Diodes PAM2845 User Manual

A

f

Product Line o

Diodes Incorporated

PAM2845

40V HIGH POWER BOOST CONVERTER with 6 CHANNEL CONSTANT CURRENT SOURCE

Description

The PAM2845 is a high-efficiency boost type LED driver. It is

designed for large LCD panel that employs an array of LEDs as back

light source.

The PAM2845 employs a current-mode step-up converter that drives

six parallel strings of LEDs connected in multiple series. This built-in

string current-control circuit achieves ±1% typical current matching

between strings, which ensures even brightness for all LEDs.

Separate feedback loops limit the output voltage if one or more LEDs

open or short. The PAM2845 has features cycle-by-cycle current limit

to provide consistent operation and soft-start capability. A thermal-

shutdown circuit provides another level of protection.

The PAM2845 has a wide +4.8V to +28V input voltage range and

provides adjustable full-scale LED current. The switching frequency of

this device can be selected among 500kHz, 1MHz and 1.6MHz

according to the application requirements.

Features

• Six Constant-Current Output Channels

• Parallel Channels Allow Higher Current per LED String

• Maximum 40V Continuous Voltage Output Limit for Each

Channel

• Adjustable Constant Output Voltage

• Adjustable Constant LED Current

• Drives 10 or more LEDs Each String as Long as the String

Voltage Less Than 40V

• Internal 2.5A Power MOSFET

• Allows Digital PWM and Analog Dimming

• Wide (100:1) PWM Dimming Range without Color Shift

• Independent Dimming and Shutdown Control of the LED Driver

• ±1% Typical Current Matching between Strings

• Short LED Protection

• 3 Frequencies Selection: 1.6MHz/1MHz/500kHz

• Wide Input Voltage Range: 4.8V to 28V

• Over Temperature Protection

• Available in 24-pin 4mmx4mm QFN Package

• Pb-free Package

Pin Assignments

Applications

• White or RGB Backlighting for LCD, TV, LCD Monitor, Notebook,

Handy Terminals, and Avionics Displays Panels

• LED Lighting Devices

PAM2845

Document number: DSxxxxx Rev. 1 - 2

1 of 14

www.diodes.com

October 2012

A

f

Typical Applications Circuit

Product Line o

Diodes Incorporated

PAM2845

Pin Descriptions

Number

1 VIN Supply Input

2

3 GND Ground

4 ENA Enable Input

5 PWMD PWM Dimming Control

6 LED1 LED1 Cathode Terminal

7 LED2 LED2 Cathode Terminal

8 LED3 LED3 Cathode Terminal

9 GND Ground

10 GND Ground

11 LED4 LED4 Cathode Terminal

12 LED5 LED5 Cathode Terminal

13 LED6 LED6 Cathode Terminal

14

15

16 VC Boost Stage Compensation Pin

17

18 FB Feedback

19 PGND Power Ground

20 PGND Power Ground

21 PGND Power Ground

22 SW Power MOS Drain

23 SW Power MOS Drain

24 SW Power MOS Drain

Pin Name

QFN4x4-24

V

-Driver

CC

I

SET

V

-5V

CC

F

SEL

5V Linear Regulator Output for Power MOS Driver

LED Current Adjustment Pin

5V Linear Regulator

Oscillator Frequency Selection Pin

Function

PAM2845

Document number: DSxxxxx Rev. 1 - 2

2 of 14

www.diodes.com

October 2012

A

f

Functional Block Diagram

Product Line o

Diodes Incorporated

PAM2845

Absolute Maximum Ratings (@T

These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground.

Parameter Rating Unit

VIN, ENA -0.3 to +30

SW, LED -0.3 to +40

VCC -5V, VCC–Driver, VC

PWMD. F

Storage Temperature -65 to +170

Maximum Junction Temperature 170

Soldering Temperature 300, 5sec

PAM2845

Document number: DSxxxxx Rev. 1 - 2

SEL

, FB, I

SET

= +25°C, unless otherwise specified.)

A

-0.3 to +6.0

3 of 14

www.diodes.com

V

°C

October 2012

A

f

Product Line o

Diodes Incorporated

PAM2845

Recommended Operating Conditions (@T

Parameter Rating Unit

Supply Voltage Range 4.8 to 28 V

Operation Temperature Range -40 to +85

Junction Temperature Range -40 to +150

= +25°C, unless otherwise specified.)

A

°C

Thermal Information

Parameter Package Symbol Max Unit

Thermal Resistance (Junction to Case)

Thermal Resistance (Junction to Ambient)

Electrical Characteristics (@T

Parameter Test Conditions Min Typ Max Units

Input Voltage Range 4.8 28 V

Quiescent Current

VDD_5V 4.5 5 5.5 V

VDD_5V Current Limit 14 74 90 mA

VDD_5V UVLO Threshold 3.9 4.2 4.5 V

VDD_5V UVLO Hysteresis 40 mV

VDD_Driver 4.5 5 5.5 V

VDD_Driver Current_Limit 14 74 90 mA

VDD_Driver UVLO Threshold 3.9 4.2 4.5 V

VDD_Driver UVLO Hysteresis 70 mV

Feedback Voltage 1.2 V

Switch RDS(ON)

Switch Current Limit 2.5 A

Switch Leakage Current 1 µA

Switching Frequency

Minimum Duty Cycle

Maximum Duty Cycle 90 %

VC Source Current 60 µA

VC Sink Current 60 µA

PAM2845

Document number: DSxxxxx Rev. 1 - 2

QFN4x4-24

= +25°C, VIN = ENA = 12V, L = 22µH, R

A

E NA = high (no switching frequency) 1 2

F

= high (1.6M switching frequency)

SEL

F

= high (1M switching frequency)

SEL

F

= high (500k switching frequency)

SEL

E NA = low 5 20 µA

V

_5V = 5V

CC

F

= VCC_5V

SEL

F

= Open

SEL

F

= GND

SEL

= VCC_5V

F

SEL

F

= Open

SEL

F

= GND

SEL

www.diodes.com

θ

JC

θ

JA

LDO Stage

Boost Stage

4 of 14

12

30

= 10kΩ, unless otherwise specified.)

SET

°C/W

10

6

3

0.2 Ω

1.6 MHz

1.0 MHz

500 kHz

20 %

10 %

5 %

October 2012

mA

A

f

Product Line o

Diodes Incorporated

PAM2845

Electrical Characteristics (cont.) (@T

Parameter Test Conditions Min Typ Max Units

I = 190*1.2V/R

Full-Scale LED_Output Current

LED Current Matching -3 1 +3 %

ISET Voltage 1.2 V

Minimums LED Voltage 400 mV

Analog Dimming Range

PWM Dimming Frequency 100 1k Hz

LED_Overvoltage Threshold 4.6 4.9 5.1 V

LED_Overvoltage Hysteresis 1 V

Thermal-Shutdown 150 °C

Thermal-Shutdown Hysteresis 30 °C

EN High 1.5 V

EN Low 0.4 V

PWMD High 1.5 V

PWMD Low 0.4 V

FSEL High

FSEL Midlevel 1 2 V

FSEL Low 0.5 V

EN Min Pulse Width 0.5 µs

EN Max Pulse Width 10 µs

EN Off Delay 10 µs

PAM2845

Document number: DSxxxxx Rev. 1 - 2

I = 190*1.2V/R

= +25°C, VIN = ENA = 12V, L = 22µH, R

A

LED Controller Stage

, R

ISET

= 7.68k

ISET

, R

= 11.3k

ISET

, R

= 22.6k

ISET

Fault Protection

Control Interface

5 of 14

www.diodes.com

= 10kΩ, unless otherwise specified.)

SET

30 mA

20 mA

10 mA

I/32 I mA

_5V -

V

CC

0.5

V

October 2012