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PDF PAM2845 Data sheet ( Hoja de datos )
| Número de pieza | PAM2845 | |
| Descripción | 40V High Power Boost Convertor | |
| Fabricantes | Power Analog Micoelectronics | |
| Logotipo |  |
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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
1 page  
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
Input Voltage Range
ENA=high (no switching)
Fsel=high (1.6M switching frequency)
Quiescent Current
Fsel =high (1M switching frequency)
Fsel =high (500k switching frequency)
ENA=low
LDO Stage
Vcc_5V
Vcc_5V current_limit
Vcc_5V UVLO Threshold
Vcc_5V UVLO Hysteresis
Vcc_driver
Vcc_driver current_limit
Vcc_driver UVLO Threshold
Vcc_driver UVLO Hysteresis
Boost Stage
Feedback Voltage
Switch Rdson
Vcc_5V=5V
Switch Current Limit
Switch Leakage Current
www.DataSheet4U.com
Switching Frequency
Fsel =Vcc_5V
Fsel =Open
Fsel =Gnd
Fsel =Vcc_5V
Minimums Duty Cycle
Fsel =Open
Fsel =Gnd
Maximums Duty Cycle
VC Source Current
VC Sink Current
Min
4.8
4.5
14
3.9
4.5
14
3.9
Typ Max Units
28 V
12
10
mA
6
3
5 20 μA
5 5.5 V
74 90 mA
4.2 4.5
V
70 mV
5 5.5 V
74 90 mA
4.2 4.5
V
70 mV
1.2 V
0.2 Ω
2.5 A
1 μA
1.6 MHz
1.0 MHz
500 kHz
20 %
10 %
5%
90 %
60 μA
60 μA
Power Analog Microelectronics,Inc
www.poweranalog.com
5
08/2008 Rev 1.0
5 Page 
PAM2845
40V High Power Boost Convertor
with 6 Channel Constant Current Source
Method 1: LED Current Setting with External
Resistor RISET
The most basic means of setting the LED current
is connecting a resistor between RISET and GND.
The LED current is decided by ISET Resistor.
I =LED 228/ RISET
Method 2: LED Current Setting Using PWM
Signal to PWMD Pin
This circuit uses resistor RISET to set the on state
current and the average LED current, then
proportional to the percentage of on-time when
the PWMD pin is logic low. Average LED current is
approximately equal to:
I= (ton*I)/ (ton+ t )off
Also, the recommended PWM frequency is
between 100Hz and 1kHz. Frequency <100Hz can
cause the LEDs to blink visibly.
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 ILED. Dimming is done
by pulsing ENA low (500ns to 10μs pulse width).
Each pulse reduces the LED current by 1/32, so
after one pulse the LED current is 31/32*I .LED The
32th pulse sets the LED current back to I .LED
Figure 1 shows a timing diagram for EN.
wwwS.DeatttaiSnhgeetth4Ue.cOomutput Voltage
The FB pin is connected to the center tap of a
resistive voltage divider (R1 and R2 in Figure 1)
from the high-voltage output.
V =OUT V (FB 1+R2/R1)
The recommend procedure is to choose
R2=300kΩ and R1=9.2kΩ to set VOUT =MAX 40V.
Generally the Vout must be higher than total LED
voltage. For 10-LED application, R1=9.1kΩ,
R2=270kΩ, Vout=36.8V, higher than V =LED 33V.
One or more of the LED1-6 pins could be floating
if not used because the PAM2845 uses external
resistor to set the output voltage. One or more
LEDx pins floating is just like change of output
loadings.
LED Short Protection
The PAM2845 uses LED FB function to protect
devices when one or more LED(s) is/are shorted.
VLED = VOUT – Vf N
Normally VLED is around 0.4V and VOUT is decided
by LED numbers. When one or more LED(s)
is/are shorted, the PAM2845 will clamp VOUT to
make sure all LED pins’ voltage is less then 5V.
With this function VOUT will be clamped at
(5V+VfN )MIN .
Note:
V :LED LED pin voltage
V :OUT Output voltage
Vf: LED forward voltage
N :MIN The minimum LED
strings.
numbers
among
all
Power Analog Microelectronics,Inc
www.poweranalog.com
11
08/2008 Rev 1.0
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet PAM2845.PDF ] | |
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