Richtek RT8241 User Manual

RT8241

DS8241-03 January 2014 www.richtek.com

High Efficiency Single Synchronous Buck PWM Controller

General Description

The RT8241 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 RT8241 supports on chip voltage progra mming function between 0.675V and 0.9V by controlling GX digital inputs.

The constant-on-time PWM control sche me handles 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 RT8241 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 buck conversion allows this device to directly step down high voltage batteries at the highest possible efficiency . The RT8241 is intended for CPU core, chipset, DRAM, or other low voltage supplies as low as

0.675V. The RT8241 is available in a WQFN-12L 2x2 pack age.

Features

z Meet Intel VCCSA Voltage Slew Rate z Built-in 1% Reference Voltage z 2-Bit Programma ble Output V oltage with Integrated

Tra n sition Support

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 Internal Ramp Current Limit Soft-Start Control z Drives Large Synchronous Rectifier FET s z Integrated Boost Switch z Over/Under Voltage Protection z Thermal Shutdown z Power Good Indicator z RoHS Compliant and Halogen Free

Pin Configurations

(TOP VIEW)

WQFN-12L 2x2

Ordering Information

Applications

z Notebook Computers z CPU/GPU Core Supply z Chipset/RAM Supply z Generic DC/DC Power Regulator

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.

LGATE PGOOD

UGATE

PHASE

BOOT

VCC

GNDCSFB

654

12 1011

1 2

9 8

GND

RT8241

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)

Switching Frequency Operation A : 300kHz B : 400kHz C : 500kHz

DS8241-03 January 2014www.richtek.com

RT8241

Typical Application Circuit

For Fixed V oltage Regulator :

For Adjustable Voltage Regulator :

VCC

RT8241

PGOOD

12, 13 (Exposed Pad)

GND

BOOT

1 7

UGATE

PHASE

LGATE

BYPASS

R5*

C2*

OUT

* : Optional

Chip Enable

VCC

RT8241

PGOOD

12, 13 (Exposed Pad)

GND

BOOT

1 7

UGATE

PHASE

LGATE

BYPASS

R5*

C2*

OUT

* : Optional

C3*

FB1

FB2

Chip Enable

Marking Information

30W

30 : Product Code W : Date Code

RT8241AGQW

41W 40W

41 : Product Code W : Date Code

40 : Product Code W : Date Code

30 : Product Code W : Date Code

41 : Product Code W : Date Code

40 : Product Code W : Date Code

RT8241BGQW RT8241CGQW

RT8241AZQW RT8241BZQW RT8241CZQW

G0 G1 VFB

0 0 0.9V 0 1 0.8V 1 0 0.725V 1 1 0.675V

Table 1. VID Table

30W 41W 40W

DS8241-03 January 2014 www.richtek.com

RT8241

Functional Pin Description

Pin N o. Pin N am e Pin Fu nc t io n

1 LGATE Gate Dr ive Output for Low Side Ext er nal 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

refere nce v ol tag e for on time gener at ion.

3 UGATE Gate Drive Output for the H igh Side External MOSFET. 4 BOOT

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

5 VCC

Control Voltage Input. Provides the power for the buck controller, the low side dr iv er and t he bootstrap circuit for high side driver. Bypass to GND wi t h

a 4.7μF ceramic capa citor. 6 EN Chi p Enabl e (Ac tive Hi gh) . 7 G0 2-Bit Input Pin.

8 G1 2- Bit Input Pin. 9 PGOOD

Open Drain Power Good Indicator. High impedance indicates power is

good.

10 FB Output Vol tage Feedback Input . 11 CS

Current Limit Threshold Setting Input. Connect a setting resistor to GND

and the current limit threshold is equal to 1/8 of the voltage seen at this pin.

12, 13 (Exposed Pad) GND

Ground. The expos ed pad must be soldered to a large PCB and conn ecte d

to GND for maxi mu m pow er dissipation.

Function Block Diagram

DRV

1/8

10µA

Diode

Emuation

Min toff

TRIGQ

One shot

TRIG

On-time compute

PHASE

One shot

Thermal

Shutdown

85% V

REF

Voltage

Programmer

0.45V

S1 Q

Latch

1.1V

S1 Q

Latch

REF

COMP

TON

ZCD

OC threshold

leakage

LG R

DS(ON)

UG R

DS(ON)

BST switch resistance

VCC

PGOOD

GND

BOOT UGATE PHASE

LGATE

(Internal)

DS8241-03 January 2014www.richtek.com

RT8241

Electrical Characteristics

Absolute Maximum Ratings (Note 1)

z VCC, FB, PGOOD, EN, CS, G0, G1 to GN D----------------------------------------------------------------------- −0.3V to 6V z PHASE to GND

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

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

DC----------------------------------------------------------------------------------------------------------------------------- −0.3V to 6V <20ns ------------------------------------------------------------------------------------------------------------------------ −5V to 7.5V

z LGATE to GND

z Power Dissipation, P

@ T

= 25°C

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

z Package Thermal Re sistance (Note 2)

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

z Junction T emperature----------------------------------------------------------------------------------------------------- 150°C z Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------- 260°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

Recommended Operating Conditions (Note 4)

z Supply Input V oltage, V

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

z Control Voltage, V

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

z Junction T emperature Range-------------------------------------------------------------------------------------------- −40°C to 125°C z Ambient T emperature Range-------------------------------------------------------------------------------------------- −40°C to 85°C

= 5V, V

= 8V, V

= 5V, T

= 25°C, unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Unit

PWM Controller

VCC Quiescent Supply Current IQ

FB forced above the regulation point, V

= 5V

-- 500 1250 μA

VCC Shutdown Current I

SHDN

VCC current, V

= 0V -- -- 1 μA

CS Shutdown Current CS pull to GND -- -- 1 μA

TA = 25°C −1 0 1

FB Error Comparator Threshold VFB

= −40°C to 85°C (Note 5) −1.5 0 1.5

OUT

Voltage Rang e V

OUT

0.675 -- 3.3 V

RT8241A VFB = 0.9V (f

= 300kHz) -- 400 --

RT8241B VFB = 0.9V (f

= 400kHz) -- 300 -- On-Time, Pulse Width

RT8241C

tON

= 0.9V (f

= 500kHz) -- 240 --

Minimum Off-Time t

OFF

250 400 550 ns

DS8241-03 January 2014 www.richtek.com

RT8241

Parameter Symbol Test Conditions Min Typ Max Unit

Current Sensing

CS Source Current 9 10 11 μA CS Source Current

Temperature Coefficient

-- 4700 -- ppm/°C

Zero Crossing Threshold

PHASE − GND −10

-- 5 mV

Protection Function

Current Limit Threshold Offset

GND − PHASE = VCS/8 −20 0 20 mV

Neg ative Cur ren t Limit Threshold Offset

PHASE − GND = VCS/8 -- 3 -- mV

Under Voltage Protection UVP Detect, Falling Edge 0.41 0.45 0.49 V UVP Fa ult Delay VFB = 0.375V -- 3.5 -- μs Over Voltage Protection OVP Detect, Rising Edge 1.065 1.1 1.133 V OVP F ault Delay VFB = 1.183V -- 5 -- μs

VCC Under Voltage Lockout (UVLO) Threshold

UVLO

Falling edge, PWM disabled below this level

3.5 3.7 3.9 V

VCC UVLO Hysteresis ΔV

UVLO

-- 100 -- mV

VOUT Soft-Start From EN = High to V

OUT

= 95% -- 0.8 - - ms Dynamic VID Slew Rat e SGX G0/G1 Transition 1.75 -- 10 mV/μs UVP Blank Time Fr om EN signal going high -- 3 - ms T herm al Shut d ow n TSD -- 150 --

T herm al Shut d ow n Hysteresis

ΔT

-- 10 --

°C

Driver On-Resistance

UGATE Driver Source

UGATEsr

BOOT−PHASE forced to 5V, U GATE Hig h St a t e

-- 1.8 3.6 Ω

UGATE Driver Sink

UGATEsk

BOOT−PHASE forced to 5V, UGATE Low State

-- 1.2 2.4 Ω

LGATE Driver Source

LGATEsr

LGATE, High State

-- 1.8 3.6 Ω

LGAT E Driver Sink

LGATEsk

LGATE, Low State

-- 0.8 1.34 Ω

LGATE Rising (V

PHASE

= 1.5V)

Dead Time

U GATE Ris ing

Internal Boost Charging Swit c h On- Re si sta nc e

VCC to BOOT, 10mA

EN Threshold

Logic-High

1.8 -- --

EN Threshold Voltage

Logic-Low

-- -- 0.5

Voltage Programming (G0, G1)

Logic-High 750 -- --

G0, G1 I nput Threshold Voltage

Logic-Low -- -- 300

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Richtek RT8241 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual