NSC LM3535TME

LM3535
Multi-Display LED Driver with Ambient Light Sensing and
Dynamic Backlight Control Compatibility
General Description
Features
The LM3535 is a highly integrated LED driver capable of driving 8 LEDs in parallel for large display applications. Independent 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 driving 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 regulation 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.
■ 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
30082441
Minimum Layout
30082468
© 2010 National Semiconductor Corporation
300824
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LM3535 Multi-Display LED Driver with Ambient Light Sensing and Dynamic Backlight Control
Compatibility
August 12, 2010
LM3535
Connection Diagram
20 Bump micro SMD Package
NS Package Number TMD20AAA
30082469
Pin Descriptions
Bump #s
TMD20AAA
Pin Names
Pin Descriptions
A3
VIN
A2
VOUT
Input voltage. Input range: 2.7V to 5.5V.
Charge Pump Output Voltage
A1, C1, B1, B2
C1+, C1-, C2+, C2-
Flying Capacitor Connections
D3, E3,E4, D4
D1A-D4A
LED Drivers - GroupA
C4, B4
D53, D62
LED Drivers - Configurable Current Sinks. Can be assigned to GroupA or GroupB
B3
D1B / INT
LED Driver/ ALS Interrupt - GroupB Current Sink or ALS Interrupt Pin. In ALS Interrupt
mode, a pull-up resistor is required. A '0’ means a change has occurred, while a ‘1’
means no ALS adjustment has been made.
C3
D1C / ALS
LED Driver / ALS Input - Indicator LED current sink or Ambient Light Sensor Input
D2
PWM
E1
HWEN
C2
SDIO
Serial Data Input/Output Pin
E2
SCL
Serial Clock Pin
A4
GND
(LM3535)
ALSB
(LM3535-2ALS)
D1
GND
External PWM Input - Allows the current sinks to be turned on and off at a frequency
and duty cycle externally controlled. Minimum On-Time Pulse Width = 15µsec.
Hardware Enable Pin. High = Normal Operation, Low = RESET
Ground for LM3535 or Ambient Light Sensor B for LM3535-2ALS
Ground
Ordering Information
Order Information
Package
Supplied As
LM3535TME
LM3535TMX
LM3535TME-2ALS
250 Units, Tape & Reel
3000 Units, Tape & Reel
TMD20AAA
250 Units, Tape & Reel
LM3535TMX-2ALS
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3000 Units, Tape & Reel
2
Operating Rating
2)
(Note 1, Note 2)
Input Voltage Range
LED Voltage Range
Junction Temperature (TJ) Range
Ambient Temperature (TA) Range
(Note 6)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN pin voltage
SCL, SDIO, HWEN, PWM pin
voltages
IDxx Pin Voltages
Continuous Power Dissipation
(Note 3)
Junction Temperature (TJ-MAX)
Storage Temperature Range
Maximum Lead Temperature
(Soldering)
ESD Rating(Note 5)
Human Body Model
LM3535
Absolute Maximum Ratings (Note 1, Note
-0.3V to 6.0V
-0.3V to (VIN+0.3V)
w/ 6.0V max
-0.3V to
(VVOUT+0.3V)
w/ 6.0V max
Internally Limited
2.7V to 5.5V
2.0V to 4.0V
-30°C to +110°C
-30°C to +85°C
Thermal Properties
Junction-to-Ambient Thermal
Resistance (θJA),
TMD20 Package
(Note 7)
40°C/W
150°C
-65°C to +150° C
(Note 4)
Electrical Characteristics
2.0kV
(Note 2, Note 8)
Limits in standard typeface are for TA = 25°C, and limits in boldface type apply over the full operating temperature range (-30°C to
+85°C). Unless otherwise specified: VIN = 3.6V; VHWEN = VIN; VPWM = 0V;VDxA = VDxB = VDxC = 0.4V; GroupA = GroupB = GroupC
= Fullscale Current; ENxA, ENxB, ENxC Bits = “1”; 53A, 62A Bits = "0"; C1 = C2 = CIN= COUT= 1.0µF. (Note 9)
Symbol
Parameter
Condition
Min
Typ
Max
Units
2.7V ≤ VIN ≤ 5.5V
EN1A to EN4A = '1', 53A = 62A = '0'', EN53
= EN62 = ENxB = ENxC = '0'
4 LEDs in GroupA
23.6
(-5.6%)
25
26.3
(+5.2%)
mA
(%)
2.7V ≤ VIN ≤ 5.5V
EN1A to EN4A = EN53 = EN62 = '1', 53A =
62A = '1'', ENxB = ENxC = '0'
6 LEDs in GroupA
23.2
(-7.2%)
25
26.3
(+5.2%)
mA
(%)
Output Current Regulation
GroupB
2.7V ≤ VIN ≤ 5.5V
EN1B = EN53 = EN62 = '1', 53A = 62A = '0', 23.3
(-6.8%)
ENxA = ENC = '0'
3 LEDs in GroupB
25
26.0
(+4.0%)
mA
(%)
Output Current Regulation
IDC
2.7V ≤ VIN ≤ 5.5V
ENC = '1', ENxA = ENxB = '0'
25
26.8
(+7.2%)
mA
(%)
Output Current Regulation
GroupA
IDxx
IDxx-
25
DxA
Output Current Regulation
GroupA, GroupB, and GroupC
Enabled
3.2V ≤ VIN ≤ 5.5V
VLED = 3.6V
LED Current Matching(Note 10)
2.7V ≤ VIN ≤ 5.5V
MATCH
23.8
(-4.8%)
25
DxB
mA
25
DxC
GroupA (4 LEDs)
0.25
2.40
GroupA (6 LEDs)
0.55
2.78
GroupB (3 LEDs)
0.25
2.41
%
VDxTH
VDxx 1x to 3/2x Gain Transition
Threshold
VDxA and/or VDxB Falling
130
mV
VHR
Current sink Headroom Voltage
Requirement
(Note 11)
IDxx = 95% ×IDxx (nom.)
(IDxx (nom) = 25mA)
100
mV
ROUT
Open-Loop Charge Pump Output
Resistance
Gain = 3/2
2.4
Gain = 1
0.5
3
Ω
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LM3535
Symbol
Parameter
Condition
Min
Typ
Max
Gain = 3/2, No Load
2.86
4.38
Gain = 1, No Load
1.09
2.31
Units
IQ
Quiescent Supply Current
ISB
Standby Supply Current
2.7V ≤ VIN ≤ 5.5V
HWEN = VIN, All ENx bits = "0"
1.7
4.0
µA
ISD
Shutdown Supply Current
2.7V ≤ VIN ≤ 5.5V
HWEN = 0V, All ENx bits = "0"
1.7
4.0
µA
fSW
Switching Frequency
1.33
1.56
MHz
tSTART
Start-up Time
VALS
RALS
1.10
VOUT = 90% steady state
ALS Reference Voltage Accuracy
ALS Resistor Accuracy
250
0.95
(-5%)
1
µs
1.05
(+5%)
RALSA = 9.08kΩ
-5
+5
RALSA = 5.46kΩ
-5
+5
RALSB = 9.13kΩ
-5
+5
RALSB = 5.52kΩ
-5
+5
0
0.45
1.2
VIN
VHWEN
HWEN Voltage Thresholds
2.7V ≤ VIN ≤ 5.5V
Reset
VPWM
PWM Voltage Thresholds
2.7V ≤ VIN ≤ 5.5V
Diodes Off
0
0.45
Diodes On
1.2
VIN
VOL-INT
Interrupt Output Logic Low '0'
Normal Operation
ILOAD = 3mA
mA
V
%
V
V
400
mV
I2C Compatible Interface Voltage Specifications (SCL, SDIO)
VIL
Input Logic Low '0'
2.7V ≤ VIN ≤ 5.5V
0
0.45
V
VIH
Input Logic High '1'
2.7V ≤ VIN ≤ 5.5V
1.225
VIN
V
SDIO Output Logic Low '0'
ILOAD = 3mA
400
mV
VOL
I2C Compatible Interface Timing Specifications (SCL, SDIO)(Note 12)
t1
SCL (Clock Period)
t2
Data In Setup Time to SCL High
t3
Data Out stable After SCL Low
t4
SDIO Low Setup Time to SCL Low
(Start)
t5
SDIO High Hold Time After SCL High
(Stop)
(Note 13)
2.5
µs
100
ns
0
ns
100
ns
100
ns
30082413
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation
of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions,
see the Electrical Characteristics tables.
Note 2: All voltages are with respect to the potential at the GND pins.
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4
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
30082467
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LM3535
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.).
LM3535
Typical Performance Characteristics
Unless otherwise specified: TA = 25°C; VIN = 3.6V; VHWEN = VIN; CIN= 1µF, COUT = 1µF, C1=C2= 1µF.
ILED vs Input Voltage
ILED vs Input Voltage
6 LEDs
30082420
30082419
ILED vs Brightness Code
Linear Scale
ILED vs Brightness Code
Log Scale
30082423
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30082422
6
LED Drive Efficiency vs Input Voltage
4 LEDs
30082463
30082464
Input Current vs Input Voltage
6 LEDs
LED Drive Efficiency vs Input Voltage
6 LEDs
30082460
30082424
Input Current vs Input Voltage
8 LEDs
LED Drive Efficiency vs Input Voltage
8 LEDs
30082461
30082462
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LM3535
Input Current vs Input Voltage
4 LEDs
LM3535
LED Drive Efficiency vs Input Voltage
Tri-Temp 6 LEDs
ILED Matching vs Input voltage
6 LEDs
30082421
30082426
Switching Frequency vs Input Voltage
Tri-Temp
Shutdown Current vs Input Voltage
VIO = 0V
30082431
30082427
Shutdown Current vs Input Voltage
VIO = 2.5V
Quiescent Current vs Input Voltage
1× Gain
30082428
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30082429
8
ALS Boundary Voltage vs. Boundary Code
Falling ALS Voltage
30082470
30082430
ALS Boundary Voltage vs. Boundary Code
Falling ALS Voltage (Zoom)
Diode Current vs PWM Duty Cycle
30082453
30082471
Ambient Light Sensor Response
Diode Current Ramp-Up
tSTEP = 6ms
30082454
30082458
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LM3535
Quiescent Current vs Input Voltage
3/2× Gain
LM3535
Diode Current Ramp-Down
tSTEP = 6ms
30082459
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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 conditions, 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).
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 appropriate 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.
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 connected 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.
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 operation, 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 Characteristics section of the datasheet for required voltage thresholds.
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.
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.
Ambient Light Sensing (ALS) and Interrupt
The LM3535 provides an Ambient Light Sensing input (2 inputs 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 resistor will toggle to a '0' alerting the controller. See the I2C
interface section for more details regarding the register configurations.
30082425
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
FIGURE 1. Data Validity Diagram
A pull-up resistor between the controller's VIO line and SDIO
must be greater than [ (VIO-VOL) / 3mA] to meet the VOL requirement on SDIO. Using a larger pull-up resistor results in
lower switching current with slower edges, while using a
11
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LM3535
LM3535 require approximately 15µs. to reach steady-state
target current. This turn-on time sets the minimum usable
PWM pulse width for DBC/CABC.
Circuit Description
LM3535
smaller pull-up results in higher switching currents with faster
edges.
TRANSFERRING DATA
Every byte put on the SDIO line must be eight bits long, with
the most significant bit (MSB) transferred first. Each byte of
data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated by the master. The
master releases the SDIO line (HIGH) during the acknowledge clock pulse. The LM3535 pulls down the SDIO line
during the 9th clock pulse, signifying an acknowledge. The
LM3535 generates an acknowledge after each byte is received. There is no acknowledge created after data is read
from the LM3535.
After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an eighth
bit which is a data direction bit (R/W). The LM3535 7-bit address is 38h. For the eighth bit, a “0” indicates a WRITE and
a “1” indicates a READ. The second byte selects the register
to which the data will be written. The third byte contains data
to write to the selected register.
START AND STOP CONDITIONS
START and STOP conditions classify the beginning and the
end of the I2C session. A START condition is defined as SDIO
signal transitioning from HIGH to LOW while SCL line is
HIGH. A STOP condition is defined as the SDIO transitioning
from LOW to HIGH while SCL is HIGH. The I2C master always
generates START and STOP conditions. The I2C bus is considered to be busy after a START condition and free after a
STOP condition. During data transmission, the I2C master
can generate repeated START conditions. First START and
repeated START conditions are equivalent, function-wise.
30082411
FIGURE 2. Start and Stop Conditions
30082412
FIGURE 3. Write Cycle
w = write (SDIO = "0")
r = read (SDIO = "1")
ack = acknowledge (SDIO pulled down by either master or slave)
id = chip address, 38h for LM3535
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LM3535
I2C COMPATIBLE CHIP ADDRESS
The 7-bit chip address for LM3535 is 111000, or 0x38.
INTERNAL REGISTERS OF LM3535
Register
Internal Hex
Address
Power On Value
Diode Enable
Register
0x10
0000 0000 (0x00)
Configuration
Register
0x20
0000 0000 (0x00)
Options
Register
0x30
0000 0000 (0x00)
ALS Zone
Readback
0x40
1111 0000 (0xF0)
ALS Control
Register
0x50
1 ALS
Version
0000 0011 (0x03)
2 ALS
Version
0000 0000 (0x00)
ALS Resistor
Register
0x51
0000 0000 (0x00)
ALS Select
Register
0x52
LM3535-2ALS
Only
1111 0001 (0xF1)
ALS Zone
Boundary #0
0x60
0011 0011 (0x33)
ALS Zone
Boundary #1
0x61
0110 0110 (0x66)
ALS Zone
Boundary #2
0x62
1001 1001 (0x99)
ALS Zone
Boundary #3
0x63
1100 1100 (0xCC)
ALS Brightness 0x70
Zone #1
1001 1001 (0x99)
ALS Brightness 0x71
Zone #2
1011 0110 (0xB6)
ALS Brightness 0x72
Zone #3
1100 1100 (0xCC)
ALS Brightness 0x73
Zone #4
1110 0110 (0xE6)
ALS Brightness 0x74
Zone #5
1111 1111 (0xFF)
Group A
0xA0
Brightness
Control Register
1000 0000 (0x80)
Group B
0xB0
Brightness
Control Register
1100 0000 (0xC0)
Group C
0xC0
Brightness
Control Register
1111 1000 (0xF8)
30082404
FIGURE 4. Diode Enable Register Description
Internal Hex Address: 0x10
Each ENx Bit controls the state of the corresponding current
sink. Writing a '1' to these bits enables the current sinks. Writing a '0' disables the current sinks. In order for current to begin
flowing through the BankA current sinks, the brightness codes
stored in either the BankA Brightness register or the ALS
Brightness registers (with ALS enabled) must be non-zero.
The BankA current sinks can be disabled in two different
manors. Writing '0' to the ENx bits when the current sinks are
active will disable the current sinks without going through the
ramp down sequence. Additionally, setting the BankA brightness code to '0' when the current sinks are active (ENx = '1')
does force the diode current to ramp down. All ramping behavior is tied to the BankA Brightness or ALS Brightness
Register settings. Any change in these values will cause the
LM3535 brightness state machine to ramp the diode current.
Writing a '1 to ENC, EN1B, EN62 and EN53 (when EN62 and
EN53 are assigned to BankB) by default will enable the corresponding current sinks and drive the LEDs to the current
value stored in the BankB and BankC brightness registers.
Writing a '0' to these bits immediately disables the current
sinks.
The ENC and EN1B bits are ignored if the D1C/ALS pin is
configured as an ALS input and if the D1B/INT is configured
as an interrupt flag.
30082405
FIGURE 5. Configuration Register Description
Internal Hex Address:0x20
•
•
•
•
•
•
13
PWM-EN: PWM Input Enable. Writing a '1' = Enable, and
a '0' = Ignore (default).
PWM-P: PWM Input Polarity. Writing a '0' = Active High
(default) and a '1' = Active Low.
53A: Assign D53 diode to BankA. Writing a '0' assigns D53
to BankB (default) and a '1' assigns D53 to BankA.
62A: Assign D62 diode to BankA. Writing a '0' assigns D62
to BankB (default) and a '1' assigns D62 to BankA.
ALS-ENA: Enable ALS on BankA. Writing a '1' enables
ALS control of diode current and a '0' (default) forces the
BankA current to the value stored in the BankA brightness
register. The ALS-EN bit must be set to a '1' for the ALS
block to control the BankA brightness.
ALS-ENB: Enable ALS on BankB. Writing a '1' enables
ALS control of diode current and a '0' (default) forces the
BankB current to the value stored in the BankB brightness
register. The ALS-EN bit must be set to a '1' for the ALS
block to control the BankB brightness. The ALS function
for BankB is different than bankA in that the ALS will only
enable and disable the BankB diodes depending on the
ALS zone chosen by the user. BankA utilizes the 5
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LM3535
•
•
different zone brightness registers (Addresses 0x70 to
0x74).
ALS-EN: Enables ALS monitoring. Writing a '1' enables
the ALS monitoring circuitry and a '0' disables it. This
feature can be enabled without having the current sinks or
charge pump active. The ALS value is updated in register
0x40 (ALS Zone Register)
ALSF: ALS Interrupt Enable. Writing a '1' sets the D1B/INT
pin to the ALS interrupt pin and writing a '0' (default) sets
the pin to a BankB current sink.
30082410
30082414
FIGURE 7. Brightness Control Register Description
Internal Hex Address: 0xA0 (GroupA), 0xB0 (GroupB),
0xC0 (GroupC)
Note: DxA6-DxA0: Sets Brightness for DxA pins (GroupA).
1111111=Fullscale. Code '0' in this register disables the BankA current sinks.
DxB2-DxB0: Sets Brightness for DxB pins (GroupB). 111=Fullscale
ALSZT2-ALSZT0: Sets the Brightness Zone boundary used to enable
and disable BankB diodes based upon ambient lighting conditions.
DxC2-DxC0: Sets Brightness for D1C pin. 111 = Fullscale
The BankA Current can be approximated by the following equation
where N = BRC = the decimal value stored in either the BankA Brightness Register or the five different ALS Zone Brightness Registers:
30082406
FIGURE 6. Options Register
Internal Hex Address: 0x30
•
RD0-RD2: Diode Current Ramp Down Step Time. : ‘000’
= 6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ =
6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms
• RU0-RU2: Diode Current Ramp Up Step Time. : ‘000’ =
6µs, ‘001’ = 0.77ms, ‘010’ = 1.5ms, ‘011’ = 3ms, ‘100’ =
6ms, ‘101’ = 12ms, ‘110’ = 25ms, ‘111’ = 50ms
• GT0-GT1: Gain Transition Filter. The value stored in this
register determines the filter time used to make a gain
transition in the event of an input line step. Filter Times =
‘00’ = 3-6ms, ‘01’ = 0.8-1.5ms, ‘10’ = 20µs, On
LM3535-2ALS, '11' = 1µs, On LM3535, ‘11’ = DO NOT
USE
The Ramp-Up and Ramp-Down times follow the following
equations: TRAMP = (NStart - NTarget) × Ramp-Step Time
30082418
30082409
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14
LM3535
TABLE 1. ILED vs. Brightness Register Data
BankA or
ALS
Brightness
Data
% of
ILED_MAX
BankA or ALS % of ILED_MAX BankA or ALS % of ILED_MAX BankA or ALS % of ILED_MAX
Brightness
Brightness Data
Brightness
Data
Data
0000000
0.000%
0100000
0.803%
1000000
4.078%
1100000
20.713%
0000001
0.166%
0100001
0.845%
1000001
4.290%
1100001
21.792%
0000010
0.175%
0100010
0.889%
1000010
4.514%
1100010
22.928%
0000011
0.184%
0100011
0.935%
1000011
4.749%
1100011
24.122%
0000100
0.194%
0100100
0.984%
1000100
4.996%
1100100
25.379%
0000101
0.204%
0100101
1.035%
1000101
5.257%
1100101
26.701%
0000110
0.214%
0100110
1.089%
1000110
5.531%
1100110
28.092%
0000111
0.226%
0100111
1.146%
1000111
5.819%
1100111
29.556%
0001000
0.237%
0101000
1.205%
1001000
6.122%
1101000
31.096%
0001001
0.250%
0101001
1.268%
1001001
6.441%
1101001
32.716%
0001010
0.263%
0101010
1.334%
1001010
6.776%
1101010
34.420%
0001011
0.276%
0101011
1.404%
1001011
7.129%
1101011
36.213%
0001100
0.291%
0101100
1.477%
1001100
7.501%
1101100
38.100%
0001101
0.306%
0101101
1.554%
1001101
7.892%
1101101
40.085%
0001110
0.322%
0101110
1.635%
1001110
8.303%
1101110
42.173%
0001111
0.339%
0101111
1.720%
1001111
8.735%
1101111
44.371%
0010000
0.356%
0110000
1.809%
1010000
9.191%
1110000
46.682%
0010001
0.375%
0110001
1.904%
1010001
9.669%
1110001
49.114%
0010010
0.394%
0110010
2.003%
1010010
10.173%
1110010
51.673%
0010011
0.415%
0110011
2.107%
1010011
10.703%
1110011
54.365%
0010100
0.436%
0110100
2.217%
1010100
11.261%
1110100
57.198%
0010101
0.459%
0110101
2.332%
1010101
11.847%
1110101
60.178%
0010110
0.483%
0110110
2.454%
1010110
12.465%
1110110
63.313%
0010111
0.508%
0111011
2.582%
1010111
13.114%
1110111
66.611%
0011000
0.535%
0110111
2.716%
1011000
13.797%
1111000
70.082%
0011001
0.563%
0111000
2.858%
1011001
14.516%
1111001
73.733%
0011010
0.592%
0111001
3.007%
1011010
15.272%
1111010
77.574%
0011011
0.623%
0111010
3.163%
1011011
16.068%
1111011
81.616%
0011100
0.655%
0111011
3.328%
1011100
16.905%
1111100
85.868%
0011101
0.689%
0111100
3.502%
1011101
17.786%
1111101
90.341%
0011110
0.725%
0111101
3.684%
1011110
18.713%
1111110
95.048%
0011111
0.763%
0111111
3.876%
1011111
19.687%
1111111
100.000%
Internal Hex Address: 0x40
GroupB and GroupC Brightness Levels = 2.5, 5, 7.5, 10, 12.5,
15, 17.5, 25mA
•
•
ZONE0-ZONE2: ALS Zone information: '000’ = Zone0,
‘001’ = Zone1, ‘010’ = Zone2, ‘011’ = Zone3, ‘100’ = Zone4.
Other combinations not used
FLAG: ALS Transition Flag. '1' = Transition has occurred.
'0' = No Transition. The FLAG bit is cleared once the 0x40
register has been read.
30082407
FIGURE 8. ALS Zone Register Description
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LM3535
30082465
30082417
ALS Select Register (2-ALS Version Only)
Internal Hex Address: 0x52
FIGURE 9. ALS Control / Silicon Revision Register
Description
Internal Hex Address: 0x50
•
•
FIGURE 11.
Rev0-Rev1 : Stores the Silicon Revision value. LM3535 =
'11', LM3535-2ALS = '00'
AVE2-AVE0: Sets Averaging Time for ALS sampling.
Need two to three Averaging periods to make transition
decision.‘000’ = 25ms, ‘001’ = 50ms, ‘010’ = 100ms, ‘011’
= 200ms, ‘100’ = 400ms, ‘101’ = 800ms, ‘110’ = 1.6s, ‘111’
= 3.2s
•
•
•
30082466
ALS Resistor Control Register Description
Internal Hex Address: 0x51
CP-EN: Forces the LM3535 to operate in the gain of 1.5x
exclusively when the Dx current sinks are enabled.
PASS-EN: Forces the LM3535 to operate in the 1x PassMode exclusively when the Dx current sinks are enabled.
CP-EN
PASS-EN
RESULT
0
0
Normal Operation
0
1
Pass-Mode Only
1
0
1.5x Gain Only
1
1
1.5x Gain Only
SEL1-SEL0: ALS Selection Bits. SEL1 and SEL0
determine how the ALS sensor information is processed.
'00' = Min. of ALSA and ALSB used, '01' = ALSA used and
ALSB ignored (DEFAULT), '10' = ALSB Used and ALSA
ignored, '11' = Max. of ALSA and ALSB used.
FIGURE 10.
•
•
•
R3A-R0A are valid on both the LM3535 and
LM3535-2ALS.
R3B-R0B are only valid on LM3535-2ALS.
R0-R3: Sets the internal ALS resistor value
Internal ALS Resistor Table
R3x
R2x
R1x
R0x
ALSA
Resistor
Value (Ω)
0
0
0
0
0
0
0
1
13.6k
13.65k
0
0
1
0
9.08k
9.13k
0
0
1
1
5.47k
5.52k
0
1
0
0
2.32k
2.37k
0
1
0
1
1.99k
2.05k
0
1
1
0
1.86k
1.92k
0
1
1
1
1.65k
1.70k
1
0
0
0
1.18k
1.24k
1
0
0
1
1.10k
1.15k
1
0
1
0
1.06k
1.11k
1
0
1
1
986
1.04
1
1
0
0
804
858
1
1
0
1
764
818
1
1
1
0
745
799
1
1
1
1
711
765
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30082415
ALSB
Resistor
Value (Ω)
FIGURE 12. Zone Boundary Register Descriptions
•
High Impedance
•
•
•
•
16
ZB7-ZB0: Sets Zone Boundary Lines with a Falling ALS
voltage.
0xFF w/ ALS Falling = 992.3mV (typ.).
VTRIP-LOW (typ) = [Boundary Code × 3.874mV] + 4.45mV
For boundary codes 2 to 255. Code 0 and Code1 are
mapped to equal the Code2 value.
Each zone line has approx. 5.5mV of hysteresis between
the falling and rising ALS trip points..
Zone Boundary 0 is the line between ALS Zone 0 and Zone
1. Default Code = 0x33 or approx. 200mV
Zone Boundary 1 is the line between ALS Zone 1 and Zone
2. Default Code = 0x66 or approx. 400mV
Zone Boundary 2 is the line between ALS Zone 2 and Zone
3. Default Code = 0x99 or approx. 600mV
Zone Boundary 3 is the line between ALS Zone 3 and Zone
4. Default Code = 0xCC or approx. 800mV
•
•
30082416
•
FIGURE 13. Zone Brightness Region Register
Description
•
•
B7-B0: Sets the ALS Zone Brightness Code. B7 always =
'1' (unused). Use the formula found in the BankA
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LM3535
•
Brightness Register Description (Figure 7) to set the
desired target brightness. Default values can be
overwritten
Zone0 Brightness Address = 0x70. Default = 0x99 (25) or
0.084mA
Zone1 Brightness Address = 0x71. Default = 0xB6 (54) or
0.164mA
Zone2 Brightness Address = 0x72. Default = 0xCC (76) or
1.45mA
Zone3 Brightness Address = 0x73. Default = 0xE6 (102)
or 6.17mA
Zone4 Brightness Address = 0x74. Default = 0xFF (127)
or 25mA
LM3535
Furthermore, the ambient light sensing inputs (ALSA and
ALSB(LM3535-2ALS)) features 15 internal software selectable voltage setting resistors. This allows the LM3535 the
capability of interfacing with a wide selection of ambient light
sensors. Additionally, the ALS inputs can be configured as
high impedance, thus providing for a true shutdown during low
power modes. The ALS resistors are selectable through the
ALS Resistor Select Register (see Internal ALS Resistor Table). Figure 14 shows a functional block diagram of the ambient light sensor input.
Application Information
AMBIENT LIGHT SENSING
Ambient Light Sensor Block
The LM3535 incorporates an Ambient Light Sensing interface
(ALS) which translates an analog output ambient light sensor
to a user specified brightness level. The ambient light sensing
circuit has 4 programmable boundaries (ZB0 – ZB3) which
define 5 ambient brightness zones. Each ambient brightness
zone corresponds to a programmable brightness threshold
(Z0T – Z4T).
30082442
FIGURE 14. Ambient Light Sensor Functional Block Diagram
grammed through the four (8-bit) Zone Boundary Registers.
These zone boundaries define 5 ambient brightness zones.
On start-up the 4 Zone Boundary Registers are pre-loaded
with 0x33 (51d), 0x66 (102d), 0x99 (153d), and 0xCC (204d).
The ALS input has a 1V active input voltage range which
makes the default Zone Boundaries approx. set at:
Zone Boundary 0 = 200mV
Zone Boundary 1 = 400mV
Zone Boundary 2 = 600mV
Zone Boundary 3 = 800mV
These Zone Boundary Registers are all 8-bit (readable and
writable) registers. By Default, the first zone (Z0) is defined
between 0 and 200mV, Z1’s default is defined between
200mV and 400mV, Z2 is defined between 400mV and
600mV, Z3 is defined between 600mV and 800mV, and Z4 is
defined between 800mV and 1V. The default settings for the
5 Zone Target Registers are 0x19, 0x33, 0x4C, 0x66, and
0x7F. This corresponds to LED brightness settings of 84µA,
164µA, 1.45mA, 6.17mA and 25mA of current respectively.
See Figure 15.
ALS Operation
The ambient light sensor input has a 0 to 1V operational input
voltage range. The Typical Application Circuit shows the
LM3535 with an ambient light sensor (AVAGO, APDS-9005)
and the internal ALS Resistor Select Register set to 0x40
(2.32kΩ). This circuit converts 0 to 1000 LUX light into approximately a 0 to 850mV linear output voltage. The voltage
at the active ambient light sensor input is compared against
the 8 bit values programmed into the Zone Boundary Registers (ZB0-ZB3). When the ambient light sensor output crosses one of the ZB0 – ZB3 programmed thresholds the internal
ALS circuitry will smoothly transition the LED current to the
new 7 bit brightness level as programmed into the appropriate
Zone Target Register (Z0T – Z4T, See Figure 13).
With bits [6:4] of the Configuration Register set to 1 (Bit6 =
ALS Block Enable, Bit5 = BankB ALS Enable, Bit4 = BankA
ALS Enable), the LM3535 is configured for Ambient Light
Current Control. In this mode the ambient light sensing input
(ALS) monitors the output of analog output ambient light
sensing photo diode and adjusts the LED current depending
on the ambient light. The ambient light sensing circuit has 4
configurable Ambient Light Boundaries (ZB0 – ZB3) pro-
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18
LM3535
30082443
ALS Zone to LED Brightness Mapping
FIGURE 15.
This Example still applies to the LM3535-2ALS version using
two ambient light sensors. The ALS selector block makes the
front end decision as to which sensor to use.
ALS Configuration Example
As an example, assume that the APDS-9005 is used as the
ambient light sensing photo diode with its output connected
to the ALSA input. The ALS Resistor Select Register (Address
0x51) is loaded with 0x40 which configures the ALS input for
a 2.32kΩ internal pull-down resistor (see Internal ALS Resistor Table). This gives the output of the APDS-9005 a typical
voltage swing of 0 to 875mV with a 0 to 1k LUX change in
ambient light (0.875mV/Lux). Next, the Configuration Register (Address 0x20) is programmed with 0xDC, the ALS Control Register (Address 0x50) programmed to 0x40 and the
Control Register is programmed to 0x3F . This configures the
LM3535’s ambient light sensing interface for:
• Ambient Light Current Control for BankA Enabled
• ALS circuitry Enabled
• Assigns D53 and D62 to bankA
• Sets the ALS Averaging Time to 400ms
Next, the Control Register (Address 0x10) is programmed
with 0x3F which enables the 6 LEDs via the I2C compatible
interface.
Now assume that the APDS-9005 ambient light sensor detects a 100 LUX ambient light at its input. This forces the
ambient light sensors output (and the ALS1 input) to 87.5mV
corresponding to Zone 0. Since Zone 0 points to the brightness code programmed in Zone Target Register 0 (loaded
with code 0x19), the LED current becomes:
ALS Averaging Time
The ALS Averaging Time is the time over which the Averager
block collects samples from the A/D converter and then averages them to pass to the discriminator block (see ). Ambient
light sensor samples are averaged and then further processed by the discriminator block to provide rejection of noise
and transient signals. The Averager is configurable with 8 different averaging times to provide varying amounts of noise
and transient rejection (see Figure 9). The discriminator block
algorithm has a maximum latency of two averaging cycles,
therefore the averaging time selection determines the amount
of delay that will exist between a steady state change in the
ambient light conditions and the associated change of the
backlight illumination. For example, the A/D converter samples the ALS inputs at 16kHz. If the averaging time is set to
800ms, the Averager will send the updated zone information
to the discriminator every 800ms. This zone information contains the average of approximately 12800 samples (800ms ×
16kHz). Due to the latency of 2 averaging cycles, when there
is a steady state change in the ambient light, the LED current
will begin to transition to the appropriate target value after
approximately 1600ms have elapsed.
The sign and magnitude of these Averager outputs are used
to determine whether the LM3535 should change brightness
zones. The Averager block follows the following rules to make
a zone transition:
• The Averager always begins with a Zone0 reading stored
at start-up. If the main display LEDs are active before the
ALS block is enabled, it is recommended that the ALS-EN
bit be enabled at least 3 averaging cycles times before the
ALS-ENA bit is enabled.
• The Averager will always round down to the lower zone in
the case of a non-integer zone average (1.2 rounds to 1
and 1.75 also rounds to 1). Figure 16 shows an example
of how the Averager will make the zone decisions for
different Ambient conditions.
Next assume that the ambient light changes to 500 LUX (corresponding to an ALS1 voltage of 437.5mV). This moves the
ambient light into Zone 2 which corresponds to Zone Target
Register 2 (loaded with code 0x4C) the LED current then becomes:
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LM3535
Using the diagram for the ALS block (Figure 14), Figure 18
shows the flow of information starting with the A/D, transitioning to the Averager, followed by the Discriminator. Each state
filters the previous output to help prevent unwanted zone to
zone transitions.
30082450
FIGURE 16. Averager Calculation
•
The two most current averaging samples are used to make
zone change decisions.
• To make a zone change, data from three averaging cycles
are needed. (Starting Value, First Transition, Second
Transition or Rest)
• To Increase the brightness zone, a positive Averager zone
output must be followed by a second positive Averager
output or a repeated Averager zone. ('+' to '+' or '+' to
'Rest')
• To decrease the brightness zone, a negative Averager
zone output must be followed by a second negative
Averager output or a repeated Averager zone. ('-' to '-' or
'-' to 'Rest')
• In the case of two increases or decreases in the Averager
output, the LM3535 will transition to zone equal to the last
Averager output.
Figure 17 provides a graphical representation of the
Averager's behavior.
30082448
FIGURE 18. Ambient Light Input to Backlight Mapping
When using the ALS averaging functionality, it is important to
remember that the averaging cycle is free running and is not
synchronized with changing ambient lighting conditions. Due
to the nature of the Averager round down, an increase in
brightness can take between 2 and 3 averaging cycles to
change zones while a decrease in brightness can take between 1 and 2 averaging cycles to change. See Figure 9 for
a list of possible Averager periods. Figure 19 shows an example of how the perceived brightness change time can vary.
30082451
FIGURE 19. Perceived Brightness Change Time
Ambient Light Current Control + PWM
The Ambient Light Current Control can also be a function of
the PWM input duty cycle. Assume the LM3535 is configured
as described in the previous example, but this time the Enable
30082449
FIGURE 17. Brightness Zone Change Examples
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20
LM3535
PWM bit set to ‘1’ (Configuration Register bit [0]). Figure 20
shows how the different blocks (PWM and ALS) influence the
LED current.
30082446
FIGURE 20. Current Control Block Diagram
assigns D53 and D62 to the GroupB lighting region. With this
added flexibility, the LM3535 is capable of supporting applications 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.
ALS + PWM Example
In this example, the APDS-9005 sensor detects that the ambient light has changed to 1 kLux. The voltage at the ALS input
is now around 875mV and the ambient light falls within Zone
5. This causes the LED brightness to be a function of Zone
Target Register 5 (loaded with 0x7F). Now assume the PWM
input is also driven with a 50% duty cycle pulsed waveform.
The LED current now becomes:
MAXIMUM OUTPUT CURRENT, MAXIMUM LED
VOLTAGE, MINIMUM INPUT VOLTAGE
The LM3535 can drive 8 LEDs at 25mA each (GroupA ,
GroupB, GroupC) from an input voltage as low as 3.2V, so
long as the LEDs have a forward voltage of 3.6V or less (room
temperature).
The statement above is a simple example of the LED drive
capability of the LM3535. The statement contains the key application parameters that are required to validate an LEDdrive design using the LM3535: LED current (ILEDx), number
of active LEDs (Nx), LED forward voltage (VLED), and minimum input voltage (VIN-MIN).
The equation below can be used to estimate the maximum
output current capability of the LM3535:
LED CONFIGURATIONS
The LM3535 has a total of 8 current sinks capable of sinking
200mA of total diode current. These 8 current sinks are configured 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 LM3535 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 configuration). 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 assigned to the GroupA lighting region. Writing a '0' to these bits
ILED_MAX = [(1.5 x VIN) - VLED - (IADDITIONAL × ROUT)] /
[(Nx x ROUT) + kHRx] (eq. 1)
ILED_MAX = [(1.5 x VIN ) - VLED - (IADDITIONAL × 2.4Ω)] /
[(Nx x 2.4Ω) + kHRx]
IADDITIONAL is the additional current that could be delivered to
the other LED Groups.
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LM3535
PLEDTOTAL = (VLEDA × NA × ILEDA) +
(VLEDB × NB × ILEDB) + (VLEDC × ILEDC)
ROUT – Output resistance. This parameter models the internal
losses of the charge pump that result in voltage droop at the
pump output VOUT. Since the magnitude of the voltage droop
is proportional to the total output current of the charge pump,
the loss parameter is modeled as a resistance. The output
resistance of the LM3535 is typically 2.4Ω (VIN = 3.6V, TA =
25°C). In equation form:
PIN = VIN × IIN
PIN = VIN × (GAIN × ILEDTOTAL + IQ)
E = (PLEDTOTAL ÷ PIN)
The LED voltage is the main contributor to the charge-pump
gain selection process. Use of low forward-voltage LEDs
(3.0V- to 3.5V) will allow the LM3535 to stay in the gain of 1×
for a higher percentage of the lithium-ion battery voltage
range when compared to the use of higher forward voltage
LEDs (3.5V to 4.0V). See the LED Forward Voltage Monitoring section of this datasheet for a more detailed description
of the gain selection and transition process.
For an advanced analysis, it is recommended that power consumed by the circuit (VIN x IIN) for a given load be evaluated
rather than power efficiency.
VVOUT = (1.5 × VIN) – [(NA× ILEDA + NB × ILEDB + NC × ILEDC) ×
ROUT]
(eq. 2)
kHR – Headroom constant. This parameter models the minimum voltage required to be present across the current sinks
for them to regulate properly. This minimum voltage is proportional to the programmed LED current, so the constant has
units of mV/mA. The typical kHR of the LM3535 is 4mV/mA. In
equation form:
(VVOUT – VLEDx) > kHRx × ILEDx
(eq. 3)
Typical Headroom Constant Values
kHRA = kHRB = kHRC = 4 mV/mA
POWER DISSIPATION
The power dissipation (PDISS) and junction temperature (TJ)
can be approximated with the equations below. PIN is the
power generated by the 3/2× - 1× charge pump, PLED is the
power consumed by the LEDs, TA is the ambient temperature,
and θJA is the junction-to-ambient thermal resistance for the
micro SMD 20-bump package. V IN is the input voltage to the
LM3535, VLED is the nominal LED forward voltage, N is the
number of LEDs and ILED is the programmed LED current.
The "ILED-MAX" equation (eq. 1) is obtained from combining the
ROUT equation (eq. 2) with the kHRx equation (eq. 3) and solving for ILEDx. Maximum LED current is highly dependent on
minimum input voltage and LED forward voltage. Output current capability can be increased by raising the minimum input
voltage of the application, or by selecting an LED with a lower
forward voltage. Excessive power dissipation may also limit
output current capability of an application.
PDISS = PIN - PLEDA - PLEDB - PLEDC
Total Output Current Capability
The maximum output current that can be drawn from the
LM3535 is 200mA.
DRIVER TYPE
MAXIMUM Dxx CURRENT
DxA
25mA per DxA Pin
DxB
25mA per DxB Pin
D1C
25mA
PDISS= (GAIN × VIN × IGroupA + GroupB + GroupC ) - (VLEDA × NA ×
ILEDA) - (VLEDB × NB × ILEDB) - (VLEDC × ILEDC)
TJ = TA + (PDISS x θJA)
The junction temperature rating takes precedence over the
ambient temperature rating. The LM3535 may be operated
outside the ambient temperature rating, so long as the junction temperature of the device does not exceed the maximum
operating rating of 110°C. The maximum ambient temperature rating must be derated in applications where high power
dissipation and/or poor thermal resistance causes the junction temperature to exceed 110°C.
PARALLEL CONNECTED AND UNUSED OUTPUTS
Connecting the outputs in parallel does not affect internal operation of the LM3535 and has no impact on the Electrical
Characteristics and limits previously presented. The available
diode output current, maximum diode voltage, and all other
specifications provided in the Electrical Characteristics table
apply to this parallel output configuration, just as they do to
the standard LED application circuit.
All Dx current sinks utilize LED forward voltage sensing circuitry to optimize the charge-pump gain for maximum efficiency. Due to the nature of the sensing circuitry, it is not
recommended to leave any of the Dx pins open when the
current sinks are enabled (ENx bits are set to '1'). Leaving Dx
pins unconnected will force the charge-pump into 3/2× mode
over the entire VIN range negating any efficiency gain that
could have been achieved by switching to 1× mode at higher
input voltages.
If the D1B or D1C drivers are not going to be used, make sure
that the ENB and ENC bits in the general purpose register are
set to '0' to ensure optimal efficiency.
THERMAL PROTECTION
Internal thermal protection circuitry disables the LM3535
when the junction temperature exceeds 150°C (typ.). This
feature protects the device from being damaged by high die
temperatures that might otherwise result from excessive power dissipation. The device will recover and operate normally
when the junction temperature falls below 125°C (typ.). It is
important that the board layout provide good thermal conduction to keep the junction temperature within the specified
operating ratings.
CAPACITOR SELECTION
The LM3535 requires 4 external capacitors for proper operation (C1 = C2 = CIN = COUT = 1µF). Surface-mount multi-layer
ceramic capacitors are recommended. These capacitors are
small, inexpensive and have very low equivalent series resistance (ESR <20mΩ typ.). Tantalum capacitors, OS-CON
capacitors, and aluminum electrolytic capacitors are not recommended for use with the LM3535 due to their high ESR,
as compared to ceramic capacitors.
For most applications, ceramic capacitors with X7R or X5R
temperature characteristic are preferred for use with the
LM3535. These capacitors have tight capacitance tolerance
(as good as ±10%) and hold their value over temperature
POWER EFFICIENCY
Efficiency of LED drivers is commonly taken to be the ratio of
power consumed by the LEDs (PLED) to the power drawn at
the input of the part (PIN). With a 3/2× - 1× charge pump, the
input current is equal to the charge pump gain times the output
current (total LED current). The efficiency of the LM3535 can
be predicted as follow:
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22
+85°C range; Z5U: +22%, -56% over +10°C to +85°C range).
Under some conditions, a nominal 1µF Y5V or Z5U capacitor
could have a capacitance of only 0.1µF. Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to
meet the minimum capacitance requirements of the LM3535.
The recommended voltage rating for the capacitors is
10V to account for DC bias capacitance losses.
23
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LM3535
(X7R: ±15% over -55°C to 125°C; X5R: ±15% over -55°C to
85°C).
Capacitors with Y5V or Z5U temperature characteristic are
generally not recommended for use with the LM3535. Capacitors with these temperature characteristics typically have
wide capacitance tolerance (+80%, -20%) and vary significantly over temperature (Y5V: +22%, -82% over -30°C to
LM3535
Physical Dimensions inches (millimeters) unless otherwise noted
TMD20AAA: 20 Bump 0.4mm micro SMD
X1 = 1.650mm
X2 = 2.055mm
X3 = 0.6mm
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24
LM3535
Notes
25
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LM3535 Multi-Display LED Driver with Ambient Light Sensing and Dynamic Backlight Control
Compatibility
Notes
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