Datasheet for MSL3086/MSL3088 - Complete

Phase Shifted Dimming
______________ General Description
The MSL3086/87/88 8-channel LED drivers with integrated boost
regulator controller offer a complete solution to drive up to eight
parallel LED strings at up to 40V. The LED current sinks control
up to 60mA peak for up to 24W of LED power. A single resistor
sets LED current with string matching and accuracy within ±3%.
____________________Key Features
Up to 8 parallel 60mA LED strings with up to 14 series white
LEDs per string
Integrated boost controller (MSL3086/88)
Controls external DC/DC (MSL3087)
Shares DC/DC with other drivers
Offers true 4095:1 (12-bit) LED dimming at 200Hz
String open circuit and LED short circuit fault detection and
automatic correction
±3% current accuracy and current balance
Single resistor sets current for all LED strings
Simple to use external PWM dimming
Optional internal PWM dimming
Automatic string phasing reduces EMI and supply ripple
Synchronizes PWM dimming to LCD panel refresh rate
Frequency multiplier allows PWM dimming at multiples of
LCD panel refresh frequency (see Programming Guide)
1MHz I²C/SMBus interface; use optional
Resistor programmable LED short circuit threshold
Die over-temperature cut-off protection
-40°C to +85°C operating temperature range
Lead free, halogen free, RoHS compliant package






Atmel MSL3086 / MSL3088
The advanced integrated PWM circuitry allows up to 4095:1
dimming, and offers simple PWM dimming control. The MSL3086
and MSL3087 use a single PWM input to control the LED
dimming signals. The MSL3088 has two inputs, one for frequency
and the other for duty cycle. Additionally, internal registers,
2
available through the I C interface, optionally control PWM
dimming frequency and/or duty cycle.







8-String 60mA LED Drivers with Integrated
Boost Controller and Phase Shifted Dimming
The MSL3086/87/88 feature phase-shifted PWM dimming to
reduce the boost regulator transient response. The integrated
fault detection circuitry detects and acts upon string open-circuit
and LED short circuit faults, boost regulator over-voltage faults,
and die over-temperature faults.
Features:
A proprietary Efficiency Optimizer maintains sufficient boost
regulator output voltage for proper LED current while minimizing
power use. A 1MHz I2C/SMBus serial interface allows optional
dimming control, fault inspection and control of device
parameters; for serial interface information see the
MSL3040/50/60/86/87/88/89 Programming Guide. Multiple
parallel
60mA LED
strings
with more
up to
MSL3086/87/88‘s
interconnect
to operate
than10
8 strings
while maintaining optimum efficiency.





FULL DATASHEET
_______________ Application Circuit
• Up to 8
series white LEDs per string
The MSL3086/87/88 are offered in the 24-pin VQFN lead-free,
• Integrated boost
controller (MSL3086/88)
halogen-free, RoHS compliant package and operate over -40°C
to +85°C. (12-bit) LED dimming at 120Hz
• Offers true 4095:1
_____________________Applications
• String open circuit
and LED short circuit fault
Long
Life, Efficient LED
Backlighting for:
detection and
automatic
correction
Televisions and Desktop Monitors
• ±3% current accuracy
current
balance
Medicaland
and Industrial
Instrumentation
Automotive Audio-Visual Displays
• Single resistor
sets
current for all LED strings
Channel
Signs
Architectural Lighting
• Simple to use
external PWM dimming
_____________
Ordering Information
• Optional internal
PWM dimming
PART
DESCRIPTION
PKG
• Automatic string
phasing reduces
EMI and supply ripple
8-CH LED driver with integrated boost
controller and resistor
basedpanel
LED Short
• SynchronizesMSL3086
PWM dimming
to LCD
refresh rate
Circuit threshold setting.
24 pin
8-CH LED driver
with dimming
power supply at multiples
• Frequency multiplier allows
PWM
4 x 4 x 0.75mm
feedback to interface with external
MSL3087
VQFN
DC/DC converter
and resistor
based
of LCD panel refresh
frequency
(see
Programming
Guide)
LED Short Circuit threshold setting.
8-CH LED driver with integrated boost
• 1MHz I²C/SMBus
MSL3088interface; use optional
and SYNC input.
• Resistor programmable LED short circuit threshold
I²C and SMBus are trademarks of their respective owners.
• Die over-temperature
protection
Revision 0, Junecut-off
2011
Page 1 of 26
© Atmel Inc., 2011. All rights reserved.
• -40°C to +85°C operating temperature range
• Lead free, halogen free, RoHS compliant package
CGND
application circuit
Description
The MSL3086/88 8-channel LED drivers with integrated boost regulator controller offer a complete
solution to drive up to eight parallel LED strings at up to 40V. The LED current sinks control up to 60mA
peak for up to 19W of LED power. A single resistor sets LED current with string matching and accuracy
within ±3%.
The advanced integrated PWM circuitry allows up to 4095:1 dimming, and offers simple PWM dimming
control. The MSL3086 uses a single PWM input to control the LED dimming signals. The MSL3088
has two inputs, one for frequency and the other for duty cycle. Additionally, internal registers, available
through the I2C interface, optionally control PWM dimming frequency and/or duty cycle.
The MSL3086/88 feature phase-shifted PWM dimming to reduce the boost regulator transient response.
The integrated fault detection circuitry detects and acts upon string open-circuit and LED short circuit
faults, boost regulator over-voltage faults, and die over-temperature faults.
A proprietary Efficiency Optimizer maintains sufficient boost regulator output voltage for proper LED
current while minimizing power use. A 1MHz I2C/SMBus serial interface allows optional dimming
control, fault inspection and control of device parameters; for serial interface information see the
MSL3040/50/60/80/86/87/88/89 Programming Guide.
The MSL3086/88 are offered in the 24-pin VQFN lead-free, halogen-free, RoHS compliant package and
operate over -40°C to +85°C.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
1
DBIE-20120828
Table of Contents
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Packages and Pin Connections.................................................................. 3
Pin Descriptions........................................................................................... 4
Absolute Maximum Ratings........................................................................ 5
Electrical Characteristics............................................................................ 6
Typical Operating Characteristics.............................................................. 7
Block Diagram............................................................................................ 10
Typical Application Circuit........................................................................ 11
Detailed Description.................................................................................. 12
8.1
Differences between the MSL3086 and MSL3088.........................................................12
8.2
Operating the MSL3086/88............................................................................................12
8.3
Boost Regulator Overview..............................................................................................13
8.4
Error Amplifier.................................................................................................................13
8.5
Gate Driver.....................................................................................................................14
8.6Soft-Start........................................................................................................................14
8.7
Boost Fault Monitoring and Protection...........................................................................14
8.8
LED Current Regulators and PWM Dimming Modes.....................................................14
8.9
Efficiency Optimizer (EO)...............................................................................................14
8.10
Fault Monitoring and Auto-Handling...............................................................................14
8.11
Internal Supervisory and LDO........................................................................................15
8.12
Internal Oscillator............................................................................................................15
8.13
Over Temperature Shutdown..........................................................................................15
8.14
Power Saving Modes......................................................................................................15
8.15I2C Serial Interface and Driver Control...........................................................................15
9.0 Application Information............................................................................. 16
9.1
Bypassing VIN and PVIN................................................................................................16
9.2
Setting the LED Current.................................................................................................16
9.3
Fault Monitoring and Automatic Fault Handling..............................................................16
9.4
Setting the LED Short-Circuit Threshold on the MSL3086.............................................16
9.5
Boost Regulator..............................................................................................................17
9.6
The Efficiency Optimizer (EO)........................................................................................18
9.7
Setting the Boost Regulator Output Voltage...................................................................19
9.8
Choosing the Input and output Capacitors.....................................................................19
9.9
Choosing the Inductor....................................................................................................19
9.10 Setting the External MOSFET Current Limit...................................................................20
9.11 Choosing the Switching MOSFET..................................................................................20
9.12 Choosing the Output Rectifier........................................................................................20
9.13 Loop Compensation.......................................................................................................20
10.0 LED Dimming Control................................................................................ 22
10.1
External I2C Control of LED Brightness..........................................................................22
10.2
Phase Shifted LED Dimming Signals.............................................................................22
11.0 Ordering Information................................................................................. 23
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
2
7
8
9
10
11
12
STR1
STR2
STR3
STR4
STR5
STR6
1.0 Packages and Pin Connections
PHASE SHIFTED LED DIMMING SIGNALS
FBO
1
VIN
2
SDA
3
SCL
4
19
By default, string PWM dimming is staggered in time to reduce the transient current demand on
Package
24
23
22
21
20
19
MSL3040/41 automatically
determine
theInformation
stagger
times
based
on the number of enabled strings
frequency.
18 GATE
FBO 1
18 GATE
Package Information
MSL3086
(TOP VIEW)
ED LED D
IMMING SIGNALS
SCTH 5
PVIN
PVIN
20
FLTB
FLTB
21
EN
EN
22
CS
CS
23
PHASE SHIFTED LED DIMMING SIGNALS
COMP
COMP
24
By default, string PWM dimming is staggered in time to reduce th
MSL3040/41 automatically determine the stagger times based on
frequency.
GND
GND
Figure 1.1 24 pin 4 x 4 x 0.75mm VQFN Package
17
PGND
16
VIN
2
ILED
SDA
3
15
CGND
SCL
4
14
PWM
SYNC
5
MSL3088
(TOP VIEW)
17
PGND
16
ILED
15
CGND
14
PWM
21
20
19
STR6
22
12
STR5
23
11
STR4
24
10
STR3
STR6
STR2
STR5
9
PVIN
STR4
8
STR1
STR3
7
FLTB
12
EN
11
CS
10
COMP
9
GND
8
STR2
SIGNALS
7
STR1
g PWM dimming is staggered in time to reduce the transient current demand on the boost regulator. The
STR0 6
13 STR7
STR0 6
13 STR7
utomatically determine the stagger times based on the number of enabled strings and the PWM dimming
FBO
1
18
GATE
VIN
2
17
PGND
SDA
3
16
ILED
SCL
4
15
CGND
SYNC
5
14
PWM
STR0
6
13
STR7
nformation
taggered in time to reduce the transient current demand on the boost regulator. The
e the stagger times based on the number of enabled strings and the PWM dimming
MSL3088
10
11
12
STR5
STR6
STR2
9
STR4
8
STR3
7
STR1
(TOP VIEW)
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
Page 22 of 22
3
2.0 Pin Descriptions
Table 2.1 Pin Assignments
Name
FB
VIN
SDA
SCL
SYNC
SCTH
STR0
STR1
STR2
STR3
STR4
STR5
STR6
STR7
PWM
CGND
ILED
PGND
GATE
PVIN
FLTB
EN
CS
COMP
GND
EP
MSL
3086 3088 Pin Description
VLED Voltage Regulator Feedback Input: Connect a resistive voltage divider from the boost regulator output, VLED, to FB to set the un-optimized
1
1
boost regulator output voltage. The feedback regulation voltage is 2.5V.
2
2
Power Supply Input: Power supply input. Apply 4.5V to 5.5V to VIN. Decouple VIN to GND a 1uF or greater capacitor placed close to VIN.
I²C Serial Data I/O: SDA is the I²C serial interface data input/output. Connect SDA to VIN when unused. For interface information see the
3
3
MSL3040/50/60/80/86/87/88/89 Programming Guide.
I²C Serial Clock Input: SCL is the I²C serial interface clock input. Connect SCL to VIN when unused. For interface information see the
4
4
MSL3040/50/60/80/86/87/88/89 Programming Guide.
PWM Synchronization Input: A signal of 20Hz to 50kHz applied to SYNC controls the LED PWM dimming frequency. The signal at PWM
5
controls the LED PWM dimming duty cycle. For serial interface controlled PWM dimming, connect SYNC to GND and refer to the register definitions
section for registers 0x10 through 0x14 in the MSL3040/50/60/80/86/87/88/89 Programming Guide.
String Short Circuit Threshold Level Setting Input: SCTH programs the LED string short-circuit detection threshold. Connect a resistor from
5
SCTH to GND to set the short-circuit threshold level to 4.9V (1kΩ), 5.8V (27kΩ), 6.8V (68kΩ) or 7.6V (330kΩ). A short circuit is detected when
the STRn voltage is above the threshold while STRn is on.
6
6
LED String 0 Current Sink: Connect the cathode end of series LED String 0 to STR0. If not used, connect STR0 to GND.
7
7
LED String 1 Current Sink: Connect the cathode end of series LED String 1 to STR1. If not used, connect STR1 to GND.
8
8
LED String 2 Current Sink: Connect the cathode end of series LED String 2 to STR2. If not used, connect STR2 to GND.
9
9
LED String 3 Current Sink: Connect the cathode end of series LED String 3 to STR3. If not used, connect STR3 to GND.
10
10
LED String 4 Current Sink: Connect the cathode end of series LED String 4 to STR4. If not used, connect STR4 to GND.
11
11
LED String 5 Current Sink: Connect the cathode end of series LED String 5 to STR5. If not used, connect STR5 to GND.
12
12
LED String 6 Current Sink: Connect the cathode end of series LED String 6 to STR6. If not used, connect STR6 to GND.
13
13
LED String 7 Current Sink: Connect the cathode end of series LED String 7 to STR7. If not used, connect STR7 to GND.
PWM Dimming and Synchronization Input: Drive PWM with a pulse-width modulated signal with duty cycle of 0% to 100% and frequency of
14
20Hz to 50kHz to control the duty cycle and the frequency of all LED strings. For serial interface controlled PWM dimming connect PWM to GND and
refer to the register definitions section for registers 0x10 through 0x14 in the MSL3040/50/60/80/86/87/88/89 Programming Guide.
PWM Dimming Input: Drive PWM with a pulse-width modulated signal with duty cycle of 0% to 100% and frequency of 20Hz to 50kHz to control
the duty cycle of all LED strings. The frequency of the signal applied to SYNC controls the LED PWM frequency. For serial interface controlled PWM
14
dimming, connect PWM to GND and refer to the register definitions section for registers 0x10 through 0x14 in the MSL3040/50/60/80/86/87/88/89
Programming Guide.
15
15
Connect To Ground: Connect to CGND to GND close to driver.
Maximum LED Current Control Input: Connect a resistor from ILED to GND to set the full-scale LED current. See the section “Setting the LED
16
16
Current” beginning on page15 for more information.
17
17
Power Ground: Ground of the boost regulator gate driver. Connect PGND to CGND and EP as close to the MSL3086/88 as possible.
18
18
Gate Drive Output: Connect GATE to the gate of the boost regulator switching MOSFET
Boost Regulator Power Supply Input: PVIN is the power supply input for the external MOSFET gate driver. Apply 4.5V to 5.5V to PVIN.
19
19
Decouple PVIN with two 1uF capacitors placed close to PVIN.
Fault Output: FLTB sinks current to GND when a fault is detected. The Boost Over-Voltage Fault does not latch; the fault goes away when the fault
20
20
condition no longer exists, all other faults latch. Clear faults by toggling EN low and then high, or by cycling input power off and on. Additionally,
fault control is available through the I2C compatible serial interface; see the MSL3040/50/60/80/86/87/88/89 Programming Guide for information.
Enable Input: Drive EN high to turn on the device, drive it low to turn it off. For automatic startup connect EN to VIN. Toggle EN low then high to
21
21
reset FLTB.
Boost Regulator Current Sense Input: Connect the current sense resistor from CS and the MOSFET source to GND to set the boost regulator
22
22
current limit. The current limit threshold is 100mV. See the section “Setting the Current Limit” beginning on page 20 for more information.
Boost Regulator Compensation Node: Connect the compensation network components from COMP to FB to compensate the boost regulator
23
23
control loop, as shown in the Typical Applications Circuit on page 11. See the section “Loop Compensation” beginning on page 21 for more
information.
24
24
Signal Ground: Connect GND to EP as close to the device as possible.
Exposed Die-Attach Paddle : Connect EP to CGND, PGND and to the system ground. EP is the return path for the LED current as well as the
EP
EP
primary thermal path to remove heat generated in the MSL3086/88. Use a large circuit board trace to connect from EP to the boost supply output
capacitor ground and to the input supply ground return. Connect EP to a large copper ground plane for best thermal and electrical performance.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
4
3.0 Absolute Maximum Ratings
Voltage (with respect to GND)
VIN, PVIN, EN, SDA, SCL, PWM, FLTB..................................................... -0.3V to +5.5V
SYNC, SCTH, CS, COMP, FB, GATE.........................................................-0.3V to +5.5V
ADDR, ILED, SCTH.................................................................................. -0.3V to +2.75V
STR0 to STR7............................................................................................. -0.3V to +40V
PVIN to VIN................................................................................................................ ±1V
PGND, CGND, EP.....................................................................................-50mV to 50mV
Current (into pin)
VIN.............................................................................................................................50mA
GATE, PVIN.........................................................................................................±1250mA
STR0 to STR7...........................................................................................................75mA
EP, PGND, GND.................................................................................................. -1000mA
All other pins.............................................................................................. -20mA to 20mA
Continuous Power Dissipation
24-Pin 4mm x 4mm VQFN (derate 25mW/°C above TA = +70°C)...................... 1850mW
Ambient Operating Temperature Range TA = TMIN to TMAX................................... -40°C to +85°C
Junction to Ambient Thermal Resistance (θJA), 4-Layer (Note 8)..................................... 29°C/W
Junction to Ambient Thermal Resistance (θJA), 2-Layer (Note 8)..................................... 38°C/W
Junction to Case Thermal Resistance (θJC)..................................................................... 8.6°C/W
Junction Temperature ....................................................................................................... +125°C
Storage Temperature Range.............................................................................. -65°C to +125°C
Lead Soldering Temperature, 10s......................................................................................+300°C
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
5
4.0 Electrical Characteristics
VVIN = 5V, VEN = 5V, Default Register Settings of Table 1, TA = -40°C to 85°C, unless otherwise noted. Typical values are at TA = +25°C
Parameter
DC Electrical Characteristics
VIN Operating Supply Voltage
VIN Operating Supply Current
VIN Shutdown Supply Current
SDA, SCL, PWM, SYNC Input High Voltage
SDA, SCL, PWM, SYNC Input Low Voltage
Minimum PWM On-Time
PWM, SYNC Input Frequency Range
SDA, FLTB Output Low Voltage
EN Threshold
ILED Regulation Voltage
STR0 to STR7 LED Regulation Current
STR0 to STR7 LED Current Load Regulation
STR0 to STR7 LED Current Matching
STR0 to STR7 Minimum Headroom
STR0 to STR7 Short Circuit Fault Threshold
FB Feedback Output Current
FB Feedback Output Current Step Size
Thermal shutdown temperature
Boost Regulator Electrical Characteristics
Switching Frequency
Gate Voltage Rise/Fall Time
CS Current Limit Threshold Voltage
Maximum Duty Cycle
Minimum On Time
Boost Regulator Leading-Edge Blanking Period
FB Regulation Voltage
I²C Switching Characteristics
SCL Clock Frequency
Bus Timeout Period
STOP to START Condition Bus Free Time
Repeated START condition Hold Time
Repeated START condition Setup Time
STOP Condition Setup Time
SDA Data Hold Time
SDA Data Valid Acknowledge Time
SDA Data Valid Time
SDA Data Set-Up Time
SCL Clock Low Period
SCL Clock High Period
SDA, SCL Fall Time
SDA, SCL Rise Time
SDA, SCL Input Suppression Filter Period
Note 1.
Note 2.
Note 3.
Note 4.
Note 5.
Note 6.
Note 7.
Note 8.
Note 9.
Conditions and Notes
Min
Typ
4.5
All STRn outputs 100% duty
EN = GND
Max
Unit
5.5
18
1
V
mA
µA
V
V
ns
Hz
V
V
V
mA
%/V
%
V
V
V
µA
µA
°C
1.82
0.72
20
Sinking 6mA
VEN rising
Minimum RILED = 60kΩ
RILED = 100kΩ, TA= 25°C VSTRn = 1V
RILED = 100kΩ VSTRn = 1V to 5V
String to average of all strings
VSTRn = 60mA
MSL3086, RSCTH = 1.0kΩ
MSL3088, scThrshLvl[1:0] = 00
FBO DAC = 0xFF, VFB = 0
58.2
1.25
60.0
0.15
-3
3.98
3.98
224
61.8
3
0.5
4.96
4.96
350
1.1
135
569
CGATE = 1nF
75
At factory set boost frequency
fBOOST = 350kHz to 1MHz (contact factory for boost frequencies different
from 625kHz)
2.4
Bus timeout disabled (Note 1)
TA = 25°C (Note 7)
(Note 7)
(Note 7)
(Note 7)
(Note 7)
(Note 7)
(Note 2) (Note 7)
(Note 3) (Note 7)
(Note 7)
(Note 7)
(Note 7)
(Note 4) (Note 5) (Note 7)
(Note 7)
(Note 6) (Note 7)
50,000
0.4
1.5
Temperature Rising, 10°C Hysteresis
1/tSCL
ttimeout
tBUF
tHD:STA
tSU:STA
tSU:STOP
tHD:DAT
tVD:ACK
tVD:DAT
tSU:DAT
tLOW
tHIGH
tf
tr
tSP
400
200
0
29
0.5
0.26
0.26
0.26
0
0.05
0.05
100
0.5
0.26
665
50
111
90.1
762
147
kHz
ns
mV
%
241
300
ns
130
2.5
2.6
ns
V
1000
30
0.55
0.55
120
120
50
kHz
ms
µs
µs
µs
µs
ns
µs
µs
ns
µs
µs
ns
ns
ns
Minimum SCL clock frequency is limited by the bus timeout feature, which resets the serial bus interface if either SDA or SCL is held low for timeout.
tVD:ACK = SCL LOW to SDA (out) LOW acknowledge time.
tVD:DAT = minimum SDA output data-valid time following SCL LOW transition.
A master device must internally provide an SDA hold time of at least 300ns to ensure an SCL low state.
The maximum SDA and SCL rise times is 300ns. The maximum SDA fall time is 250ns. This allows series protection resistors to be connected between SDA and SCL inputs and
the SDA/SCL bus lines without exceeding the maximum allowable rise time.
MSL3086/88 include input filters on SDA and SCL that suppress input noise less than 50ns
Parameter is guaranteed by design and not production tested.
Per JEDEC specification JESD51-5 and JESD51-12.
Tests performed at TA = 25°C, specifications over temperature guaranteed by design.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
6
Note 6.
Note 7.
Note 8.
Note 9.
to be connected between SDA and SCL inputs and the SDA/SCL bus lines without exceeding the maximum allowable rise
time.
MSL3086/87/88 include input filters on SDA and SCL that suppress input noise less than 50ns
Parameter is guaranteed by design and not production tested.
Per JEDEC specification JESD51-5 and JESD51-12.
Tests performed at TA = 25°C, specifications over temperature guaranteed by design.
5.0 Typical Operating Characteristics
Typical Operating Characteristics (Typical Application Circuit, unless otherwise stated)
(Typical Operating Circuit, unless otherwise stated, TA = +25°C, unless otherwise noted)
BOOST REGULATOR EFFICIENCY vs.
OUTPUT CURRENT
100
10000
1000000
90
100000
1000
60
50
40
30
VPWR = 12V
20
fBOOST = 625kHz
0
0
200
400
600
800
100
RISET (k )
EN = 1
sleep = slpPwrSv = 1
EN
EN==00
(V)
VV
ININ(V)
POWER-UP WAVEFORMS INTO 100% DUTY CYCLE
STR n CURRENT vs. RISET
10
10
1
0.01
0.01
4.5
4.5 4.6
4.6 4.7
4.7 4.8
4.8 4.9
4.9 5.0
5.0 5.1
5.1 5.2
5.2 5.3
5.3 5.4
5.4 5.5
5.5
1,000
OUTPUT CURRENT (mA)
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
10
100
EN = 1
sleep = slpPwrSv = 0
BOOST NOT SWITCHING
1
0.1
0.1
VLED  37V
10
STRn CURRENT (mA
EN = 1
EN = 1
sleep = slpPwrSv = 1 sleep = slpPwrSv = 0
BOOST NOT SWITCHING
10000
100
1000
70
IIN (µA)
IIN (µA)
EFFICIENCY (%)
80
SUPPLYCURRENT
CURRENT
SUPPLY
vs.SUPPLY
SUPPLYVOLTAGE
VOLTAGE
vs.
1000
MSL3086/MSL3087/MSL3088
Datasheet
CH1 = VEN, CH2 = VLED, CH3 = VSTRx, CH4 = IPWR
BOOST WAVEFORMS
10% LED DUTY CYCLE
POWER-UP WAVEFORMS INTO 100% DUTY CYCLE
(ZOOM IN)
© Atmel Inc., 2011. All rights reserved.
CH1 = VEN, CH2 = VLED, CH3 = VSTRx, CH4 = IPWR
AUTO CALIBRATION
Page 6 of 26
CH1 = VLED, CH2 = VGATE, CH3 = IINDUCTOR
BOOST WAVEFORMS
Atmel
Datasheet
100%
LEDMSL3086/MSL3088
DUTY CYCLE
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
7
VLED, CH3 = VSTRx, CH4 (continued)
= IPWR
= VEN, CH2 =Characteristics
5.0 TypicalCH1
Operating
CH1 = VLED, CH2 = VGATE, CH3 = IINDUCTOR
(Typical Operating Circuit, unless otherwise stated, TA = +25°C, unless otherwise noted)
AUTO CALIBRATION
CH2 = VLED, CH3 = VSTRx
BOOST WAVEFORMS
100% LED DUTY CYCLE
MSL3086/MSL3087/MSL3088 Datasheet
CH1 = VLED, CH2 = VGATE, CH3 = IINDUCTOR
BOOST REGULATOR WAVEFORMS
10% TO 99.5% LED DUTY CYCLE
© Atmel Inc., 2011. All rights reserved.
EXTERNAL SYNC AND PWM
MSL3088
Page 7 of 26
CH1 = VLED, CH2 = VGATE, CH3 = VPWM, CH4 = IINDUCTOR
AUTOMATIC PHASE SHIFTED PWM DIMMING
CH1 = VSTR0, CH2 = VSTR2, CH3 = VSTR4, CH4 = VSTR6
CH1 = VSYNC, CH2 = VPWM, CH3 = VSTR0
EXT SYNC AND PWM, FREQUENCY MULTIPLIED
MSL3088
CH1 = VSYNC, CH2 = VPWM, CH3 = VSTR0
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
8
5.0 Typical Operating Characteristics
(continued)
MSL3086/MSL3087/MSL3088
(Typical Operating Circuit, unless otherwise stated, TA = +25°C, unless otherwise noted)
BOOST REGULATOR GATE DRIVE RISE/FALL
WITH 3nF CAPACITIVE LOAD
Datasheet
DRIVER RISE TIME
This scope image shows the voltage (VSTR0) and current (ISTR0)
waveforms for string zero, and their turn-on rise times and delay
from PWM rising. Also shown is the string power supply output
(VLED), which shows little disturbance. For this photo string 0 is
enabled with all other strings disabled.
CH2 = VGATE
DRIVER FALL TIME
This scope image shows the voltage (VSTR0) and current (ISTR0)
waveforms for string zero, and their turn-off fall times. Also shown
is the string power supply output (VLED), which shows very little
disturbance. For this photo string 0 is enabled with all other strings
disabled, and a 220pF capacitor in series with a 11Ω resistor in
series is placed from STR0 to GND at the device.
© Atmel Inc., 2011. All rights reserved.
Page 9 of 26
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
9
MSL3086/MSL3087/MSL3088 Datasheet
6.0 Block Diagram
Block Diagram
Figure 6.1. Block Diagram
L1
D1
LED
SUPPLY
5V – 32V
CBULK
VLED
Q1
CIN
COUT1
COUT2
RTOP
RCS
GATE
CS
EN
VIN
5V
EFFICIENCY
OPTIMIZER
REG
VDD
RBOTTOM
EO DAC
C1
FB
GATE DRIVE
PVIN
REF
RCOMP
CCOMP2
C2
C3
COMP
CCOMP1
FREQ SET
FAULT DETECT
DUTY
CYCLE SET
STR0
STR1
PWM
STRING
DRIVE LOGIC
SCTH (SYNC)
CGND
FLTB
STR2
ONE OF 8
STRING DRIVERS
SHOWN
STR3
STR4
SCL
STR5
SDA
ILED
RILED
STR6
MSL3086
(MSL3088)
GND
EP
STR7
PGND
Figure 1. MSL3086/MSL3088 Block Diagram
© Atmel Inc., 2011. All rights reserved.
Page 10 of 26
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
10
MSL3086/MSL3087/MSL3088 Datasheet
7.0 Typical Application Circuit
Typical
Application
Circuit
Figure 7.1. Typical
Application Circuit
VPWR = 6.5V TO 16V
10 F
VIN = 5V
1 F
2
VIN
ENABLE
21
3
I2C
INTERFACE
4
PWM
INPUT
14
FAULT
OUTPUT
20
5
18
GATE
22
CS
VLED
43.2k
SDA
MSL3086
FB
1
30k
PWM
100nF
FLTB
COMP
3.12k
220pF
23
SCTH
STR0
STR1
ILED
STR2
STR3
93.1k
STR4
STR5
15
FDC5612
12.5m
EN
SCL
2x
10 F
B380
19
PVIN
82k
16
10 H
2x 1 F
STR6
CGND
PGND
17
EP
STR7
GND
24
6
7
8
9
10
11
12
13
Figure 2. Typical Operating Circuit for Eight 60mA Strings of 10 LEDs each for VIN = 6.5V to 16V.
Detailed Description
The MSL3086/87/88 are LED drivers with eight internal current regulators capable of driving up to 60mA LED current
each. The MSL3086/88 feature an integrated boost regulator controller to power the LED strings, while the MSL3087
controls an external DC/DC converter. They provide a complete LED driver solution for multi-LED string applications. A
single resistor sets the LED current for all strings. The MSL3086/87/88 support PWM LED dimming up to 4095:1 and
feature automatic phase shifted dimming, and dimming synchronized with external digital signals. The MSL3088 features
independent frequency and duty cycle control inputs. All devices feature optional register-set PWM dimming, fault and
other controls via the I2C serial interface; for interface information see the MSL3040/50/60/86/87/88/89 Programming
Guide.
The MSL3086/87/88 include comprehensive fault monitoring and automatic fault handling. Automatic fault handling allows
the MSL3086/87/88 to operate without any microcontroller or FPGA, while control via I2C allows customized fault handling
and device control for more complex applications.
© Atmel Inc., 2011. All rights reserved.
Page 11 of 26
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
11
8.0 Detailed Description
The MSL3086/88 are LED drivers with eight internal current regulators capable of driving up to 60mA LED current each. The MSL3086/88
feature an integrated boost regulator controller to power the LED strings. They provide a complete LED driver solution for multi-LED string
applications. A single resistor sets the LED current for all strings. The MSL3086/88 support PWM LED dimming up to 4095:1 and feature
automatic phase shifted dimming, and dimming synchronized with external digital signals. The MSL3088 features independent frequency and
duty cycle control inputs. All devices feature optional register-set PWM dimming, fault and other controls via the I2C serial interface; for interface
information see the “MSL3040/50/60/80/86/87/88/89 Programming Guide”.
The MSL3086/88 include comprehensive fault monitoring and automatic fault handling. Automatic fault handling allows the MSL3086/88 to
operate without any microcontroller or FPGA, while control via I2C allows customized fault handling and device control for more complex
applications.
The small 4x4mm VQFN package allows a small overall LED driver solution, while the high package power dissipation offers high output power
capability.
8.1 Differences between the MSL3086 and MSL3088
The MSL3086 requires only power and a single PWM input to set both the frequency and duty cycle of the LED drive signals, and
includes a boost converter controller. The MSL3088 accepts an additional SYNC signal that sets the frequency of the LED dimming
signals, while the PWM input sets the LED duty cycle. Similar devices are presented in Table 8.1 for comparison:
Table 8.1. LED Driver Comparison with Similar Parts
PART
NUMBER
OF LED
STRINGS
MAX
CURRENT
PER
STRING
PHASE
SHIFTED
STRING
DRIVERS
INTERNAL
BOOST
CONTROLLER
RESISTOR SET
LED SHORT
CIRCUIT
THRESHOLD
SEPARATE
SYNC
INPUT***
MSL3086
8
60mA
YES
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
MSL3087*
8
60mA
YES
NO
YES
NO
SMALL TV
MSL3088
8
60mA
YES
YES
NO
YES
SMALL TV
8
60mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
4**
120mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
2**
240mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
MSL3080
BEST FOR
1**
480mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
MSL3040*
4
120mA
YES
YES
YES
NO
MONITOR, AUTOMOTIVE
MSL3041*
4
120mA
YES
YES
YES
YES
MONITOR, AUTOMOTIVE
5
60mA
NO
YES
YES
NO
INDUSTRIAL PANEL
1**
300mA
NO
YES
YES
NO
INDUSTRIAL PANEL
6
60mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
3**
120mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
2**
180mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
1**
360mA
NO
YES
YES
NO
MONITOR, INDUSTRIAL PANEL
MSL3050*
MSL3060*
* Future product, contact factory for information.
** Drivers without phase shift allow parallel connection of string drive outputs for increased string current.
*** Drivers with separate SYNC input expect two control signals, one for dimming duty cycle and one for dimming frequency.
8.2 Operating the MSL3086/88
The MSL3086/88 are simple to operate; set up the boost regulator (see the section “Boost Regulator” beginning on page 17), set the
string on-current (see the section “Setting the LED Current” beginning on page 16), supply a PWM control signal to the PWM input
(MSL3088 requires a second control signal applied to the SYNC input), set the LED short circuit threshold voltage (see the section
“Setting the LED Short-Circuit Threshold” beginning on page 16), connect the LED strings and apply power (decoupled as instructed
in the section “Bypassing VIN and PVIN” beginning on page 16).
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
12
8.3 Boost Regulator Overview
The MSL3086/88 boost regulator boosts the input voltage up to the regulated output voltage. For design details see the section “Boost
Regulator” beginning on page 17, the following text presents an overview of the boost regulator controller.
The boost regulator uses an external switching MOSFET, current sense resistor, inductor, rectifier, and input and output capacitors for
this purpose (Figure 8.1). Because the MOSFET and current sense resistor are external, the boost regulator operates over a wide range
of input and output voltage, and LED current configurations. It includes a 2.5V reference voltage, fixed slope compensation and external
voltage regulator compensation to optimize the control loop for each configuration. Because the boost regulator components are external,
it is useful for a number of topologies such as SEPIC, flyback, and single-switch forward converters. The boost regulator includes softstart, adjustable cycle-by-cycle current limiting, and output over-voltage fault detection.
MSL3086/MSL3087/MSL3088 Datasheet
Figure 8.1. Power section of MSL3086/MSL3088
5V
VPWR
PVIN
CIN
L1
D1
GATE DRIVE
GATE
LIMIT
1.1V
CURRENT
CS
0.1 V
A = 11
SENSE
SLOPE
COMP
0.4V
+
1.5V
EFFICIENCY
OPTIMIZER
SOFT
START
VLED
Q1
COUT
RESR
RCS
GND
RTOP
FB
RCOMP
CCOMP2
CCOMP1
RBOTTOM
COMP
COMPENSATION:
CCOMP2 = POLE
CCOMP1, RCOMP = ZERO
REF
DROPOUT DETECT
MSL3086
STRn
LED
CURRENT
SINK
Figure 3. Power section of MSL3086/MSL3088
ERROR
AMPLIFIER
8.4 Error
Amplifier
The internal error amplifier compares the external divided output voltage at FB to the internal 2.5V reference voltage to set
The
erroroutput
amplifier
compares
external
divided
output
voltageat
atCOMP
FB to the
2.5Vaccessible
reference voltage
set the
theinternal
regulated
voltage.
Thethe
error
amplifier
output
voltage
is internal
externally
and is to
used
in regulated
output voltage. The error amplifier output voltage at COMP is externally accessible and is used in conjunction with an external RC
conjunction with an external RC network to compensate the voltage regulator. FB also drives the integrated boost overnetwork to compensate the voltage regulator. FB also drives the integrated boost over-voltage comparator that detects if the output
voltage comparator that detects if the output voltage exceeds the regulation voltage, to generate a fault condition. The
voltage exceeds the regulation voltage, to generate a fault condition. The error amplifier internally controls the current mode PWM
error
amplifier internally controls the current mode PWM regulator.
regulator.
GATE DRIVER
The gate driver drives the gate of the external boost regulator switching MOSFET. The drain of the switching MOSFET in
turn drives the boost inductor and rectifier to boost the input voltage to the regulated output voltage. The gate driver
sources and sinks up to 1A allowing fast switching speed and allows the use of MOSFETs with high gate capacitance.
The gate driver power is separated from the internal circuitry power to reduce internal noise and to allow separate gate
driver bypassing for optimal performance.
SOFT-START
The boost regulator includes a built in soft-start to prevent excessive input current overshoot at turn-on. The soft-start
ramps the output regulation voltage from 0V at turn-on to the as-configured regulation
output voltage over
1.6ms. Note 13
Atmel MSL3086/MSL3088
Datasheet
8-String 60mA
Drivers
withvoltage;
Integrated Boost
Controller
and Phase Shifted
that the boost regulator only controls output voltages greater
thanLED
the
input
when
the soft-start
setsDimming
the regulation
voltage below the input voltage, the actual output voltage remains at approximately the input voltage.
8.5 Gate Driver
The gate driver drives the gate of the external boost regulator switching MOSFET. The drain of the switching MOSFET in turn drives the
boost inductor and rectifier to boost the input voltage to the regulated output voltage. The gate driver sources and sinks up to 1A allowing
fast switching speed and allows the use of MOSFETs with high gate capacitance. The gate driver power is separated from the internal
circuitry power to reduce internal noise and to allow separate gate driver bypassing for optimal performance.
8.6 Soft-Start
The boost regulator includes a built in soft-start to prevent excessive input current overshoot at turn-on. The soft-start ramps the output
regulation voltage from 0V at turn-on to the as-configured regulation output voltage over 1.6ms. Note that the boost regulator only
controls output voltages greater than the input voltage; when the soft-start sets the regulation voltage below the input voltage, the actual
output voltage remains at approximately the input voltage.
8.7 Boost Fault Monitoring and Protection
The boost regulator includes fault monitoring and protection circuits to indicate faults and prevent damage to the boost regulator or other
circuitry. The boost regulator has cycle by cycle current limiting that prevents excessive current through the power MOSFET. The current
limit is has a fixed threshold voltage across the current sense resistor, thus the current limit is set by choosing the proper value current
sense resistor.
The boost regulator includes an output over-voltage fault monitor that indicates a fault when the voltage at FB exceeds the 2.8V overvoltage protection (OVP) threshold. When an over-voltage fault occurs FLTB sinks current to GND to indicate that a fault has occurred.
OVP fault is non-latching, the fault clears when the over-voltage condition disappears.
8.8 LED Current Regulators and PWM Dimming Modes
The MSL3086/88 include eight open-drain LED current regulators that regulate LED current up to 60mA per channel and sustain up to
40V, allowing them to drive up to 10 white LEDs each. The current regulators control the Efficiency Optimizers which in turn controls the
boost regulator output voltage to minimize LED voltage while maintaining sufficient headroom for LED current regulators.
The LED regulation current is set by a single resistor from ILED to GND. LED dimming is by PWM, and is controlled by default through
an external signal(two signals in the case of the MSL3088), or optionally by internal registers accessed through the I2C compatible serial
interface (for interface information see the MSL3040/50/60/80/86/87/88/89 Programming Guide). LED drive dimming signals are phase
shifted, where LED string on-times are successively delayed by 1/8th cycle from STR0 to STR7, reducing boost regulator transient
response and increasing the transient frequency of the boost regulator. The MSL3088 features synchronized dimming mode where
separate PWM and SYNC inputs control PWM dimming duty cycle and frequency.
8.9 Efficiency Optimizer (EO)
The efficiency optimizer monitors LED strings and controls the boost regulator output voltage to minimize LED current regulator overhead
voltage while maintaining sufficient voltage for accurate current regulation. The efficiency optimizer injects a current into the boost
regulator FB input node to reduce the boost regulator output voltage.
The efficiency optimizer has two modes of operation, initial calibration and auto calibration. Initial calibration happens at turn-on and
optimizes boost regulator output voltage. Auto calibration happens once per second to re-optimize the boost output voltage in response
to changing LED forward voltage due to aging or temperature effects. The efficiency optimizer requires that strings have a minimum ontime of 2µs for proper EO operations to maintain current regulation.
8.10 Fault Monitors
The MSL3086/88 include comprehensive fault monitoring and corrective action. They monitor the LED current regulators for LED string
open circuit and LED short circuit faults. They also monitor the boost regulator for output over-voltage. Strings with LED Short Circuit or
Open Circuit faults are turned off and ignored by the Efficiency Optimizer.
FLTB sinks current to GND when a fault is detected. The Boost Over-Voltage Fault does not latch, the fault goes away when
the fault condition no longer exists and FLTB is released; all other faults latch. Clear faults by toggling EN low and then high,
or by cycling input power off and on. Additionally, fault control is available through the I2C compatible serial interface; see the
MSL3040/50/60/80/86/87/88/89 Programming Guide for information. For more information about string faults and automatic fault
handling see the section “Fault Monitoring and Automatic Fault Handling” beginning on page 15.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
14
8.11 Internal Supervisory and LDO
The MSL3086/88 have a Power-On-Reset circuit that monitors VIN and allows operation when VIN exceeds 4.25V. The MSL3086/88
have built-in LDOs that generate 2.5V to power the logic and oscillator sections. An integrated supervisor ensures that the LDO and
internal oscillator are stable before enabling the boost controller. The boost controller goes through a soft-start before the LED drivers are
enabled.
8.12 Internal Oscillator
The MSL3086/88 include a 20MHz internal oscillator that is divided down to drive the boost controller, and the LED PWM engine. The
oscillator is factory trimmed. Contact the factory if required to change the 20MHz default oscillator frequency, available frequencies fall
between 16MHz and 24MHz
8.13 Over Temperature Shutdown
The MSL3086/88 include automatic over-temperature shutdown. When the die temperature exceeds 135°C, the device turns off, as if EN
is pulled low, and is held off until the die temperature drops below 120°C, at which time it turns back on. While MSL3086/88 is in overtemperature shutdown the onboard regulators are off, register values reset and the serial interface is disabled.
8.14 Power Saving Modes
The MSL3086/88 have 3 primary power save modes available through the I2C compatible serial interface. See the
MSL3040/50/60/80/86/87/88/89 Programming Guide for information.
8.15 I2C Serial Interface and Driver Control
The I2C serial interface allows control of PWM dimming, fault monitoring, and various other control functions. For a detailed explanation
of interface operation see the “MSL3040/50/60/80/86/87/88/89 Programming Guide”.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
15
9.0 Application Information
9.1 Bypassing VIN and PVIN
Bypass VIN with a capacitor of at least 1µF. Bypass PVIN with at least 2µF. Place all bypass capacitors close to the device.
9.2 Setting the LED Current
Set the on-current for all LED strings with a resistor from ILED to GND. Choose the resistor using:
where ILED is the LED on-current in Amps.
The maximum LED current per-string is 60mA. Driving all eight strings with 60mA at high duty cycles and elevated ambient temperatures
requires proper thermal management to avoid over-temperature shutdown. Connect the exposed pad (EP) to a large copper ground
plane for best thermal and electrical performance.
9.3 Fault Monitoring and Automatic Fault Handling
The MSL3086/88 monitor the LED strings to detect LED short-circuit, LED string open-circuit and Boost Over-voltage faults. String faults
latch the open drain fault output FLTB low. A boost over-voltage fault pulls FLTB low but is not latching.
When shorted LEDs are detected in a string the string is disabled and no longer monitored by the Efficiency Optimizer. The MSL3086/88
pulls FLTB low and recalibrates the LED power supply voltage. Set the short circuit voltage threshold with a resistor between SCTH
and GND, as explained in the section “Setting the LED Short-Circuit Threshold” beginning on page 16. Additionally, strings with shorted
LEDs are flagged in registers 0x05 through 0x08. For information about the fault registers and the I2C compatible serial interface see the
MSL3040/41/50/60/80/86/87/88 Programming Guide.
When an open circuit occurs, the Efficiency Optimizer detects a loss of current regulation which must persist for greater than 2µs to be
detected therefore the minimum on-time for the strings is 2µs. In this case the Efficiency Optimizer keeps increasing the LED voltage
(boost regulator output voltage), in an attempt to bring the string back in to regulation. This continues until the voltage is at the maximum
level. The MSL3086/88 then determine that any LED strings that are not regulating current are open circuit. It disables those strings, pulls
FLTB low and recalibrates the LED power supply voltage. When the boost regulator is at its maximum value, fictitious LED short circuit
faults can occur when the LED short circuit threshold is set to a low value and/or the string LEDs exhibit excessive voltage mismatch.
Toggle EN low and then high to clear all faults and return the MSL3086/88 to controlling and monitoring all strings. Fault conditions
that persist re-establish fault responses. Additionally, strings with open circuits faults are flagged in registers 0x05 through 0x08. For
information about the fault registers and the I2C compatible serial interface see the MSL3040/41/50/60/80/86/87/88 Programming Guide.
9.4 Setting the LED Short-Circuit Threshold on the MSL3086
When a given string, STRn, is sinking LED string current, the fault detection circuit monitors the STRn voltage. Typical optimized STRn
on-voltage is 0.5V. When one or more LED’s of a string are shorted out, the STRn voltage increases above the nominal. When the
voltage is above the Short-Circuit Threshold the fault circuit generates an LED short circuit fault. In most cases, two LEDs in a string must
be shorted to cause a short circuit fault, but because LED VF differs for different LEDs, the number of shorted LEDs required to generate
a fault varies. Set the LED short-circuit threshold with a resistor from SCTH to GND using:
Table 9.1 Short Circuit Threshold Resistor
RSCTH
Threshold Voltage
1.0kΩ (or GND)
4.9V
27kΩ
5.8V
68kΩ
6.8V
330kΩ (or open)
7.6V
RSCTH is queried at power up, and when EN is taken high, to set the threshold level. The MSL3088 does not have an SCTH
input; the threshold is pre-set to 6.8V. Additionally, register 0x04 holds the Short Circuit Threshold level, changeable through
the I2C compatible serial interface. For information about the Short Circuit Threshold register and the serial interface see the
“MSL3040/50/60/80/86/87/88/89 Programming Guide”.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
16
Figure 9.1 Open-Circuit and Short-Circuit Detection Block Diagram
9.5 Boost Regulator
The boost regulator boosts the input voltage to the regulated output voltage that drives the LED anodes. The MSL3086/88 boost
regulators use external MOSFET switches and current sense resistors, allowing a wide variety of input/output voltage combinations and
load currents. The boost regulator switching frequency is 625kHz. Switching frequencies of 350kHz, 500kHz, 750kHz, 875kHz and 1Mhz
are also available; contact the factory for information.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
17
MSL3086/MSL3087/MSL3088 Da
required to power the LEDs. This ensures that there is sufficient voltage available for LED current control,
9.6 The
Efficiency
supply
noiseOptimizer
rejection,(EO)
while minimizing power dissipation. It does this my injecting a small current into the
steps
(8-bit
resolution).
A256
voltage
divider
from the
boost regulator output voltage to FB sets the regulation voltage (RTOP and RBOTTOM in Figure 8.1 on page 13).
The EO improves power efficiency by dynamically adjusting the power supply output voltage to the minimum required to power the LEDs.
This
ensures
that there
sufficient
available
for LED
current control,
good EN
powerissupply
rejection,
whileEN
minimizing
When
turned
on,iseither
byvoltage
applying
input
voltage
to VINand
while
high,noise
or by
driving
high with
power dissipation. It does this by injecting a small current into the FB input over 256 steps (8-bit resolution).
voltag
VIN, the EO begins an initial calibration cycle by monitoring the external LED current regulators. If all the c
When
turned on,
either by applying
input voltage
to VIN whilethe
EN is
high,
or by driving
EN high
voltage applied
to VIN, the
regulators
maintain
LED current
regulation
EO
output
current
is with
increased
to reduce
theEOboost output v
begins an initial calibration cycle by monitoring the external LED current regulators. If all the current regulators maintain LED current
4ms
power
supply
settling
time,
it
rechecks
the
regulators,
and
if
they
are
maintaining
regulation
the proce
regulation the EO output current is increased to reduce the boost output voltage. After the 4ms power supply settling time, it rechecks
one
or
more
current
regulator
looses
regulation.
This
step
requires
that
the
strings
are
turned
on
for a min
the regulators, and if they are maintaining regulation the process repeats until one or more current regulator looses regulation. This
step
requires
that
the
strings
are
turned
on
for
a
minimum
of
2µs
to
detect
current
regulation.
The
EO
then
decreases
the
output
current
detect current regulation. The EO then decreases the output current to increase boost output voltage, givi
to increase boost output voltage, giving the regulator enough headroom to maintain regulation with minimal power dissipation. The
enough
headroom to maintain regulation with minimal power dissipation. The oscilloscope picture Figure 5
oscilloscope picture Figure 9.2 shows this procedure. The EO automatically re-calibrates VOUT every 1 second, and always increases
automatically
VOUT every 1 second, and always increases the string volta
procedure.
the string voltageThe
whenEO
a string
is detected withre-calibrates
insufficient current.
string is detected with insufficient current.
Figure 9.2 Efficiency Optimizer (EO)
Figure 5. Efficiency Optimizer (EO)
Atmel MSL3086/MSL3088 Datasheet
8-StringV
60mA
LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
SETTING THE BOOST REGULATOR OUTPUT
OLTAGE
18
Select the voltage divider resistors (RTOP and RBOTTOM in Figure 3 on page 13) by first determining VOUT(MIN
for the current regulator headroom brings VOUT(MIN) to 35.5V and VOUT(MAX) to 38.5. Next determine RTOP using:

VOUT ( MIN) V f ( MIN )  # ofLEDs  0.5 , and
Figure 5. Efficiency Optimizer (EO)
VOUT ( MAX )  VOUT ( MIN )
.
RTOP 

VOUT ( MAX ) V f ( MAX )  # ofLEDs  0.5 ,
365  10 6
9.7 Setting the Boost Regulator Output Voltage
SETTING THE BOOST REGULATOR OUTPUT VOLTAGE
Then determine RBOTTOM using:
Vf(MAX)
the LED’s minimum and
Vf(MIN) and
Select the
voltage
divider
resistors
(RTOPresistors
and RBOTTOM
in Figure
on pagein13)
by where
first3determining
V
andare
V
OUT(MIN)
OUT(MAX), the minimum
Select
the
voltage
divider
(RTOP
and 8.1
RBOTTOM
Figure
on page
12)
by first
determining
VOUT(MIN) and V
(page 15). For example, if the LED minimum
forward
and maximum
LED
string
anode
power
supply
(boost
regulator)
voltage,
using:
the minimum and maximum LED string anode power supply (boost regulator) voltage, using:
LEDs in a string, the total minimum and maximum vo
2.5
 RTOP 
.
R BOTTOM
to
for the current regulator headroom brings V
 2.5

VOUT ( MAX ) V f ( MAX )  # ofLEDs  0.5 , OUT(MIN)

VOUT ( MIN) VVfOUT
( MIN(MAX
)  )# ofLEDs  0.5 , and and












VOUT ( MAX )  VOUT ( MIN )
full-scale

. minimum
R atV22the
and Vcurrent
theRILED
LED’s
and ma
where
where Vf(MIN) and Vf(MAX) are the LED’s minimum and maximum forward voltage
set6by
(page
16).
f(MIN)
f(MAX) are
Pagedrops
17 ofTOP

365
10
is
V
=
3.8V,
using
10
LEDs
in
a
string,
the
total
For example,
if
the
LED
minimum
forward
voltage
is
V
(page
14).
For
example,
if
the
LED
minimum
forward
vo
f(MIN) = 3.5V and maximum
f(MAX)
© Atmel Inc., 2011. All rights reserved.
minimum
and maximum
voltageAND
drop across
a string
is 35V and 38V. Adding allowance
for the
headroom
brings
LEDs inofa0.5V
string,
thecurrent
total regulator
minimum
and maximum
voltag
CHOOSING
THE INPUT
OUTPUT
CAPACITORS
VOUT(MIN) to 35.5V and VOUT(MAX) to 38.5. Next determine RTOP using:
Then determine RBOTTOM using:
to 35
fordue
the current
regulator
headroom
brings
VOUT(MIN)
The input and output capacitors carry the high frequency current
to the boost
regulator
switching.
The
input capac
prevents this high frequency current from travelling back to the input voltage source, reducing conducted and radiated
2.5
Then current
determineto the load,
Vin
noise. The output capacitor prevents high frequency
OUTthis
OUTLEDs,
( MAX
)  Vthe
( MIN ) and also
.

prevents
R BOTTOM
Rcase
TOP 
RBOTTOM using: RTOP


. loop
conducted and radiated noise. The output capacitors also have a large effect on the boost
regulator
stability and
6
2
.
5
V
OUT (MAX )

365
10
transient response, and so are critical to optimal boost regulator operation.
9.8 Choosing the Input and output Capacitors
Then determine RBOTTOM using:
The input and output capacitors carry the high frequency current due to the boost regulator switching. The input capacitor prevents this
high
frequency current
travelling
to the input
voltage source, reducing conducted and radiated noise. The output capacitor
CHOOSING
THE Ifrom
NPUT
AND back
OUTPUT
CAPACITORS
2.5AND
CHOOSING
THE
INPUT
UTPUT CAPACITOR
prevents high frequency current to the load, in this case the LEDs, and also prevents
conducted and
noise.
The O
output
.

radiated

R BOTTOM
Rand
Use
ceramic
input
and
output
capacitors
that
their rated
capacitance
values
at the
expected
operating
voltages. T
TOPso
capacitors also have a large effect on the boost regulator keep
loop stability
and transient
response,
are
critical
to
optimal
boost the high
The input and output
capacitors
carry
freque

2
.
5
V
OUT
(MAX
)
Typical
Application
Circuit
on
page
11
shows
recommended
values
for
and
10
LEDs
and
60mA
per
string.
Use
a bulk
regulator operation.
prevents this high frequency current from travelling b
electrolytic capacitor where power enters the circuit board.
The output
capacitor
prevents
high frequency
Use ceramic input and output capacitors that keep their rated capacitance values atnoise.
the expected
operating
voltages. The
“Typical
and Use
radiated
noise. The
output capacitors
Application Circuit” on page 11 shows recommended values for and 10 LEDs andconducted
60mA per string.
a bulk electrolytic
capacitor
where power enters the circuit board.
transient response, and so are critical to optimal boo
CHOOSING THE INDUCTOR
CHOOSING THE INPUT AND OUTPUT CAPACITORS
The boost
and and
directs
thatcapacitors
current to carry
the load.
the prop
9.9 Choosing
theregulator
Inductorinductor takes the current from the input source
The input
output
the Using
high frequency
inductor is critical to proper boost regulator operation. Choose prevents
an inductor
with
sufficient
inductance
to
keep
the
induct
this
high
frequency
current
from
travelling
back
CHOOSING
THE INPUT AND OUTPUT CAPACITOR
The
boost
regulator
inductor
takesand
the current
from the input
sourcehandling
and directs
that current
to
the
load.
Using the
proper
inductor
isfrequency cur
ripple
current
within
limits,
with sufficient
current
capability
steady-state
and
transient
conditions.
noise.
Thefor
output
capacitor
prevents
high
Use ceramic
andripple
output
capacitors
that keep th
critical to proper boost regulator operation. Choose an inductor with sufficient inductance
to keep theinput
inductor
current
within limits,
conducted and radiated noise. The output capacitors als
and with sufficient current handling capability for steady-state and transient conditions.
Typical Application Circuit on page 11 shows recomm
The boost regulator switching causes ripple current through thetransient
inductor.response,
The current
during
thetoon-time
fallsr
andrises
so are
critical
optimaland
boost
electrolytic capacitor where power enters the circuit
during
off time.
The causes
slope of
thecurrent
inductor
current
is a function
of rises
the voltage
the total
The
boostthe
regulator
switching
ripple
through
the inductor.
The current
during theacross
on-time the
and inductor,
falls during and
the offso
time.
The
slope of
inductor∆I
current
is a current
function of
the voltage
acrossby
thethe
inductor,
so the
total change
in current,
is the
current
slope
multiplied
timeand
in that
phase
(on time,
tON, Δ
orIL,off
time,
tOFF). In steady
change
in the
current,
L, is the
slope
multiplied
theload
time current,
in that phase
(on voltage,
time, tON, or
off time,
tOFFvoltage
). In steady-state,
where the load
current,
inputcurrent
voltage,does
and output
state,
where by
the
input
and
output
are
all
constant,
the
inductor
not change o
CHOOSING
THE
Icurrent
NPUT rises
ANDduring
OUTPUT
CAPACITORS
voltage are all constant, the inductor current does not change over one cycle, and
so
the amount
the
the on time
CHOOSING
THE
INDUCTOR
one
cycle,
and
so
the
amount
the
current
rises
during
the
on
time
is
the
same
as
the
amount
the
current
drops
during t
is the same as the amount the current drops during the off time. Calculate the duty
cycle
(equalinput
to the and
on-time
divided
by the switching
Use
ceramic
output
capacitors
that keep their
off
time.
Calculate
the
duty
cycle
(equal
to
the
on-time
divided
by
the
switching
period)
using:
The
boost
regulator
inductor
takes
the
current
from t
period) using:
Typical Application Circuit on page 10 shows recommen
inductor is critical to proper boost regulator operation
electrolytic capacitor where power enters the circuit boa
ripple current within limits, and with sufficient current
VOUT  VIN
D D
,
VOUT
VIN
t ON
,
V
The boost regulator switching causes ripple current t
f SWIN VOUT f SW
C
HOOSING
INDUCTOR
theTHE
off time.
The slope of the inductor current
in seconds
using:
where VOUT is the output voltage and VIN is the input voltage. Calculate the on-timeduring
where VOUT is the output voltage and VIN is the input voltage. Thechange
current
slope multiplied
in current,
∆IL, is the
boost regulator
inductor
takes
the current
from the i
where fSW is the boost regulator switching frequency.
state,iswhere
current,
voltage,
and outp
inductor
criticalthe
to load
proper
boost input
regulator
operation.
C
Calculate the on-time in seconds using:
one
cycle,within
and solimits,
the amount
the
current rises
durin
ripple
current
and with
sufficient
current
ha
Calculate the inductor ripple current using:
off time. Calculate the duty cycle (equal to the on-tim
The
Page 20 of 26 boost regulator switching causes ripple current thro
t ON regulator
V IN Vswitching
Vfrequency.
during
the
off time. The slope of the inductor current is a
OUT
IN
where
fSWV
isIN
the2011.
boost
Calculate the inductor ripple
current
Vusing:
© Atmel
Inc.,
All
rights
reserved.
OUT  VIN
IL
,
D in current,
change
∆I,L, is the current slope multiplied by
L
VOUT f SW L
IN load current, input voltage, and output v
state, where V
the
one cycle, and so the amount the current rises during th
where L is the inductance value in Henrys. Choose a value for off
L that
produces
ripple
current
in(equal
the
range
25%
tod5
voltage
and
isofon-time
the
input
where
VOUT isathe
time.
Calculate
theoutput
duty
cycle
toVIN
the
of the steady state DC inductor current. The steady state DC inductor current is equal to the input current. Estimate the
where L is the inductance value in Henrys. Choose a value for L that produces a ripple current in the range of 25% to 50% of the steady
steady-state
inputThe
current
on-time
in seconds
using:
state
DC inductorDC
current.
steady using:
state DC inductor current is equal to the inputCalculate
current.
the steady-state
DC input
current
V
Estimate
Vthe
IN
using:
D  OUT
,
MSL3086/MSL3087/MSL3088 Datashee
V
I IN  I LOAD   OUT
 V IN

,

VIN
© Atmel Inc., 2011. All rights reserved.
where VOUT is the output voltage and VIN is the input volt
where ILOAD is the sum of all strings steady-state LED currents with all LEDs on simultaneously, VOUT is the maximum (un-optimized)
boost
regulator
output
is thesteady-state
minimum boostLED
regulator
input voltage.
the voltage,
sum ofand
all VIN
strings
currents
with all LEDs
on simultaneously,
where
ILOAD is
Calculate
the on-time
in seconds V
using:
OUT is the
optimized) boost regulator output voltage, and VIN is the minimum boost regulator input voltage.
VOUT  V IN
D MSL3086/MSL3088
Atmel
Datasheet
maximum (
19
, Make
t ON with

Inductors have two types of maximum current ratings,
current
and
saturation
current.
sure that the peak
8-String RMS
60mA LED
Drivers
Integrated
Boost Controller
and Phase
Shifted Dimming
f SW loadVcurrent
inductor current is less than the saturation current rating. Note that during
IN  f SWtransients, which occur whenev
the LEDs are turned on or off (due to PWM dimming), the inductor current may overshoot its steady state value. How
Inductors have two types of maximum current ratings, RMS current and saturation current. Make sure that the peak inductor current is
less than the saturation current rating. Note that during load current transients, which occur whenever the LEDs are turned on or off (due
to PWM dimming), the inductor current may overshoot its steady state value. How much it overshoots depends on the boost regulator
loop dynamics. If unsure of the loop dynamics, a typical value to use for the overshoot is 50% of the steady-state current. Add half of the
inductor ripple current to this value to determine the peak inductor current. With inductor ripple current in the 25% to 50% range, estimate
the inductor RMS current as 115% of the DC steady state inductor current.
9.10 Setting the Current Limit
The current sense resistor, connected from the switching MOSFET source to GND, sets the boost regulator current limit. The cycle-bycycle current limit turns-off the boost regulator switching MOSFET when the current sense input detects instantaneous current above the
current limit threshold. This causes the current to drop until the end of the switching cycle. The current limit threshold is 100mV typical,
and 75mV minimum. Choose the current sense resistor value to set the current limit using:
MSL3086/MSL3087/MSL3088 Datashee
MSL3086/MSL3087/MSL3088 Datashe
where IL(MAX) is the maximum inductor current.
CHOOSING
OUTPUT
RECTIFIER
9.11 Choosing
theTHE
Switching
MOSFET
The output rectifier passes the inductor current to the output capacitor and load during the switching off-time. Due to th
The
MSL3086/88
use an external logicfrequency
level MOSFET to implement the boost converter. Choose a MOSFET designed to pass twice at
high
boost regulator
CHOOSING
THE Oswitching
UTPUT RECTIFIER use a Schottky rectifier. Use a Schottky diode that has a current rating at leas
least the peak inductor current, and that has the lowest possible RDSon while maintaining minimal gate charge for fast switching speed.
high
as
that
of
the
external
MOSFET,
and
a voltage
rating
higher
than the
boost
voltage.
Make
that the
MOSFET
drain-source
voltage
rating
is above
theoutput
maximum
un-optimized
boost
voltage,
with some output
extra
Thesure
output
rectifier
passes
the inductor
current
to the
capacitor
andmaximum
loadoutput
during
theregulator
switching
off-time.
Due to t
Schottky
rectifiers
have
very
low
on
voltage
and
fast
switching
speed,
however
at
high
voltage
and
temperatures
Scho
margin
for
voltage
overshoot
due
to
excess
circuit
board
stray
inductance
and
output
rectifier
recovery
artIfacts.
Make
sure
that
the
high boost regulator switching frequency use a Schottky rectifier. Use a Schottky diode that has a current rating at
lea
leakage
current
can
be
significant.
Make
sure
that
the
rectifier
power
is
within
the
rectifier
specifications.
MOSFET
package
can
withstand
the worst-case
power
dissipation
while
maintaining
diedissipation
temperature within
the MOSFET
ratings.
high as that of the external MOSFET, and a voltage rating higher than the maximum boost regulator output voltage.
Place
the MOSFET
and rectifier
together
and
asswitching
close to the
output
capacitor(s)
possible
totemperatures
reduce circuitSch
boa
Schottky
rectifiers have
very lowclose
on voltage
and
fast
speed,
however
at highasvoltage
and
radiated
emissions.
9.12 Choosing
the
Output
Rectifier
leakage current can be significant. Make sure that the rectifier power dissipation is within the rectifier specifications.
Place
the
MOSFET
rectifier
close
and as close
toduring
the output
capacitor(s)
as possible
reduce circuit bo
The
output
rectifier
passes and
the inductor
current
to together
the output capacitor
and load
the switching
off-time. Due
to the high to
boost
L
OOP
C
OMPENSATION
radiated
emissions.
regulator switching frequency use a Schottky rectifier. Use a Schottky diode that has a current rating at least as high as that of the
external
MOSFET,
and
a voltagefrom
ratingCOMP
higher than
the maximum
boost regulator
output voltage. regulation
Schottky rectifiers
have very3low
Use a series
RC
network
to FB
to compensate
the MSL3086/88
loop (Figure
ononpage 13). Th
voltage
and fast
switching
speed,are
however
at hightovoltage
and
temperatures
Schottky
leakage
current
can
be significant.
Make
sure
regulation
loop
dynamics
sensitive
output
capacitor
and
inductor
values.
To
begin,
determine
the
right-half-plan
LOOP COMPENSATION
that the rectifier power dissipation is within the rectifier specifications. Place the MOSFET and rectifier close together and as close to the
zero
frequency:
output
as possible
to from
reduceCOMP
circuit board
radiated
emissions. the MSL3086/88 regulation loop (Figure 3 on page 13). T
Use capacitor(s)
a series RC
network
to FB
to compensate
regulation loop dynamics
are sensitive to output capacitor and inductor values. To begin, determine the right-half-pla
2
zeroCompensation
frequency:
9.13 Loop
V IN
R LOAD
,
f RHPZ
L to FB to compensate the MSL3086/88 regulation loop (Figure 8.1 on page 13). The regulation loop
VOUT
Use a series RC
network
2 from2COMP
dynamics are sensitive
capacitor and inductor values. To begin, determine the right-half-plane zero frequency:
V IN to output
R LOAD
,
f RHPZ
the minimum
where RLOADVis
2Lequivalent load resistor, or
OUT
V is the minimum equivalent load resistor, or
RLOAD OUT
.
Rwhere
LOAD
where RLOAD
is the minimum equivalent load resistor, or
I OUT
(MAX )
VOUT
.
R LOAD 
The output Icapacitance
and type of capacitor affect the regulation loop and method of compensation. In the case of
OUT (MAX )
ceramic capacitors the zero caused by the equivalent series resistance (ESR) is at such a high frequency that it is not
The output capacitance and type of capacitor affect the regulation loop and method of compensation. In the case of ceramic capacitors
consequence.
In the caseand
ofseries
electrolytic
or(ESR)
tantalum
capacitors
the ESR
is
significant,
must
be considered when
the
zerooutput
causedcapacitance
by the equivalent
resistance
is
at such
a high
frequency
that and
it is not
of consequence.
In the case ofIn the case of
The
type
of capacitor
affect
the
regulation
loop
method
ofsocompensation.
compensating
the
regulation
loop.
Determine
the
ESR
zero
frequency
by
the
equation:
electrolytic
tantalum capacitors
thecaused
ESR is significant,
so must be considered
when compensating
loop. Determine
thethat it is no
ceramicorcapacitors
the zero
by the equivalent
series resistance
(ESR) isthe
atregulation
such a high
frequency
ESR zero frequency by the equation:
consequence. In the case of electrolytic or tantalum capacitors the ESR is significant, so must be considered when
1 regulation loop. Determine the ESR zero frequency by the equation:
the
fcompensating

ESRZ
2  ESR  C OUT
1
where
COUT
f ESRZ
 is the value of the output capacitor, and ESR is the Equivalent Series Resistance of the output capacitor. Assure that the loop
the output capacitor, and ESR is the Equivalent Series Resistance of the output capacitor.
where Cfrequency
crossover
is value
at least
1/5th
2isthe
ESR
 Cof
OUT
OUT of the ESR zero frequency.
th
Assure that the loop crossover frequency is at least 1/5 of the ESR zero frequency.
is the Equivalent Series Resistance of the output capacitor.
where COUT is the value of the output capacitor, and ESR
th
thefrequency.
ESR zero fESRZ, the right-half-plane zero fRH
Next
determine
desired
crossover
frequency
as 1/5
thelower
ESR of
zero
Assure
that thethe
loop
crossover
frequency
is at least
1/5thofofthe
or the switching frequency fSW. The crossover frequency equation is:
Next determine the desired crossover frequency as 1/5th of the lower of the ESR zero fESRZ, the right-half-plane zero f
 frequency
 R
 equation is:
R
or the switching
fSW. The crossover
1 frequency
f C   COMP    LOAD   
,
 RTOP  11  RCS   2  R LOAD  C OUT 
R
  R
 

1
Atmel MSL3086/MSL3088 Datasheet
20
, LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
f C   COMP    LOAD   
8-String 
60mA
the crossover
is the top
side
where fC isRTOP
R LOAD
C OUT
CS 
 11  Rfrequency,
 2RTOP
 voltage divider resistor (from the output voltage to FB), RCOMP
the resistor of the series RC compensation network. Rearranging the factors of this equation yields the solution for RCO
Assure that the loop crossover frequency is at least 1/5th of the ESR zero frequency.
where COUT is the value of the output capacitor, and ESR is the Equivalent Series Resistance of the output capacitor.
thelower
ESR of
zero
Assure
that thethe
loop
crossover
frequency
is at least
1/5ththofofthe
thefrequency.
ESR zero fESRZ, the right-half-plane zero fR
Next
determine
desired
crossover
frequency
as 1/5
or the switching frequency fSW. The crossover frequency equation is:
Next determine the desired crossover frequency as 1/5th of the lower of the ESR zero fESRZ, the right-half-plane zero f
Next
determine
the desired
crossover
as 1/5th of frequency
the lower of the
ESR zero fESRZ, the right-half-plane zero fRHPZ or the
The crossover
or the
switching
frequency
fSWfrequency
 The
 . frequency
 equation is:
RCOMP fSW.
R LOAD
1
switchingfrequency
crossover
equation
is:
fC  


,
 R
RTOP  11R RCS  2  R LOAD
1  C OUT 
f C   COMP    LOAD   
,



R
11
R
2

R
C
MSL3086/MSL3087/MSL3088
Datashe
TOP
CS
LOAD
OUT





 voltage divider resistor (from the output voltage
to FB), RCOMP
where fC is the crossover frequency, RTOP is the top side
MSL3086/MSL3087/MSL3088 Datashee
MSL3086/MSL3087/MSL3088 Datashee
the resistor of the series RC compensation network. Rearranging the factors of this equation yields the solution for R
MSL3086/MSL3087/MSL3088
Datashee
as:

R
.
:  R  2  f  C
Solving
forRC  11
the resistor
of the series
RC R
compensation
network. Rearranging the factors of this equation yields the solution for RC
frequency,
where
fC is the crossover
TOP is the top side voltage divider resistor (from the output voltage to FB), RCOMP is the resistor of
the crossover
frequency,
RTOP
the top
side
voltage
divider
resistor
the output voltage to FB), RCOM
where
as:
C is
the
series fRC
compensation
network.
Rearranging
theis
factors
of this
equation
yields
the solution
for R(from
COMP as:
C
COMP
TOP
COMP
CS
C
OUT
: 11  Rif thecompensation
Solving
for C

RCOMP
RCOMP
2if the
 f Ccompensation
C
.
These
equations
are 
accurate
zero
(formed
by
the (formed
compensation
resistor
RCOMP and theresistor
compensation
capacitor
TOP
CS
OUT
and the
These
equations
accurate
zero
by the
compensation
RCOMP
:are frequency
Solving
for CCOMP
C
at a lower
than crossover. Therefore the next step is to choose the compensation capacitor such that the
COMP) happens
)
happens
at
a
lower
frequency
than
crossover.
Therefore
the
next
step
is to choose
compensation
capacitor
C
COMP
compensation
or:
COMP zero is 1/5th of the crossover frequency,
.
th
5
th
C
: are R
Solving
CCOMP
5 that
Thesefor
equations
accurate
if the
compensation
the crossover
compensation
resistoror:RCOMP and the
of the
frequency,
compensation
capacitor
such
the
compensationzero
zero(formed
is 1/5 by
2

f
C
Ccompensation
5CCOMP) happens
crossover. Therefore the next step is to choose th
capacitorCOMP
COMP
. at a lower frequency than
th
2

R
f
Ccompensation
of
the crossover frequency, or:
capacitor
such
that
the
compensation
zero
is
1/5
COMP
C
COMP
.
fC
5 1
Example:
2

R
f
.
f COMPZ
C
COMP
C
COMP
Solving
for C 5 :
2 R RCOMP1 CfCOMP.
f
2

Example:
C
C
As an example, set the COMP
maximum (un-optimized)
output voltage to 39V, using voltage divider as follows:
COMP
f COMPZ
Example:
.
2 RCOMP C COMP
RTOP = 49.9k5
Page 22 of 26
As
an example,
setAllthe
maximum
(un-optimized) output voltage to 39V, using voltage divider as follows:
©BOTTOM
Atmel
Inc.,
2011.
rights
reserved.
Example:
= 3.40k
R
49.9k
R
As
an= example,
set the maximum (un-optimized) outputPage
voltage
to 39V, using voltage divider as follows:
TOP
22 of 26
Example:
=
3.40k
R
=
49.9k
R
BOTTOM
TOP
©
Atmel
Inc.,current
2011.
reserved.
As
an
example,
set All
the
maximum
(un-optimized)
output
voltagea to
39V,output
usingcapacitor,
voltage divider
follows:
Let
the
load
berights
800mA
maximum,
use 10uH
inductor,
20F
a 12Vas
input
voltage, a 12m R
= 3.40k
RBOTTOM
As
an =
example,
set the frequency
maximum (un-optimized)
49.9k
R
and
switching
is 625kHz.output voltage to 39V, using voltage divider as follows:
TOP the
Let the load
current be 800mA maximum, use 10uH inductor, a 20F output capacitor, a 12V input voltage, a 12m RC
R
BOTTOM = 3.40k
= 49.9k
R
TOPload
and
the
switching
frequency
is 625kHz.
Let the
current
be 800mA
maximum, use 10uH inductor, a 20F output capacitor, a 12V input voltage, a 12m RC
RBOTTOMV
=OUT
3.40k
39V
and
the
switching
frequency
is
625kHz.
R the load
 current
 be 800mA
 48.maximum,
75
Let
use 10uH inductor, a 20F output capacitor, a 12V input voltage, a 12m R
LOAD
0.8VAmaximum,
VI OUT
39
Let the
load
current
800mA
use 10µH inductor, a 20µF output capacitor, a 12V input voltage, a 0.25Ω RCS, and the
and
the
switching
is 625kHz.
LOAD befrequency
C
R LOAD 
625kHz.
switching
frequency
is
V
39V  48.75
OUT
R LOAD  I LOAD
2 0.8 A  48.75 2
V
39
I OUT
0.8VA


LOAD

V
RLOAD
48.75
 12  
RfLOAD 
 48.75

IN 


 73kHz
2
RHPZ
I LOAD 2 0.8A

6 
 12
  2 4810
2
L
39

VOUT


10

R
.
75







  73kHz
f RHPZ   VIN 2   RLOAD    12 2  
 6 
48
.75
IN
LOAD
V
2
L
39

2

10

10

   th 2  
f RHPZ   OUT 2  
  73kHz
 6 
: 2 48
Set
the crossover
frequency
VOUT
.75
R2LOAD
12
L to 1/5
39fRHPZ

10

10
IN 

  73kHz

f RHPZ  

 
6 
th 
to1/5
 39
f
:
Set the crossover
frequency
V
2
L

2

10

10

RHPZ
 


 OUT  
RHPZ
Set
the fcrossover
frequency
to 1/5th fRHPZ:
.

f

14
.
6
kHz
SetCthe crossover frequency to 1/5th fRHPZ: th
5
Set the fcrossover
frequency to 1/5 fRHPZ:
RHPZ

fC
 14.6kHz .
f RHPZ
5  the

f C calculate
14.6compensation
kHz .
Next
resistor value to achieve the 15kHz crossover frequency, or
f RHPZ
5
.

f

14
.
6
kHz
C
Next
calculate
compensation value
resistorachieve
valuethe
to achieve
the 15kHz
crossover frequency, or
Next
compensation
frequency,
5 Rthe the
R calculate

 11  R resistor
 2  f to C
 4915kHz
.9k crossover
11  .025
 2 or15k  20 F  25.9k








COMP
TOPthe compensation
CS
C
OUT
Next
calculate
resistor
value to achieve the 15kHz crossover frequency, or
RCOMP
 RTOPthe
 11
 RCS  2 resistor
f C  C OUT
to
49achieve
.9k  11the
 .025
 2crossover
 15k  20
F  th25or
.9k
Next
calculate
compensation
value
15kHz
frequency,
compensation
of.9
the
Then
RCOMPcalculate
 RTOP the
11compensation
 RCS  2  capacitor,
f C  C OUT CCOMP
49.,9to
k set
11the
 .025
 2  15k zero
 20to
F1/5 25
kcrossover frequency, o
3kHz
Then
calculate
the 
compensation
to set
the
zero
to
the
crossover
frequency,
3kHz
compensation
of.9
the
frequency, or
Then
calculate
the
C
RCOMP
 RTOP
11compensation
 RCS capacitor,
2  capacitor,
f CCCOMP
 C,OUT
49compensation
.,9to
k set
11the
 .025
 1/5th
2 of15
kzero
 20to
F1/5
th25
kor
crossover
COMP
th
3kHz
Then calculate the compensation capacitor, CCOMP, to set the compensation zero to 1/5 of the crossover frequency, o
1
1
3kHz

 2set
C COMP
.1nF
the.compensation zero to 1/5th of the crossover frequency, or
Then
calculate
the compensation 
capacitor, CCOMP, to
2  RCOMP
1  f COMPZ 2  25
1 k  3k
3kHz

C COMP 
1
1k  3k  2.1nF .
 Rcircuit
 f COMPZ
2  25
 the
When
laying
place the
divider
resistors
resistor/capacitors as close to the MSL3086/88
 2out
 voltage
 2.and
C COMP
1nFcompensation
.
COMPboard,
1trace
1COMP
as possible and
 RCOMP
 lengths
2minimize
f COMPZconnected
2 to25
k  3and
k FB.

 place the voltage
 divider
CWhen
2.1nF .resistors and compensation resistor/capacitors as close to
out the circuit board,
COMP laying
2 asRpossible
2 trace
25k lengths
3k
COMP  f COMPZ
MSL3086/88
and minimize
connected to COMP and FB.
When laying out the circuit board, place the voltage divider resistors and compensation resistor/capacitors as close to t
MSL3086/88
as possible
and
minimize
lengthsdivider
connected
to COMP
and FB.
When laying out
the circuit
board,
placetrace
the voltage
resistors
and compensation
resistor/capacitors as close to
MSL3086/88
as
possible
and
minimize
trace
lengths
connected
to
COMP
and
FB.
LED
Dimming
Control
When laying out the circuit board, place the voltage divider resistors and compensation resistor/capacitors as close to t
MSL3086/88
as possible
and minimize trace lengths connected to COMP and FB.
LED Dimming
Control
2
EXTERNAL
AND IControl
C CONTROL OF LED BRIGHTNESS
LED
Dimming
2
MSL3086/87
brightness
usingBRIGHTNESS
Pulse Width Modulation (PWM) with a PWM signal applied to the external
LED
Dimming
EControl
XTERNAL
AND IControl
C LED
CONTROL
OF LED
2
PWM
input. AND
The PWM
dimming
signals
(outputs)
take the frequency Atmel
and duty
cycle of the input
signal but are
staggere
MSL3086/MSL3088
Datasheet
E
XTERNAL
I
C
C
ONTROL
OF
LED
BRIGHTNESS
21external
Control MSL3086/87 LED brightness using Pulse 8-String
Width60mA
Modulation
(PWM)
withController
a PWM
signal
applied
to the
LED
Drivers
with
Integrated
Boost
and
Phase
Shifted
Dimming
in time so that they
start
at
evenly
spaced
intervals
relative
to
the
PWM
input
signal.
When
one
or
more
strings
are
2
PWM
input.
The PWM
signals
(outputs)
take
theModulation
frequency (PWM)
and duty cycle
of thesignal
input applied
signal but
are external
staggere
Control
MSL3086/87
brightness
using
Pulse
Width
a PWM
to the
E
XTERNAL
C LED
Cdimming
ONTROL
OF LED
BRIGHTNESS
disabled
by AND
fault Iresponse,
the stagger
delays
automatically
re-calculate forwith
the remaining
enabled strings.
in
timeinput.
so
that
they
start
atbrightness
evenly
spaced
intervals
relative
to the PWM
signal.
When
oneapplied
or
morebut
are
PWM
The
PWM
dimming
signals
(outputs)
take
the
frequency
andinput
duty
cycle
of
the
input
signal
areexternal
staggere
Control
MSL3086/87
LED
using
Pulse Width
Modulation
(PWM)
with
a PWM
signal
tostrings
the
10.0 LED Dimming Control
10.1 External and I2C Control of LED Brightness
Control MSL3086 LED brightness using Pulse Width Modulation (PWM) with a PWM signal applied to the external PWM input. The
PWM dimming signals (outputs) take the frequency and duty cycle of the input signal but are staggered in time so that they start at
evenly spaced intervals relative to the PWM input signal. When one or more strings are disabled by fault response, the stagger delays
automatically re-calculate for the remaining enabled strings.
The MSL3088 accepts two input signals, SYNC and PWM. SYNC provides the frequency information for the PWM dimming, and PWM
provides the duty cycle information. The LED PWM dimming signals are staggered based on the frequency at SYNC.
For all devices, use PWM and SYNC inputs frequency between 20Hz and 50kHz and duty cycle between 0% and 100% (avoid duty
cycles above 99.97% and less than 100%).
Additionally, internal registers accessed using the I2C compatible serial interface allow control of the PWM dimming frequency and duty
cycle. For programming details see the MSL3040/50/60/80/86/87/88/89 Programming Guide.
10.2 Phase Shifted LED Dimming Signals
By default, string PWM dimming is staggered in time to reduce the transient current demand on the boost regulator. The MSL3086/88
automatically determine the stagger times based on the number of enabled strings and the PWM dimming frequency.
Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
22
11.0 Ordering Information
Table 11.1 Ordering Information
PART
DESCRIPTION
MSL3086-IU
8-CH LED driver with integrated boost controller and resistor based LED Short Circuit threshold setting.
MSL3088-IU
8-CH LED driver with integrated boost and SYNC input.
Atmel Corporation
2325 Orchard Parkway
San Jose, CA 95131
USA
Tel: (+1)(408) 441-0311
Fax: (+1)(408) 487-2600
www.atmel.com
PKG
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Tel: (+852) 2245-6100
Fax: (+852) 2722-1369
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Business Campus
Parkring 4
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GERMANY
Tel: (+49) 89-31970-0
Fax: (+49) 89-3194621
24 pin
4 x 4 x 0.75mm
VQFN
Atmel Japan
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1-24-8 Shinkawa
Chuo-ku, Tokyo 104-0033
JAPAN
Tel: (+81)(3) 3523-3551
Fax: (+81)(3) 3523-7581
© 2012 Atmel Corporation. All rights reserved. / Rev.: MSL3086/MSL3088 DBIE-20120828
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Atmel MSL3086/MSL3088 Datasheet
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
23
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