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PDF LM3535 Data sheet ( Hoja de datos )
| Número de pieza | LM3535 | |
| Descripción | Multi-Display LED Driver | |
| Fabricantes | National Semiconductor | |
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LM3535
August 12, 2010
Multi-Display LED Driver with Ambient Light Sensing and
Dynamic Backlight Control Compatibility
General Description
The LM3535 is a highly integrated LED driver capable of driv-
ing 8 LEDs in parallel for large display applications. Indepen-
dent LED control allows for a subset of the 6 main display
LEDs to be selected for partial illumination applications. In
addition to the main bank of 6, the LM3535 is capable of driv-
ing an additional 2 independently controlled LEDs to support
Indicator applications.
The LED driver current sinks are split into three independently
controlled groups. The primary group can be configured to
drive up to six LEDs for use in the main phone display. Groups
B and C are provided for driving secondary displays, keypads
and indicator LEDs. All of the LED current sources can be
independently turned on and off providing flexibility to address
different application requirements.
The LM3535 provides multi-zone Ambient Light Sensing (1 or
2 ALS inputs depending on option) allowing autonomous
backlight intensity control in the event of changing ambient
light conditions. A PWM input is also provided to give the user
a means to adjust the backlight intensity dynamically based
upon the content of the display.
The LM3535 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 regu-
lation is chosen, based on LED forward voltage, so that
efficiency is maximized over the input voltage range.
The LM3535 is available in National’s tiny 20-bump, 0.4mm
pitch, thin micro SMD package.
Features
■ Drives up to 8 LEDs with up to 25mA of Diode Current
Each
■ External PWM input for Dynamic Backlight Control
■ Multi-Zone Ambient Light Sensing (ALS)
■ Dual-ALS Sensor Inputs (LM3535-2ALS only)
■ ALS Interrupt Reporting
■ Independent On/Off Control for all Current Sinks
■ 128 Exponential Dimming Steps with 600:1 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
■ Up to 90% Efficiency
■ 0.55% Accurate Current Matching
■ Internal Soft-Start Limits Inrush Current
■ True Shutdown Isolation for LEDs
■ Wide Input Voltage Range (2.7V to 5.5V)
■ Active High Hardware Enable
■ Total Solution Size < 16mm2
■ Low Profile 20 Bump micro SMD Package
(1.650mm × 2.055mm × 0.6mm)
Applications
■ Smart-Phone LED Backlighting
■ Large Format LCD Backlighting
■ General LED Lighting
Typical Application Circuit
30082468
© 2010 National Semiconductor Corporation 300824
www.DataSheet.in
Minimum Layout
30082441
www.national.com
1 page  
Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and disengages at TJ
= 125°C (typ.).
Note 4: For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale
Package (AN-1112).
Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. (MIL-STD-883 3015.7)
Note 6: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be
derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 110°C), the maximum power
dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the
following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Note 7: Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power dissipation
exists, special care must be paid to thermal dissipation issues in board design. For more information, please refer to National Semiconductor Application Note
1112: Micro SMD Wafer Level Chip Scale Package (AN-1112).
Note 8: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
Note 9: CIN, CVOUT, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
Note 10: 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 11: 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 12: SCL and SDIO should be glitch-free in order for proper brightness control to be realized.
Note 13: SCL is tested with a 50% duty-cycle clock.
Block Diagram
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30082467
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5 Page 
Circuit Description
OVERVIEW
The LM3535 is a white LED driver system based upon an
adaptive 3/2× - 1× CMOS charge pump capable of supplying
up to 200mA of total output current. With three separately
controlled Groups of constant current sinks, the LM3535 is an
ideal solution for platforms requiring a single white LED driver
IC for main display, sub display, and indicator lighting. The
tightly matched current sinks ensure uniform brightness from
the LEDs across the entire small-format display.
Each LED is configured in a common anode configuration,
with the peak drive current set to 25mA. An I2C compatible
interface is used to enable the device and vary the brightness
within the individual current sink Groups. For GroupA , 128
exponentially-spaced analog brightness control levels are
available. GroupB and GroupC have 8 linearly-spaced analog
brightness levels.
Additionally, the LM3535 provides 1 or 2 inputs (LM3535 has
1 and LM3535-2ALS has 2) for an Ambient Light Sensor to
adaptively adjust the diode current based on ambient condi-
tions, and a PWM pin to allow the diode current to be pulse
width modulated to work with a display driver utilizing dynamic
or content adjusted backlight control (DBC or CABC).
CIRCUIT COMPONENTS
Charge Pump
The input to the 3/2× - 1× charge pump is connected to the
VIN pin, and the regulated output of the charge pump is con-
nected to the VOUT pin. The recommended input voltage
range of the LM3535 is 2.7V to 5.5V. The device’s regulated
charge pump has both open loop and closed loop modes of
operation. When the device is in open loop, the voltage at
VOUT is equal to the gain times the voltage at the input. When
the device is in closed loop, the voltage at VOUT is regulated
to 4.3V (typ.). The charge pump gain transitions are actively
selected to maintain regulation based on LED forward voltage
and load requirements.
Diode Current Sinks
Matched currents are ensured with the use of tightly matched
internal devices and internal mismatch cancellation circuitry.
There are eight regulated current sinks configurable into 3
different lighting regions.
Ambient Light Sensing (ALS) and Interrupt
The LM3535 provides an Ambient Light Sensing input (2 in-
puts on LM3535-2ALS version) for use with ambient backlight
control. By connecting the anode of a photo diode / sensor to
the sensor input pins, and configuring the appropriate ALS
resistors, the LM3535 or -2ALS version, can be configured to
adjust the diode current to five unique settings, corresponding
to four adjustable light region trip points. Additionally, when
the LM3535 determines that an ambient condition has
changed, the interrupt pin, when connected to a pull-up re-
sistor will toggle to a '0' alerting the controller. See the I2C
interface section for more details regarding the register con-
figurations.
Dynamic Backlight Control Input (PWM Pin)
A PWM (Pulse Width Modulation) pin is provided on the
LM3535 to allow a display driver utilizing dynamic backlight
control (DBC), to adjust the LED brightness based on the
content. The PWM input can be turned on or off (Acknowledge
or Ignore) and the polarity can be flipped (active high or active
low) through the I2C interface. The current sinks of the
LM3535 require approximately 15µs. to reach steady-state
target current. This turn-on time sets the minimum usable
PWM pulse width for DBC/CABC.
LED Forward Voltage Monitoring
The LM3535 has the ability to switch gains (1x or 3/2x) based
on the forward voltage of the LED load. This ability to switch
gains maximizes efficiency for a given load. Forward voltage
monitoring occurs on all diode pins. At higher input voltages,
the LM3535 will operate in pass mode, allowing the VOUT
voltage to track the input voltage. As the input voltage drops,
the voltage on the Dxx pins will also drop (VDXX = VVOUT –
VLEDx). Once any of the active Dxx pins reaches a voltage
approximately equal to 130mV, the charge pump will switch
to the gain of 3/2. This switch-over ensures that the current
through the LEDs never becomes pinched off due to a lack of
headroom across the current sinks. Once a gain transition
occurs, the LM3535 will remain in the gain of 3/2 until an
I2C write to the part occurs. At that time, the LM3535 will
re-evaluate the LED conditions and select the appropri-
ate gain.
Only active Dxx pins will be monitored.
Configurable Gain Transition Delay
To optimize efficiency, the LM3535 has a user selectable gain
transition delay that allows the part to ignore short duration
input voltage drops. By default, the LM3535 will not change
gains if the input voltage dip is shorter than 3 to 6 milliseconds.
There are four selectable gain transition delay ranges (4 for
LM3535-2ALS and 3 for LM3535) available on the LM3535.
All delay ranges are set within the VF Monitor Delay Register .
Please refer to the INTERNAL REGISTERS section of this
datasheet for more information regarding the delay ranges.
Hardware Enable (HWEN)
The LM3535 has a hardware enable/reset pin (HWEN) that
allows the device to be disabled by an external controller
without requiring an I2C write command. Under normal oper-
ation, the HWEN pin should be held high (logic '1') to prevent
an unwanted reset. When the HWEN is driven low (logic '0'),
all internal control registers reset to the default states and the
part becomes disabled. Please see the Electrical Character-
istics section of the datasheet for required voltage thresholds.
I2C Compatible Interface
DATA VALIDITY
The data on SDIO line must be stable during the HIGH period
of the clock signal (SCL). In other words, state of the data line
can only be changed when SCL is LOW.
FIGURE 1. Data Validity Diagram
30082425
A pull-up resistor between the controller's VIO line and SDIO
must be greater than [ (VIO-VOL) / 3mA] to meet the VOL re-
quirement on SDIO. Using a larger pull-up resistor results in
lower switching current with slower edges, while using a
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| PDF Descargar | [ Datasheet LM3535.PDF ] | |
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