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PAM2845 Schematic ( PDF Datasheet ) - Power Analog Micoelectronics

Teilenummer PAM2845
Beschreibung 40V High Power Boost Convertor
Hersteller Power Analog Micoelectronics
Logo Power Analog Micoelectronics Logo 




Gesamt 14 Seiten
PAM2845 Datasheet, Funktion
PAM2845
40V High Power Boost Convertor
with 6 Channel Constant Current Source
Features
n Six Constant-Current Output Channels
n Parallel Channels Allow Higher Current
per LED String
n Maximum 40V Continuous Voltage Output
Limit for Each Channel
n Adjustable Constant Output Voltage
n Adjustable Constant LED Current
n Drives 10 or more LEDs Each String as Long
as the String Voltage Less Than 40V
n Internal 2.5A Power MOSFET
n Allows Digital PWM and Analog Dimming
n Wide (100:1) PWM Dimming Range without
Color Shift
n Independent Dimming and Shutdown
Control of the LED Driver
n ±1% Typical Current Matching between Strings
n Short LED Protection
n 3 Frequencies Selection: 1.6MHz/1MHz/500kHz
n Wide Input Voltage Range: 4.8V to 28V
n Over Temperature Protection
n Available in 24-pin 4mmx4mm QFN Package
n Pb-free Package
Applications
n White or RGB Backlighting for LCD
TV, LCD Monitor, Notebook, Handy
Terminals, and Avionics Displays Panels
n LED Lighting Devices
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.
Typical Application
www.DataSheet4U.com
VIN: 4.8V to 28V
10μF
22μH
L
100nF
PWMD
Fsel
ENA
PWMD
Fsel
VIN
SW
SW
SW
FB
PAM2845
VC
Vcc-5V
Vcc-driver
1μF 1μF
Iset
10kΩ
LED1
LED2
LED3
LED4
LED5
LED6
GND
PGND PGND PGND
3A/40V
R1
270kΩ
R2
9.1kΩ
10μF
Total 10
LEDs
per
string
Power Analog Microelectronics,Inc
www.poweranalog.com
1
08/2008 Rev 1.0






PAM2845 Datasheet, Funktion
PAM2845
40V High Power Boost Convertor
with 6 Channel Constant Current Source
Electrical Characteristic
TA=25°C, V =IN ENA=12V, L=22μH, Rset=10kΩ,unless otherwise noted.
PARAMETER
Conditions
Min
LED Controller Stage
I=190*1.2V/Riset, Riset=7.68k
Full-Scale LED_Output Current
I=190*1.2V/Riset, Riset=11.3k
I=190*1.2V/Riset, Riset=22.6k
LED current matching
-3
Iset Voltage
Minimums LED voltage
Analog Dimming Range
I=190*1.2V /Riset
I/32
PWM Dimming Frequency
100
Fault Protection
LED_ Overvoltage Threshold
4.6
LED_ Overvoltage Hysteresis
Thermal-Shutdown
Thermal-Shutdown Hysteresis
Controll Interface
EN High
1.5
EN Low
PWMD High
1.5
PWMD Low
Fsel High
Vcc_5V-0.5
Fsel Midlevel
www.DataSheet4U.com
Fsel Low
1
EN Min pulse width
0.5
EN Max pulse width
EN off delay
Typ
30
20
10
1
1.2
400
4.9
1
150
30
100
Max Units
mA
mA
mA
+3 %
V
mV
I mA
1k Hz
5.1 V
V
°C
°C
V
0.4 V
V
0.4 V
V
2V
0.5 V
μs
10 μs
μs
Power Analog Microelectronics,Inc
www.poweranalog.com
6
08/2008 Rev 1.0

6 Page









PAM2845 pdf, datenblatt
PAM2845
40V High Power Boost Convertor
with 6 Channel Constant Current Source
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
PAM2845 Evaluation Board
noise spikes. Create an analog ground island
(GND) consisting of the output voltage
detection-divider ground connection, the ISET
resistor connections, VCC-5V and VCC-driver
capacitor connections, and the device's exposed
backside pad. Connect the GND and PGND
islands by 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 PAM2845 Evaluation board for an
example of proper board layout.
www.DataSheet4U.com
Power Analog Microelectronics,Inc
www.poweranalog.com
12
08/2008 Rev 1.0

12 Page





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