Richtek RT8452GQW, RT8452GS Schematic [ru]

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

l High Voltage Capability : V

60V

l Boost or Buck-Boost Operation
l Current Mode PWM with 1MHz Switching

Frenquency

l Easy Dimming : Analog, PWM Digital or PWM

Converting to Analog with One External Capacitor

l Programmable Soft Start to Avoid Inrush Current
l Programmable Over Voltage Protection to Limit

Output Voltage

l V

Undervoltage Lockout and Thermal Shutdown

IN

l 16-Lead WDFN and SOP Packages.
l RoHS Compliant and 100% Lead (Pb)-Free

Up to 40V, V

IN

OUT

Up to

Applications

l General Industrial High Power LED Lighting
l Desk Lights and Room Lighting
l Building and Street Lighting
l 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 Commer­ cial Standard)

Note :
Richtek Green 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.
}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

VCCENOVP

GBIAS

PWMOUT

PWMOUT

PWMDIM

1
2

GATE

ISW

GND

3
4

ISP

PWMDIM

WQFN-16L 3x3

GBIAS

GATE

ISW

ISP
ISN

2
3
4
5
6
7

VCACTL

SOP-16

13141516

12

NC

11

SS

10

DCTL

17

9

ACTL

8765

VC

ISN

16

GND

15

VCC

14

OVP

13

EN

12

NC

11

SS

10

DCTL

98

DS8452-02C March 2008www.richtek.com

1

RT8452

Typical Application Circuit

V

Analog

Dimming

R1

10k

C2
3nF

R1

10k

C2
3nF

IN

5V

C3
10nF

Figure 1. Analog Dimming in Boost Configuration

V

IN

5V

C3
10nF

C4

4.5V to 40V

4.5V to 40V

PWM
Dimming control

C1

15
13

10

11

C4

C1

C5

0.5uF

9

8

1

15
13

10

8

11

1

9

Conceptual

L

10uH

RT8452

VCC
EN

ACTL
DCTL

VC
SS

GBIAS

VCC
EN

DCTL

VC
SS

GBIAS
ACTL

PWMOUT

PWMDIM

GND

L

10uH

RT8452

PWMOUT

PWMDIM

GND

2

GATE

4

ISW

6

ISP

7

ISN

14

OVP

3
5

16, Exposed Pad (17)

2

GATE

4

ISW

6

ISP

7

ISN

14

OVP

3
5

16, Exposed Pad (17)

R3

R3

C5
1uF

R5

C6
1uF

R5

R4

R4

R2

180mV

R2

180mV

V

V

OUT

OUT

V

OUT

60V MAX

V

OUT

60V MAX

Figure 2. PWM to Analog Dimming in Boost Configuration

V

OUT

V

4.5V to 40V

R1

10k

C2
3nF

5V

L

VCC
EN

ACTL
DCTL
VC

SS
GBIAS

10uH

RT8452

GATE

ISW

ISP

ISN

PWMOUT

PWMDIM

OVP

GND

16, Exposed Pad (17)

14

2
4

6
7
3

5

R3

IN

C1

15
13

9

10

8

11

C3
10nF

1

C4

C5
1uF

R5

180mV

R4

R2

V

OUT

60V MAX

Figure 3. True PWM Dimming in Boost Configuration

DS8452-02C March 2008www.richtek.com

2

Sense Pin. Connect the current

V

4.5V to 40V

IN

5V

Analog

Dimming

R1

10k

C2
3nF

C3
10nF

C1

C4

Figure 4. Analog Dimming in Buck-Boost Configuration

Functional Pin Description

15
13

9

10

8

11

1

Conceptual

RT8452

VCC
EN

ACTL
DCTL

VC
SS

GBIAS

PWMOUT

PWMDIM

GND

L

10uH

2

GATE

4

ISW

7

ISN

6

ISP

3
5
14

OVP

16, Exposed Pad (17)

R3

R5

R4

C5
1uF

R2

180mV

V

OUT

V

OUT

60V MAX

RT8452

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 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

11 11 SS

signal on DCTL pin can be averaged and converted into analog

dimming signal on the ACTL pin following the formula below.

V

= 1.2V x PWM Dimming Duty Cycle.

ACTL

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

14 14 OVP

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

chip is in shutdown mode.
The Over Voltage Protection Pin. The PWM converter turns off when
The voltage of the pin goes higher than 1.2V.

15 15 VCC

16

16

Exposed Pad (17)

DS8452-02C March 2008www.richtek.com

GND

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

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

3