Diodes PAM2846 User Manual

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Description

The PAM2846 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 PAM2846 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. The

device is able to adapt to different numbers of LEDs in each string or

different forward voltage for different types of LEDs and keep the

string current constant.

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

open or short. The limit voltage of over voltage protection is

adjustable by changing the feedback resistor ratio. The PAM2846 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 PAM2846 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 1.6 MHz

according to the application requirements.

Features

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PAM2846

INTEGRATED 6 STRING LED BOOST TYPE DRIVER

Pin Assignments

Applications

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

Handy Terminals, and Avionics Displays Panels

 LED Lighting Devices

 Six Constant-Current Output Channels

 Parallel Channels Allow Higher Current per LED String

 Maximum 40V Continuous Voltage Output Limit for Each

Channel

 Self-adaptive V

 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

 Low 400mV Feedback Voltage at Full Current Improves

Efficiency

 Allows Digital PWM and Analog Dimming

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

 Independent Dimming and Shutdown Control of the LED Driver

 Open LED Protection: Adjustable Clamp Voltage

 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

to Fit Different LED Number

OUT

PAM2846

Document number: DSxxxxx Rev. 1 - 2

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Typical Applications Circuit

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PAM2846

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

PAM2846

Document number: DSxxxxx Rev. 1 - 2

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

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Function

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Functional Block Diagram

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PAM2846

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

PAM2846

Document number: DSxxxxx Rev. 1 - 2

SEL

, OVP, I

SET

= +25°C, unless otherwise specified.)

A

-0.3 to +6.0

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°C

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PAM2846

Recommended Operating Conditions (@T

Parameter Rating Unit

Supply Voltage Range 4.8 to 28V V

Junction Temperature Range -40 to +150

Ambient Temperature Range -40 to +85

= +25°C, unless otherwise specified.)

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Thermal Information

Parameter Package Symbol Max Unit

Thermal Resistance (Junction to Case)

Thermal Resistance (Junction to Environment)

QFN4x4-24

θ

JC

θ

JA

12

30

°C/W

Electrical Characteristics

(@TA = +25°C, VIN = ENA = 12V, R

Parameter Test Conditions Min Typ Max Units

Input Voltage Range 4.8 28 V

Quiescent Current

VDD_5V No switching 4.7 5.0 5.5 V

VDD_5V Current Limit No switching 14 74 90 mA

VDD_5V UVLO Threshold No switching 3.9 4.2 4.5 V

VDD_5V UVLO Hysteresis No switching 70 mV

VDD_Driver No switching 4.7 5.0 5.5 V

VDD_Driver Current_Limit No switching 14 74 90 mA

VDD_Driver UVLO Threshold No switching 3.9 4.2 4.5 V

VDD_Driver UVLO Hysteresis No switching 70 mV

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

PAM2846

Document number: DSxxxxx Rev. 1 - 2

= 10kΩ, L = 22µH, unless otherwise specified.)

SET

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

LDO Stage

Boost Stage

V

_5V = 5V

CC

= VCC_5V

F

SEL

F

= Open

SEL

F

= GND

SEL

= VCC_5V

F

SEL

F

= Open

SEL

F

= GND

SEL

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10

6

3

0.2 Ω

1.6 MHz

1.0 MHz

500 kHz

20 %

10 %

5 %

mA

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PAM2846

Electrical Characteristics (cont.)

(@TA = +25°C, VIN = ENA = 12V, R

Parameter Test Conditions Min Typ Max Units

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

Overvoltage Threshold 1.2 V

Overvoltage Hysteresis 80 mV

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 Single Wire Dimming Low Level 0.5 µs

EN Max Pulse Width Single Wire Dimming Low Level 10 µs

EN Off Delay Single Wire Dimming Low Level 200 µs

PAM2846

Document number: DSxxxxx Rev. 1 - 2

= 10kΩ, L = 22µH, unless otherwise specified.)

SET

LED Controller Stage

I = 190*1.2V/R

, R

ISET

= 7.68k

ISET

, R

= 11.3k

ISET

, R

= 22.6k

ISET

Fault Protection

Control Interface

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30 mA

20 mA

10 mA

I/32 I mA

V

CC

_5V -0.5

V

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