LM3435SQ/NOPB [TI]
具有 IC 控制接口的紧凑型顺序模式 RGB LED 驱动器 | RSB | 40 | -40 to 125;
| 型号： | LM3435SQ/NOPB |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 具有 IC 控制接口的紧凑型顺序模式 RGB LED 驱动器 | RSB | 40 | -40 to 125 驱动 接口集成电路 显示驱动器 驱动程序和接口 |
| 文件： | 总25页 (文件大小：979K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM3435
Compact Sequential Mode RGB LED Driver with I2C Control Interface
General Description
Key Specifications
The LM3435, a Synchronously Rectified non-isolated Flyback
Converter, features all required functions to implement a high-
ly efficient and cost effective RGB LED driver. Different from
conventional Flyback converter, LEDs connect across the
VOUT pin and the VIN pin through internal passing elements
at corresponding LED pins. Thus, voltage across LEDs can
be higher than, equal to or lower than the input supply voltage.
Support up to 2A LED current
●
●
●
Typical ±3% LED current accuracy
Integrated N-Channel main and P-Channel synchronous
MOSFETs
3 Integrated N-Channel current regulating pass switches
LED Currents programmable via I2C bus independently
●
●
●
●
Input voltage range 2.7V - 5.5V
Load current to LEDs is up to 2A with voltage across LEDs
ranging from 2.0V to 4.5V. Integrated N-Channel main MOS-
FET, P-Channel synchronous MOSFET and three N-Channel
current regulating pass switches allow low component count,
thus reducing complexity and minimize board size. The
LM3435 is designed to work exceptionally well with ceramic
output capacitors with low output ripple voltage. Loop com-
pensation is not required resulting in a fast load transient
response. Non-overlapping RGB LEDs are driven sequential-
ly through individual control. Output voltage hence can be
optimized for different forward voltage of LEDs during the non-
overlapping period. I2C interface eases the programming of
the individual RGB LED current up to 1,024 levels per chan-
nel.
Thermal shutdown
Thermally enhanced LLP-40 package
●
Features
Sequential RGB driving mode
●
●
●
Low component count and small solution size
Stable with ceramic and other low ESR capacitors, no loop
compensation required
Fast transient response
●
●
●
●
Programmable converter switching frequency up to 1 MHz
MCU interface ready with I2C bus
Peak current limit protection for the switcher
LED fault detection and reporting via I2C bus
The LM3435 is available in the thermally enhanced LLP-40
package.
●
Applications
Li-ion batteries / USB Powered RGB LED driver
●
●
Pico / Pocket RGB LED Projector
PRODUCTION DATA information is current as of
publication date. Products conform to specifications per
the terms of the Texas Instruments standard warranty.
Production processing does not necessarily include
testing of all parameters.
301625 SNVS724B
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
Typical Application Circuit
30162501
2
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
Connection Diagram
30162502
Top View
40-pin Leadless Leadframe Package (LLP)
5.0 x 5.0 x 0.8mm, 0.4mm pitch
NS Package Number SQF40A
Ordering Information
Order Number
LM3435SQ
Spec.
NOPB
NOPB
Package Type
LLP-40
NSC Package Drawing
SQF40A
Supplied As
1000 Units, Tape and Reel
4500 Units, Tape and Reel
LM3435SQX
LLP-40
SQF40A
Copyright © 1999-2012, Texas Instruments Incorporated
3
LM3435
Pin Descriptions
Pin
Name
Type
Description
Application Information
1, 2, 38, 39,
40
PGND
Ground
Power Ground
Ground for power devices, connect to GND.
3
4
5
6
7
8
CG
CB
Output
Output
Output
Output
Output
Output
GREEN LED capacitor
BLUE LED capacitor
RED LED capacitor
Connect a capacitor to Ground for GREEN LED.
Minimum 1nF.
Connect a capacitor to Ground for BLUE LED. Minimum
1nF.
CR
Connect a capacitor to Ground for RED LED. Minimum
1nF.
IREFG
IREFB
IREFR
Current Reference for GREEN LED Connect a resistor to Ground for GREEN LED current
reference generation.
Current Reference for BLUE LED
Connect a resistor to Ground for BLUE LED current
reference generation.
Current Reference for RED LED
Connect a resistor to Ground for RED LED current
reference generation.
9
10, 29
11
GND
SGND
SVDD
SDATA
Ground
Ground
Power
Ground
I2C Ground
I2C VDD
Ground for I2C control, connect to GND.
VDD for I2C control.
12
Input /
Output
DATA bus
Data bus for I2C control.
13
SCLK
VIN
Input
CLOCK bus
Clock bus for I2C control.
14, 15, 16,
17, 37
Power
Input supply voltage
Supply pin to the device. Nominal input range is 2.7V to
5.5V.
18
19
GCTRL
BCTRL
RCTRL
RLED
BLED
GLED
FAULT
EN
Input
Input
GREEN LED control
BLUE LED control
RED LED control
RED LED cathode
BLUE LED cathode
GREEN LED cathode
Fault indicator
On/Off control signal for GREEN LED. Internally pull-low.
On/Off control signal for BLUE LED. Internally pull-low.
On/Off control signal for RED LED. Internally pull-low.
Connect RED LED cathode to this pin.
20
Input
21, 22
23, 24
25, 26
27
Output
Output
Output
Output
Input
Connect BLUE LED cathode to this pin.
Connect GREED LED cathode to this pin.
Pull-up when LED open or short is being detected.
28
Enable pin
Internally pull-up. Connect to a voltage lower than 0.2 x
VIN to disable the device.
30, 31, 32
33
VOUT
RT
Input /
Output
Output voltage
ON-time control
Connect anodes of LEDs to this pin.
Input
Output
Ground
An external resistor connected from VOUT to this pin sets
the main MOSFET on-time, hence determine the
switching frequency.
34, 35, 36
EP
SW
EP
Switch node
Exposed Pad
Internally connected to the drain of the main N-channel
MOSFET and the P-channel synchronous MOSFET.
Connect to the output inductor.
Thermal connection pad, connect to the GND pin.
4
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for
availability and specifications.
VIN to GND
-0.3V to 6.0V
-0.3V to 5.5V
-0.3V to 5.5V
-0.3V to 11.5V
VOUT, RT to VIN
RLED, GLED, BLED to VIN
SW to GND
SW to GND (Transient)
-2V to 13V
(<100 ns)
All other inputs to GND
ESD Rating (Note 2)
Human Body Model
Storage Temperature
Junction Temperature (TJ)
-0.3V to 6.0V
±1.5 kV
-65°C to +150°C
-40°C to +125°C
Operating Ratings (Note 1)
Supply Voltage Range (VIN)
Junction Temp. Range (TJ)
Thermal Resistance (θJB) (Note 3)
2.7V to 5.5V
-40°C to +125°C
28°C/W
Electrical Characteristics Specification with standard type are for TA = TJ = +25°C only; limits in boldface type
apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum are guaranteed through test, design or
statistical correlation. Typical values represent the most likely parametric norm at TJ = +25°C, and are provided for reference
purposes only. Unless otherwise stated the following conditions apply: VIN = 5V and VOUT – VIN = 3V.
Symbol
Parameter
Conditions
Min
Typ
Max Units
Supply Characteristics
IIN
IIN operating current
No switching
5
8
10
30
1
mA
µA
µA
V
IIN-SD
IIN Shutdown current
VEN = 0V
ISVDD
SVDD standby supply current
VIN under-voltage lock-out
VIN under-voltage lock-out hysteresis
VSVDD = 5V, I2C Bus idle
VIN decreasing
VIN increasing
VINUVLO
VINUVLO_hys
Enable Input
VEN
2.5
0.2
V
EN Pin input threshold
VEN rising
VEN falling
VEN = 0V
0.8 x
VIN
V
V
0.2 x
VIN
IEN
Enable Pull-up Current
5
µA
Logic Inputs (RCTRL, GCTRL and BCTRL)
VCTRL CTRL pins input threshold
VCTRL rising
1.35
V
(VIN = 2.7V to 5.5V)
VCTRL falling
0.63
(VIN = 2.7V to 5.5V)
Switching Characteristics
RDS-M-ON Main MOSFET RDS(ON)
VGS(MAIN) =VIN = 5.0V
ISW(sink) = 100mA
0.04
0.06
0.1
0.2
Ω
Ω
RDS-S-ON
Syn. MOSFET RDS(ON)
VGS(SYN) = VOUT - 5.0V
ISW(source) = 100mA
Current Limit
ICL
Peak current limit through main MOSFET
threshold
6
8.5
A
ON/OFF Timer
tON
ON timer pulse width
750
80
ns
ns
RRT = 499 kΩ
tON-MIN
ON timer minimum pulse width
Copyright © 1999-2012, Texas Instruments Incorporated
5
LM3435
Symbol
Parameter
Conditions
Min
Typ
Max Units
tOFF
OFF timer minimum pulse width
155
ns
RGB Driver Characteristics (RLED, BLED and GLED)
RDS(RED)
RDS(BLU)
RDS(GRN)
Red LED Switch RDS
Blue LED Switch RDS
Green LED Switch RDS
VOUT - VIN = 3.3V
ILED = 1.5A
I2C code = 3FFh
0.1
0.1
0.1
0.2
0.2
0.2
Ω
Ω
Ω
A
VOUT - VIN = 3.3V
ILED = 1.5A
I2C code = 3FFh
VOUT - VIN = 3.3V
ILED = 1.5A
I2C code = 3FFh
ILEDMAX
Max. LED current (Note 4)
Current accuracy (3FFh)
VIN = 4.5V to 5.5V,
2
0°C ≤ TA ≤ 50°C
VIN = 2.7V to 5.5V
I1.5A,3FFh
1.455
1.5
1.545
A
A
RIREF = 16.5 kΩ,
1.425
1.575
VOUT – VIN = 2.4V (RLED),
I1.5A,1FFh
I1.5A,001h
Current (1FFh)
Current (001h)
0.8
1.2
A
3.3V (GLED/BLED)
mA
FAULT Output Characteristics
VOH Output high voltage
VIN = 2.7V to 5.5V,
IOH = -100µA
VIN –
0.1
V
V
V
V
VIN = 2.7V to 5.5V,
IOH = -5mA
VIN –
0.5
VOL
Output low voltage
VIN = 2.7V to 5.5V,
IOL = 100µA
0.1
0.5
VIN = 2.7V to 5.5V,
IOL = 5mA
Thermal Shutdown
TSD
Thermal shutdown temperature
TJ rising
163
20
°C
°C
TSD-HYS
Thermal shutdown temperature hysteresis TJ falling
I2C Logic Interface Electrical Characteristics (1.7 V < SVDD < VIN
)
Logic Inputs SCL, SDA
VIL
Input Low Level
Input High Level
0.2 x
SVD
D
V
V
VIH
0.8 x
SVDD
IL
Logic Input Current
Clock Frequency
-1
1
µA
fSCL
400
kHz
Logic Output SDA
VOL
IL
Output Low Level
ISDA = 3mA
VSDA = 2.8V
0.3
0.5
2
V
Output Leakage Current
µA
Note 1: Absolute Maximum Ratings are limits which damage to the device may occur. Operating ratings are conditions under which operation of the device is
intended to be functional. For guaranteed specifications and test conditions, see the electrical characteristics.
Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 3: θJB is junction-to-board thermal characteristic parameter. For packages with exposed pad, θJB is significantly dependent on PC boards. So, only when
the PC board under end-user environments is similar to the 2L JEDEC board, the corresponding θJB can be used to predict the junction temperature. θJB value
is obtained by NS Thermal Calculator© for reference only.
Note 4: Maximum LED current measured at VIN = 4.5V to 5.5V with heat sink on top of LM3435 with no air flow at 0°C ≤ TA ≤ 50°C. Operating conditions differ
from the above is not guaranteed.
6
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
Typical Performance Characteristics All curves taken at VIN = 5V with configuration in typical application
for driving one red (OSRAM LRW5AP-KZMX), one green (OSRAM LTW5AP-LZMY) and one blue (OSRAM LBW5AP-JYKX) LEDs
with IOUT per channel = 1.5A under TA = 25°C, unless otherwise specified.
IIN-SD vs VIN
IIN (no switching) vs VIN
12
10
8
6.0
5.5
5.0
4.5
4.0
3.5
3.0
125°C
25°C
125°C
25°C
6
-40°C
-40°C
4
2
0
2
2
2
3
4
IN
5
6
2
2
5
3
4
IN
5
6
V
(V)
V
(V)
30162505
30162506
ISVDD vs VIN
RDS-M-ON vs VIN
25
20
15
10
5
70
60
50
40
30
20
125°C
125°C
25°C
25°C
-40°C
-40°C
0
3
4
5
6
3
4
IN
5
6
V
(V)
V
(V)
SVDD
30162504
30162503
RDS-S-ON vs VIN
RIREFx vs ILEDx
90
80
70
60
50
40
30
2.5
2.0
1.5
1.0
0.5
0.0
125°C
25°C
-40°C
5
3
4
6
15
25
35
(kΩ)
45
55
V
(V)
R
IN
IREFx
30162507
30162531
Copyright © 1999-2012, Texas Instruments Incorporated
7
LM3435
ILED(RED) vs VIN
RDS(RED) vs VIN
1.54
1.52
1.50
1.48
1.46
160
140
120
100
80
125°C
125°C
25°C
25°C
-40°C
-40°C
60
40
2
2
2
3
4
IN
5
6
6
6
2
2
2
3
4
IN
5
5
5
6
V
(V)
V
(V)
30162508
30162510
30162512
30162509
ILED(GRN) vs VIN
RDS(GRN) vs VIN
1.54
1.52
1.50
1.48
1.46
160
140
120
100
80
125°C
125°C
-40°C
25°C
25°C
-40°C
60
40
3
4
IN
5
3
4
6
V
(V)
V
(V)
IN
30162511
ILED(BLU) vs VIN
RDS(BLU) vs VIN
1.54
1.52
1.50
1.48
1.46
160
140
120
100
80
125°C
-40°C
125°C
25°C
25°C
-40°C
60
40
3
4
5
3
4
6
V
(V)
V
(V)
IN
IN
30162513
8
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
RED Efficiency vs VIN @ TA = 25°C
GREEN Efficiency vs VIN @ TA = 25°C
100
100
90
80
70
60
50
90
80
70
60
50
2
3
4
IN
5
6
2
3
4
IN
5
6
V
(V)
V
(V)
30162528
30162529
BLUE Efficiency vs VIN @ TA = 25°C
Power Up Transient
100
90
80
70
60
50
2
3
4
IN
5
6
V
(V)
30162524
30162530
10ms/DIV
RGB Sequential Mode Operation
Color Transition Delay
30162525
30162526
1ms/DIV
100µs/DIV
Copyright © 1999-2012, Texas Instruments Incorporated
9
LM3435
Simplified Functional Block Diagram
30162514
Operation Description
INTRODUCTION
The LM3435 is a sequential LED driver for portable and pico projectors. The device is integrated with three high current regulators,
low side MOSFETs and a synchronous flyback DC-DC converter. Only single LED can be enabled at any given time. The DC-DC
converter quickly adjusts the output voltage to an optimal level based on each LED’s forward voltage. This minimizes the power
dissipation at the current regulators and maximizes the system efficiency. The I2C compatible synchronous serial interface provides
access to the programmable functions and registers of the device. I2C protocol uses a two-wire interface for bi-directional com-
munications between the devices connected to the bus. The two interface lines are the Serial Data Line (SDA), and the Serial Clock
Line (SCL). These lines should be connected to a positive supply, via a pull-up resistor and remain HIGH even when the bus is
idle. Every device on the bus is assigned an unique address and acts as either a Master or a Slave depending on whether it
generates or receives the serial clock (SCL).
SYNCHRONOUS FLYBACK CONVERTER
The LM3435 integrates a synchronous flyback DC-DC converter to power the three-channel current regulator. The LEDs are
connected across VOUT of the flyback converter and VIN through an internal power MOSFET connecting to corresponding LED
channel. The maximum current to LED is 2A and the maximum voltage across VOUT and VIN is limited at around 4.7V. The LM3435
integrates the main N-channel MOSFET, the synchronous P-channel MOSFET of the flyback converter and three N-channel
MOSFETs as internal passing elements connecting to LED channels in order to minimize the solution components count and PCB
space.
The flyback converter of LM3435 employs a proprietary Projected On-Time (POT) control scheme to determine the on-time of the
main N-channel MOSFET with respect to the input and output voltages together with an external switching frequency setting resistor
connected to RT pin, RRT. POT control use information of the current passing through RRT from VOUT, voltage information of VOUT
and VIN to find an appropriate on-time for the circuit operations. During the on-time period, the inductor connecting to the flyback
converter is charged up and the output capacitor is discharged to supply power to the LED. A cycle-by-cycle current limit of typical
6A is imposed on the main N-channel MOSFET for protection. After the on-time period, the main N-channel MOSFET is turned off
and the synchronous P-channel MOSFET is turned on in order to discharge the inductor. The off state will last until VOUT is dropped
below a reference voltage. Such reference voltage is derived from the required LED current to be regulated at a particular LED
channel. The flyback converter under POT control can maintain a fairly constant switching frequency that depends mainly on value
of the resistor connected across VOUT and RT pins, RRT. The relationship between the flyback converter switching frequency,
FSW and RRT is approximated by the following relationship:
10
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
RRT in Ω and FSW in kHz
In addition, POT control requires no external compensation and achieves fast transient response of the output voltage changes
that perfectly matches the requirements of a sequential RGB LED driver. The POT flyback converter only operates at Continuous
Conduction Mode. Dead-time between main MOSFET and synchronous MOSFET switching is adaptively controlled by a minimum
non-overlap timer to prevent current shoot through. Initial VOUT will be regulated at around 3.2V to 3.5V above VIN before any
control signals being turned on. Three small capacitors connected to CR, CG and CB pins are charged by an internal current source
and act as soft-start capacitors of the flyback converter during start-up. Once initial voltage of VOUT is settled, the capacitors will
be used as a memory element to store the VOUT information for each channel respectively. This information will be used for VOUT
regulation of respective LED channel during channel switching. In between the channel switching, a small I2C programmable blank
out time of 5 µs to 35 µs is inserted so that the LED current is available after the correct VOUT for the color is stabilized. This control
scheme ensures the minimal voltage headroom for different color LED and hence best conversion efficiency can be achieved.
HIGH CURRENT REGULATORS
The LM3435 contains three internal current regulators powered by the output of the synchronous Flyback Converter, VOUT. Three
low side power MOSFETs are included. These current regulators control the current supplied to the LED channels individually and
maintain accurate current regulation by internal feedback and control mechanism. The regulation is achieved by a Gm-C circuit
comparing the sensing voltage of the internal passing N-channel MOSFET and an internal LED current reference voltage generated
from the external reference current setting resistor, RIREFx connect to IREFG, IREFB or IREFR pin, of the corresponding LED
channel. The nominal maximum LED current is governed by the equation in below:
RIREFx in Ω and ILEDx in Ampere
The LED current setting can be in the range of 0.5A up to 2A maximum. The nominal maximum of the device is 1.5A and for
applications need higher than 1.5A LED current, VIN and thermal constrains must be complied. The actual LED current can be
adjusted on-the-fly by the internal ten bits register for individual channel. The content of these registers are user programmable via
I2C bus connection. The user can control the LED output current on-the-fly during normal operation. The resolution is 1 out of 1024
part of the LED current setting. The user can program the registers in the range of 1(001H) to 1023(3FFH) for each channel
independently, provided the converter is not entered the Discontinuous Conduction Mode. Whenever the converter operation en-
tered the Discontinuous Conduction Mode, the regulation will be deteriorated. A value of “0” may cause false fault detection, so it
must be avoided.
SEQUENTIAL MODE RGB TIMING
LM3435 is a sequential mode RGB driver dedicatedly designed for pico and portable projector applications. By using this device,
the system only require one power driver stage for three color LEDs. With LM3435, only single LED can be enabled at any given
time period and the DC-DC converter can quickly adjusts the output voltage to an optimized level by controlling the current flowing
into the respective LED channel. This approach minimizes the power dissipation of the internal current regulator and effectively
maximizes the system efficiency. Timing of the RGB LEDs depends solely on the RCTRL, GCTRL and BCTRL inputs. The Timing
Chart in below shows a typical timing of two cycles of even RGB scan. In real applications, the RGB sequence is totally controlled
by the system or the video processor. It’s not mandatory to follow the simple RGB sequence, but for any change instructed by the
I2C control will only take place at the falling edge of the corresponding CTRL signal.
30162520
RGB Control Signals Timing Chart
PRIORITIES OF LED CONTROL SIGNALS
The LM3435 does not support color overlapping mode operation. At any instant, only one LED will be enabled even overlapping
control signals applied to the control inputs. The decision logics of the device determine which LED channel should be enabled in
case overlapping control signals are detected at the control inputs. The GREEN channel has the higher priority over BLUE channel
and the RED channel has the lowest priority. However, if a low priority channel is already turned on before the high priority channel
Copyright © 1999-2012, Texas Instruments Incorporated
11
LM3435
control signal comes in, the low priority channel will continue to take the control until the control signal ceased. The timing diagram
in below illustrates some typical cases during operation.
30162521
Priorities of LED Control Signals
LED OPEN FAULT REPORTING
The fly-back converter tries to keep VOUT to the forward voltage required by the LED with the desired LED current output. However,
if the LED channel is being opened no matter it is due to LED failure or no connection, the fly-back converter will limit the VOUT
voltage at around 4.7V above VIN. Once such voltage is achieved, an open-fault-suspect signal will go high. If this open-fault-
suspect signal is being detected at 3 consecutive falling edges of the opened channel control signal, “Fault” pin will be latched high
and the corresponding channel open fault will be reported through I2C. The open fault report can be removed either by pulling EN
pin low for less than 100ns (a true shutdown will be triggered if the negative pulse on EN is more than 100ns) or by writing a “0” to
“bit 0” of the I2C register ”05h”. The “Fault” pin will be cleared and the I2C fault register will be reset. In order to reinstate the fault
reporting feature, the system need to write a “1” to “bit 0” of the I2C register “05h”.
LED SHORT FAULT REPORTING
If the VOUT is prohibited to regulate at a potential higher than 1.5V above VIN at a LED channel, such LED is considered being
shorted and a short-fault-suspect signal will go high. If this short-fault-suspect signal is being detected at 3 consecutive falling edges
of the shorted channel control signal, “Fault” pin will be latched high and the corresponding channel short fault will be reported
through I2C. The short fault report can be removed either by pulling EN pin low for less than 100ns (a true shutdown will be triggered
if the negative pulse on EN is more than 100ns) or by writing a “0” to “bit 0” of the I2C register ”05h”. The “Fault” pin will be cleared
and the I2C fault register will be reset. In order to reinstate the fault reporting feature, the system need to write a “1” to “bit 0” of the
I2C register “05h”. Persistently short of LED can cause permanent damage to the device. Whenever the short fault is detected, the
system should turn off the faulty channel immediately by pulling the corresponding PWM control pin to GND.
THERMAL SHUTDOWN
Internal thermal shutdown circuitry is included to protect the device in the event that the maximum junction temperature is exceeded.
The threshold for thermal shutdown in LM3435 is around 160°C and it will be resumed to normal operation again once the tem-
perature cools down to below around 140°C.
I2C Compatible Interface
INTERFACE BUS OVERVIEW
The I2C compatible synchronous serial interface provides access to the programmable functions and registers on the device. This
protocol uses a two-wire interface for bi-directional communications between the devices connected to the bus. The two interface
lines are the Serial Data Line (SDA), and the Serial Clock Line (SCL). These lines should be connected to a positive supply, via a
pull-up resistor and remain HIGH even when the bus is idle. Every device on the bus is assigned a unique address and acts as
either a Master or a Slave depending on whether it generates or receives the serial clock (SCL).
DATA TRANSACTIONS
One data bit is transferred during each clock pulse. Data is sampled during the high state of the serial clock (SCL). Consequently,
throughout the clock’s high period, the data should remain stable. Any changes on the SDA line during the high state of the SCL
and in the middle of a transaction, aborts the current transaction. New data should be sent during the low SCL state. This protocol
permits a single data line to transfer both command/control information and data using the synchronous serial clock.
I2C DATA VALIDITY
The data on SDA 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 CLK is LOW.
12
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
30162515
I2C Signals : Data Validity
I2C START and STOP CONDITIONS
START and STOP bits classify the beginning and the end of the I2C session. START condition is defined as SDA signal transitioning
from HIGH to LOW while SCL line is HIGH. STOP condition is defined as the SDA transitioning from LOW to HIGH while SCL is
HIGH. The I2C master always generates START and STOP bits. The I2C bus is considered to be busy after START condition and
free after STOP condition. During data transmission, I2C master can generate repeated START conditions. First START and
repeated START conditions are equivalent, function-wise.
30162516
I2C Start and Stop Conditions
I2C ADDRESSES AND TRANSFERRING DATA
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) being transferred first. Each byte of data
has to be followed by an acknowledge bit. The acknowledge bit related clock pulse is generated by the master. The transmitter
releases the SDA line (HIGH) during the acknowledge clock pulse. The receiver must pull down the SDA line during the 9th clock
pulse, signifying an acknowledgement. A receiver which has been addressed must generate an acknowledge bit after each byte
has been received. 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 LM3435 address is 50h or 51H which is determined by the R/W bit. I2C address
(7 bits) for LM3435 is 28H. 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.
30162517
I2C Chip Address
Register changes take an effect at the SCL rising edge during the last ACK from slave.
30162532
Copyright © 1999-2012, Texas Instruments Incorporated
13
LM3435
w = write (SDA = “0”)
r = read (SDA = “1”)
ack = acknowledge (SDA pulled down by either master or slave)
rs = repeated start
id = 7-bit chip address, 50H (ADDR_SEL=0) or 51H (ADDR_SEL=1) for LM3435.
I2C Write Cycle
When a READ function is to be accomplished, a WRITE function must precede the READ function, as shown in the Read Cycle
waveform.
30162533
I2C Read Cycle
I2C TIMING PARAMETERS (VIN = 2.7V to 5.5V, SVDD = 1.7V to VIN)
30162534
I2C Timing Diagram
Symbol
Parameter
Limit
Units
Min
0.6
Max
1
2
Hold Time (repeated) START Condition
Clock Low Time
µs
µs
ns
ns
ns
ns
ns
ns
ns
ns
µs
1.3
3
Clock High Time
600
4
Setup Time for a Repeated START Condition
Data Hold Time (Output direction)
Data Hold Time (Input direction)
Data Setup Time
600
5
300
5
0
6
100
7
Rise Time of SDA and SCL
Fall Time of SDA and SCL
Set-up Time for STOP condition
20+0.1Cb
15+0.1Cb
600
300
300
8
9
10
Bus Free Time between a STOP and a START
Condition
1.3
Cb
Capacitive Load for Each Bus Line
10
200
pF
Note: Data guaranteed by design.
14
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
I2C REGISTER DETAILS
The I2C bus interacts with the LM3435 to realize the features of LED current program inter-color delay time program and Fault
reporting function. The operation of these functions requires the writing and reading of the internal registers of the LM3435. In below
is the master register map of the device.
Master Register Map
ADDR
00h
01h
02h
03h
05h
06h
07h
REGISTER
LEDLO
D7
D6
D5
D4
D3
D2
D1
D0
DEFAULT
0011 1111
1111 1111
1111 1111
1111 1111
0
0
RLED[1:0]
BLED[1:0]
GLED[1:0]
GLEDH
BLEDH
RLEDH
FLT_RPT
DELAY
GLED[9:2]
BLED[9:2]
RLED[9:2]
0
0
0
1
0
0
0
0
1
0
0
FLT_RPT 0000 0001
RDLY[1:0]
BDLY[1:0]
BO BS
GDLY[1:0]
1111 1111
0000 0000
FAULT
GO
GS
RO
RS
LED Current Register Definitions
The LED currents for each color can be accurately adjusted by 10 bits resolution (1024 steps) independently. By writing control
bytes into the LM3435 LED current Registers, the LED currents can be precisely set to any value in the range of IMIN to IREF
.
In below is the LED Current Low register bit definition:
ADDR
REGISTER
D7
D6
D5
D4
D3
D2
D1
D0
DEFAULT
00h
LEDLO
0
0
RLED[1:0]
BLED[1:0]
GLED[1:0]
0011 1111
Bits
7:6
Description
Reserved. These bits always read zeros.
5:4
The least significant bits of the 10-bit RLED register. This register is for programming the level of current for the
Red LED.
3:2
1:0
The least significant bits of the 10-bit BLED register. This register is for programming the level of current for the
Blue LED.
The least significant bits of the 10-bit GLED register. This register is for programming the level of current for the
Green LED.
In below is the LED Current High register bit definition:
ADDR
01h
REGISTER
GLEDH
D7
D6
D5
D4
D3
GLED[9:2]
BLED[9:2]
RLED[9:2]
D2
D1
D0
DEFAULT
1111 1111
1111 1111
1111 1111
02h
BLEDH
03h
RLEDH
Bits
7:0
Description
The most 8 significant bits of the 10-bit GLED, BLED and RLED registers respectively. These registers are for
programming the level of current of the Green LED, Blue LED and Red LED independently.
Fault Reporting Register Definition
The fault reporting feature of the LM3435 can be selected by the system designer according to their application needs. To select
or de-select this feature is realized by writing one bit into the FLT_RPT register.
ADDR
REGISTER
D7
D6
D5
D4
D3
D2
D1
D0
DEFAULT
05h
FLT_RPT
0
0
0
0
0
0
0
FLT_RPT 0000 0001
Bits
Description
7:1
0
Reserved. These bits always read zeros.
This bit defines the mode of fault report feature. Writing a “ 1 “ into this bit enables the fault reporting feature,
otherwise no Fault signal output at Pin 27.
Color Transition Delay Register Definition
The transition of one color into next color is not executed immediately. Certain delay is inserted in between to guarantee the LED
rail voltage stabilized before turning the next LED on. This delay is user programmable by writing control bits into the DELAY register
Copyright © 1999-2012, Texas Instruments Incorporated
15
LM3435
for each color individually. The power up default delay time is 35µs and this delay can be programmed from 5 µs to 35 µs maximum
in step of 10 µs.
ADDR REGISTER
D7
D6
D5
D4
D3
D2
D1
D0
DEFAULT
06h
DELAY
RDLY[1:0]
1
BDLY[1:0]
1
GDLY[1:0]
1111 1111
Bits
7:6
5
Description
These two bits are for programming the Red transition delay.
Reserved. This bit always read “ 1“.
4:3
2
These two bits are for programming the Blue transition delay.
Reserved. This bit always read “ 1“.
1:0
These two bits are for programming the Green transition delay.
Fault Register Definition
The LM3435 features LED fault detection capability. Whenever a LED fault is detected (open or short), the FAULT output (pin 27)
will go high to indicate a LED fault is detected. The details of the fault can be investigated by reading the FAULT register. The
FAULT register is read only. The fault status can be cleared by clearing and then re-enabling the FLT_RPT register or power up
reset of the device.
ADDR REGISTER
07h FAULT
D7
D6
D5
D4
D3
D2
D1
D0
DEFAULT
GO
GS
0
BO
BS
0
RO
RS
0000 0000
Bits
7
Description
GO – Green Open. This read only register bit indicates the presence of an OPEN fault of the GREEN LED.
GS – Green Short. This read only register bit indicates the presence of an SHORT fault of the GREEN LED.
Reserved. This bit always read “ 0 “.
6
5
4
BO – Blue Open. This read only register bit indicates the presence of an OPEN fault of the BLUE LED.
BS – Blue Short. This read only register bit indicates the presence of an SHORT fault of the BLUE LED.
Reserved. This bit always read “ 0 “.
3
2
1
RO – Red Open. This read only register bit indicates the presence of an OPEN fault of the RED LED.
RS – Red Short. This read only register bit indicates the presence of an SHORT fault of the RED LED.
0
16
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
Design Procedures
This section presents a design example of a typical pico projector application. By using LM3435, the system requires only single
DC-DC converter to drive three color LEDs instead of using three DC-DC converters with conventional design. The suggested
approach not only saves components cost, but also releases invaluable PCB space to the system and enhances system reliability.
The handy projector is powered by a single lithium battery cell or a 5Vdc wall mount adaptor. The key specifications of the design
are as in below:
Supply voltage range, VIN = 2.7V to 5.5V
Preset LED current per channel, ILED = 1.5A
Minimum LED current per channel, ILED(MIN) = 600mA
Maximum LED forward voltage drop, VLED = 3.5V @ 1.5A
Flyback converter switching Frequency, FSW = ~500kHz
SETTING THE FLYBACK CONVERTER SWITCHING FREQUENCY, FSW
The LM3435 employs a proprietary Projected On-Time (POT) control scheme, the switching frequency, FSW of the converter is
simply set by an external resistor, RRT across RT pin of LM3435 and VOUT of the converter. The flyback converter under POT
control can maintain a fairly constant switching frequency that depends mainly on the value of RRT. The relationship between the
flyback converter switching frequency, FSW and RRT is approximated by the following relationship:
RRT in Ω and FSW in kHz
In order to set the flyback converter switching frequency, FSW to 500kHz, the value of RRT can be calculated as in below:
A standard resistor value of 499kΩ can be used in place and the period of switching, TSW is about 2µs.
SETTING THE NOMINAL LED CURRENT
The nominal LED current of the LEDs are set by resistors connected to IREFR, IREFG and IREFB pins. The current for each
channel can be set individually and it is not mandatory that all channel currents are the same. Just for simplicity, we assume all
channels are set to 1.5A in this example. The LED current and the value of RIREFR, RIREFG and RIREFB is governed by the following
equation.
RIREFx in Ω and ILEDx in Ampere
The resistance value for the current setting resistors is calculated as in below:
In order to achieve the required LED current accuracy, high quality resistors with tolerance not higher than +/-1% are recommended.
INDUCTOR SELECTION
Selecting the correct inductor is one of the major task in application design of a LED driver system. The most critical inductor
parameters are inductance, current rating, DC resistance and size. As an rule of thumb, for same physical size inductor, higher the
inductance means higher the DC resistance, consequently more power loss with the inductor and lower the DC-DC conversion
efficiency. With LM3435, the inductor governs the inductor ripple current and limits the minimum LED current that can be supported.
However for the POT control in LM3435, a minimum inductor ripple current of about 300mApk-pk is required for proper operation.
The relationship of the ON-Duty, D and the input/output voltages can be derived by applying the Volt-Second Balance equation
across the inductor. The waveforms of the inductor current and voltage are shown in below.
Copyright © 1999-2012, Texas Instruments Incorporated
17
LM3435
30162547
Inductor Switching Waveforms
Applying the Volt-Second Balance equation with the inductor voltage waveform,
Referring to the inductor current waveform, the average inductor current, IL(AVG) can be derived as in below:
The minimum LED current, ILED(MIN) happens when the inductor current just entered the Critical Conduction Mode operation, i.e.
ILripple(MIN)=0.
Applying this condition to the last equation:
The relationship of the LED current, ILED and the average inductor current, IL(AVG) is shown in below:
By combining last two equations, the minimum LED current, ILED(MIN) can be calculated as in below:
18
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
By rearranging the terms, the inductance, L required for any specific minimum LED current, ILED(MIN) can be found with the equation
in below:
From the equation, it can be noted that for lower minimum LED current, the inductance required will be higher. As mentioned in
before, higher the inductance means higher DC resistance in same size inductor. Additionally, the POT control in LM3435, a
minimum inductor ripple current is required to maintain proper operation. The restrictions limit the lowest current can be programed
by I2C control.
In this example, the ILED(MIN)=600mA and the highest ripple will happen when the input voltage is maximum, i.e. VIN=5.5V. The ON
Duty, D with average LED forward voltage of 3.5V is calculated in below:
The required inductance for this case is:
A standard inductance value of 2.2µH is suggested and the minimum LED current, ILED(MIN) is about 595mA @ VIN=5.5V.
Other than the inductance, the worst case inductor current, IL(MAX) must be calculated so that an inductor with appropriate saturation
current level can be specified. The maximum inductor current, IL(MAX) can be calculated with the equation in below:
The highest inductor current occurs when the input voltage is minimum, i.e. VIN=2.7V. The ON Duty, D for this condition can be
calculated as in below:
The maximum inductor current, IL(MAX) is calculated in below:
The calculated maximum inductor current is 4.1A, however the inductance can drop as temperature rise. In order to accommodate
all possible variations, an inductor with saturation current specification not less than 5A is suggested.
INPUT CAPACITORS SELECTION
Input capacitors are required for all supply input pins to ensure that VIN does not drop excessively during high current switching
transients. LM3435 have supply input pins located in different sides of the device. Individual capacitors are needed for the supply
input pins locally. All capacitors must be placed as close as possible to the supply input pins and have low impedance return ground
path to the device grounds and back to supply ground. Capacitors CIN1 and CIN2 are the main input capacitors and additionally,
CIN3 is added to de-couple high frequency interference. The capacitance for CIN1 and CIN2 is recommended in the range of 22μF
to 47µF and CIN3 is 0.1µF. Compact applications normally have stringent space limitations, small size surface mount capacitors
are usually preferred. Low ESR Multi-Layer Ceramic Capacitors (MLCC) are the best choices. MLCC capacitors with X5R and X7R
dielectrics are recommended for its low leakage and low capacitance variation against temperature and frequency.
Copyright © 1999-2012, Texas Instruments Incorporated
19
LM3435
OUTPUT CAPACITORS SELECTION
Two output capacitors are required with LM3435 configuration, one for VOUT to Ground, COUT2 and one for de-coupling the LED
current ripple, COUT1. The LM3435 operates at frequencies high enough to allow the use of MLCC capacitors without compromising
transient response. Low ESR characteristic of the MLCC allow higher inductor ripple without significant increase of the output ripple.
The capacitance recommended for COUT1 is 10µF and COUT2 is 22µF. Again, high quality MLCC capacitors with X5R and X7R
dielectrics are recommended. For certain conditions, acoustic problem may be encountered with using MLCC, Low Acoustic Noise
Type capacitors are strongly recommended for all output capacitors. Alternatively, the acoustic noise can also be lowered by using
smaller size capacitors in parallel to achieve the required capacitance.
OTHER CAPACITORS SELECTION
Three small startup capacitors connected to CG, CB and CR pins are needed for proper operation. The suggested capacitance for
CCR, CCG and CCB is 1nF. Also three capacitors connected to GLED, BLED and RLED pins to protect the device from high transient
stress due to the inductance of the connecting wires for the LEDs. The suggested capacitance for CG, CB and CR is 0.47µH. MLCC
capacitors with X5R and X7R dielectrics are recommended. All capacitors must be placed as close as possible to the device pins.
DIODE SELECTION
A schottky barrier diode is added across the SW and VOUT pins, equivalently, its across the internal P-channel MOSFET of the
synchronous converter, that can help to improve the conversion efficiency by few percents. A very low forward voltage and 1A
rated forward current part is suggested in the schematic diagram. The key selection criteria are the forward voltage and the rated
forward current.
PCB LAYOUT CONSIDERATIONS
The performance of any switching converters depends as much upon the layout of the PCB as the component selection. PCB
layout considerations are therefore critical for optimum performance. The layout must be as neat and compact as possible, and all
external components must be as close as possible to their associated pins. The PGND connection to CIN and VOUT connection
to COUT should be as short and direct as possible with thick traces. The inductor should connect close to the SW pin with short and
thick trace to reduce the potential electro-magnetic interference.
It is expected that the internal power elements of the LM3435 will produce certain amount of heat during normal operation, good
use of the PC board's ground plane can help considerably to dissipate heat. The exposed pad on the bottom of the IC package
can be soldered to a copper pad with thermal vias that can help to conduct the heat to the bottom side ground plane. The bottom
side ground plane should be as large as possible.
20
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
Schematic of the Example Application for Pico Projector
30162535
Copyright © 1999-2012, Texas Instruments Incorporated
21
LM3435
Physical Dimensions inches (millimeters) unless otherwise noted
LLP-40 Pin Package (SQF)
For Ordering, Refer to Ordering Information Table
NS Package Number SQF40A
22
Copyright © 1999-2012, Texas Instruments Incorporated
LM3435
Notes
Copyright © 1999-2012, Texas Instruments Incorporated
23
Notes
Copyright © 1999-2012, Texas Instruments
Incorporated
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