RT8509 [RICHTEK]

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型号：	RT8509
厂家：	RICHTEK TECHNOLOGY CORPORATION
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RT8509

3A, 14V Step-Up DC-DC Converter

General Description

Features

^90% Efficiency

The RT8509 is a high performance switching boost

converter that provides a regulated supply voltage for active

matrix thin film transistor (TFT) liquid crystal displays

(LCDs).

^Adjustable Output Up to 24V

^2.8V to 14V Input Supply Voltage

^Input Supply Under Voltage Lockout

^Fixed 1.2MHz Switching Frequency

^Programmable Soft-Start

The RT8509 incorporates current mode, fixed-frequency,

pulse width modulation (PWM) circuitry with a built in

N-MOSFET to achieve high efficiency and fast transient

response.

^V_OUTOver Voltage Protection

^Over Temperature Protection

^Thin 10-Lead WDFN Package

^RoHS Compliant and Halogen Free

The RT8509 has a wide input voltage range from 2.8V to

14V. In addition, the output voltage can be adjusted up to

24V via an external resistive voltage divider. The maximum

peak current is limited to 3.5A(typ.). Other features include

programmable soft-start, over voltage protection, and over

temperature protection.

Applications

 GIP TFT LCDPanels

Pin Configuration

The RT8509 is available in a WDFN-10L 3x3 package.

(TOP VIEW)

COMP

GND

Ordering Information

VIN

VSUP

RT8509

Package Type

QW : WDFN-10L 3x3 (W-Type)

Lead Plating System

WDFN-10L 3x3

G : Green (Halogen Free and Pb Free)

Note :

Marking Information

Richtek products are :

 RoHS compliant and compatible with the current require-

ments of IPC/JEDEC J-STD-020.

H4= : Product Code

H4=YM

YMDNN : Date Code

DNN

 Suitable for use in SnPb or Pb-free soldering processes.

Typical Application Circuit

4.7µH

OUT

18V

12V

OUT

6, 7

134k

10µF x 2

4.7µF x 3

VSUP

1µF

10k

VIN

RT8509

1µF

Chip Enable

33nF

56k

4, 5, 11 (Exposed Pad)

COMP

GND

1nF

is a registered trademark of Richtek Technology Corporation.

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RT8509

Functional Pin Description

Pin No.

Pin Name

Pin Function

COMP

Compensation pin for error amplifier. Connect a series RC from COMP to ground.

Feedback. The FB regulation voltage is 1.25V nominal. Connect an external

resistive voltage divider between the step-up regulator’s output (V

with the center tap connected to FB. Place the divider close to the IC and minimize

the trace area to reduce noise coupling.

) and GND,

OUT

Chip enable. Drive EN low to turn off the Boost.

4, 5,

Ground. The Exposed Pad must be soldered to a large PCB and connected to

GND for maximum power dissipation.

GND

11 (Exposed Pad)

Switch. LX is the drain of the internal MOSFET. Connect the inductor/rectifier diode

junction to LX and minimize the trace area for lower EMI.

6, 7

Boost converter over voltage protection input. Bypass VSUP with a minimum 1F

ceramic capacitor directly to GND.

VSUP

VIN

Supply input. Bypass VIN with a minimum 1μF ceramic capacitor directly to GND.

Soft-start control. Connect a soft-start capacitor (C ) to this pin. The soft-start

capacitor is charged with a constant current of 5A. The soft-start capacitor is

discharged to ground when EN is low.

Functional Block Diagram

VIN

Soft

Start

Protection

OTP

COMP

Summing

Comparator

Error Amplifier

Control

and

Driver

Logic

1.25V

VSUP

OVP

GND

Clock

Current

Sense

Slope

Compensation

Oscillator

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RT8509

Absolute Maximum Ratings (Note 1)

 LX, VSUP toGND --------------------------------------------------------------------------------------------------------- −0.3V to 28V

 VIN, ENtoGND ------------------------------------------------------------------------------------------------------------ −0.3V to 16.5V

 Other Pins to GND -------------------------------------------------------------------------------------------------------- −0.3V to 6.5V

 Power Dissipation, P_D@ T_A= 25°C

WDFN-10L 3x3 ------------------------------------------------------------------------------------------------------------- 1.429W

 Package Thermal Resistance (Note 2)

WDFN-10L 3x3, θ_JA------------------------------------------------------------------------------------------------------- 70°C/W

WDFN-10L 3x3, θ_JC------------------------------------------------------------------------------------------------------- 8.2°C/W

 Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C

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

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

 ESD Susceptibility (Note 3)

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

MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V

Recommended Operating Conditions (Note 4)

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

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

Electrical Characteristics

(V_IN= 3.3V, V_OUT= 10V, T_A=25°C unless otherwise specified)

Parameter

Supply Current

Symbol

Test Conditions

Min

Typ

Max

Unit

Input Voltage Range

Output Voltage Range

2.8

OUT

Under Voltage Lockout

Threshold

2.5

rising

UVLO

UVLO Hysteresis

200

V

UVLO

= 1.3V, LX not switching

= 1V, LX switching

VIN Quiescent Current

Thermal Shutdown Threshold

Temperature rising

155

C

Thermal Shutdown

Hysteresis

VSUP Over Voltage

Threshold

T

VSUP rising

Oscillator

Oscillator Frequency

Maximum Duty Cycle

Error Amplifier

1000

1200

1500

kHz

OSC

MAX

FB Regulation Voltage

FB Input Bias Current

FB Line Regulation

1.25

REF

100

0.2

0.05

%/V

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RT8509

Parameter

Symbol

Test Conditions

I = ±2.5μA at V = 1V

Min

Typ

100

700

Max

Unit

A/V

V/V

Transconductance

Voltage Gain

COMP

FB to COMP

N-MOSFET

Current Limit

3.5

100

LIM

On-Resistance

Leakage Current

250

m

A

DS(ON)

LEAK

= 24V

Current Sense

Transresistance

0.25

V/A

Soft-Start

Charge Current

Control Inputs

A

Logic-High

Logic-Low

1.5

EN Input

Voltage

0.5

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. θ_JAis measured under natural convection (still air) at T_A= 25°C with the component mounted on a high effective-

thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. θ_JCis 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.

is a registered trademark of Richtek Technology Corporation.

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DS8509-02 March 2018

RT8509

Typical Operating Characteristics

Boost Efficiency vs. Load Current

100

V_IN= 5V

V_IN= 14V

_IN= 12V

_IN= 10V

V_IN= 3.3V

V_OUT= 13.5V, f_OSC= 1.2MHz

V_OUT= 18V, f_OSC= 1.2MHz

0.9 1.2 1.5

0.1

0.2

0.3

0.4

0.5

-50

0.3

0.6

Load Current (A)

Boost Reference Voltage vs. Temperature

Boost Frequency vs. Temperature

1.5

1400

1300

1200

1100

1000

900

1.4

1.3

1.2

1.1

V_IN= 3.3V

100 125

V_IN= 3.3V

100 125

-25

-50

-25

Temperature (°C)

Boost Reference Voltage vs. Input Voltage

Boost Current Limit vs. Input Voltage

1.5

1.4

1.3

1.2

1.1

Input Voltage (V)

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RT8509

Application Information

Output Voltage Setting

The RT8509 is a high performance step-up DC-DC

converter that provides a regulated supply voltage for panel

source driver ICs. The RT8509 incorporates current mode,

fixed frequency, Pulse Width Modulation (PWM) circuitry

with a built in N-MOSFET to achieve high efficiency and

fast transient response. The following content contains

detailed description and information for component

selection.

The regulated output voltage is shown as the following

equation :







= V

x 1

, where V

= 1.25V (typ.)

OUT

REF







REF

The recommended value for R2 should be at least 10kΩ

without some sacrificing. Place the resistive voltage divider

as close as possible to the chip to reduce noise sensitivity.

Loop Compensation

Boost Regulator

The voltage feedback loop can be compensated with an

external compensation network consisting of R3. Choose

R3 to set high frequency integrator gain for fast transient

response and C1 to set the integrator zero to maintain

loop stability. For typical application, V_IN= 5V,

V_OUT= 13.6V, C_OUT= 4.7μF x 3, L1 = 4.7μH, while the

recommended value for compensation is as follows :

R3 = 56kΩ, C1 = 1nF.

The RT8509 is a current mode boost converter integrated

with a 24V/3.5Apower switch, covering a wide V_INrange

from 2.8V to 14V. It performs fast transient responses to

generate source driver supplies for TFT LCDdisplay. The

high operation frequency allows use of smaller

components to minimize the thickness of the LCD panel.

The output voltage can be adjusted by setting the resistive

voltage-divider sensing at the FB pin. The error amplifier

varies the COMP voltage by sensing the FB pin to regulate

the output voltage. For better stability, the slope

compensation signal summed with the current sense

signal will be compared with the COMP voltage to

determine the current trip point and duty cycle.

Over Current Protection

The RT8509 boost converter has over current protection

to limit the peak inductor current. It prevents large current

from damaging the inductor and diode.During the On-time,

once the inductor current exceeds the current limit, the

internal LX switch turns off immediately and shortens the

duty cycle. Therefore, the output voltage drops if the over

current condition occurs. The current limit is also affected

by the input voltage, duty cycle, and inductor value.

Soft-Start

The RT8509 provides soft-start function to minimize the

inrush current. When powered on, an internal constant

current charges an external capacitor. The rising voltage

rate on the COMP pin is limited from V_SS= 0V to 1.24V

and the inductor peak current will also be limited at the

same time. When powered off, the external capacitor will

be discharged until the next soft-start time.

Over Temperature Protection

The RT8509 boost converter has thermal protection function

to prevent the chip from overheating. When the junction

temperature exceeds 155°C, the function shuts down the

device. Once the device cools down by approximately

10°C, it will automatically restart to normal operation. To

guarantee continuous operation, do not operate over the

maximum junction temperature rating of 125°C.

The soft-start function is implemented by the external

capacitor with a 5μAconstant current charging to the soft-

start capacitor. Therefore, the capacitor should be large

enough for output voltage regulation. A typical value for

soft-start capacitor is 33nF. The available soft-start capacitor

range is from 10nF to 100nF.

Inductor Selection

The inductance depends on the maximum input current.

As a general rule, the inductor ripple current range is 20%

to 40% of the maximum input current. If 40% is selected

If C_SS< 220pF, the internal soft-start function will be turned

on and period time is approximately 1ms.

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RT8509

as an example, the inductor ripple current can be

calculated according to the following equations :





















Q 

_{ IN} I_LI_{OUT } _I_IN I_LI_{OUT }









x I

OUT(MAX)

OUT

 C_OUTx V_OUT1

IN(MAX)

V_OUT

f_OSC

 x V

= 0.4 x I

IN(MAX)

RIPPLE

where f_OSCis the switching frequency, and ΔI_Lis the

inductor ripple current. Bring C_OUTto the left side to

estimate the value of ΔV_OUT1according to the following

equation :

where η is the efficiency of the converter, I_IN(MAX)is the

maximum input current, and I_RIPPLEis the inductor ripple

current. The input peak current can then be obtained by

adding the maximum input current with half of the inductor

ripple current as shown in the following equation :

D x I_OUT

V_OUT1



 x C_OUTx f_OSC

where D is the duty cycle and η is the boost converter

efficiency. Finally, taking ESR into account, the overall

output ripple voltage can be determined by the following

1.2 x I

IN(MAX)

PEAK

Note that the saturated current of the inductor must be

greater than I_PEAK. The inductance can eventually be

determined according to the following equation :

 x (V )²x(V_OUT V )

equation :

D x I_OUT

V_OUT I x ESR 

 x C_OUTx f_OSC

L 

0.4 x (V_OUT)²xI_OUT(MAX)x f_OSC

The output capacitor, C_OUT, should be selected accordingly.

where f_oscis the switching frequency. For better system

performance, a shielded inductor is preferred to avoid EMI

problems.

ΔI

Input Current

Inductor Current

Diode Selection

Schottky diodes are chosen for their low forward voltage

drop and fast switching speed. When selecting a Schottky

diode, important parameters such as power dissipation,

reverse voltage rating, and pulsating peak current should

all be taken into consideration.Asuitable Schottky diode's

reverse voltage rating must be greater than the maximum

output voltage and its average current rating must exceed

the average output current. Last of all, the chosen diode

should have a sufficiently low leakage current level, since

it will increase with temperature.

Output Current

Time

(1-D)T

Output Ripple

Voltage (ac)

Time

ΔV

OUT1

Figure 1. The Output Ripple Voltage without the

Contribution of ESR

Output Capacitor Selection

Input Capacitor Selection

The output ripple voltage is an important index for

estimating chip performance. This portion consists of two

parts. One is the product of the inductor current with the

ESR of the output capacitor, while the other part is formed

by the charging and discharging process of the output

capacitor. As shown in Figure 1, ΔV_OUT1can be evaluated

based on the ideal energy equalization. According to the

definition of Q, the Q value can be calculated as the

following equation :

Low ESR ceramic capacitors are recommended for input

capacitor applications. Low ESR will effectively reduce

the input voltage ripple caused by switching operation. A

10μF capacitor is sufficient for most applications.

Nevertheless, this value can be decreased for lower output

current requirement. Another consideration is the voltage

rating of the input capacitor which must be greater than

the maximum input voltage.

is a registered trademark of Richtek Technology Corporation.

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RT8509

Thermal Considerations

Layout Considerations

The junction temperature should never exceed the

absolute maximum junction temperature T_J(MAX), listed

under Absolute Maximum Ratings, to avoid permanent

damage to the device. The maximum allowable power

dissipation depends on the thermal resistance of the IC

package, the PCB layout, the rate of surrounding airflow,

and the difference between the junction and ambient

temperatures. The maximum power dissipation can be

calculated using the following formula :

For high frequency switching power supplies, the PCB

layout is important to get good regulation, high efficiency

and stability. The following descriptions are the guidelines

for better PCB layout.

 For good regulation, place the power components as

close as possible. The traces should be wide and short

enough especially for the high current output loop.

 The feedback voltage divider resistors must be near the

feedback pin. The divider center trace must be shorter

and the trace must be kept away from any switching

nodes.

P_D(MAX)= (T_J(MAX)− T_A) / θ_JA

where T_J(MAX)is the maximum junction temperature, T_Ais

the ambient temperature, and θ_JAis the junction-to-ambient

thermal resistance.

 The compensation circuit should be kept away from the

power loops and be shielded with a ground trace to

prevent any noise coupling.

For continuous operation, the maximum operating junction

temperature indicated under Recommended Operating

Conditions is 125°C. The junction-to-ambient thermal

resistance, θ_JA, is highly package dependent. For a

WDFN-10L 3x3, the thermal resistance, θ_JA, is 70°C/W

on a standard JEDEC 51-7 high effective-thermal-

conductivity four-layer test board. The maximum power

dissipation at T_A= 25°C can be calculated as below :

 Minimize the size of the LX node and keep it wide and

shorter. Keep the LX node away from the FB.

 The exposed pad of the chip should be connected to a

strong ground plane for maximum thermal consideration.

Place C as close

The compensation circuit

to VIN as possible.

should be kept away from the

power loops and should be

shielded with a ground trace to

prevent any noise coupling.

GND

P_D(MAX)= (125°C − 25°C) / (70°C/W) = 1.429Wfor

a WDFN-10L 3x3 package.

GND

The maximum power dissipation depends on the operating

ambient temperature for the fixed T_J(MAX)and the thermal

resistance, θ_JA. The derating curves in Figure 2 allows

the designer to see the effect of rising ambient temperature

on the maximum power dissipation.

COMP

GND

VIN

VSUP

OUT

The feedback voltage-divider

resistors must be near the

1.6

feedback pin. The divider center

Four Layer PCB

trace must be shorter and avoid the

trace near any switching nodes.

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

GND

Place the power components as

close to the IC as possible. The

traces should be wide and short,

especially for the high-current loop.

Figure 3. PCB Layout Guide

100

125

Ambient Temperature (°C)

Figure 2.Derating Curve of Maximum PowerDissipation

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Outline Dimension

SEE DETAIL A

DETAILA

Pin #1 ID and Tie Bar Mark Options

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

but must be located within the zone indicated.

Dimensions In Millimeters

Dimensions In Inches

Symbol

Min

Max

Min

Max

0.700

0.000

0.175

0.180

2.950

2.300

2.950

1.500

0.800

0.050

0.250

0.300

3.050

2.650

3.050

1.750

0.028

0.000

0.007

0.116

0.091

0.116

0.059

0.031

0.002

0.010

0.012

0.120

0.104

0.120

0.069

0.500

0.020

0.350

0.450

0.014

0.018

W-Type 10L DFN 3x3 Package

Richtek Technology Corporation

14F, No. 8, Tai Yuen 1^stStreet, 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.

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RT8509 [RICHTEK]

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