RT8239AZQW - Richtek - Datasheet.Directory

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

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.

High Efficiency, Main Power Supply Controller

for Notebook Computers

General Description

The RT8239A/B/C is a dual step down, Switch Mode Power

Supply (SMPS) controller which generates logic supply

voltages for battery powered systems. It includes two

Pulse Width Modulation (PWM) controllers adjustable

from 2V to 5.5V and also two fixed 5V/3.3V linear

regulators. One of the controllers (LDO5) provides

automatic switch over to the BYP1 input connected to

the main SMPS1 output for maximized efficiency. An

optional external charge pump can be monitored through

SECFB (RT8239B/C). Other features include on board

power up sequencing, a power good output, internal soft-

start, and a soft discharge output that prevents negative

voltage during shutdown.

A constant on-time PWM control scheme operates without

sense resistors and assures fast load transient response

while maintaining nearly constant switching frequency. To

eliminate noise in audio applications, an ultrasonic mode

is included, which maintains the switching frequency

above 25kHz. Moreover, a diode emulation mode

maximizes efficiency for light load applications. The

SMPS1/SMPS2 switching frequency can be adjustable

from 200kHz/233kHz to 400kHz/466kHz respectively.

The RT8239A/B/C is available in a WQFN-20L 3x3

package, and operates over an extended temperature range

from −40°C to 85°C.

Features

z5.5V to 25V Input Voltage Range

z2V to 5.5V Output Voltage Range

zNo Current Sense Resistor Needed

z5V/3.3V Linear Regulators

z4700ppm/°°

°°

°C RDS(ON) Current Sensing

zInternal Current Limit Soft-Start and Soft Discharge

Output

zBuilt In OVP/UVP/OCP

zSelectable Operation Mode with Switcher Enable

Control (RT8239A)

zSECFB Input Maintains Charge Pump Voltage

(RT8239B/C)

zPower Good Indicator (RT8239B/C includes SECFB)

zRoHS Compliant and Halogen Free

Applications

zNotebook computers

zSystem Power Supplies

z3- and 4- Cell Li+ Battery-Powered Device

RT8239A/B/C

Package Type

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

Lead Plating System

G : Green (Halogen Free and Pb Free)

Z : ECO (Ecological Element with

Halogen Free and Pb free)

Pin Function With

A : ENM

B : SECFB

C : SECFB, Ultrasonic Mode

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

Pin Configurations

(TOP VIEW)

RT8239B/CRT8239A

WQFN-20L 3x3

BYP1

BOOT1

ENTRIP2

TON

FB1

ENTRIP1

LDO3

LDO5

ENLDO

ENM

PGOOD

BOOT2

PHASE2 PHASE1

UGATE1

LGATE1

FB2 VIN

LGATE2

UGATE2

17181920

9876

GND

115

LDO3

LDO5

ENTRIP2

TON

FB1

ENTRIP1

ENLDO

SECFB

PGOOD

BOOT2

PHASE2

BYP1

BOOT1

PHASE1

UGATE1

LGATE1

FB2 VIN

LGATE2

UGATE2

17181920

9876

GND

115

Marking Information

JB=YM

DNN

JB YM

DNN

JB= : Product Code

YMDNN : Date Code

JB : Product Code

YMDNN : Date Code

RT8239A

JC=YM

DNN

JC YM

DNN

JC : Product Code

YMDNN : Date Code

JC= : Product Code

YMDNN : Date Code

RT8239B

JD=YM

DNN

JD YM

DNN

JD : Product Code

YMDNN : Date Code

JD= : Product Code

YMDNN : Date Code

RT8239C

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

Typical Application Circuit

Figure 1. RT8239A NB Main Supply Typical Application Circuit

3.3V

RT8239A

PHASE1

LGATE1

BOOT1

UGATE1

VIN

PHASE2

LGATE2

BOOT2

UGATE2

FB2

VIN

10µF

0.1µF

5.5V to 25V

21 (Exposed Pad) GND

0.1µF

6.5k

L1C4

0.1µF

15k

10k

FB1

BYP1

10µF

ENLDO

100k

ENTRIP2 4

ENTRIP1 2

LDO3 15

4.7µF

LDO5 14

PGOOD 6

R10

100k

C10

5V Always On

TON

RTON

ENM

1µF

Chip Enable

3.3V Always On

VOUT2

VOUT1

10µF

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

Figure 2. RT8239B/C NB Main Supply Typical Application Circuit

RT8239B/C

PHASE1

LGATE1

BOOT1

UGATE1

VIN

PHASE2

LGATE2

BOOT2

UGATE2

FB2

VIN

10µF

0.1µF

5.5V to 25V

21 (Exposed Pad)

GND

3.3V

0.1µF

6.5k

L1C4

0.1µF

15k

10k

FB1

BYP1

10µF

ENLDO

100k

ENTRIP2 4

ENTRIP1 2

Off

LDO3 15

4.7µF

LDO5 14

PGOOD 6

R10

100k

C10

5V Always On

TON

RTON

C11

0.1µF

C12

0.1µF

SECFB

R11

200k

R12

39k

VCP

C13

0.1µF

C14

0.1µF

1µF

C15

3.3V Always On

VOUT1

VOUT2

10µF

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

Pin No. Pin Name Pin Function

1 FB1 SMPS1 Feedback Input. Connect FB1 to a resistive voltage divider from SMPS1

output to GND for adjustable output from 2V to 5.5V.

2 ENTRIP1

Channel 1 Enable and Current Limit Setting Input. Connect resistor to GND to set

the threshold for Channel 1 synchronous RDS(ON) sense. The GND-PHASE1

current limit threshold is 1/10th the voltage seen at ENTRIP1 over a 0.5V to 3V

range. There is an internal 10μA current source from LDO5 to ENTRIP1. Leave

ENTRIP1 floating or drive it above 4.5V to shut down channel 1.

3 TON ON-Time/Frequency Adjustment Input. Connect to GND with 56kΩ to 100kΩ.

4 ENTRIP2

Channel 2 Enable and Current Limit Setting Input. Connect resistor to GND to set

the threshold for Channel 2 synchronous RDS(ON) sense. The GND-PHASE2

current limit threshold is 1/10th the voltage seen at ENTRIP2 over a 0.5V to 3V

range. There is an internal 10μA current source from LDO5 to ENTRIP2. Leave

ENTRIP2 floating or drive it above 4.5V to shut down channel 2.

5 FB2 SMPS2 Feedback Input. Connect FB2 to a resistive voltage divider from SMPS2

output to GND for adjustable output from 2V to 5.5V.

Power Good Output for Channel 1 and Channel 2 (RT8239A).

6 PGOOD

Power Good Output for Channel 1, Channel 2 and SECFB (RT8239B/C).

7 BOOT2

Boost Flying Capacitor Connection for SMPS2. Connect to an external capacitor

according to the typical application circuits.

8 UGATE2

Upper Gate Driver Output for SMPS2. UGATE2 swings between PHASE2 and

BOOT2.

9 PHASE2

Switch Node for SMPS2. PHASE2 is the internal lower supply rail for the UGATE2

high side gate driver. PHASE2 is also the current sense input for the SMPS2.

10 LGATE2 Lower Gate Drive Output for SMSP2. LGATE2 swings between GND and LDO5.

11 VIN Supply Input for LDO5.

12 ENLDO Master Enable Input. LDO5/LDO3 is enabled if it is within logic high level and

disabled if it is less than the logic low level.

ENM

(RT8239A)

Mode Selection with Enable Input. Pull up to LDO5 (Ultrasonic mode) or LDO3

(DEM) to turn on both switch Channels. Short to GND for shutdown.

13 SECFB

(RT8239B/C)

Change Pump Feedback Pin. The SECFB is used to monitor the optional external

charge pump. Connect a resistive divider from the change pump output to GND to

detect the output. If SECFB drops below its feedback threshold, an ultrasonic

pulse occurs to refresh the charge pump driven by LGATE1 or LGATE2.

If SECFB drops below its UV threshold, the switcher channels stop working and

enter into discharge-mode. Pull up to LDO5 or LDO3 to disable SECFB UVP

function.

14 LDO5

5V Linear Regulator Output. LDO5 is the supply voltage for the low side MOSFET

driver and also the analog supply voltage for the device. Bypass a minimum 4.7μF

ceramic capacitor to GND

15 LDO3 3.3V Linear Regulator Output. Bypass a minimum 4.7μF ceramic capacitor to

GND.

16 LGATE1 Lower Gate Driver Output for SMPS1. LGATE1 swings between GND and LDO5.

17 PHASE1

Switch Node SMPS1. PHASE1 is the internal lower supply rail for the UGATE1

high side gate driver. PHASE1 is also the current sense input for the SMPS1.

Functional Pin Description

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

Function Block Diagram

Pin No. Pin Name Pin Function

18 UGATE1

Upper Gate Driver Output for SMPS1. UGATE1 swings between PHASE1 and

BOOT1.

19 BOOT1

Boost Flying Capacitor Connection for SMPS1. Connect to an external

capacitor according to the typical application circuits.

20 BYP1 Switch Over Source Voltage Input for LDO5.

21 (Exposed Pad) GND Analog Ground and Power Ground. The exposed pad must be soldered to a

large PCB and connected to GND for maximum power dissipation.

ENM (RT8239A)

SECFB (RT8239B/C)

SMPS2

PWM

Buck

Controller

BOOT2

UGATE2

PHASE2

LGATE2

GND

LDO5

FB2

ENTRIP2

PGOOD

SMPS1

PWM

Buck

Controller

BOOT1

UGATE1

PHASE1

LGATE1

LDO5

FB1

ENTRIP1

LDO5 REF

Switch Over Threshold

VIN

LDO5

On Time

TON

LDO3 LDO3

BYP1

Power-On

Sequence

Clear Fault Latch

ENLDO

LDO5

10µA

LDO5

10µA

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

Recommended Operating Conditions (Note 4)

zSupply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 5.5V to 25V

zJunction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C

zAmbient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C

Absolute Maximum Ratings (Note 1)

zVIN, ENLDO to GND ------------------------------------------------------------------------------------------------------ −0.3V to 30V

zBOOTx to PHASEx ------------------------------------------------------------------------------------------------------- −0.3V to 6V

zENTRIPx, FBx, TON, BYP1, PGOOD, LDO5, LDO3, ENM/SECFB to GND ------------------------------- −0.3V to 6V

zPHASEx to GND

DC ----------------------------------------------------------------------------------------------------------------------------- −0.3V to 30V

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

zUGATEx to PHASEx

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

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

zLGATEx to GND

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

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

zPower Dissipation, PD @ TA = 25°C

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

zPackage Thermal Resistance (Note 2)

WQFN-20L 3x3, θJA ------------------------------------------------------------------------------------------------------- 30°C/W

WQFN-20L 3x3, θJC ------------------------------------------------------------------------------------------------------ 7.5°C/W

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

zJunction Temperature ----------------------------------------------------------------------------------------------------- 150°C

zStorage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C

zESD Susceptibility (Note 3)

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

Parameter Symbol Test Conditions Min Typ Max Unit

Input Supply

Rising Threshold -- 5.1 5.5

VIN Power On Reset Falling Threshold 3.5 -- 4.5 V

VIN Shutdown Current IVIN_SHDN V

ENLDO = GND -- 20 40

VIN Standby Supply Current IVIN_SBY Both SMPS Off -- 250 350 μA

Quiescent Power Consumption IQ Both SMPSs on, FBx = 2.1V,

BYP1 = 5V, ENM = 3.3V (RT8239A) -- 5 7 mW

SMPS Output and FB Voltage

FBx, CCM Operation -- 2 --

FBx Regulation Voltage VFBx FBx, DEM Operation 1.98 2.006 2.03 V

(VIN = 12V, VENLDO = 5V, VENTRIPx = 2V, VBYP1 = 5V, No Load on LDO5, LDO3, TA = 25°C, unless otherwise specified)

Electrical Characteristics

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

Parameter Symbol Test Conditions Min Typ Max Unit

Output Voltage Adjustable

Range SMPS1, SMPS2 2 -- 5.5

SECFB Voltage VSECFB RT8239B 1.92 2 2.08

On-Time

VPHASE1 = 2V -- 256 --

On-Time Pulse Width tUGATEx VIN = 20V

RTON = 56kΩ VPHASE2 = 2V -- 220 -- ns

Minimum Off-Time tLGATEx V

FBx = 1.8V -- -- 400 ns

fSMPS1 SMPS1 Operating Frequency 200 -- 400

Frequency Range fSMPS2 SMPS2 Operating Frequency 233 -- 466 kHz

Ultrasonic Mode Frequency fASM RT8239C, VPHASEx = 50mV 25 -- -- kHz

Soft-Start

Soft-Start Time tSSx Zero to 200mV Current Limit Threshold

from ENTRIPx Enable -- 2 -- ms

Current Sense

Current Limit Current Source IENTRIPx V

ENTRIPx = 0.9V 9.4 10 10.6 μA

Temperature Coefficient of

IENTRIPx On The Basis of 25°C -- 4700 --

ppm/°C

Current Limit Adjustment

Range VENTRIPx = IENTRIPx x RENTRIPx 0.5 -- 2.7 V

Current Limit Threshold VENTRIPx GND − PHASEx, VENTRIPx = 2V 180 200 225 mV

Zero-Current Threshold VZC GND − PHASEx, FBx = 2.1V -- 3 -- mV

Internal Regulator and Refer ence

VBYP1 = 0V, ILDO5 < 100mA 4.8 5 5.2

VBYP1 = 0V, ILDO5 < 100mA ,

6.5V < VIN < 25V 4.75 -- 5.25

LDO5 Output Voltage VLDO5

VBYP1 = 0V, ILDO5 < 50mA,

5.5V < VIN < 25V 4.75 -- 5.25

LDO5 Output Current ISHORT5 V

BYP1 = 0V, VLDO5 = 4.5V -- 225 -- mA

5V Switchover Threshold VBYP1TH Falling Edge, Rising Edge with FB1

Regulation Point 4.53 4.66 4.79 V

5V Switch RDS(ON) R

BYPSW V

BYP1 = 5V, ILDO5 = 50mA -- 1.5 3 Ω

VBYP1 = 0V, ILDO3 < 100mA 3.2 3.3 3.46 V

LDO3 Output Voltage VLDO3 VBYP1 = 5V, ILDO3 < 100mA 3.2 3.3 3.46

LDO3 Output Current ISHORT3 V

BYP1 = 0V, VLDO3 = 2.9V -- 150 -- mA

UVLO

Rising Edge -- 4.35 4.5

LDO5 UVLO Threshold VUVLO5 Falling Edge 3.9 4.05 4.2 V

LDO3 UVLO Threshold VUVLO3 Both SMPS Off -- 2.2 --

Power Good

PGOOD Threshold VPGOOD PGOOD Detect, Rising edge with

soft-start delay time. Hysteresis = 2.5% −14 −10 −6 %

PGOOD Propagation Delay tPD_PGOOD Falling Edge -- 5 -- μs

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

Parameter Symbol Test Conditions Min Typ Max Unit

PGOOD Leakage Current ILK_PGOOD High State, Forced to 5.5V -- -- 1 μA

PGOOD Output Low Voltage VSINK_PGOOD I

SINK = 4mA -- -- 0.4 V

SECFB Power Good

Threshold VSFB_PGOOD SECFB with Respect to 2V

(RT8239B/C) 40 50 60 %

Fault Detection

Over Voltage Protection Trip

Threshold VOVP OVP Detect, FBx Rising Edge 108 112 116 %

Over Voltage Protection

Propagation Delay tDLY_OVP Rising Edge -- 5 -- μs

VUVP UVP Detect, FBx Falling Edge. 53 58 63 %

Under Voltage Protection Trip

Threshold VSFB_UVP UVP Detect, SECFB Falling Edge. 0.8 -- 1.2 V

Under Voltage Protection

Shutdown Blanking Time tSSHx From ENTRIPx or ENM Enable -- 5 -- ms

Thermal Shutdown

Thermal Shutdown TSD -- 150 -- °C

Thermal Shutdown Hysteresis ΔTSD -- 10 -- °C

Logic Input

ENTRIPx Input Voltage VENTRIPx Clear Fault Level/SMPSx Off Level 4.5 -- -- V

Rising Edge Threshold 1.2 1.6 2

ENLDO Input Voltage VENLDO Falling Edge Threshold 0.9 0.95 1 V

Clear Fault Level/SMPSs Off Level -- -- 0.8

SMPSs On, DEM Operation 2.3 -- 3.6

ENM Input Voltage

(RT8239A) VENM

SMPSs On, Ultrasonic Mode

Operation 4.5 -- --

IFBx V

FBx = 0V or 5V −1 -- 1

IP13 ENM/SECFB = 0V or 5V −1 -- 1

Input Leakage Current

IENLDO ENLDO = 0V or 5V −1 -- 3

μA

Internal BOOT Switch

Internal Boost Charging

Switch On-Resistance RBOOTx LDO5 to BOOTx, 10mA -- -- 90 Ω

Power MOSFET Drivers

RUGATEsr Source, VBOOTx − VUGATEx = 0.1V -- 5 8

UGATEx On-Resistance RUGATEsk Sink, VUGATEx − VPHASEx = 0.1V -- 2 4

RLGATEsr Source, VLDO5 − VLGATEx = 0.1V -- 5 8

LGATEx On-Resistance RLGATEsk Sink, VLGATEx = 0.1V -- 1.5 3 Ω

tLGATERx UGATEx Off to LGATEx On -- 30 --

Dead Time tUGATERx LGATEx Off to UGATEx On -- 40 -- ns

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

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. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is

measured at the exposed pad of the package.

Note 3. Devices are ESD sensitive. Handling precaution is recommended.

Note 4. The device is not guaranteed to function outside its operating conditions.

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

Typical Operating Characteristics

VOUT2 Efficiency vs. Load Current

100

0.001 0.01 0.1 1 10

Load Current (A)

Efficiency (%)

VIN = 12V, RTON = 100kΩ, VENTRIP1 = 5V,

VENTRIP2 = 1.5V, ENLDO = 5V

DEM

ASM

VOUT2 Efficiency vs. Load Current

100

0.001 0.01 0.1 1 10

Load Current (A)

Efficiency (%)

VIN = 20V, RTON = 100kΩ, VENTRIP1 = 5V,

VENTRIP2 = 1.5V, ENLDO = 5V

DEM

ASM

VOUT2 Efficiency vs. Load Current

100

0.001 0.01 0.1 1 10

Load Current (A)

Efficiency (%)

VIN = 8V, RTON = 100kΩ, VENTRIP1 = 5V,

VENTRIP2 = 1.5V, ENLDO = 5V

DEM

ASM

VOUT1 Efficiency vs. Load Current

100

0.001 0.01 0.1 1 10

Load Current (A)

Efficiency (%)

VIN = 20V, RTON = 100kΩ, VENTRIP1 = 1.5V

VENTRIP2 = 5V, ENLDO = 5V

DEM

ASM

VOUT1 Efficiency vs. Load Current

100

0.001 0.01 0.1 1 10

Load Current (A)

Efficiency (%)

VIN = 8V, RTON = 100kΩ, VENTRIP1 = 1.5V

VENTRIP2 = 5V, ENLDO = 5V

DEM

ASM

VOUT1 Efficiency vs. Load Current

100

0.001 0.01 0.1 1 10

Load Current (A)

Efficiency (%)

VIN = 12V, RTON = 100kΩ, VENTRIP1 = 1.5V

VENTRIP2 = 5V, ENLDO = 5V

DEM

ASM

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

VOUT1 Switching Frequency vs. Load Current

100

120

140

160

180

200

220

240

0.001 0.01 0.1 1 10

Load Current (A)

Switching Frequency (kHz) 1

VIN = 8V, RTON = 100kΩ,

ENLDO = VIN, VENTRIP1 = 1.5V,

VENTRIP2 = 5V

ASM

DEM

VOUT1 Switching Frequency vs. Load Curre nt

100

120

140

160

180

200

220

240

260

0.001 0.01 0.1 1 10

Load Current (A)

Switch Frequency (kHz) 1

VIN = 12V, RTON = 100kΩ,

ENLDO = VIN, VENTRIP1 = 1.5V,

VENTRIP2 = 5V

ASM

DEM

VOUT1 Switching Frequency vs. Load Current

100

120

140

160

180

200

220

240

260

0.001 0.01 0.1 1 10

Load Current (A)

Switching Frequency (kHz) 1

VIN = 20V, RTON = 100kΩ,

ENLDO = VIN, VENTRIP1 = 1.5V,

VENTRIP2 = 5V

ASM

DEM

VOUT2 Switching Frequency vs. Load Current

100

120

140

160

180

200

220

240

260

280

300

0.001 0.01 0.1 1 10

Load Current (A)

Switching Frequency (kHz) 1

VIN = 12V, RTON = 100kΩ,

ENLDO = VIN, VENTRIP1 = 5V,

VENTRIP2 = 1.5V

ASM

DEM

VOUT2 Switching Frequency vs. Load Current

100

120

140

160

180

200

220

240

260

280

300

0.001 0.01 0.1 1 10

Load Current (A)

Switching Frequency (kHz) 1

VIN = 20V, RTON = 100kΩ,

ENLDO = VIN, VENTRIP1 = 5V,

VENTRIP2 = 1.5V

ASM

DEM

VOUT2 Switching Frequency vs. Load Current

100

120

140

160

180

200

220

240

260

280

0.001 0.01 0.1 1 10

Load Current (A)

Switching Frequency (kHz) 1

VIN = 8V, RTON = 100kΩ,

ENLDO = VIN, VENTRIP1 = 5V,

VENTRIP2 = 1.5V

ASM

DEM

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

VOUT2 Output Voltage vs. Loa d Current

3.372

3.378

3.384

3.390

3.396

3.402

3.408

3.414

3.420

0.001 0.01 0.1 1 10

Load Current (A)

Output Voltage (V)

VIN = 12V, RTON = 100kΩ, ENLDO = VIN,

VENTRIP1 = 5V, VENTRIP2 = 1.5V

ASM

DEM

VOUT1 Output Voltage vs. Load Current

5.010

5.013

5.016

5.019

5.022

5.025

5.028

5.031

5.034

0.001 0.01 0.1 1 10

Load Current (A)

Output Voltage (V)

VIN = 12V, RTON = 100kΩ, ENLDO = VIN,

VENTRIP1 = 1.5V, VENTRIP2 = 5V

ASM

DEM

Standby Input Current vs . Input Vo ltage

226

228

230

232

234

236

238

240

6 8 10 12 14 16 18 20 22 24 26

Input Voltage (V)

Standby Input Current (μA) 1

VENTRIP1 = VENTRIP2 = 5V, ENLDO = VIN, No Load

LDO5 Output Vo ltage vs . Output Current

5.048

5.052

5.056

5.060

5.064

5.068

5.072

0 102030405060708090100

Output Current (mA)

Output Voltage (V)

VIN = 12V, VENTRIP1 = VENTRIP2 = 5V, ENLDO = VIN

LDO3 Output Voltage vs. Output Current

3.334

3.336

3.338

3.340

3.342

3.344

3.346

3.348

3.350

3.352

3.354

0 102030405060708090100

Output Current (mA)

Output Voltage (V)

VIN = 12V, VENTRIP1 = VENTRIP2 = 5V, ENLDO = VIN

No Load Battery Current vs. Input Voltage

0.1

100

6 7 8 9 10111213141516171819202122232425

Input Voltage (V)

Battery Current (mA

)

RTON = 100kΩ, VENTRIP1 = VENTRIP2 =1.5V,

EVLDO = VIN

ASM

DEM

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

Power On from ENLDO

Time (2ms/Div)

VIN = 12V, VENTRIP1 = VENTRIP2 = 1.5V

LDO5

(2V/Div)

LDO3

(2V/Div)

ENLDO

(10V/Div)

ENLDO = VIN, RTON = 100kΩ, No Load

Shutdown Input Current vs . Input Voltage

6 8 10 12 14 16 18 20 22 24 26

Input Voltage (V)

Shutdown Input Current (μA) 1

VENTRIP1 = VENTRIP2 = 5V, ENLDO = GND, No Load

Power Off from ENTRIP1

Time (4ms/Div)

RT8239B/C

VIN = 12V, VENTRIP1 = VENTRIP2 = 1.5V,

ENLDO = VIN, RTON = 100kΩ, No Load

VIN = 12V, VENTRIP1 = VENTRIP2 = 1.5V,

ENLDO = VIN, RTON = 100kΩ, No Load

VOUT1

(2V/Div)

PGOOD

(5V/Div)

ENTRIP1

(5V/Div)

RT8239B/C

Power On from ENTRIP1

Time (1ms/Div)

VIN = 12V, VENTRIP1 = VENTRIP2 = 1.5V,

ENLDO = VIN, RTON = 100kΩ, No Load

VOUT1

(2V/Div)

PGOOD

(5V/Div)

ENTRIP1

(5V/Div)

RT8239B/C

Power Off from ENM

Time (10ms/Div)

VOUT1

(5V/Div)

PGOOD

(5V/Div)

ENM

(5V/Div)

VOUT2

(5V/Div)

RT8239A VIN = 12V, VENM = 5V, RTON = 100kΩ,

VENTRIP1 = VENTRIP2 = 1.5V,

ENLDO = VIN, No Load

Power On from ENM

Time (1ms/Div)

VOUT1

(2V/Div)

PGOOD

(5V/Div)

ENM

(5V/Div)

RT8239A

VOUT2

(2V/Div)

VENTRIP1 = VENTRIP2 = 1.5V, ENLDO = VIN, No Load

VIN = 12V, VENM = 5V, RTON = 100kΩ

RT8239A/B/C

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OVP

Time (10ms/Div)

VIN = 12V, RTON = 100kΩ, ENLDO = VIN, No Load

VOUT1

(2V/Div)

PGOOD

(5V/Div)

VOUT2

(2V/Div)

UVP

Time (100μs/Div)

VIN = 12V, RTON = 100kΩ, ENLDO = VIN

VOUT1

(2V/Div)

LGATE1

(10V/Div)

UGATE1

(50V/Div)

PGOOD

(5V/Div)

VOUT2 DEM-MODE Load Transient Response

Time (20μs/Div)

ENLDO = VIN, IOUT2 =1A to 8A

VOUT2_AC

(50mV/Div)

Inductor

Current

(5A/Div)

UGATE2

(20V/Div)

LGATE2

(5V/Div)

VIN = 12V, RTON = 100kΩ,

Power Off from ENTRIP2

Time (20ms/Div)

VIN = 12V, VENTRIP1 = VENTRIP2 = 1.5V,

ENLDO = VIN, RTON = 100kΩ, No Load

VOUT2

(1V/Div)

PGOOD

(10V/Div)

ENTRIP2

(5V/Div)

RT8239B/C

VOUT1 DEM-MODE Load Transient Response

Time (20μs/Div)

VIN = 12V, RTON = 100kΩ,

ENLDO = VIN, IOUT1 =1A to 8A

VOUT1_AC

(50mV/Div)

Inductor

Current

(5A/Div)

UGATE1

(20V/Div)

LGATE1

(5V/Div)

Power On from ENTRIP2

Time (1ms/Div)

VIN = 12V, VENTRIP1 = VENTRIP2 = 1.5V,

ENLDO = VIN, RTON = 100kΩ, No Load

VOUT2

(1V/Div)

PGOOD

(5V/Div)

ENTRIP2

(5V/Div)

RT8239B/C

RT8239A/B/C

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Application Information

The RT8239A/B/C is a dual, Mach ResponseTM

DRVTM

mode synchronous buck controller targeted for notebook

system power supply solutions. RICHTEK's Mach

ResponseTM technology provides fast response to load

steps. The topology circumvents the poor load transient

timing problems of fixed frequency current mode PWMs

while avoiding the problems caused by widely varying

switching frequency in conventional constant on-time and

constant off-time PWM schemes. A special adaptive on-

time control trades off the performance and efficiency over

wide input voltage range. The RT8239A/B/C includes 5V

(LDO5) and 3.3V (LDO3) linear regulators. The LDO5 linear

regulator steps down the battery voltage to supply both

internal circuitry and gate drivers. The synchronous switch

gate drivers are directly powered by LDO5. When VOUT1

rises above 4.66V, an automatic circuit disconnects the

linear regulator and allows the device to be powered by

VOUT1 via the BYP1 pin.

PWM Operation

The Mach ResponseTM DRVTM mode controller relies on

the output filter capacitor's Effective Series Resistance

(ESR) to act as a current sense resistor, so that the output

ripple voltage provides the PWM ramp signal. Referring to

the RT8239A/B/C's Function Block Diagram, the

synchronous high side MOSFET will be turned on at the

beginning of each cycle. After the internal one-shot timer

expires, the MOSFET will be turned off. The pulse width

of this one-shot is determined by the converter's input

voltage and the output voltage to keep the frequency fairly

constant over the entire input voltage range. Another one-

shot sets a minimum off-time (400ns typ). The on-time

one-shot will be triggered if the error comparator is high,

the low side switch current is below the current limit

threshold, and the minimum off-time one-shot has timed

out.

PWM Frequency and On-time Control

For each specific input voltage range, the Mach

ResponseTM control architecture runs with pseudo constant

frequency by feed forwarding the input and output voltage

into the on-time one-shot timer. The high side switch on-

time is inversely proportional to the input voltage as

measured by VIN and proportional to the output voltage.

There are two benefits of a constant switching frequency.

First, the frequency can be selected to avoid noise

sensitive regions such as the 455kHz IF band. Second,

the inductor ripple current operating point remains

relatively constant, resulting in easy design methodology

and predictable output voltage ripple. The frequency for

3V SMPS is set higher than the frequency for 5V SMPS.

This is done to prevent audio frequency “beating” between

the two sides, which switch asynchronously for each side.

The TON pin is connected to GND through the external

resistor, RTON, to set the switching frequency.

The RT8239A/B/C adaptively changes the operation

frequency according to the input voltage. Higher input

voltage usually comes from an external adapter, so the

RT8239A/B/C operates with higher frequency to have

better performance. Lower input voltage usually comes

from a battery, so the RT8239A/B/C operates with lower

switching frequency for lower switching losses. For a

specific input voltage range, the switching cycle period is

given by :

For 5.5V < VIN < 6.5V :

tS1 = 61.28p x RTON

tS2 = 44.43p x RTON

For 6.5V < VIN < 12V :

tS1 = 51.85p x RTON

tS2 = 44.43p x RTON

For 12V < VIN < 25V :

tS1 = 45.75p x RTON

tS2 = 39.2p x RTON

The on-time guaranteed in the Electrical Characteristics

table is influenced by switching delays in the external

high side power MOSFET. Two external factors that

influence switching frequency accuracy are resistive drops

in the two conduction loops (including inductor and PC

board resistance) and the dead time effect. These effects

are the largest contributors to the change of frequency

with changing load current. The dead time effect increases

the effective on-time by reducing the switching frequency

RT8239A/B/C

DS8239A/B/C-05 August 2012 www.richtek.com

++−

OUT DROP1 ON IN DROP1 DROP2

f = (V V ) / (t x (V V V ))

where VDROP1 is the sum of the parasitic voltage drops in

the inductor discharge path, including synchronous

rectifier, inductor, and PC board resistances; VDROP2 is

the sum of the resistances in the charging path; and tON

is the on-time calculated by the RT8239A/B/C.

Operation Mode Selection

The RT8239A/B supports two operation modes : Diode

Emulation Mode and Ultrasonic Mode. The RT8239C only

supports Ultrasonic Mode. The operation mode can be

set via the ENM pin for RT8239A or SECFB pin for

RT8239B.

0tON

Slope = (VIN-VOUT)/L

IPEAK

ILOAD = IPEAK/2

Figure 3. Boundary condition of CCM/DEM

IN OUT

LOAD(SKIP) ON

(V V )

−

≈×

where tON is the on-time.

The switching waveforms may appear noisy and

asynchronous when light loading causes diode emulation

operation. This is normal and results in high efficiency.

Trade offs in PFM noise vs. light load efficiency is made

by varying the inductor value. Generally, low inductor values

produce a broader efficiency vs. load curve, while higher

values result in higher full load efficiency (assuming that

the coil resistance remains fixed) and less output voltage

ripple. Penalties for using higher inductor values include

larger physical size and degraded load transient response

(especially at low input voltage levels).

Ultra sonic Mode

The RT8239A/B/C activates a unique type of Diode

Emulation Mode with a minimum switching frequency of

25kHz, called Ultrasonic Mode. This mode eliminates

audio-frequency modulation that would otherwise be

present when a lightly loaded controller automatically

skips pulses. In Ultrasonic Mode, the low side switch gate

driver signal is “OR”ed with an internal oscillator

(>25kHz). Once the internal oscillator is triggered, the

as one or both dead times. It occurs only in PWM mode

when the inductor current reverses at light or negative

load currents. With reversed inductor current, the

inductor's EMF causes PHASEx to go high earlier than

normal, hence extending the on-time by a period equal to

the low to high dead time. For loads above the critical

conduction point, the actual switching frequency is :

Diode Emulation Mode

In Diode Emulation Mode, the RT8239A/B automatically

reduces switching frequency at light load conditions to

maintain high efficiency. This reduction of frequency is

achieved smoothly. As the output current decreases from

heavy-load condition, the inductor current is also reduced,

and eventually comes to the point that its current valley

touches zero, which is the boundary between continuous

conduction and discontinuous conduction modes. By

emulating the behavior of diodes, the low side MOSFET

allows only partial negative current to flow when the

inductor free wheeling current becomes negative. As the

Part Number RT8239A RT8239B RT8239C

Pin Name ENM SECFB SECFB

Pin-13

Voltage Range Mode State

4.5V to 5V ASM ASM ASM

2.3V to 3.6V DEM DEM ASM

1.2V to 1.8V ASM ASM ASM

Below 0.8V Shutdown UVP UVP

Table 1. Operation Mode Setting

load current is further decreased, it takes longer and longer

time to discharge the output capacitor to the level that

requires the next “ON” cycle. The on-time is kept the

same as that in the heavy load condition. In reverse, when

the output current increases from light load to heavy load,

the switching frequency increases to the preset value as

the inductor current reaches the continuous conduction.

The transition load point to the light load operation is shown

in Figure 3. and can be calculated as follows :

RT8239A/B/C

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IPEAK

ILOAD

ILIMIT

Figure 4. “Valley” Current Limit

The RT8239A/B/C uses the on resistance of the

synchronous rectifier as the current sense element and

supports temperature compensated MOSFET RDS(ON)

sensing. The RILIM resistor between the ENTRIPx pin and

ultrasonic controller pulls LGATEx high and turns on the

low side MOSFET to induce a negative inductor current.

After the output voltage falls below the reference voltage,

the controller turns off the low side MOSFET (LGATEx

pulled low) and triggers a constant on-time (UGATEx driven

high). When the on-time has expired, the controller re-

enables the low side MOSFET until the controller detects

that the inductor current dropped below the zero crossing

threshold.

Linear Regulators (LDOx)

The RT8239A/B/C includes 5V (LDO5) and 3.3V (LDO3)

linear regulators. The regulators can supply up to 100mA

for external loads. Bypass LDOx with a minimum 4.7μF

ceramic capacitor. When VOUT1 is higher than the switch

over threshold (4.66V), an internal 1.5Ω P-MOSFET switch

connects BYP1 to the LDO5 pin while simultaneously

disconnects the internal linear regulator.

Current Limit Setting (ENTRIPx)

The RT8239A/B/C has cycle-by-cycle current limit control.

The current limit circuit employs a unique “valley” current

sensing algorithm. If the magnitude of the current sense

signal at PHASEx is above the current limit threshold,

the PWM is not allowed to initiate a new cycle (Figure 4).

The actual peak current is greater than the current limit

threshold by an amount equal to the inductor ripple current.

Therefore, the exact current limit characteristic and

maximum load capability are a function of the sense

resistance, inductor value, and battery and output voltage.

GND sets the current limit threshold. The resistor, RILIM,

is connected to a current source from ENTRIPx which is

10μA (typ.) at room temperature. The current source has

a 4700ppm/°C temperature slope to compensate the

temperature dependency of the RDS(ON). When the voltage

drop across the sense resistor or low side MOSFET

equals 1/10 the voltage across the RILIM resistor, positive

current limit will be activated. The high side MOSFET will

not be turned on until the voltage drop across the MOSFET

falls below 1/10 the voltage across the RILIM resistor.

Choose a current limit resistor according to the following

equation :

VILIM = (RILIM x 10μA) / 10 = IILIM x RDS(ON)

RILIM = (IILIM x RDS(ON)) x 10 / 10μA

Carefully observe the PC board layout guidelines to ensure

that noise and DC errors do not corrupt the current sense

signal at PHASEx and GND. Mount or place the IC close

to the low side MOSFET.

Charge Pump (SECFB)

The external 14V charge pump is driven by LGATEx. When

LGATEx is low, C1 will be charged by VOUT1 through D1.

C1 voltage is equal to VOUT1 minus the diode drop. When

LGATEx becomes high, C1 transfers the charge to C2

through D2 and charges C2 voltage to VLGATEX plus C1

voltage. As LGATEx transitions low on the next cycle, C3

is charged to C2 voltage minus a diode drop through D3.

Finally, C3 charges C4 through D4 when LGATEx switches

high. Thus, the total charge pump voltage, VCP, is :

VCP = VOUT1 + 2 x VLGATEx − 4 x VD

where VLGATEx is the peak voltage of the LGATEx driver

which is equal to LDO5 and VD is the forward voltage

dropped across the Schottky diode.

The SECFB pin in the RT8239B/C is used to monitor the

charge pump via a resistive voltage divider to generate

approximately 14V DC voltage and the clock driver uses

VOUT1 as its power supply. In the event where SECFB

drops below its feedback threshold, an ultrasonic pulse

will occur to refresh the charge pump driven by LGATEx.

If there's an overload on the charge pump in which SECFB

can not reach more than its feedback threshold, the

RT8239A/B/C

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Figure 5. Charge pump circuit connected to SECFB

MOSFET Gate Driver (UGA TEx, LGA TEx)

The high side driver is designed to drive high current, low

RDS(ON) N-MOSFET(s). When configured as a floating driver,

5V bias voltage is delivered from the LDO5 supply. The

average drive current is also calculated by the gate charge

at VGS = 5V times switching frequency. The instantaneous

drive current is supplied by the flying capacitor between

BOOTx and PHASEx pins. A dead time to prevent shoot

through is internally generated from high side MOSFET

off to low side MOSFET on and low side MOSFET off to

high side MOSFET on.

The low side driver is designed to drive high current low

RDS(ON) N-MOSFET(s). The internal pull down transistor

that drives LGATEx low is robust, with a 1.5Ω typical on-

resistance. A 5V bias voltage is delivered from the LDO5

supply. The instantaneous drive current is supplied by an

input capacitor connected between LDO5 and GND.

For high current applications, some combinations of high

and low side MOSFETs may cause excessive gate drain

coupling, which leads to efficiency killing, EMI producing,

shoot through currents. This is often remedied by adding

a resistor in series with BOOTx, which increases the turn

on time of the high side MOSFET without degrading the

turn-off time. See Figure 6.

Figure 6. Increasing the UGATEx Rise Time

Soft-Start

The RT8239A/B/C provides an internal soft-start function

to prevent large inrush current and output voltage overshoot

when the converter starts up. The soft-start (SS)

automatically begins once the chip is enabled. During soft-

start, the internal current limit circuit gradually ramps up

the inductor current from zero. The maximum current limit

value is set externally as described in previous section.

The soft-start time is determined by the current limit level

and output capacitor value. The current limit threshold ramp

up time is typically 2ms from zero to 200mV after

ENTRIPx is enabled. A unique PWM duty limit control

that prevents output over voltage during soft-start period

is designed specifically for FBx floating.

UVLO Protection

The RT8239A/B/C has LDO5 under voltage lock out

protection (UVLO). When the LDO5 voltage is lower than

4.05V (typ.) and the LDO3 voltage is lower than 2.2V (typ.),

both switch power supplies are shut off. This is a non-

latch protection.

Power Good Output (PGOOD)

PGOOD is an open-drain type output and requires a pull

up resistor. PGOOD is actively held low in soft-start,

standby, and shutdown. It is released when both output

voltages are above 90% of the nominal regulation point

for RT8239A. For RT8239B/C, besides requiring both

output voltages to be above 90% of nominal regulation

point, the SECFB threshold must also be above 50% of

nominal regulation point in order for PGOOD to be released.

The PGOOD signal goes low if either output turns off or is

10% below its nominal regulation point.

SECFB

LGATE1

VOUT1

D1 D2 D3

CFRCP1

RCP2

Charge Pump

BOOTx

RBOOT

UGATEx

VIN

PHASEx

controller will enter Ultrasonic Mode. Special care should

be taken to ensure that enough normal ripple voltage is

present on each cycle to prevent charge pump shutdown.

The robustness of the charge pump can be increased by

reducing the charge pump decoupling capacitor and placing

a small ceramic capacitor, CF (47pF to 220pF), in parallel

with the upper leg of the SECFB resistor feedback network,

RCP1, as shown below in Figure 5.

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Output Over Voltage Protection (OVP)

The output voltage can be continuously monitored for over

voltage. If the output voltage exceeds 12% of its set voltage

threshold, the over voltage protection is triggered and the

LGATEx low side gate drivers are forced high. This

activates the low side MOSFET switch, which rapidly

discharges the output capacitor and pulls the input voltage

downward.

The RT8239A/B/C is latched once OVP is triggered and

can only be released by either toggling ENLDO, ENTRIPx

or cycling VIN. There is a 5μs delay built into the over

voltage protection circuit to prevent false transition.

Note that latching LGATEx high will cause the output

voltage to dip slightly negative due to previously stored

energy in the LC tank circuit. For loads that cannot tolerate

a negative voltage, place a power Schottky diode across

the output to act as a reverse polarity clamp.

If the over voltage condition is caused by a short in high

side switch, turning the low side MOSFET on 100% will

create an electrical short between the battery and GND,

hence blowing the fuse and disconnecting the battery from

the output.

Output Under Voltage Protection (UVP)

The output voltage can be continuously monitored for under

voltage. If the output is less than 58% of its set voltage

threshold, the under voltage protection will be triggered

and then both UGATEx and LGATEx gate drivers will be

forced low. The UVP is ignored for at least 5ms (typ.)

after a start up or a rising edge on ENTRIPx. Toggle

ENTRIPx or cycle VIN to reset the UVP fault latch and

restart the controller.

Thermal Protection

The RT8239A/B/C features thermal shutdown to prevent

damage from excessive heat dissipation. Thermal

shutdown occurs when the die temperature exceeds

150°C. All internal circuitry is inactive during thermal

shutdown. The RT8239A/B/C triggers thermal shutdown

if LDOx is not supplied from VOUTx, while input voltage on

VIN and drawing current from LDOx are too high.

Nevertheless, even if LDOx is supplied from VOUTx,

overloading LDOx can cause large power dissipation on

automatic switches, which may still result in thermal

shutdown.

Discharge Mode (Soft Discharge)

When ENTRIPx is low and a transition to standby or

shutdown mode occurs, or the output under voltage fault

latch is set, the output discharge mode will be triggered.

During discharge mode, an internal switch creates a path

for discharging the output capacitors' residual charge to

GND.

Shutdown Mode

SMPS1, SMPS2, LDO3 and LDO5 all have independent

enabling control. Drive ENLDO, ENTRIP1 and ENTRIP2

below the precise input falling edge trip level to place the

RT8239A/B/C in its low power shutdown state. The

RT8239A/B/C consumes only 20μA of input current while

in shutdown. When shutdown mode is activated, the

reference turns off. The accurate 0.95V falling edge

threshold on ENLDO can be used to detect a specific

analog voltage level and to shutdown the device. Once in

shutdown, the 1.6V rising edge threshold activates,

providing sufficient hysteresis for most applications.

Power Up Sequencing and On/Off Controls

(ENTRIPx, ENM)

ENTRIP1 and ENTRIP2 control SMPS power up

sequencing. When the RT8239A/B/C is applied in the

single channel mode, ENTRIPx disables the respective

output when ENTRIPx voltage rises above 4.5V.

Furthermore, when the RT8239A is applied in the dual

channel mode, the outputs are enabled when ENM voltage

rises above 2.3V.

RT8239A/B/C

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Table1. Operation Mode Truth Table

Mode Condition Comment

Power Up LDOx < UVLO threshold

Transitions to discharge mode after VIN POR and

after REF becomes valid. LDO5 and LDO3 remain

active.

Run ENLDO = high, VOUT1 or VOUT2 are

enabled Normal Operation.

Over Voltage

Protection Either output > 112% of the nominal level.

LGATEx is forced high. LDO3 and LDO5 are active.

Exit by VIN POR or by toggling ENLDO, ENTRIPx,

and ENM.

Under Voltage

Protection

Either output < 58% of the nominal level

after 3ms time-out expires and output is

enabled

Both UGATEx and LGATEx are forced low and

enter discharge mode. LDO3 and LDO5 are active.

Exit by VIN POR or by toggling ENLDO, ENTRIPx,

and ENM.

Discharge Either output is still high in standby mode

or shutdown mode

During discharge mode, there is one path to

discharge the output capacitors’ residual charge to

GND via an internal switch.

Standby ENTRIPx or ENM < startup threshold,

ENLDO = high. LDO3 and LDO5 are active.

Shutdown ENLDO = low All circuitry are off.

Thermal

Shutdown TJ > 150°C All circuitry are off. Exit by VIN POR or by toggling

ENLDO, ENTRIPx, and ENM.

Table 2. Power up Sequencing (RT8239A)

ENLDO (V) ENM (V) ENTRIP1

(V) ENTRIP2

(V) LDO5 LDO3 SMPS1 SMPS2

Low Low X X Off Off Off Off

“>1.6V”

=> High Low X X On On Off Off

“>1.6V”

=> High

“>2.3V”

=> High Off Off On On Off Off

“>1.6V”

=> High

“>2.3V”

=> High Off On On On Off On

“>1.6V”

=> High

“>2.3V”

=> High On On On On On On

“>1.6V”

=> High

“>2.3V”

=> High On Off On On On Off

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Output Voltage Setting (FBx)

Connect a resistive voltage divider at the FBx pin between

VOUTx and GND to adjust the output voltage between 2V

and 5.5V (Figure 7). Choose R2 to be approximately 10kΩ,

and solve for R1 using the equation :

⎛⎞

=×+

⎜⎟

⎝⎠

OUT FBx

VV1

where VFBx is 2V (typ.).

UGATEx

PHASEx

LGATEx

PGND

FBx

GND

VOUTx

VIN

Figure 7. Setting VOUTx with a resistive voltage divider

Output Inductor Selection

The switching frequency (on-time) and operating point (%

ripple or LIR) determine the inductor value as shown

below :

×−

=×

ON IN OUTx

LOAD(MAX)

t(VV )

LLIR I

where LIR is the ratio of the peak-to-peak ripple current to

the average inductor current.

Find a low-loss inductor having the lowest possible DC

resistance that fits in the allotted dimensions. Ferrite cores

are often the best choice, although powdered iron is

inexpensive and can work well at 200kHz. The core must

be large enough not to saturate at the peak inductor

current, IPEAK :

IPEAK = ILOAD(MAX) + [ (LIR / 2) x ILOAD(MAX) ]

The calculation above shall serve as a general reference.

To further improve transient response, the output

inductance can be further reduced. Of course, besides

the inductor, the output capacitor should also be

considered when improving transient response.

Output Capacitor Selection

The capacitor value and ESR determine the amount of

output voltage ripple and load transient response. Thus,

the capacitor value must be greater than the largest value

calculated from below equations.

Δ××+

=⎡⎤

×××−

⎣⎦

LOAD ON OFF(MIN)

SAG

OUT IN ON OUTx ON OFF(MIN)

(I ) L (t t )

V2C V t V (t + t )

()

LOAD

SOAR

OUT OUTx

V2C V

Δ×

=××

−

⎛⎞

=× ×

⎜⎟

××

⎝⎠

P P LOAD(MAX)

OUT

V LIR I ESR + 8C f

where VSAG and VSOAR are the allowable amount of

undershoot and overshoot voltage during load transient,

Vp-p is the output ripple voltage, and tOFF(MIN) is the

minimum off-time.

Thermal Considerations

For continuous operation, do not exceed absolute

maximum junction temperature. The maximum power

dissipation depends on the thermal resistance of the IC

package, PCB layout, rate of surrounding airflow, and

difference between junction and ambient temperature. The

maximum power dissipation can be calculated by the

following formula :

PD(MAX) = (TJ(MAX) − TA) / θJA

where TJ(MAX) is the maximum junction temperature, TA is

the ambient temperature, and θJA is the junction to ambient

thermal resistance.

For recommended operating condition specifications, the

maximum junction temperature is 125°C. The junction to

ambient thermal resistance, θJA, is layout dependent. For

WQFN-20L 3x3 packages, the thermal resistance, θJA, is

30°C/W on a standard JEDEC 51-7 four-layer thermal test

board. The maximum power dissipation at TA = 25°C can

be calculated by the following formula :

PD(MAX) = (125°C − 25°C) / (30°C/W) = 3.33W for

WQFN-20L 3x3 package

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ(MAX) and thermal

RT8239A/B/C

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resistance, θJA. The derating curve in Figure 8 allows the

designer to see the effect of rising ambient temperature

on the maximum power dissipation.

Figure 8. Derating Curve of Maximum Power Dissipation

Layout Considerations

Layout is very important in high frequency switching

converter design. Improper PCB layout can radiate

excessive noise and contribute to the converter’s

instability. Certain points must be considered before

starting a layout with the RT8239A/B/C.

`Place the filter capacitor close to the IC, within 12mm

(0.5 inch) if possible.

`Keep current limit setting network as close as possible

to the IC. Routing of the network should avoid coupling

to high-voltage switching node.

`Connections from the drivers to the respective gate of

the high side or the low side MOSFET should be as

short as possible to reduce stray inductance. Use

0.65mm (25 mils) or wider trace.

`All sensitive analog traces and components such as

FBx, ENTRIPx, PGOOD, and TON should be placed

away from high voltage switching nodes such as

PHASEx, LGATEx, UGATEx, or BOOTx nodes to avoid

coupling. Use internal layer(s) as ground plane(s) and

shield the feedback trace from power traces and

components.

`Place ground terminal of VIN capacitor(s), VOUTx

capacitor(s), and source of low side MOSFETs as close

to each other as possible. The PCB trace of PHASEx

node, which connects to source of high side MOSFET,

drain of low side MOSFET and high voltage side of the

inductor, should be as short and wide as possible.

0.0

0.6

1.2

1.8

2.4

3.0

3.6

0 25 50 75 100 125

Ambient Temperature (°C)

Maximum Power Dissipation (W) 1

Four-Layer PCB

RT8239A/B/C

DS8239A/B/C-05 August 2012www.richtek.com

Richtek Technology Corporation

5F, No. 20, Taiyuen Street, Chupei City

Hsinchu, Taiwan, R.O.C.

Tel: (8863)5526789

Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should

obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot

assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be

accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third

parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.

Outline Dimension

Dimen sions In Millimeters Dimen sions In Inches

Symbol Min Max Min Max

A 0.700 0.800 0.028 0.031

A1 0.000 0.050 0.000 0.002

A3 0.175 0.250 0.007 0.010

b 0.150 0.250 0.006 0.010

D 2.900 3.100 0.114 0.122

D2 1.650 1.750 0.065 0.069

E 2.900 3.100 0.114 0.122

E2 1.650 1.750 0.065 0.069

e 0.400 0.016

L 0.350 0.450

0.014 0.018

W-Type 20L QFN 3x3 Package

Note : The configuration of the Pin #1 identifier is optional,

but must be located within the zone indicated.

DETAIL A

Pin #1 ID and Tie Bar Mark Options