Richtek RT8228AGQW, RT8228AZQW Schematic [ru]

Single Synchronous Buck PWM Controller

RT8228A

General Description

The RT8228A PWM controller provides high efficiency, excellent transient response, a nd high DC output a ccuracy 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 ha ndles wide input/output voltage ratios with ea se and provides 100ns “instant-on” response to load transients while maintaining a relatively constant switching frequency .

The RT8228A a chieves high eff iciency 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 buck conversion allows this device to directly step down high voltage batteries at the highest possible efficiency. The Audio Skipping Mode (ASM) setting maintains the switching frequency above 25kHz, which eliminates noise in audio a pplications. The RT8228A is intended for CPU core, chipset, DRAM, or other low voltage supplies as low a s 0.5V . The R T8228A is available in a WQFN-12L 2x2 package.

Ordering Information

RT8228A

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)

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.

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/

Side R

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 FETs z Integrated Boost Switch z Over/Under Voltage Protection z Thermal Shutdown z Power Good Indicator z RoHS Compliant and Halogen Free

°°

°C Programmable Current Limit by Low

°°

Sensing

DS(ON)

Applications

z Notebook Computers z CPU Core Supply z Chipset/RAM Supply a s Low as 0.5V z Generic DC/DC Power Regulator

Pin Configurations

(TOP VIEW)

GND

TON

12 1011

LGATE PGOOD

PHASE UGATE

GND

2 3

BOOT

WQFN-12L 2x2

9 8

VCC

MODE

654

DS8228A-06 January 2014 www.richtek.com

RT8228A

Marking Information

RT8228AGQW

CQ : Product Code

CQW CQW

W : Date Code

Typical Application Circuit

U P

Chip Enable

C 4

(

RT8228AZQW

C 0

CQ : Product Code W : Date Code

)

RT8228A-06 January 2014www.richtek.com

Functional Pin Description

Pin No. Pin Name Pin Function

1 LGATE Gate Drive Output for Low Side External MOSFET.

External Inductor Connection Pin for PWM Converter. It behaves as the current

2 PHASE

3 UGATE Gate Drive Output for High Side External MOSFET. 4 BOOT

5 VCC

6 FB

7 MODE

8 EN PWM Chip Enable. P ull low to GND to disable the PWM .

9 PGOOD Open Drain Power Good Indicator. High impedance indicates power is good. 10 CS 11 TON On-time Setting. Connect a resistor between this pin and VIN.

12,

13 (Exposed Pad)

GND

sense comparator input for Low Side MOSFET R voltage for on time generation.

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

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 4.7μF ceramic capacitor.

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

OUT

GND to adjust the output from 0.5V to 3.3V Pull Down t o G ND for F orced CCM Mode .

Pull Up to 2.5V for Audio Skipping Mode (ASM). Pull Up to 5V for Diode Emulation Mo d e (DEM).

Curr ent Limit Threshold Setting Input. Connect a setting resistor to GND and the current limit threshold is equal to 1/10 of the voltage at this pin.

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

RT8228A

sensing and reference

DS(ON)

OUT

Function Block Diagram

TRIG

Timer

On-time

Compute

1-SHOT

0.5V V

125% V

90% V

TON

VCC

PHASE

125% V

10µA

70% V

POR

PSR

REF

Latch

S1 Q

Latch

S1 Q

REF

Thermal

Shutdown

COMP

BOOT

PWM

Min. T

QTRIG

DEM/FCCM/ASM

OFF

1-SHOT

X(-1/10)

DRV

VCC

DRV

UGATE

PHASE

LGATE GND MODE PGOOD

RT8228A-06 January 2014 www.richtek.com

RT8228A

Absolute Maximum Ratings (Note 1)

z VCC to GND ---------------------------------------------------------------------------------------------------------–0.3V to 6V z FB, PGOOD, EN, CS, MODE to GND ------------------------------------------------------------------------–0.3V to (VCC + 0.3V) z TO N to G ND----------------------------------------------------------------------------------------------------------–0.3V to 32V z BOOT to PHASE ---------------------------------------------------------------------------------------------------–0.3V to 6.5V z PHASE to GND

DC----------------------------------------------------------------------------------------------------------------------−0.3V to 32V < 20ns ----------------------------------------------------------------------------------------------------------------−8V to 38V

z UGATE to PHASE

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

z LGA TE to GND

z Power Dissipation, P

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

z Package Thermal Re sistance (Note 2)

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

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

HBM (Human Body Mode) ---------------------------------------------------------------------------------------2kV MM (Ma chine Mode)-----------------------------------------------------------------------------------------------200V

@ TA = 25°C

Recommended Operating Conditions (Note 4)

z Input V oltage, V z Control Voltage, V z Junction T emperature Range-------------------------------------------------------------------------------------−40°C to 125°C z Ambient T emperature Range-------------------------------------------------------------------------------------−40°C to 85°C

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

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

RT8228A-06 January 2014www.richtek.com

RT8228A

Electrical Characteristics

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

Parameter Symbol Test Conditions Min Typ Max Unit

PWM Con tro ller

VCC Quiescent Supply Current IQ VCC Shutdown Current I

TON Operat ing Curre nt TON Shut dow n Curr ent R CS Shutdown Curr ent CS pul l to GND -- -- 1 μA

FB Error Compar at or Threshold Vol tage

FB Input Bias Cu rrent V Output V olta ge Ran ge 0.5 -- 3. 3 V

On-Time Minimum Off-Time

Current Sensing Threshold

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

MODE

= 5V, R

= 500kΩ, T

TON

FB f orced above the regulati on point , V

VCC Current, V

SHDN

TON TON

CC FB

MODE

= 25°C, unless otherwise specified)

= 5V

= 500k

= 0V

-- 0.5 1.25 mA

-- -- 1

-- 30 --

μA μA

= 500k -- -- 1 μA

= 4.5V to 5.5V, D EM

495 500 505 mV

= 0.5V −1 0.1 1 μA

=15V, V

PHASE

= 0V

= 0V, FB = 0.45V

= 1.25V,

267 334 401 ns 250 400 550 ns

Zero Crossing Threshold V ASM Min Frequ ency

> 1.8V, PH ASE − GND −10 -- 5 mV

MODE

MODE =

2.5V

-- 25 -- kHz

Protection Func t i on

Current Limit Thr eshol d GND − PHASE, V

= 1V 85 100 115 mV

UV Threshold UVP Detect, FB Falling Edge 60 70 80 % OVP Threshold OVP Detect, FB Rising Edge 120 125 130 % OV Fault Delay FB f orced above OV threshold -- 5 -- μs

VCC Power O n Reset (P OR) Threshold

Rising Edge 3.7 3.9 4.2 V

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

Soft-Start

Enabl e to curr ent limit threshold = 50mV

-- 900 -- μs

UV Blank Ti me Fro m EN signa l goi ng high -- 4.5 -- ms Thermal S hut dow n Thermal S hut dow n Hyst er esis

T ΔT

-- 150 -- °C

-- 10 -- °C

Driver On -Resi st ance

UGATE Driver Source

UGATEsr

UGATE Dr iver Si nk R UGATEsk

BOOT − PHASE forced to 5V, UGATE High St at e

BOOT − PHASE fo rced to 5V, UGATE Low St ate

-- 2.5 5

-- 1.5 3 Ω

LGATE Driver So ur ce RLGATEsr LGATE High State -- 2.5 5 Ω LGATE Driver Sin k RLGATEsk L GATE Low St ate -- 0.8 1.5 Ω

Dead Time

LGATE Rising (Phase = 1.5V ) -- 30 --

UGATE Rising -- 30 --

RT8228A-06 January 2014 www.richtek.com

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