Servers
Personal Video Recorders
Flat Panel Television and Monitors
Distributed Power Systems
Simplified Application Circuit
D1
V
OUT
C1
C2
C3
C4
C5
D2
D3
D4
V
CP
V
IN
C
IN
V
LDO
VIN
EN
LDO
C
LDO
R
BYP
C
BYP
CLK
RT7291A/B
R
B
BOOT
C
B
L
SW
VOUT
PGND
C
OUT
V
OUT
V
OUT
VBYP
PGOOD
VCC
ENLDO AGND
R
PGOOD
V
CC
C
VCC
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7291A/B-03 January 2018
www.richtek.com
1
RT7291A/B
Ordering Information
RT7291A/B
Package Type
QUF : UQFN-16L 3x3 (FC) (U-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Output Voltage
A : 5V
B : 5.1V
VIN
PGND
Pin Configuration
(TOP VIEW)
AGND
EN
ENLDO
VCC
BOOT
14 13 12 11 10
1
15
2
9
SW
SW
SW
16
Note :
½
SW
3
4
5
6
7
8
Richtek products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
½
Suitable for use in SnPb or Pb-free soldering processes.
UQFN-16L 3x3 (FC)
Marking Information
RT7291AGQUF
39= : Product Code
RT7291BGQUF
4M= : Product Code
YMDNN : Date Code
39=YM
DNN
4M=YM
DNN
YMDNN : Date Code
Functional Pin Description
Pin No.
1
2
3
4
5
6
7
8, 9, 15, 16
10
Pin Name
VIN
PGND
VBYP
PGOOD
CLK
LDO
VOUT
SW
BOOT
Pin Function
Power input connect to high-side MOSFET drain.
Power ground.
Switch over source voltage for VCC. A low pass filter should be connected to
AGND, if VBYP is applied. If VBYP is not used, then connect to AGND
.
Do not
connect to VCC pin.
Open-drain power good indicator output.
300kHz clock output to drive the external charge pump.
5V linear regulator output. Decouple with a minimum 4.7F ceramic capacitor.
Output voltage sense input. An internal discharging circuit is connected to this pin.
Switch node.
Bootstrap supply for high-side gate driver. A capacitor is needed to drive the power
switch's gate above the supply voltage. It is connected between the SW and
BOOT pins to form a floating supply across the power switch driver.
5V linear regulator output for internal control circuit. A capacitor (typical 2.2F)
should be connected to AGND. V
CC
can only supply internal circuits. Do not
connect to external loads.
Enable control input for linear regulator. This pin is internally pulled up to high by
10A.
Enable control input. Do not leave this pin floating.
Analog ground.
is a registered trademark of Richtek Technology Corporation.
11
VCC
12
13
14
ENLDO
EN
AGND
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
VBYP
PGOOD
CLK
LDO
VOUT
DS7291A/B-03 January 2018
RT7291A/B
Functional Block Diagram
VCC
VBYP
V
IN
Soft-Start
VOUT
V
REF
V
FB
+
+
-
POR &
Reference
V
CC
Switch-Over
On-Time
One shot
Min off Time
BSTREG
V
IN
BOOT
Gate
Control
Logic
SW
V
CC
EN
V
OUT
SW
V
OC
+
-
PGND
OCP
PGOOD
Fault
Logic
120% x V
REF
-
+
OVP
-
+
90% x V
REF
POK
60% x V
REF
+
-
AGND
UVP
V
OUT
CLK
CLK
Generator
V
CC
V
CC
Regulator
LDO
Control
LDO
Switch-Over
V
OUT
VIN
ENLDO LDO
Operation
Overall
The RT7291A/B is a synchronous step-down converter
with advanced constant on-time control mode. Using the
ACOT
TM
control mode can reduce the output capacitance
and provide fast transient response. It can minimize the
component size without additional external compensation
network.
Internal VCC Regulator
The regulator provides 5V power to supply the internal
control circuit. Connecting a 2.2μF ceramic capacitor for
decoupling and stability is required.
Soft-Start
In order to prevent the converter output voltage from
overshooting during the startup period, the soft-start
function is necessary. The soft-start time is internal setting
and the duration is around 1.5ms
CLK Generator
Provide a 300kHz clock to drive external charge pump.
VCC Switch-Over
The internal regulator output will switch over to VBYP if
VBYP level is higher than 4.6V.
LDO
Built-in 5V, 100mA LDO with 1% accuracy. The LDO output
will switch over to VOUT once PGOOD goes high.
is a registered trademark of Richtek Technology Corporation.
OCP
The inductor valley current is monitored via the internal
switches in cycle-by-cycle. Once the output voltage drops
below UV threshold, the device enters latch mode.
Power Good
After soft-start is finished, the power good function will be
activated. The PGOOD pin is an open-drain output.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
DS7291A/B-03 January 2018
www.richtek.com
3
RT7291A/B
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------
−0.3V
to 27V
Switch Voltage, SW -----------------------------------------------------------------------------------------
−0.3V
to (V
IN
+ 0.3V)
<30ns -----------------------------------------------------------------------------------------------------------
−5V
to 28V
BOOT Switch Voltage --------------------------------------------------------------------------------------- (V
SW
−
0.3V) to (V
SW
+ 6V)
EN, ENLDO Pin Voltages ----------------------------------------------------------------------------------
−0.3V
to 27V
Other I/O Pin Voltages --------------------------------------------------------------------------------------
−0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25°C
UQFN-16L 3x3 (FC) ------------------------------------------------------------------------------------------ 1.4W
Package Thermal Resistance (Note 2)
UQFN-16L 3x3 (FC),
θ
JA
------------------------------------------------------------------------------------ 70°C/W
UQFN-16L 3x3 (FC),
θ
JC
------------------------------------------------------------------------------------ 15°C/W
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------ 260°C
Junction Temperature ---------------------------------------------------------------------------------------- 150°C
Storage Temperature Range -------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) --------------------------------------------------------------------------------- 2kV
MM (Machine Model) ---------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------- 5V to 23V
Junction Temperature Range -------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25°C, unless otherwise specified)
Parameter
Supply Current
Shutdown Current
Quiescent Current
Standby Current
Switch On-Resistance
Switch On-Resistance
Current Limit
Current Limit
Switching Frequency
Minimum Off-Time
Protections
OVP Trip Threshold
OVP Propagation Delay
Symbol
Test Conditions
V
EN
= V
ENLDO
= 0V
V
EN
= 2V, V
ENLDO
= 2V, no switching
V
EN
= 0V, V
ENLDO
= 2V, LDO load
current = 0A
Min
--
--
--
Typ
2.5
100
35
Max
5
130
45
Unit
A
A
A
R
DS(ON)_H
V
BOOT
– V
SW
= 5V
R
DS(ON)_L
I
OC
f
SW
t
OFF_MIN
V
OVP
T
OVPDLY
With respect to output voltage
Valley current of low-side switch
--
--
7.6
450
--
115
--
31
20
--
500
200
120
5
--
--
11.4
550
--
125
--
m
A
kHz
ns
%
s
Switching Frequency and Minimum Off Timer
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7291A/B-03 January 2018
RT7291A/B
Parameter
UVP Trip Threshold
UVP Propagation Delay
Reference and Soft-Start
Output Voltage Valley
Soft-Start Time
Enable and UVLO
EN Input High Voltage
EN Hysteresis
EN Input Current
VCC UVLO Rising
VCC UVLO Hysteresis
CLK Output
CLK Output
Voltage
CLK Frequency
LDO Regulator
LDO Regulator
V
LDO
RT7291A
RT7291B
EN = GND,
LDO load current = 5mA
EN = GND,
LDO load current = 100mA
R
SW
4.95
5.049
--
--
--
5
5.1
1
5
3
5.05
5.151
--
%
--
5
V
High-Level
Low-Level
V
CLKH
V
CLKL
f
CLK
I
VCLK
=
10mA
I
VCLK
= 10mA
RT7291A
RT7291B
--
--
0
--
--
--
0.1
300
5.05
5.151
0.2
--
kHz
V
V
ENH
V
ENHYS
I
EN
V
CCUVLO
V
CCHYS
V
EN
= 2V
V
EN
= 0V
RT7291A
RT7291B
1.25
1.3
--
--
--
--
--
1.35
1.4
200
1
0
4.2
400
1.45
1.5
--
--
--
--
--
V
mV
A
V
mV
V
OUT
T
SS
RT7291A
RT7291B
From EN high to PGOOD high
4.95
5.049
1
5
5.1
1.5
5.05
5.151
2
V
ms
Symbol
V
UVP
T
UVPDLY
Test Conditions
With respect to output voltage
Min
55
--
Typ
60
5
Max
65
--
Unit
%
s
LDO Load Regulation
Switch On-Resistance
VCC Regulator
RT7291A
VCC Regulator
VCC Switch Over Threshold to
VBYP
VCC Switch Over Hysteresis
Switch Over On-Resistance
V
VCC
RT7291B
RT7291A
V
BYP
rising edge
V
BYP
falling edge
RT7291B
4.805
4.905
4.45
4.542
--
--
5
5.1
4.6
4.692
200
3
5.295
V
5.395
4.75
V
4.842
--
5
mV
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7291A/B-03 January 2018
www.richtek.com
5
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