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PDF PAM2846 Data sheet ( Hoja de datos )
| Número de pieza | PAM2846 | |
| Descripción | Integrated 6 String LED Boost Type Driver | |
| Fabricantes | Power Analog Micoelectronics | |
| Logotipo |  |
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PAM2846
Integrated 6 String LED Boost Type Driver
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 Self-adaptive Vout to Fit Different LED Number
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 Low 400mV Feedback Voltage at Full
Current Improves Efficiency
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 Open LED Protection: Adjustable Clamp
Voltage
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
www.DataSheet4U.com
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
1.6MHz according to the application
requirements.
Typical Application
VIN: 4.8V to 28V
22μH
L
0-10k
100nF
PWMD
Fsel
ENA
PWMD
Fsel
VIN
SW
SW
SW
OVP
PAM2846
VC
Vcc-5V
Vcc-driver
1μ 1μ
Iset
10K
LED1
LED2
LED3
LED4
LED5
LED6
GND
PGND PGND PGND
3A/40V
R1
300k
R2
9.2k
Total 10
LEDs
per
string
Power Analog Microelectronics,Inc
www.poweranalog.com
1
07/2008 Rev 1.2
1 page  
PAM2846
Integrated 6 String LED Boost Type Driver
Electrical Characteristic
TA=25°C, VIN=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
No switching
Vcc_5V current_limit
No switching
Vcc_5V UVLO Threshold
No switching
Vcc_5V UVLO Hysteresis
Vcc_driver
No switching
No switching
Vcc_driver current_limit
No switching
Vcc_driver UVLO Threshold
Vcc_driver UVLO Hysteresis
No switching
No switching
Boost Stage
Switch Rdson
Vcc_5V=5V
Switch Current Limit
Switch Leakage Current
Fsel =Vcc_5V
Switching Frequency
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Fsel =Open
Fsel =Gnd
Minimums Duty Cycle
Fsel =Vcc_5V
Fsel =Open
Fsel =Gnd
Maximums Duty Cycle
VC Source Current
VC Sink Current
Min
4.8
4.7
14
3.9
4.7
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
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
07/2008 Rev 1.2
5 Page 
PAM2846
Integrated 6 String LED Boost Type Driver
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= (t *on I)/ (t +on 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.
Setting the Over Voltage Protection
The OVP pin is connected to the center tap of a
wwwr.eDsaitsaStihveeet4vUo.cltoamge divider (R1 and R2 in Typical
Application diagram) from the high-voltage
output.
Vout_limit=V (ov 1+R2/R1)
The recommend procedure is to choose
R2=300kΩ and R1=9.2kΩ to set Vout_l =imit 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.
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 PAM2846 will clamp VOUT to
make sure all LED pins’ voltage is less then 5V.
With this function VOUT will be clamped at
(5V+Vf*N )MIN .
Note:
V :LED LED pin voltage
V :OUT Output voltage
Vf : LED forward voltage
N :MIN The minimum LED numbers among all
strings.
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 VOUT voltage will
be limited by external resistor divider or
5V+Vf*N ,MIN whichever is lower.
Power Analog Microelectronics,Inc
www.poweranalog.com
11
07/2008 Rev 1.2
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet PAM2846.PDF ] | |
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