|
|
PDF LM2756 Data sheet ( Hoja de datos )
| Número de pieza | LM2756 | |
| Descripción | Multi-Display Inductorless LED Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LM2756 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
|
No Preview Available !
December 5, 2007
LM2756
Multi-Display Inductorless LED Driver with 32 Exponential
Dimmingwww.datasheet4u.com Steps in micro SMD
General Description
The LM2756 is a highly integrated, switched-capacitor, multi-
display LED driver that can drive up to 8 LEDs in parallel with
a total output current of 180mA. Regulated internal current
sources deliver excellent current and brightness matching in
all LEDs.
The LED driver current sinks are split into three independently
controlled groups. The primary group (Group A) can be con-
figured to drive four, five or six LEDs for use in the main phone
display, while the secondary group (Group B) can be config-
ured to drive one, two or three LEDs for driving secondary
displays, keypads and/or indicator LEDs. An additional driver,
D1C, is provided for additional indicator lighting functions.
The device provides excellent efficiency without the use of an
inductor by operating the charge pump in a gain of 3/2 or in
Pass-Mode. The proper gain for maintaining current regula-
tion is chosen, based on LED forward voltage, so that effi-
ciency is maximized over the input voltage range.
The LM2756 is available in National’s tiny 20-bump, 0.4mm
pitch, thin micro SMD package.
Features
■ Drives up to 8 LEDs with up to 30mA of Diode Current
Each
■ 32 Exponential Dimming Steps with 800:1 Dimming Ratio
for Group A (Up to 6 LEDs)
■ 8 Linear Dimming States for Groups B (Up to 3 LEDs) and
D1C (1 LED)
■ Programmable Auto-Dimming Function
■ 3 Independently Controlled LED Groups Via I2C
Compatible Interface
■ Up to 90% Efficiency
■ Total Solution Size < 21mm2
■ Low Profile 20 Bump micro SMD Package
(1.615mm × 2.015mm × 0.6mm)
■ 0.4% Accurate Current Matching
■ Internal Soft-Start Limits Inrush Current
■ True Shutdown Isolation for LED’s
■ Wide Input Voltage Range (2.7V to 5.5V)
■ Active High Hardware Enable
Applications
■ Dual Display LCD Backlighting for Portable Applications
■ Large Format LCD Backlighting
■ Display Backlighting with Indicator Light
Typical Application Circuit
© 2007 National Semiconductor Corporation 300097
30009701
www.national.com
1 page  
Note 10: The maximum total output current for the LM2756 should be limited to 180mA. The total output current can be split among any of the three Groups
(IDxA = IDxB = IDxC = 30mA Max.). Under maximum output current conditions, special attention must be given to input voltage and LED forward voltage to ensure
proper current regulation. See the Maximum Output Current section of the datasheet for more information.
Note 11: For the two groups of current sinks on a part (GroupA and GroupB), the following are determined: the maximum sink current in the group (MAX), the
minimum sink current in the group (MIN), and the average sink current of the group (AVG). For each group, two matching numbers are calculated: (MAX-AVG)/
AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the matching figure for the Group. The matching figure for a given part is
considered to be the highest matching figure of the two Groups. The typical specification provided is the most likely norm of the matching figure for all parts.
Note 12: For each Dxx pin, headroom voltage is the voltage across the internal current sink connected to that pin. For Group A, B, and C current sinks, VHRx =
VOUT -VLED. If headroom voltage requirement is not met, LED current regulation will be compromised.
Note 13: SCL and SDIO should be glitch-free in order for proper brightness control to be realized.
wwNwot.ed1a4ta: sShCeLeist4teus.cteodmwith a 50% duty-cycle clock.
Block Diagram
30009703
5 www.national.com
5 Page 
Internal Hex Address: 0xA0 (GroupA), 0xB0 (GroupB),
0xC0 (GroupC)
Note: DxA4-DxA0, D53, D62: Sets Brightness for DxA pins (GroupA).
11111=Fullscale
DxB2-DxB0: Sets Brightness for DxB pins (GroupB). 111=Fullscale
DxC2-DxC0: Sets Brightness for D1C pin. 111 = Fullscale
Full-Scale Current set externally by the following equation:
IDxx = 189 × 1.25V / RSET
wwBwr.diagtahshtenete4us.csomLevel Control Table
(GroupA)
Brightness Code (hex)
Perceived Brightness
Level (%)
00 0.125
01 0.313
02 0.625
03 1
04 1.125
05 1.313
06 1.688
07 2.063
08 2.438
09 2.813
0A 3.125
0B 3.75
0C 4.375
0D 5.25
0E 6.25
0F 7.5
10 8.75
11 10
12 12.5
13 15
14 16.875
15 18.75
16 22.5
17 26.25
18 31.25
19 37.5
1A 43.75
1B 52.5
1C 61.25
1D 70
1E 87.5
1F 100
GroupB and GroupC Brightness Levels (% of Full-Scale) =
10%, 20%, 30%, 40%, 50%, 60%, 70%, 100%
30009735
FIGURE 7. Ramp Step Time Register Description
Internal Hex Address: 20h
Note: RS1-RS0: Sets Brightness Ramp Step Time. The Brightness ramp
settings only affect GroupA current sinks. ('00' = 100µs, '01' = 25ms,
'10' = 50ms, '11' = 100ms).
30009739
FIGURE 8. VF Monitor Delay Register Description
Internal Hex Address: 60h
Note: VF1-VF0: Sets the Gain Transition Delay Time. The VF Monitor Delay
can be set to four different delay times. ('00' (Default) = 3-6msec., '01'
= 1.5-3msec., '10' = 0.4-0.8msec., '11' = 60-90µsec.).
Application Information
LED CONFIGURATIONS
The LM2756 has a total of 8 current sinks capable of sinking
180mA of total diode current. These 8 current sinks are con-
figured to operate in three independently controlled lighting
regions. GroupA has four dedicated current sinks, while
GroupB and GroupC each have one. To add greater lighting
flexibility, the LM2756 has two additional drivers (D53 and
D62) that can be assigned to either GroupA or GroupB
through a setting in the general purpose register.
At start-up, the default condition is four LEDs in GroupA, three
LEDs in GroupB and a single LED in GroupC (NOTE: GroupC
only consists of a single current sink (D1C) under any con-
figuration). Bits 53A and 62A in the general purpose register
control where current sinks D53 and D62 are assigned. By
writing a '1' to the 53A or 62A bits, D53 and D62 become as-
signed to the GroupA lighting region. Writing a '0' to these bits
assigns D53 and D62 to the GroupB lighting region. With this
added flexibility, the LM2756 is capable of supporting appli-
cations requiring 4, 5, or 6 LEDs for main display lighting,
while still providing additional current sinks that can be used
for a wide variety of lighting functions.
SETTING LED CURRENT
The current through the LEDs connected to DxA and DxB can
be set to a desired level simply by connecting an appropriately
sized resistor (RSET) between the ISET pin of the LM2756 and
GND. The DxA, DxB and D1C LED currents are proportional
to the current that flows out of the ISET pin and are a factor of
189 times greater than the ISET current. The feedback loops
of the internal amplifiers set the voltage of the ISET pin to 1.25V
(typ.). The statements above are simplified in the equations
below:
IDxA/B/C (A)= 189 × (VISET / RSET)
RSET (Ω)= 189 × (1.25V / IDxA/B/C)
Once the desired RSET value has been chosen, the LM2756
has the ability to internally dim the LEDs using analog current
scaling. The analog current level is set through the I2C com-
patible interface. LEDs connected to GroupA can be dimmed
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM2756.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LM2750 | Low Noise/ 5.0V Regulated Switched Capacitor Voltage Converter | National Semiconductor |
| LM2750 | LM2750 Low-Noise Switched-Capacitor Boost Regulator (Rev. M) |  Texas Instruments |
| LM2750LD-5.0 | Low Noise/ 5.0V Regulated Switched Capacitor Voltage Converter | National Semiconductor |
| LM2750LDX-5.0 | Low Noise/ 5.0V Regulated Switched Capacitor Voltage Converter | National Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |