Richtek RT8238A User Manual

RT8238A

®

DS8238A-07 January 2014 www.richtek.com

1

©

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

Applications

z Notebook Computers

z CPU Core Supply

z Chipset/RAM Supply as Low as 0.5V

z Generic DC/DC Power Regulator

Single Synchronous Buck PWM Controller

Features

z Built in 1% 0.5V Reference Voltage
z Adjustable 0.5V to 3.3V Output Range
z Quick Load Step Response within 100ns
z 4700ppm/

°°

°°

°C Programmable Current Limit by Low

Side R

DS(ON)

Sensing

z 4.5V to 26V Battery Input Range
z Resistor Programmable Frequency
z Internal Ramp Current Limit Soft-Start Control
z Drives Large Synchronous Re ctifier FET s
z Integrated Boost Switch
z Over/Under Voltage Protection
z Thermal Shutdown
z Power Good Indicator
z RoHS Compliant and Halogen Free

Ordering Information

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.

Pin Configurations

(TOP VIEW)

WQFN-12L 2x2

General Description

The RT8238A PWM controller provides high efficiency,

excellent transient response, and high DC output accuracy

needed for stepping down high voltage batteries to

generate low voltage CPU core, I/O, and chipset RAM

supplies in notebook computers.

The constant on-time PWM control scheme handles wide

input/output voltage ratios with ease and provides 100ns

“instant-on” response to load transients while maintaining

a relatively constant switching frequency.

The RT8238A achieves high efficiency at a reduced cost

by eliminating the current sense resistor found in

traditional current mode PWMs. Efficiency is further

enhanced by its ability to drive very large synchronous

rectifier MOSFETs and enter diode emulation mode at

light load condition. The Audio Skipping Mode (ASM)

setting maintains the switching frequency above 25kHz,

which eliminates noise in audio applications. The buck

conversion allows this device to directly step down high

voltage batteries at the highest possible efficiency. The

RT8238A is intended for CPU core, chipset, DRAM, or

other low voltage supplies as low as 0.5V. The RT8238A

is available in a WQFN-12L 2x2 package.

LGATE PGOOD

UGATE

PHASE

MODE

EN

BOOT

VCC

FB

GND

TON

CS

654

12 1011

1

2

3

9

8

7

GND

13

RT8238A

Package Type
QW : WQFN-12L 2x2 (W-Type)

Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)

RT8238A

2

RT8238A-07 January 2014www.richtek.com

©

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

Pi n No. Pin N am e Pin Fu nc t io n

1 LGATE Gate Drive Output for Low Side External MOSFET.

2 PHASE

External Inductor Connection Pin for PWM Converter. It behaves as the current
sense comparator input for Low Side MOSFET R

DS(ON)

sensing and reference

voltage for on time generation.

3 UGATE Gate Drive Output for High Side External MOSFET.

4 BOOT

Supply Input for High Side Driver. Connect through a capacitor to the floating
node (PHASE) pin.

5 VCC

Control Voltage Input. Provides the power for the buck controller, the low side
driver and the bootstrap circuit for high side driver. Bypass to GND with a 1μF
ceramic capacitor.

6 FB

V

OUT

Feedback Input. Connect FB to a resistive voltage divider from V

OUT

to

GND to adjust the output from 0.5V to 3.3V

7 MODE

Pull down to GND for Forced CCM Mode.
Pull up to 2.5V for Audio Skipping Mode (ASM).
Pull up to 5V for Diode Emulation Mode (DEM).

8 EN PWM Chip Enable. Pull low to GND to disable the PWM.

Functional Pin Description

Typical Application Circuit

V

C

C

C

S

U

G

A

T

E

F

B

R

T

8

2

3

8

A

L

G

A

T

E

B

O

O

T

P

H

A

S

E

M

O

D

E

V

I

N

P

G

O

O

D

P

G

O

O

D

G

N

D

T

O

N

V

D

D

P

R

2

C

2

R

T

O

N

Q

1

Q

2

C

1

1

V

EN

R

6

1

0

0

k

1

µ

F

0

R

4

R

5

C

3

0

0

.

1

µ

F

4

.

5

V

t

o

2

6

V

C

4

1

0

µ

F

R

7

*

C

7

*

R

8

R

9

L

1

C

5

*

C

6

*

2

2

0

µ

F

1

0

k

1

0

k

*

:

O

p

t

i

o

n

a

l

V

O

U

T

Chip Enable

T

o

5

V

:

D

E

M

T

o

2

.

5

V

:

A

S

M

T

o

G

N

D

:

F

o

r

c

e

d

-

C

C

M

1

1

5

9

1

0

8

1

2

,

1

3

(

E

x

p

o

s

e

d

P

a

d

)

7

6

1

2

3

4

Marking Information

CP : Product Code

W : Date Code

RT8238AGQW

CP : Product Code

W : Date Code

RT8238AZQW

CPW

CPW

RT8238A

3

RT8238A-07 January 2014 www.richtek.com

©

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

Function Block Diagram

Min. t

OFF

QTRIG

1-SHOT

+

-

COMP

0.5V V

REF

S1 Q

Latch

S1 Q

Latch

+

-

OV

+

-

UV

125% V

REF

70% V

REF

+

-

125% V

REF

Thermal

Shutdown

DEM/FCCM

/ASM

DRV

DRV

On-time

Compute

1-SHOT

FB

VCC

UGATE

PHASE

PGOOD

GND

LGATE

TON

BOOT

TRIG

EN

R

QS

X(-1/10)

+

-

PWM

MODE

+

-

90% V

REF

SS

Timer

POR

CS

VCC

PHASE

10µA

Pin No. Pin Name Pin Function

9 PGOOD Open Drain Power Good Indicator. High impedanc e indicates power is good.

10 CS

Current Limit Threshold Settin g Input. Conne ct a setti ng resistor to GND and the
current limit threshold is eq ual to 1/10 of the voltage at this pin.

11 TON On-time Setting. Connect a resistor bet ween this pin and VIN.

12,

13 (Exposed Pad)

GND

Groun d. The expos ed pad must be soldered to a large PCB and connected to
GND for m aximum power dissipation.

RT8238A

4

RT8238A-07 January 2014www.richtek.com

©

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

Recommended Operating Conditions (Note 4)

z Input Voltage, V

PHASE

------------------------------------------------------------------------------------------------------ 4.5V to 26V

z Control Voltage, V

CC

------------------------------------------------------------------------------------------------------- 4.5V to 5.5V

z Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C

z Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C

Absolute Maximum Ratings (Note 1)

z VCC, FB, PGOOD, EN, CS, MODE to GND ------------------------------------------------------------------------- −0.3V to 6V

z TON to GND ------------------------------------------------------------------------------------------------------------------- −0.3V to 32V

z BOOT to PHASE ------------------------------------------------------------------------------------------------------------ −0.3V to 6V

z PHASE to GND

DC------------------------------------------------------------------------------------------------------------------------------- −0.3V to 32V

< 20ns ------------------------------------------------------------------------------------------------------------------------- −8V to 38V

z UGATE to PHASE

DC------------------------------------------------------------------------------------------------------------------------------- −0.3V to 6V

< 20ns ------------------------------------------------------------------------------------------------------------------------- −5V to 7.5V

z LGATE to GND

DC------------------------------------------------------------------------------------------------------------------------------- −0.3V to 6V

< 20ns ------------------------------------------------------------------------------------------------------------------------- −2.5V to 7.5V

z Power Dissipation, P

D

@ TA = 25°C

WQFN-12L 2x2 -------------------------------------------------------------------------------------------------------------- 0.606W

z Package Thermal Resistance (Note 2)

WQFN-12L 2x2, θJA--------------------------------------------------------------------------------------------------------- 165°C/W

z Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------------- 260°C

z Junction Temperature ------------------------------------------------------------------------------------------------------- 150°C

z Storage Temperature Range ---------------------------------------------------------------------------------------------- −65°C to 150°C

z ESD Susceptibility (Note 3)

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

MM (Machine Mode) -------------------------------------------------------------------------------------------------------- 200V

RT8238A

5

RT8238A-07 January 2014 www.richtek.com

©

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

(VCC = 5V, VIN = 15V, VEN = 5V, V

MODE

= 5V, R

TON

= 500kΩ, T

A

= 25°C, unless otherwise specified)

Electrical Characteristics

Parameter Symbol Test Conditions Min Typ Max Unit

PWM Con troller

VCC Quiescent Supply Current IQ

FB forced above the regulation
point, V

EN

= 5V

-- 0.5 1.25 mA

VCC Shutdown Current I

SHDN

VCC Current, V

EN

= 0V

-- -- 1

μA

TON Operating Current

R

TON

= 500kΩ

-- 30 --

μA

TON Shutdown Current R

TON

= 500kΩ -- -- 1 μA

CS Shutdown Current CS pull to GND -- -- 1 μA
FB Error Comparator

Threshold Voltage

V

CC

= 4.5 o 5.5V, DEM

495 500 505 mV

FB Input Bias Current V

FB

= 0.5V −1 0.1 1 μA

Output Voltage Range 0.5 -- 3.3 V

On-Time

V

IN

=15V, V

PHASE

= 1.25V,

V

MODE

= 0V

267 334 401 ns

Minimum Off-Time

V

MODE

= 0V, FB = 0.45V

250 400 550 ns

Current Sensing Threshold

CS Source Current VCS = 0.5V to 2V 9 10 11 μA
CS Source Current TC On the basis of 25°C -- 4700 -- ppm/°C

Zero Crossing Threshold V

MODE

>1.8V, Phase − GND −10 -- 5 mV

ASM Min Frequency

V

MODE

= 2.5V

-- 25 -- kHz

Protection Funct ion

Current Limit Threshold GND − PHASE, V

CS

= 1V 85 100 115 mV

UVP Threshold UVP Detect, FB Falling Edge 60 70 80 %

OVP Threshold OVP Detect, FB Rising Edge 120 125 130 %
OV Fault Delay FB forced above OV threshold -- 5 -- μs

VCC Power On Reset (POR)
Threshold

Rising Edge 3.7 3.9 4.2 V

POR Threshold Hysteresis -- 100 -- mV
Current Limit Ramp at Soft

Start

Enable to current limit threshold =
50mV

-- 900 -- μs

UV Blank Time From EN signal going high -- 4.5 -- ms

Thermal Shutdown

T

SD

-- 150 -- °C

Thermal Shutdown Hysteresis

ΔT

SD

-- 10 -- °C

Driver On -Resi st ance

UGATE Driver Source

R

UGATEsr

BOOT − PHASE forced to 5V,
UGATE High State

-- 2.5 5

Ω

UGATE Driver Sink RUGATEsk

BOOT − PHASE forced to 5V,
UGATE Low State

-- 1.5 3 Ω

LGAT E Driver Sour ce RLGATEsr LGATE High State -- 2.5 5 Ω
LGAT E Driver Sink RLGATEsk LGATE Low State -- 0.8 1.5 Ω