Richtek RT7291AGQUF, RT7291BGQUF Schematic [ru]

®

RT7291A/B

6A, 23V, 500kHz, ACOTTM Synchronous Buck Converter
with LDO for System 5V

General Description

The RT7291A/B is a synchronous Buck converter with
Advanced Consta nt On-Time (ACOTTM) mode control. The
main control loop of RT7291A/B uses an ACOTTM mode
control which provides a very fast tra nsient response with
no external compensators. The RT7291A/B operates from
5V to 23V input voltage, provides a 5V LDO a nd 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 a n open-drain power
good indicator.

Applications

 Laptop Computers
 T a blet PCs
 Networking Systems
 Servers
 Personal Video Recorders
 Flat Panel Television and Monitors
 Distributed Power Systems

Features



 5V to 23V Input Voltage Range





 Up to 98% Duty for 2S Battery Application





 PWM Frequency Fixed 500kHz





 ACOT





 Integrated MOSFET s





 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



TM

Mode Performs Fast T ra nsient Re sponse

ΩΩ



 31m

Ω of High-Side MOSFET



ΩΩ

ΩΩ



 20m

Ω of Low-Side MOSFET



ΩΩ

Simplified Application Circuit

V

OUT

C1 C2

D1

V

IN

V

LDO

V

OUT

Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.

©

C

IN

C

LDO

R

BYP

DS7291A/B-02 September 2015 www.richtek.com

D2 D3

VIN

EN
LDO

VBYP

C

BYP

ENLDO

C3 C4

CLK

RT7291A/B

AGND

D4

BOOT

SW

VOUT
PGND

PGOOD

VCC

C5

R

V

CP

R

B

PGOOD

C

B

L

C

VCC

V

OUT

C

OUT

V

CC

1

RT7291A/B

Ordering Information

Pin Configurations

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

Note :
Richtek products are :

 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.

B : 5.1V

Marking Information

RT7291AGQUF RT7291BGQUF

39= : Product Code

39=YM

DNN

YMDNN : Date Code

4M=YM

DNN

(TOP VIEW)

AGND

EN

14 13 12 11 10

1

VIN

SW

PGND

2

SW

3 4 5 6 7

VBYP

PGOOD

UQFN-16L 3x3 (FC)

4M= : Product Code
YMDNN : Date Code

15

16

ENLDO

CLK

VCC

BOOT

9

SW

8

SW

LDO

VOUT

Functional Pin Description

Pin No. Pin Name Pin Function

1 VIN Power Input Connect t o High- S ide MOSFET Drain.
2 PGND Power Ground.

Switch Over Source Voltage for VCC. A low pass fil ter should be connected to

3 VBYP

4 PGOOD Open-Drain P ower Good Indicator Output.
5 CLK 300kHz Clock Output t o Drive the External Charge Pump.
6 LDO 5V Linear Regulator Output. Decouple with a minimum 4.7F ceramic capacitor.

7 VOUT

8, 9, 15, 16 SW Switch Node.

10 BOOT

11 VCC

12 ENLDO

AGND, if VBYP is applied. If VBYP is not used, then connect to AGND. Do not
connect to VCC pin.

Output Voltage Sense Input. A n internal discharging ci rcuit is connected to thi s
pin.

Bootstrap Supply for High-Side Gate Driver. A capacitor is needed to drive the
power switch's gate abov e the supply voltage. It is connected bet ween the SW
and BOOT pins to form a floati ng suppl y across the power switch driv er.

5V Linear Regulator Output for Internal Cont rol Circuit. A capacitor (typical 2.2F)
should be connected to AGND. VCC 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

10A.
13 EN Enable Control I nput. Do not leave this pin floating.
14 AGND Analog Ground.

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Function Block Diagram

RT7291A/B

VOUT

EN

CLK

Soft-Start

V

REF

V

FB

120% x V

90% x V

V

OUT

CLK

Generator

­+

Reference

+
+

-

REF

OVP

REF

VCC

POR &

­+

V

V

POK

60% x V

CC

Regulator

VBYP

V

CC

Switch-Over

On-Time
One shot

Min off Time

OUT

+

SW

-

V

OC

+

REF

-

V

CC

VIN LDO

OCP

UVP

LDO

Control

ENLDO

Gate

Control

Logic

Fault
Logic

V

IN

BSTREG

V

CC

LDO

Switch-Over

V

IN

V

OUT

BOOT

SW

PGND

PGOOD

AGND

Operation

Overall

The RT7291A/B is a synchronous step-down converter
with advanced consta nt on-time control mode. Using the
ACOTTM control mode can reduce the output ca pa citance
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 cera mic capa citor 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

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 a n open-drain output.

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% a ccuracy . The LDO output
will switch over to VOUT once PGOOD goes high.

Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.

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3

RT7291A/B

Absolute Maximum Ratings (Note 1)

 Supply Input Voltage, VIN ---------------------------------------------------------------------------------- −0.3V to 27V
 Switch Voltage, SW ----------------------------------------------------------------------------------------- −0.3V to (V

<30ns ----------------------------------------------------------------------------------------------------------- −5V to 28V

 BOOT Switch Voltage ---------------------------------------------------------------------------------------(V
 EN, ENLDO Pin Voltages ---------------------------------------------------------------------------------- −0.3V to 27V
 Other I/O Pin Voltages -------------------------------------------------------------------------------------- −0.3V to 6V
 Power Dissi pation, P

D

@ T

= 25°C

A

UQF N-16L 3x3 (FC)------------------------------------------------------------------------------------------1.4W

 Package Thermal Re sistance (Note 2)

UQF N-16L 3x3 (FC), θJA------------------------------------------------------------------------------------70°C/W
UQF N-16L 3x3 (FC), θJC------------------------------------------------------------------------------------15°C/W

 Lead T e mperature (Soldering, 10 sec.)------------------------------------------------------------------260°C
 Junction T emperature----------------------------------------------------------------------------------------150°C
 Storage T emperature Range ------------------------------------------------------------------------------- − 65°C to 150°C
 ESD Susceptibility (Note 3)

HBM (Human Body Model)---------------------------------------------------------------------------------2kV
MM (Machine Model) ---------------------------------------------------------------------------------------- 200V

− 0.3V) to (VSW + 6V)

SW

+ 0.3V)

IN

Recommended Operating Conditions (Note 4)

 Supply Input V oltage, VIN ----------------------------------------------------------------------------------5V to 23V
 Junction T emperature Range------------------------------------------------------------------------------- − 40°C to 125°C
 Ambient T emperature Range------------------------------------------------------------------------------- −40°C to 85°C

Electrical Characteristics

(V

= 12V, TA = 25°C, unless otherwise specified)

IN

Parameter Symbol Test Conditions Min Typ Max Unit

Supply Current

Shutdown Current V
Quiescent Curr ent V

Standby Current

Switch On-Resistance

R

Switch On-Resi stanc e

DS(ON)_H VBOOT

R

DS(ON)_L

Current Lim it

Current Limit IOC Valley curr ent of low-side s witch 7.6 -- 11.4 A

Switching Frequency and Minimum Off Timer

Switching Frequency fSW 450 500 550 kHz
Minimum Of f -Ti me T

-- 200 -- ns

OFF

Protections

OVP Trip Threshold V
OVP Propagation Delay T

W ith respect to output voltage 115 120 125 %

OVP
OVPDLY

-- 5 -- s

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= V

EN

= 2V, V

EN

= 0V, V

V

EN

Current = 0A

= 0V -- 2.5 5 A

ENLDO

= 2V, No Switching -- 100 130 A

ENLDO

= 2V, LDO Load

ENLDO

-- 35 45 A

– VSW = 5V -- 31 --

-- 20 --

DS7291A/B-02 September 2015www.richtek.com

m

RT7291A/B

Parameter Symbol Test Conditions Min Typ Max Unit

UVP Trip Threshold V
UVP Propagation Delay T

With respect t o output v oltage 55 60 65 %

UVP
UVPDLY

-- 5 -- s

Reference and Sof t -Start

RT7291A 4.95 5 5.05

Output Voltage Valley V

OUT

V

RT7291B 5.049 5.1 5.151

Soft-Sta r t T i me TSS F r om E N high to PGOOD high 1 1.5 2 ms

Enable and UVLO

RT7291A 1.25 1.35 1.45

EN Input High Volt age V

ENH

V

RT7291B 1.3 1.4 1.5

EN Hysteresis V

EN Input Current IEN

-- 200 -- mV

ENHYS

= 2V -- 1 --

V

EN

A

VEN = 0V -- 0 -­VCC UVLO Rising V
VCC UVLO Hysteresis V

CCUVLO
CCHYS

-- 4.2 -- V

-- 400 -- mV

CLK Output

RT7291A -- -- 5.05
CLK Output
Voltage

High-Level V

Low-Level V

I

CLKH

I

CLKL

= 10mA

VCLK

= 10mA 0 0. 1 0.2

VCLK

RT7291B -- -- 5.151

V

CLK Frequency f

-- 300 -- kHz

CLK

LDO Regulator

RT7291A 4.95 5 5.05

LDO Regulator V

LDO

RT7291B 5.049 5.1 5.151
EN = GND,

LDO Load Current = 5mA

-- 1 --

LDO Load Regulation

EN = GND,
LDO Load Current = 100mA

-- 5 --

Switch On-Resi stanc e RSW -- 3 5 

VCC Regulator

RT7291A 4.805 5 5.295

VCC Regulator V

VCC

RT7291B 4.905 5.1 5.395

VCC Switch Over Threshold to
VBYP

VCC Switch Over Hyster esi s V

V

Rising

BYP

Edge

Falli ng E dge -- 200 -- mV

BYP

RT7291A 4.45 4.6 4.75

RT7291B 4.542 4.692 4.842

Switch Over On- Resi st anc e -- 3 5 

V

%

V

V

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5

RT7291A/B

Parameter Symbol Test Conditions Min Typ Max Unit

Power Good Indicat or

PGOOD Threshold Fr om Lower V
PGOOD Low Hysteresis V
PGOOD Low to High Delay T
PGOOD Sink Current Capability V
PGOOD Leakage Current I

-- 0.5 -- ms

PGDLY
PGSINK

PGLEAK

Sink 4mA -- -- 0.4 V

V

Rising 85 90 95 %

OUT

Falling -- 10 -- %

OUT

PGOOD

= 5V -- -- 100 nA

Therma l Shutdown

Thermal Shutdown Threshol d TSD 135 150 -- °C
Thermal Shutdown Hystere si s -- 25 -- ° C

Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are

stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.

Note 2. θ
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.

is measured at T

JA

= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.

A

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