Richtek RT8249A, RT8249B, RT8249C Datasheet

®

RT8249A/B/C

Dual-Channel Synchronous DC/DC Step-Down Controller
with 5V/3.3V LDOs

General Description

The RT8249A/B/C is a dual-channel step-down, controller
generating supply voltages for battery-powered systems.
It includes two Pulse-Width Modulation (PWM) controllers
adjustable from 2V to 5.5V, and two fixed 5V/3.3V linear
regulators. Each linear regulator provides up to 100mA
output current and 3.3V linear regulator provides 1%
accura cy under 35mA. The RT8249A/B has an oscillator
output to driver the external charge pump a pplication. The
RT8249C provides a mode selection pin, SKIPSEL, to
select Diode-Emulation Mode (DEM) or Audio Skipping
Mode (ASM). Other features include on-board power-up
sequencing, a power-good output, internal soft-start, and
soft-discharge output that prevents negative voltage during
shutdown.

A con stant current ri pple PWM control scheme operates
without sense resistors and provides 100ns response to
load transient. For maximizing power efficiency, the
RT8249A/B/C automatically switches to the diode­emulation mode in light load a pplications. The RT8249A/
B/C is available in the WQFN-20L 3x3 package.

Features



 Support Connected Standby Mode for Ultrabook





 CCRCOT Control with 100ns Load Step Response





 PWM Maximum Duty Ratio > 98%





 5V to 25V Input Voltage Range





 2V to 5.5V Output Voltage Range





 5V/3.3V LDOs with 100mA Output Current





 1% Accuracy on 3.3V LDO Output





 Oscillator Driving Output for Charge Pump



Application



 Internal Frequency Setting





 RT8249A/B : 400kHz/475kHz (CH1/CH2)





 RT8249C : 500kHz/600kHz (CH1/CH2)





 Internal Soft-Start and Soft-Discharge





 4700ppm/





 Independent Switcher Enable Control





 Built in OVP/UVP/OCP/OTP





 Non-latch UVLO





 Power Good Indicator





 20-Lead WQFN Package





 RoHS Compliant and Halogen Free



°°

°C R

°°

Current Sensing

DS(ON)

Simplified Application Circuit

V

IN

GND

UGATE2

BOOT2

PHASE2
LGATE2

FB2

CS1
CS2

LDO5

PGOOD

LDO3

V

O

U

T

2

V

5

r

o

t

a

d

i

I

c

n

O

D

G

O

P

V

3

.

3

VIN

RT8249A/B/C

UGATE1
BOOT1

V

U

O

T

1

Channel 1 Enable
Channel 2 Enable

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

©

Off

On

PHASE1
LGATE1

BYP1

FB1
EN1

EN2

DS8249A/B/C-02 June 2014 www.richtek.com

1

RT8249A/B/C

Applications

 Notebook and Sub-Notebook Computers
 System Power Supplies
 3-Cell and 4-Cell Li+ Battery-Powered Devices

Ordering Information

RT8249A/B/C

Pin 1 Orientation***
(2) : Quadrant 2, Follow EIA-481-D

Package Type
QW : WQFN-20L 3x3 (W-Type)

Lead Plating System
G : Green (Halogen Free and Pb Free)

Pin Function With
A : VCLK, LDO3 Always On
B : VCLK, LDO3/LDO5 Always On
C : SKIPSEL, LDO3 Always On

Note :
***Empty means Pin1 orientation is Quadrant 1
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.

Marking Information

RT8249AGQW

2Q= : Product Code

2Q=YM

DNN

YMDNN : Date Code

Pin Configurations

(TOP VIEW)

EN1

VCLK

PHASE1

1

CS1

2

FB1

3

LDO3

FB2

CS2 LGATE2

CS1

FB1

LDO3

FB2

CS2 LGATE2

GND

4

EN2

PGOOD

PHASE2

RT8249A/B

EN1

SKIPSEL

PHASE1

1
2
3

GND

4

EN2

PGOOD

PHASE2

RT8249C

WQFN-20L 3x3

BOOT1

17181920

21

9876

BOOT2

BOOT1

17181920

21

9876

BOOT2

UGATE1

16

10

UGATE2

UGATE1

16

10

UGATE2

15

LGATE1

14

BYP1

13

LDO5

12

VIN

115

15

LGATE1

14

BYP1

13

LDO5

12

VIN

115

RT8249BGQW

2P= : Product Code

2P=YM

YMDNN : Date Code

DNN

RT8249CGQW

2N= : Product Code

2N=YM

YMDNN : Date Code

DNN

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

2

©

DS8249A/B/C-02 June 2014www.richtek.com

Functional Pin Description

Pin No. Pin Name Pin Funct ion

Curr ent Limit Setting. Connect a resistor to GND to set the threshold for Channel

1 CS1

2 FB1

3 LDO3

4 FB2

5 CS2

6 EN2 Enable Control Input for Channel 2.
7 PGOOD Power Good Indicator Output for Channel 1 and Channel 2. (Logical AND)

8 PHASE2

9 BOOT2

10 UGATE2

11 LGATE2
12 VIN Power Input for 5V and 3.3V LDO Regulators and Buck Controllers.
13 LDO5
14 BYP1 Switch-over Source Voltage Input for LDO5.
15 LGATE1

16 UGATE1

17 BOOT1

18 PHASE1

VCLK
(RT8249A/B)

19

20 EN1 Enable Control Input for Channel 1.
21

(Exposed Pad)

SKIPSEL
(RT8249C)

GND

1 synchronous R
1/8th the voltage seen at CS1 over a 0.2V to 2V range. There is an internal 50A
cur rent source from LDO5 to CS1.

Feedback Voltage Input for Channel 1. Connect FB1 to a resistive voltage divider
from VOUT1 to GND to adjust output from 2V to 5.5V.

3.3V Linear Regulator Output. It is always on when VIN is higher than VIN POR
thr eshold.

Feedback Voltage Input for Channel 2. Connect FB2 to a resistive voltage divider
from VOUT2 to GND to adjust output from 2V to 5.5V.

Curr ent Limit Setting. Connect a resistor to GND to set the threshold for Channel
2 synchronous R
1/8th the voltage seen at CS2 over a 0.2V to 2V range. There is an internal 50A
cur rent source from LDO5 to CS2.

Switch Node of Channel 2 MOSFETs. PHASE2 is the internal lower supply rail for
the UGATE2 high-side gate driver. PHA SE2 is also the current-sense input for the
Channel 2.

Bootstrap Supply for Channel 2 High-Side Gate Driver. Connect to an external
capacitor accor ding to the typical application circuits.

High-S ide Gate Driver Output for Channel 2. UGATE2 swings betw een PHA SE2
and BOOT2.

Low-Side Gate D river Output for Channel 2. LGATE2 swings between GND and
LDO5.

5V Linear Regulator Output. LDO5 is also the supply vol tage for the low-side
MOSFET and analog supply voltage for the device.

Low-Side Gate D river Output for Channel 1. LGATE1 swings between GND and
LDO5.

High-S ide Gate Driver Output for Channel 1. UGATE1 swings betw een PHA SE1
and BOOT1.

Bootstrap Supply for Channel 1 High-Side Gate Driver. Connect to an external
capacitor accor ding to the typical application circuits.

Switch Node of Channel 1 MOSFETs. PHASE1 is the internal lower supply rail for
the UGATE1 high-side gate driver. PHASE1 is also the current sense input for the
Channel 1.

Oscillat or Output for Charge Pump.
PWM Operating Mode Selection.

Diode-emulation M ode : Connect to LDO3
Audio Skipping Mode : Shor t to GND

Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.

sense. The GND  PHASE1 current limit threshold is

DS(ON)

sense. The GND  PHASE2 current limit threshold is

DS(ON)

RT8249A/B/C

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

DS8249A/B/C-02 June 2014 www.richtek.com

©

3

RT8249A/B/C

Function Block Diagram

BOOT1

UGATE1
PHASE1

LGATE1

FB1
CS1

VCLK

(RT8249A/B)

SKIPSEL

(RT8249C)

BYP1

LDO5

VIN

LDO5

BYP1

Channel 1

Buck

Controller

OSC

SW5 Threshold

LDO5

Channel 2

Buck

Controller

Power-On
Sequence

Clear Fault Latch

REF

BOOT2

UGATE2
PHASE2

LDO5

LGATE2

FB2
CS2

PGOOD

GND

EN1
EN2

LDO3 LDO3

BYP1

Operation

The RT8249A/B/C includes two constant on-time
synchronous step-down controllers and two linear
regulators.

Buck Controller

In normal operation, the high-side N-MOSFET is turned
on when the output is lower than V REF, and is turned off
after the internal one-shot timer expires. While the high­side N-MOSFET is turned of f, the low-side N-MOSFET is
turned on to conduct the inductor current until next cycle
begins.

Soft-Start

For internal soft-start function, an internal current source
charges an internal capacitor to build the soft-start ra mp
voltage. The output voltage will track the internal ramp
voltage during soft-start interval.

PGOOD

The power good output is an open-drain architecture. When

the two channels soft-start are both finished, the PGOOD
open-drain output will be high impedance.

Current Limit

The current limit circuit employs a unique “valley” current
sensing algorithm. If the magnitude of the current sense
signal at PHASE is above the current limit threshold, the
PWM is not allowed to initiate a new cycle. Thus, the
current to the load exceeds the average output inductor
current, the output voltage falls and eventually crosses
the under-voltage protection threshold, inducing IC
shutdown.

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

4

©

DS8249A/B/C-02 June 2014www.richtek.com

Over-Voltage Protection (OVP) & Under-Voltage
Protection (UVP)

The two channel output voltages are continuously
monitored for over-voltage and under-voltage conditions.
When the output voltage exceeds over-voltage threshold
(1 13% of VOUT), UGA TE goes low a nd LGA TE is forced
high. When it is less than 52% of reference voltage, under­voltage protection is triggered and then both UGA TE a nd
LGA TE gate drivers are forced low. The controller is latched
until ENx is reset or LDO5 is re-supplied.

LDO5 and LDO3

When the VIN voltage exceeds the POR rising threshold,
LDO3 will default turn-on. The LDO5 can be power on by
ENx. The linear regulator LDO5 and LDO3 provide 5V and

3.3V regulated output.

Switching Over

RT8249A/B/C

The BYP1 is connected to the Channel 1 output. After the
Channel 1 output voltage exceeds the set threshold
(4.66V), the output will be bypassed to the LDO5 output
to maximize the efficiency.

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

DS8249A/B/C-02 June 2014 www.richtek.com

©

5

RT8249A/B/C

Absolute Maximum Ratings (Note 1)

 VIN to G ND--------------------------------------------------------------------------------------------------------- −0.3V to 30V
 BOOTx to PHASEx---------------------------------------------------------------------------------------------- −0.3V to 6V
 PHASEx to GND

DC-------------------------------------------------------------------------------------------------------------------- −0.3V to 30V
<20ns --------------------------------------------------------------------------------------------------------------- −8V to 38V

 UGATEx to PHASEx

DC-------------------------------------------------------------------------------------------------------------------- − 0.3V to (LDO5 + 0.3V)
<20ns --------------------------------------------------------------------------------------------------------------- −5V to 7.5V

 LGATEx to GND

DC-------------------------------------------------------------------------------------------------------------------- − 0.3V to (LDO5 + 0.3V)
<20ns --------------------------------------------------------------------------------------------------------------- −2.5V to 7.5V

 Other Pins---------------------------------------------------------------------------------------------------------- −0.3V to 6V
 Power Dissipation, P

WQFN-20L 3x3 ---------------------------------------------------------------------------------------------------3.33W

 Package Thermal Re sistance (Note 2)

WQF N-20L 3x3, θJA---------------------------------------------------------------------------------------------- 30°C/W
WQFN-20L 3x3, θJC--------------------------------------------------------------------------------------------- 7.5°C/W

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

HBM (Human Body Model)------------------------------------------------------------------------------------- 2kV

@ T

D

= 25°C

A

Recommended Operating Conditions (Note 4)

 Supply V oltage, VIN --------------------------------------------------------------------------------------------- 5V to 25V
 Junction T emperature Range----------------------------------------------------------------------------------- −40°C to 125°C
 Ambient T emperature Range----------------------------------------------------------------------------------- −40°C to 85°C

Electrical Characteristics

(VIN = 12V, V
specified)

Input Supply

VIN Power On Reset V

VIN Standby Supply
Current

VIN Quiescent Current I

BYP1 Supply C urrent I

= V

EN1

= 3.3V, V

EN2

CS1

= V

= 2V, VCLK disable by 200Ω to GND, No Load, TA = 25°C, unless otherwise

CS2

Parameter Symbol Test Conditions Min Typ Max Unit

IN_POR

I

VIN_SBY

Falling Threshold 3.2 3.7 -­RT8249A
RT8249B -- 35 55

Both Buck C ontro llers
Off, V

EN1

= V

EN2

= GND

-- 20 35

Rising Threshold -- 4.6 4.9

RT8249C -- 20 35

VIN_nosw

BYP1_nosw

Both Buck Controlle rs On ,

= 2.05V, V

V

FBx

BYP1

Both Buck Controlle rs On ,

= 2.05V, V

V

FBx

BYP1

= 5.05V

= 5.05V

-- 15 25 A

-- 120 180 A

V

A

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

6

©

DS8249A/B/C-02 June 2014www.richtek.com

Parameter Symbol Test Conditions Min Typ Max Unit

Buck Controllers Outp ut and FB Voltage

RT8249A/B/C

FBx Valley Trip Voltag e V
BYP1 Discharge Current I

PHASEx Discharge
Current

CCM Operation 1.98 2 2.02 V

FBx

DCHG_BYP1

I

DCHG_LX

V

V

= 0.5V 10 45 -- mA

BYP1

PHASEx

= 0.5V 5 8 -- mA

Switchin g Frequency

RT8249A/B, V
RT8249A/B, VIN = 20V, V

Switching Frequency f

SWx

RT8249C, VIN = 20V, V
RT8249C, VIN = 20V, V

Minimum O ff-Time t

OFF(MIN)

V

FBx

= 1.9V -- 200 275 ns
Soft-Start
Soft-St a rt Time t

V

SSx

OUT

Ramp_Up Time -- 0.9 -- ms
Current Sense
CSx Source Current I
CSx Current

Tem per ature Coefficient
Zero-Current Thres h old VZC V

V

CSx

TCI

In Comparison with 25°C -- 4700 -- ppm/C

CSx

= 1V 47 50 53 A

CSx

= 2.05V, GND  PHASEx -- 1 -- mV

FBx

Internal Regulator

= 20V, V

IN

= 5V 320 400 480

OUT1

= 3.33V 380 475 570

OUT2

= 5V 400 500 600

OUT1

= 3.33V 480 600 720

OUT2

kHz

LDO5 Output Voltage V

LDO3 Output Voltage V

LDO5 Output Current I
LDO3 Output Current I

LDO5 Switch-over
Threshold to BYP1

LDO5 Switch-over
Equivalent Resi stance

VCLK Output, RT8249A/B
VCLK On-Resistance R
VCLK Switching

Frequency

V

= 12V, No Load 4.9 5 5.1

IN

LDO5

VIN > 5.5V, I
VIN > 5V, I

VIN > 7V, I

V

= 12V, No Load 3.267 3.3 3.333

IN

VIN > 7V, I

LDO3

VIN > 5.5V, I
VIN > 5V, I

= 4.5V, V

V

LDO5

V

LDO3

Rising Edge at BYP1 Regulation Point -- 4.66 -- V

V

SWTH

LDO5 to BYP1, 10mA -- 1.5 3 

R

SW

Pull-up and Pull-down Resistance -- 10 - - 

VCLK

-- 260 -- kHz

f

VCLK

LDO5

= 7.4V

V

IN

= 3V, VIN = 7.4V 100 175 -- m A

LDO3

< 100mA 4.8 5 5.1

LDO5

< 35mA 4.8 5 5.1

LDO5

< 20mA 4.5 4.75 5.1

LDO5

< 100mA 3.217 3.3 3.383

LDO3

< 35mA 3.267 3.3 3.333

LDO3

< 20mA 3.217 3.3 3.383

LDO3

= GND,

BYP1

100 175 -- mA

V

V

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

DS8249A/B/C-02 June 2014 www.richtek.com

©

7