Richtek RT8452GQW, RT8452GS Schematic [ru]

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Conceptual

RT8452

High Voltage High Current LED Driver

Controller for Boost

or Buck-Boost Topology

 

General Description

The RT8452 is a current mode PWM controller designed to drive an external MOSFET for high current LED applications. With a current sense amplifier threshold of 180mV, the LED current is programmable with one external current sense resistor and the power loss is minimized. With the maximum operating input voltage of 40V and output voltage up to 60V, the RT8452 is ideal for boost or buck-boost operation. (See RT8450 and RT8451 for buck mode LED driver application.)

With 1MHz operating frequency, the external inductor and capacitors can be small while mainteining high efficiency.

Dimming can be either analog or PWM digital. The unique built-in clampping comparator and filter allow easy low noise analog dimming conversion from PWM signal with only one external capacitor. PWM dimming control is made easy with a build in FET driver dedicated for the extermal dimming MOSFET.

The RT8452 is available in WQFN-16L 3x3 and SOP-16 packages.

Features

High Voltage Capability : VIN Up to 40V, VOUT Up to 60V

Boost or Buck-Boost Operation

Current Mode PWM with 1MHz Switching Frenquency

Easy Dimming : Analog, PWM Digital or PWM Converting to Analog with One External Capacitor

Programmable Soft Start to Avoid Inrush Current

Programmable Over Voltage Protection to Limit Output Voltage

VIN Undervoltage Lockout and Thermal Shutdown

16-Lead WDFN and SOP Packages.

RoHS Compliant and 100% Lead (Pb)-Free

Applications

General Industrial High Power LED Lighting

Desk Lights and Room Lighting

Building and Street Lighting

Industrial Display Backlight

Ordering Information

RT8452

Package Type

S : SOP-16

QW : WDFN-16L 3x3 (W-Type)

Operating Temperature Range

G : Green (Halogen Free with Commercial Standard)

Note :

Richtek Green products are :

}RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.

}Suitable for use in SnPb or Pb-free soldering processes. }100% matte tin (Sn) plating.

Marking Information

For marking information, contact our sales representative directly or through a Richtek distributor located in your area, otherwise visit our website for detail.

Pin Configurations

 

(TOP VIEW)

 

 

GND

VCC

OVP

EN

 

 

16

15

14

13

 

GBIAS

1

 

 

12

NC

GATE

2

GND

11

SS

PWMOUT

3

10

DCTL

 

 

ISW

 

 

17

ACTL

4

 

 

9

 

5

6

7

8

 

 

PWMDIM

ISP

ISN

VC

 

 

WQFN-16L 3x3

 

GBIAS

 

 

 

 

 

 

GND

 

 

 

16

 

 

GATE

 

 

2

15

 

 

VCC

 

 

 

 

PWMOUT

 

 

3

14

 

 

OVP

 

 

 

 

ISW

 

 

4

13

 

 

EN

 

 

 

 

PWMDIM

 

 

5

12

 

 

NC

 

 

 

 

ISP

 

 

6

11

 

 

SS

 

 

 

 

ISN

 

 

7

10

 

 

DCTL

 

 

 

 

VC

 

 

8

9

 

 

ACTL

 

 

 

 

 

 

 

 

 

 

 

 

SOP-16

DS8452-02C March 2008

www.richtek.com

1

Richtek RT8452GQW, RT8452GS Schematic

RT8452

Conceptual

Typical Application Circuit

VOUT

60V MAX

 

 

 

 

L

 

 

R2

VIN

 

 

 

10uH

 

 

180mV

4.5V to 40V

 

C1

 

 

 

C5

 

 

 

 

 

 

 

 

 

 

RT8452

 

1uF

 

 

 

 

 

 

 

 

 

15

VCC

GATE 2

R3

 

5V

 

13

EN

ISW 4

 

 

 

 

Analog

 

9

ACTL

ISP 6

 

 

Dimming

 

10

DCTL

ISN

7

 

 

 

 

R4

 

 

 

8

 

OVP 14

VOUT

 

 

VC

 

R1

 

 

PWMOUT

3

 

 

 

11

SS

R5

 

10k

 

PWMDIM 5

 

 

C3

1

GBIAS

 

 

C2

 

 

GND

 

 

 

10nF

 

 

 

 

 

3nF

 

C4

 

16, Exposed Pad (17)

 

 

Figure 1. Analog Dimming in Boost Configuration

VOUT

60V MAX

 

 

 

 

L

 

R2

 

VIN

 

 

10uH

 

180mV

4.5V to 40V

C1

 

 

C6

 

 

 

 

 

 

 

 

 

RT8452

1uF

 

 

 

 

 

 

 

 

15

VCC

GATE 2

R3

 

 

5V

13

EN

ISW 4

 

PWM

 

10

DCTL

ISP 6

 

 

Dimming control

8

VC

ISN 7

R4

 

R1

 

11

SS

OVP 14

 

VOUT

 

PWMOUT 3

 

 

10k

C3

1

GBIAS

R5

 

C2

 

 

PWMDIM 5

 

 

10nF

9 ACTL

 

 

3nF

C4

GND

 

 

 

 

C5

 

16, Exposed Pad (17)

 

 

 

 

0.5uF

 

 

 

 

Figure 2. PWM to Analog Dimming in Boost Configuration

VOUT

60V MAX

 

 

 

 

L

 

R2

VIN

 

 

 

10uH

 

180mV

4.5V to 40V

 

C1

 

 

C5

 

 

 

 

 

 

 

 

 

RT8452

1uF

 

 

 

 

 

 

 

 

15

VCC

GATE 2

R3

 

5V

 

13

EN

ISW 4

 

 

 

 

 

 

9

ACTL

ISP 6

 

 

 

 

10

DCTL

ISN 7

 

 

 

 

8

VC

PWMOUT 3

 

 

R1

 

11

SS

PWMDIM 5

R4

 

 

OVP 14

VOUT

10k

C3

1

GBIAS

 

C2

 

GND

 

 

10nF

 

 

R5

 

3nF

 

C4

 

16, Exposed Pad (17)

 

 

 

 

 

Figure 3. True PWM Dimming in Boost Configuration

www.richtek.com

DS8452-02C March 2008

2

Conceptual

RT8452

VOUT

60V MAX

 

 

 

 

 

 

L

 

 

VIN

 

 

 

 

 

10uH

 

 

4.5V to 40V

 

C1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RT8452

 

 

C5

 

 

15

VCC

 

GATE

2

 

1uF

 

 

 

R3

 

5V

 

13

EN

 

ISW

4

 

 

 

 

R2

Analog

 

9

 

 

 

 

 

 

ACTL

 

ISN

7

 

180mV

Dimming

 

 

 

 

10

DCTL

 

6

 

 

 

 

 

ISP

 

 

 

 

8

 

 

3

 

 

 

 

VC

 

PWMOUT

 

 

R1

 

11

SS

 

PWMDIM

5

R4

 

10k

 

1

 

14

VOUT

 

C3

GBIAS

OVP

 

C2

 

GND

 

 

 

10nF

 

 

 

 

R5

 

3nF

 

C4

 

 

16, Exposed Pad (17)

 

 

 

 

 

 

Figure 4. Analog Dimming in Buck-Boost Configuration

Functional Pin Description

SOP-16

 

QFN3X3-16

Pin Name

Pin Function

 

 

 

 

 

1

 

1

GBIAS

The Internal Gate Driver Bias Pin.A good bypass capacitor is required.

2

 

2

GATE

The External MOSFET Switch Gate Driver Output Pin.

3

 

3

PWMOUT

The Output Pin for the PWM Dimming FET Driver.

4

 

4

ISW

The External MOSFET Switch Current Sense Pin. Connect the current

 

sense resistor between external N-MOSFET switch and the ground.

 

 

 

 

5

 

5

PWMDIM

The Control Input Pin for the PWM Dimming FET Driver.

6

 

6

ISP

The LED Current Sense Amplifier Positive Input.

7

 

7

ISN

The LED Current Sense Amplifier Negative Input. Voltage

 

threshold between ISP and ISN is 180mV.

 

 

 

 

8

 

8

VC

The PWM Control Loop Compensation Pin.

9

 

9

ACTL

The Analog Dimming Control Pin. The effective programming

 

voltage range of the pin is between 0.3V and 1.2V.

 

 

 

 

 

 

 

 

By adding a 0.1uF filtering capacitor on ACTL pin, the PWM dimming

10

 

10

DCTL

signal on DCTL pin can be averaged and converted into analog

 

dimming signal on the ACTL pin following the formula below.

 

 

 

 

 

 

 

 

VACTL = 1.2V x PWM Dimming Duty Cycle.

11

 

11

SS

The Soft-Start Pin. A capacitor of at least 10nF is required for proper

 

soft start.

 

 

 

 

12

 

12

NC

No Internal Connection.

13

 

13

EN

The Chip Enable (Active High) Pin. When this pin voltage is low, the

 

chip is in shutdown mode.

 

 

 

 

14

 

14

OVP

The Over Voltage Protection Pin. The PWM converter turns off when

 

The voltage of the pin goes higher than 1.2V.

 

 

 

 

15

 

15

VCC

The Power Supply Pin of the Chip. For good bypass, a low ESR

 

Capacitor is required.

 

 

 

 

16

 

16

GND

The Ground Pin. The exposed pad must be soldered to a large PCB

 

Exposed Pad (17)

And connected to GND for maximum power dissipation.

 

 

 

DS8452-02C

March 2008

 

www.richtek.com

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