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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
Pin
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
-0.3 to +6.0
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V
°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.)
A
°C
Thermal Information
Parameter Package Symbol Max Unit
Thermal Resistance (Junction to Case)
Thermal Resistance (Junction to Environment)
QFN4x4-24
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
I = 190*1.2V/R
I = 190*1.2V/R
I = 190*1.2V/R
, R
ISET
ISET
ISET
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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Typical Performance Characteristics
(@TA = +25°C, VIN = ENA = 12V, R
= 10kΩ, L = 22µH, FSW = 500kHz, 10x6 LEDs, unless otherwise specified.)
SET
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PAM2846
PAM2846
Document number: DSxxxxx Rev. 1 - 2
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Typical Performance Characteristics (cont.)
(@TA = +25°C, VIN = ENA = 12V, R
= 10kΩ, L = 22µH, FSW = 500kHz, 10x6 LEDs, unless otherwise specified.)
SET
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PAM2846
PAM2846
Document number: DSxxxxx Rev. 1 - 2
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Typical Performance Characteristics (cont.)
(@TA = +25°C, VIN = ENA = 12V, R
= 10kΩ, L = 22µH, FSW = 500kHz, 10x6 LEDs, unless otherwise specified.)
SET
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PAM2846
PAM2846
Document number: DSxxxxx Rev. 1 - 2
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PAM2846
Application Information
The inductance, peak current rating, series resistance, and physical size should all be considered when selecting an inductor. These factors
affect the converter's operating mode, efficiency, maximum output load capability, transient response time, output voltage ripple, and cost.
The maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. Very high inductance
minimizes the current ripple, and therefore reduces the peak current, which decreases core losses in the inductor and I
power path. However, large inductor values also require more energy storage and more turns of wire, which increases physical size and I
copper losses in the inductor. Low inductor values decrease the physical size, but increase the current ripple and peak current. Finding the best
inductor involves the compromises among circuit efficiency, inductor size, and cost.
When choosing an inductor, the first step is to determine the operating mode: continuous conduction mode (CCM) or discontinuous conduction
mode (DCM). When CCM mode is chosen, the ripple current and the peak current of the inductor can be minimized. If a small-size inductor is
required, DCM mode can be chosen. In DCM mode, the inductor value and size can be minimized but the inductor ripple current and peak
current are higher than those in CCM.
Capacitor Selection
An input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2846. For good input decoupling, low ESR
(equivalent series resistance) capacitors should be used at the input. At least 2.2µF input capacitor is recommended for most applications. A
minimum output capacitor value of 10µF is recommended under normal operating conditions, while a 22µF or higher capacitor may be required
for higher power LED current. A reasonable value of the output capacitor depends on the LED current. The total output voltage ripple has two
components: the capacitive ripple caused by the charging and discharging on the output capacitor, and the ohmic ripple due to the capacitor's
equivalent series resistance. The ESR of the output capacitor i s the important parameter to determine the output voltage ripple of the converter,
so low ESR capacitors should be used at the output to reduce the output voltage ripple. The voltage rating and temperature characteristics of the
output capacitor must also be considered. So a value of 10µF, voltage rating (50V) capacitor is chosen.
Diodes Selection
PAM2846 is high switching frequency convertor, which demands high speed rectifier. It's indispensable to use a Schottky diode rated at 2A, 60V
with the PAM2846. Using a Schottky diode with a lower forward voltage drop can improve efficiency of the convertor. The voltage rating of the
diode should be greater than the output voltage.
Methods for Setting LED Current
There are three methods for setting and adjusting the LED current outlined here. The methods are:
1) RSET only
2) PWM Input at PWMD
3) Single wire logic signal at ENA
2
R losses in the entire
2
R
PAM2846
Document number: DSxxxxx Rev. 1 - 2
Figure 1. Timing Diagram for EN
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Application Information (cont.)
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PAM2846
● Method 1: LED Current Setting with External Resistor R
The most basic means of setting the LED current is connecting a resistor between R
I
= 228/ R
LED
ISET
ISET
and GND. The LED current is decided by I
ISET
Resistor.
SET
● Method 2: LED Current Setting with PWM Signal to PWM Signal to PWMD Pin
This circuit uses resistor R
PWMD pin is logic low. Average LED current is approximately equal to:
I = (t
*I)/(tON+t
ON
Also, the recommended PWM frequency is between 100Hz and 1kHz. Frequency <100Hz can cause the LEDs to blink visibly.
to set the on state current and the average LED current, then proportional to the percentage of on-time when the
ISET
)
OFF
● Method 3: LED Current Setting with Single Wire Logic to ENA Pin
When the LEDs are enabled by high level, the LED current initially goes to I
width). Each pulse reduces the LED current by 1/32, so after one pulse the LED current is 31/32*I
. Figure 1 shows a timing diagram for EN.
to I
LED
. Dimming is done by pulsing ENA low (500ns to 10 s pulse
LED
. The 32th pulse sets the LED current back
LED
Setting the Over Voltage Protection
The OVP pin is connected to the center tap of a resistive voltage divider (R1 and R2 in Typical Application diagram) from the high-voltage output.
V
OUT_LIMIT
The recommend procedure is to choose R
= VOV (1 + R2/R1)
= 300kΩ and R1 = 9.2kΩ to set V
2
OUT_LIMIT
= 40V. This OVP pin is used for over voltage protect, not
for output voltage regulate.
LED Short Protection
The PAM2846 uses LED_OVP function to protect devices when one or more LED(s) is/are shorted.
= V
V
Normally V
LED
LED
make sure all LED pins’ voltage is less then 5V. With this function V
– Vf * N
OUT
is around 0.4V and V
is decided by LED numbers. When one or more LED(s) is/are shorted, the PAM2846 will clamp V
OUT
will be clamped at (5V + Vf*N
OUT
MIN
).
OUT
to
Note:
V
V
: LED pin voltage
LED
: Output voltage
OUT
Vf: LED forward voltage
N
: The minimum LED numbers among all strings.
MIN
LED Open Protection
The control loop is related to all six LED sinks. When one or more LED(s) is/are opened, the sink will have no current and the device will work in
unstable open loop state. The V
PAM2846
Document number: DSxxxxx Rev. 1 - 2
voltage will be limited by external resistor divider or 5V + Vf*N
OUT
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, whichever is lower.
MIN
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PAM2846
Application Information (cont.)
PCB Layout Guidelines
Careful PCB layout is important for proper operation. Use the following guidelines for good PCB layout:
1) Minimize the area of the high current switching loop of the rectifier diode and output capacitor to avoid excessive switching noise.
2) Connect high-current input and output components with short and wide connections. The high-current input loop goes from the positive
terminal of the input capacitor to the inductor, to the SW pin. The high-current output loop is from the positive terminal of the input capacitor
through the inductor, rectifier diode, and positive terminal of the output capacitors, reconnecting between the output capacitor and input
capacitor ground terminals. Avoid using vias in the high-current paths. If vias are unavoidable, use multiple vias in parallel to reduce
resistance and inductance.
3) Create a ground island (PGND) consisting of the input and output capacitor ground and PGND pin. Connect all these together with short, wide
traces or a small ground plane. Maximizing the width of the power ground traces improves efficiency and reduces output-voltage ripple and
noise spikes. Create an analog ground island (GND) consisting of the output voltage detection-divider ground connection, the I
connections, V
connecting the GND pins directly to the exposed backside pad. Make sure no other connections between these separate ground planes.
4) Place the output voltage setting-divider resistors as close to the OVP pin as possible. The divider's center trace should be kept short. Avoid
running the sensing traces near SW Pin.
5) Place the VIN pin bypass capacitor as close to the device as possible. The ground connection of the VIN bypass capacitor should be
connected directly to GND pins with a wide trace.
6) Minimize the size of the SW node while keeping it wide and short. Keep the SW node away from the feedback node and ground. If possible,
avoid running the SW node from one side of the PCB to the other.
7) Refer to the PAM2846 Evaluation board for an example of proper board layout.
-5V and VCC-driver capacitor connections, and the device's exposed backside pad. Connect the GND and PGND islands by
CC
resistor
SET
PAM2846
Document number: DSxxxxx Rev. 1 - 2
PAM2846 Evaluation Board
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Ordering Information
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PAM2846
Part Number Marking Package Type Standard Package
PAM2846KR
P2846
XXXYW
QFN4x4 3000 Units/ Tape & Reel
Marking Information
PAM2846
Document number: DSxxxxx Rev. 1 - 2
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Package Outline Dimensions (All dimensions in mm.)
QFN4x4-24
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PAM2846
PAM2846
Document number: DSxxxxx Rev. 1 - 2
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PAM2846
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
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website, harmless against all damages.
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel.
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indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.
Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings
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This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
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use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
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Copyright © 2012, Diodes Incorporated
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IMPORTANT NOTICE
LIFE SUPPORT
PAM2846
Document number: DSxxxxx Rev. 1 - 2
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