LED Driver MSL2021 - Complete

Atmel LED Drivers
MSL2021
2-String LED Driver with Built-In Color Temperature
Compensation and Adaptive Headroom Control for High
CRI LED Luminaires
Features
 Dual-string LED driver for 2-color or unequal VF LEDs
 PWM dimming with 180° phase shift of LED strings
 Programmable look-up table for color temperature compensation
 Main LED string driven by linear current controller
Drives external N-channel MOSFET
± 3% current accuracy, no ripple current
 Adaptively controls headroom of both AC/DC and DC/DC, isolated or non-isolated
topology
 Wide PWM dimming range with 12-bit precision
 8-bit DAC for peak current control


 Color-adjust LED string uses floating buck controller
Drives external N-channel MOSFET
Temperature color compensation using programmable look-up table
 Over 100:1 dimming range with 8-bit precision
 8-bit DAC allows changing current sense threshold
 Open and short LED protection


 Over-temperature fault detection
 Operates stand-alone or with a microcontroller
 Open-drain fault indicator output
 -40°C To +105°C operating temperature range
Typical Applications

General and Architectural Lamps

High CRI LED Fixtures

Down Lights and Recessed Lights

PAR Lamps
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1.
Introduction
The MSL2021 LED driver for two-color systems includes a linear current controller for the main string, typically for white
LEDs, and a second floating buck controller for a color-adjust LED string. Both the switching and linear controllers drive
external MOSFETs to provide flexibility over a wide range of power levels (LED currents and voltages).
The MSL2021 adaptively manages the voltage powering the main LED string. A proprietary and patent pending
efficiency optimizer (EO) algorithm controls the voltage output of both AC/DC and DC/DC, isolated or non-isolated
topology, including ultra-low bandwidth single-stage PFC flyback controller.
The MSL2021 features peak current control and individual string PWM dimming, with the two strings driven at a 180out
of phase. The main LED string’s current is ripple-free and has very high accuracy. The PWM dimming frequency for both
LEDs strings is 400Hz to give a predictable and wide dimming range. A thermistor connection allows automatic
compensation of luminous efficacy in a two-color LED fixture to maintain consistent color balance across temperature.
The MSL2021 operates from 9.5V to 15V input. The color-adjust string voltage regulation loop uses a constant off-time
control algorithm to achieve stable control with good transient behavior. For flexibility of design, off-time is set with an
external resistor. LED current in both the strings can be adjusted using internal 8-bit DACs.
The internal registers are I2C accessible. Integrated non-volatile EEPROM memory, also accessed through the I2C serial
interface, allows configuration at final test in case that the factory default settings need to be modified.
The MSL2021 is available in the space-saving 24-pin 4x4mm QFN package and operate over the extended -40°C to
105°C operating range.
2.
Ordering Information
Note:
3.
Ordering code
Description
Package(1)
MSL2021IN
Two String LED Driver
4 x 4mm 24-pin QFN
1.
Lead-Free, Halogen-Free, RoHS Compliant Package
Application Circuit
WHITE LED STRING
BRIDGE
RECTIFIER
&
EMI
FILTER
AC MAINS
COLOR LED STRING
NTC
THM
SINGLE
STAGE
PFC
FLYBACK
CONTROLLER
FBO
D
LINEAR
LED
DRIVER
G
S
MSL2021
LED
DRIVER
DRV
CS
VDD
PWM1
VIN
MCU
FLOATING
BUCK LED
DRIVER
MSL2021 [DATASHEET]
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4.
Absolute Maximum Ratings
Voltage with respect to AGND
AVIN, PVIN, EN
VCC, PWM, FLTB, SDA, SCL, TOFF, REXT, FBO
-0.3V to +16.5V
-0.3V to +5.5V
VDD
-0.3V to +2.75V
THM
-0.3V to VCC+0.3V
CS, S
-0.3V to VDD+0.3V
D
G, DRV
PGND, AGND
-0.3V to +22V
-0.3V to VIN+0.3V
-0.3V to +0.3V
Current (into pin)
AVIN, PVIN, DRV, G (average)
100mA
PVIN (peak, =1% duty)
1A
DRV, G (peak, =1% duty)
±1A
PGND (peak, =1% duty)
-1A
AGND, PGND (average)
-100mA
All other pins
±10mA
Continuous Power Dissipation at 70°C
24-Pin 4mm x 4mm VQFN (derate 21.8mW/°C above TA = +70°C)
Ambient Operating Temperature Range
1200mW
-40°C to +105°C
Junction Temperature
Storage Temperature Range
+125°C
-65°C to +125°C
Lead Soldering Temperature, 10s
+300°C
MSL2021 [DATASHEET]
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5.
Electrical Characteristics
AVIN = PVIN = 12V, -40°C ≤TA ≤ 105°C, Typical Operating Circuit, unless otherwise noted.
Typical values at TA = +25°C.
Table 5-1.
DC electrical characteristics
Parameter
Conditions
AVIN, PVIN Operating Supply Voltage
Min.
Typ.
Max.
Unit
9.5
12
15
V
AVIN Operating Supply Current
LEDs on at PWM = 100%,
serial interface idle
10
AVIN Idle Supply Current
EN = SLEEP = 1,
all digital inputs = 0
7
PVIN Idle Supply Current
EN = SLEEP = 1,
all digital inputs = 0
0
AVIN Disable Supply Current
VEN = 0,
all digital inputs = 0
VCC Regulation Voltage
IVCC = 10mA peak(7)
VDD Regulation Voltage
(7)
IVDD = 10mA peak
PWM, PWM1, PWM2, SCL, SDA Input
High Voltage
μA
5
μA
5
5.5
V
2.25
2.5
2.75
V
V
0.3VVDD
V
2
V
EN Input Low Voltage
0.5
EN Input Hysteresis
V
100
Sinking 6mA
SCL, SDA, PWM, PWM1, PWM2, FLTB
leakage current
S Current Sense Regulation Voltage
Accuracy
mA
0.7VVDD
EN Input High Voltage
S Current Sense Regulation Voltage
10
4.5
PWM, PWM1, PWM2, SCL, SDA Input
Low Voltage
SDA, FLTB Output Low Voltage
mA
-5
TA = 25C, MREF = 0x64
194
Main string at 100% duty
cycle,
-3
200
mV
0.3
V
5
A
206
mV
+3
%
TA = 25C, MREF = 0x64
S Current Sense Regulation Voltage
Temperature Coefficient
-220
G Maximum Output Voltage
ppm/ºC
AVIN – 3.5
9.5
AVIN – 2.0
V
0.9
1
1.1
V
D Regulation Threshold
EOCTRL = 0xE5
CS Current Sense Regulation Voltage
CAREF = 0x64
200
VDRV = 12V, IDRV = 20mA
5.6
9
Ω
VDRV = 0V, IDRV = -20mA
5.6
9
Ω
255
340
µA
DRV Impedance
FBO Full Scale Current
170
mV
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Parameter
Conditions
Min.
Typ.
Max.
Unit
FBO LSB Current
1.0
A
THM Source Current
100
A
THM Voltage Range
Thermal Shutdown Temperature
0
Temperature rising
Thermal Shutdown Hysteresis
Table 5-2.
V
133
°C
15
°C
AC electrical characteristics
Parameter
Conditions
DRV tOFF timing
RTOFF = 45.3k
PWM Input Frequency
Min.
(8)
PWM Duty Cycle
PWM Duty Cycle Resolution
Table 5-3.
1.5
Typ.
Max.
Unit
s
0.5
60
10,000
Hz
1
100
%
MSL2021
0.4
%
I2C switching characteristics
Parameter
Symbol
SCL Clock Frequency
Conditions
Min.
(1)
0.05
Typ.
Max.
Unit
1,000
kHz
STOP to START Condition Bus Free
Time
tBUF
0.5
µs
Repeated START condition Hold Time
tHD:STA
0.26
µs
Repeated START condition Setup Time
tSU:STA
0.26
µs
STOP Condition Setup Time
tSU:STOP
0.26
µs
SDA Data Hold Time
tHD:DAT
5
ns
SDA Data Valid Acknowledge Time
(2)
0.05
0.55
µs
SDA Data Valid Time
(3)
0.05
0.55
µs
SDA Data Set-Up Time
tSU:DAT
100
ns
SCL Clock Low Period
tLOW
0.5
µs
SCL Clock High Period
tHIGH
0.26
µs
SDA, SCL Fall Time
tF
SDA, SCL Rise Time
tR
Notes:
1.
2.
3.
4.
120
ns
120
ns
(6)
SDA, SCL Input Suppression Filter
Period
Bus Timeout
(4)(5)
tTIMEOUT
(1)
50
ns
25
ms
Minimum SCL clock frequency is limited by the bus timeout feature, which resets the serial bus interface when either SDA or SCL is held low for tTIMEOUT.
SDA Data Valid Acknowledge Time is SCL LOW to SDA (out) LOW acknowledge time.
SDA Data Valid Time is 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.
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5.
6.
7.
8.
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.
Includes input filters on SDA and SCL that suppress noise less than 50ns.
Additional decoupling may be required when pulling current from VCC and/or VDD in noisy environments.
2µs minimum on time for main LED string PWM dimming.
Typical Operating Characteristics
Figure 5-1. Start-up behavior, PWM = 10% duty cycle (Test conditions).
VLED
FBO
Iin
Imain
Figure 5-2. Start-up behavior, PWM = 90% duty cycle (Test conditions).
VLED
FBO
Iin
Imain
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Figure 5-3. Normal operation, PWM = 10% duty cycle (Test conditions).
PWMin
Imain
Ica
Figure 5-4. Normal operation, PWM = 90% duty cycle (Test conditions).
PWMin
Imain
Ica
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Figure 5-5. Fault response, string open circuit (Test conditions).
PWMin
FLTB
Imain
Ica
Figure 5-6. Fault response, LED short circuit (Test conditions).
PWMin
FLTB
Imain
Ica
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Figure 5-7. Input current vs. input voltage
100
IIN
10
ISLEEP
IIN (mA)
1
f IN = 400Hz
PWM = 50%
0.1
0.01
ISHDN
0.001
0.0001
10
11
12
13
VIN (V)
14
15
Figure 5-8. Average LED current vs. input PWM duty cycle
LED CURRENT (%FS)
100
f IN = 400Hz
MAIN STRING
80
60
40
20
0
0
50
100
DUTY CYCLE (%)
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Figure 5-9. VCC and VDD regulation
5.5
5.0
4.5
VCC
4.0
VOUT (V)
3.5
3.0
2.5
VDD
2.0
1.5
1.0
f IN = 400Hz
PWM = 50%
0.5
0.0
0
20
40
60
80
100
IOUT (mA)
MSL2021 [DATASHEET]
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6.
Block Diagram
Figure 6-1. MSL2021 block diagram
AVIN
D
VDD
VCC
EFFICIENCY OPTIMIZER
REGULATORS
VREF
FBO
DAC
G
VREF
EN
CONTROL LOGIC
S
START
CLOCK
FLTB
FAULT
DETECT
PWM
OSCILLATOR
PWM DIGITIZER
SDCR REGISTER
LOOK-UP TABLE EEPROM
THM
ADC
MUX
400HZ PWM
GENERATOR
AND
DUTY CYCLE
ENGINE
PVIN
DRV
TOFF
CURRENT
GENERATOR
CURRENT
GENERATOR
S
Q
R
QB
CS
VREF
COFF
1.2V
DAC
REXT
AGND
PGND
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7.2
AVIN
D
G
Pinout MSL2021
VCC
7.1
AGND
Pinout and Pin Description
VDD
7.
24
23
22
21
20
19
17
NC
PWM
3
MSL2021
16
PVIN
SCL
4
(TOP VIEW)
15
DRV
SDA
5
14
PGND
FLTB
6
13
CS
7
8
9
10
11
12
CGND
2
DNC
EN
TOFF
S
REXT
18
THM
1
NC
FBO
Pin Descriptions
Name
Pin
FBO
1
Feedback Output
Feedback output from Efficiency Optimizer. Connect FBO to the LED power supply regulation
feedback node to control VLED. When unused connect FBO to VCC.
EN
2
Enable Input (Active High)
Drive EN high to turn on the MSL2021, drive EN low to turn it off. For automatic start-up connect EN to
AVIN.
PWM
3
PWM Dimming Input
Drive PWM with a pulse-width modulated signal to control LED brightness. See “PWM and LED
Brightness” on page 20 for details.
SCL
4
Serial Clock Input
SCL is the I²C serial interface clock input. See “I²C Serial Interface ” on page 31 details.
SDA
5
Serial Data Input/Output
SDA is the I²C serial interface data I/O. See “I²C Serial Interface ” on page 31 details.
6
Fault Output (Open Drain, Active Low)
FLTB sinks current to AGND when a fault condition exists. Toggle EN low then high to clear FLTB, or
clear faults through the serial interface (see “Fault Status register (FAULTSTAT, 0x23), Read Only” on
page 29). Use the serial interface to access fault information and to enable/disable fault response.
FLTB
Description
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Name
Pin
NC
7, 17
Description
No Internal Connection
THM
8
NTC Thermistor Sensing Input
Connect a negative temperature coefficient thermistor (ERT-J0EG103FA or equivalent) from THM to
AGND, in series with a 1.5kΩ resistor. Locate the thermistor close to the Color-Adjust LEDs to monitor
their temperature. This allows the MSL2021 to automatically temperature compensate the ColorAdjust string brightness.
REXT
9
External Resistor
Connect a 46.4k, 1% resistor from REXT to AGND.
TOFF
10
Off-Time Set Input
A resistor from TOFF to AGND controls the constant off time for the Color-Adjust string floating buck
converter, where RTOFF = tOFF  (90.9 x 109), with tOFF in seconds and RTOFF in Ohms. For example, an
off time of 0.5s results in a resistor value of 45.3k (to the nearest 1% value).
Do Not Connect
DNC
11
CGND
12
CS
13
PGND
14
PGND is the ground connection for the FET gate drivers. Connect PGND to AGND close to the
MSL2021.
DRV
15
Gate Drive for Color-Adjust (Floating Buck Regulator) MOSFET
Connect DRV to the gate of the external power MOSFET.
PVIN
16
Power Voltage Input
PVIN powers DRV, the floating buck FET gate driver. Bypass PVIN to PGND with a 1.0µF or greater
capacitor.
S
18
Source Sense Input for Main LED String MOSFET
Connect S to the source of the external MOSFET, and to the current sense resistor for the Main LED
string. The current sense threshold is 200mV.
G
19
Gate Output for Main String MOSFET
Connect G to the gate of the Main string external MOSFET.
D
20
Drain Output for Main String MOSFET
Connect D to the drain of the Main string external MOSFET.
AVIN
21
Analog Voltage Input
AVIN is the power input to the MSL2021. Bypass AVIN to AGND with a 1.0µF or greater capacitor
placed close to AVIN.
VCC
22
AGND
23
VDD
24
2.5V Internal Voltage
Connect 10uF bypass capacitor from VDD to AGND.
EP
EP
Exposed Pad
EP is the Main thermal path for heat to escape the die. Connect EP to a large copper plane connected
to PGND and AGND.
Do not make external connection to DNC.
Connect to Ground
Connect CGND to AGND.
Current Sense Input for the Color-Adjust String
Connect CS to the external current sense resistor of the Color-Adjust string. The current sense
threshold is 200mV.
Power Ground
5V Internal Voltage
Connect 10uF bypass capacitor from VCC to AGND.
Analog Ground
Connect AGND to system ground.
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8.
Typical Application Circuit
MSL2021 controlling the output of an isolated PFC controller; a linear current sink regulates the white LED string current
and a floating buck converter regulates the color LED string current.
Figure 8-1. Typical application circuit
VAC
RTOP
AC-DC
ISOLATED
With PFC
RBOTTOM
COLOR
LEDS
WHITE
LEDS
100kΩ
EN
EN
PWM
FAULT
Q1
1μF
AVIN
10μF
REXT
TOFF
VCC
VDD
AGND
45.3kΩ
G
S
PVIN
46.4kΩ
1μF
D
PWM
FLTB
1μF
+
12V
-
FBO
ERTJ0EG103FA
MSL2021
LED DRIVER
820μH
0.56Ω
D1
THM
1.50kΩ
Q2
DRV
CS
PGND
0.56Ω
SDA SCL
10uF
CONFIGURATION INTERFACE
(OPTIONAL)
9.
Detailed Description
The MSL2021 drives two LED strings, the main string and the color-adjust string. The main string LEDs are typically
white and used to provide accurate light intensity control.The color-adjust string LEDs are used to control the color
temperature. The combined light output is a blended high CRI light, for example, than what white LEDs can alone
produce. The main string is directly controlled by a Pulse Width Modulated (PWM) constant current controller (current
sink to ground). An Efficiency Optimizer (EO) output controls the main string voltage, via feed-back to the LED string
power supply, to minimize the voltage across the LED current controller, minimizing power loss.
The color-adjust string is regulated by a floating buck controller. The buck controller converts the voltage of the main
string’s supply to a voltage appropriate for the color-adjust LEDs. Additionally, the MSL2021 has a programmable 8-bit
registers that allows adjustment of the current by changing the source feedback reference voltages (see“Block Diagram”
on page 11).
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10.
Fault Conditions
The MSL2021 detects fault conditions, and takes corrective action when faults are verified.
String open circuit and LED short circuit conditions of the color-adjust string are monitored. When one of these faults
occurs, FLTB pulls low to indicate a fault condition and the color-adjust LEDs turn off. Read Fault Status register 0x23 to
determine the fault type. Clear these faults by toggling EN low then high. Faults that persist re-establish the fault
response. Mask string faults using Fault Disable register 0x22.
For the main LED string, when an open LED occurs, the voltage of the AC/DC or DC/DC input power supply reaches the
maximum allowed.
Over-temperature protection puts the device to sleep when the die temperature is above 133C. The device turns back
on when the die temperature falls below 118C, and normal operation resumes. While asleep, the I2C interface remains
active; see “Fault Disable register (FAULT, 0x22)” and “Fault Status register (FAULTSTAT, 0x23), Read Only” on page
29 for more information about thermal shutdown.
Table 10-1. Fault Conditions, Response and Recovery
Fault
Response
Recovery action
Die Temperature > 133C
Asleep (I2C still active)
When die temperature falls below 118C operation
resumes as if EN is pulled high
Color-adjust string has
shorted LEDs
Color-adjust string turns off, FLTB pulls
low, and bit 0 of the Fault Status register
0x23 sets high
Correct the short condition in LED string. Toggle EN low to
high to resume operation
Color-adjust string is open
circuit
Color-adjust string turns off, FLTB pulls
low, and bit 1 of the Fault Status register
0x23 sets high
Correct the open condition in LED string. Toggle EN low to
high resume operation
11.
Applications Information
11.1
Turn-On Sequence
The MSL2021 waits for 250ms after power is applied to allow the AC/DC or DC/DC input supply to establish the default
voltage. Then the MSL2021 starts to optimize the LED string voltage (VLED), and then starts to drive the LED strings. It is
critical that the AC/DC or DC/DC converter that powers the LED strings reaches its nominal output voltage in less than
250ms after power is applied. When the 250ms start-up delay is complete, the efficiency optimizer adjusts the LED
voltage to the proper level to drive the main string. After the voltage is set, normal PWM operation begins for both the
main and color-adjust strings. This turn-on sequence allows the light to come up at the proper color and intensity without
flashing or flicker.
11.2
Setting the Main String Current with RS
The Main string LED on-current regulates by monitoring the voltage at the S pin, the main string MOSFET source resistor
connection. The default feedback voltage at the S pin is 200mV. Choose the string current sense resistor RS using:
0.2
R S = ------------ 
I LED
where ILED is the main string regulation current. The main string reference voltage (MREF) register 0x20 sets the
feedback voltage, to 200mV, at 2mV per LSB. The regulation voltage, VS(FB), is:
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V S  FB  =  0.002  MREF V
where MREF is the decimal equivalent of the value in register 0x20. The default value for MREF is 0x64, for a feedback
voltage of 0.2V. Change the feedback voltage by changing the value in register 0x20 using the serial interface. LED
average current is within ±3% of the targeted value when a 1% resistor is used for RS.
11.3
Setting AC/DC Output Voltage
The efficiency optimizer output, FBO, connects to the AC/DC or DC/DC converter’s output voltage feedback node, and
pulls current from the node to force the converter’s output voltage up. The MSL2021 works with any input power
converter topology that uses a resistor divider to set its output voltage. Operation with a AC/DC PFC converter is
described below.
Select the two resistors that set the nominal AC/DC LED power supply’s output voltage by first determining the minimum
output voltage using:
V OUT  MIN    V fMIN    N  + 0.2V
where VfMIN is the minimum LED forward voltage for the Main string LEDs at the expected LED current, N is the number
of LEDs in the string, and 0.2V is the minimum overhead required for the current sense resistor and the FET. Then
determine the maximum output voltage using:
V OUT  MAX  =  V fMAX    N  + 1.2V
where VfMAX is the maximum LED forward voltage for the Main string LEDs at the operating LED current, N is the number
of LEDs in the string, and 1.2V is the maximum overhead required for the current sense resistor and the FET. Determine
the value for the upper voltage setting resistor using:
V OUT  MAX  – V OUT  MIN  
R TOP  ----------------------------------------------------------------- 
–6
170  10
where 170A is the minimum FBO full scale current. Determine the lower resistor using:
V FB
R BOTTOM = R TOP  -------------------------------------------- 
V OUT  MIN  – V FB
where VFB is the feedback regulation voltage of the switch mode converter.
11.4
Selecting the Main String MOSFET
The Main string MOSFET sinks the string current to ground through current sense resistor RS. Output of pin G drives the
gate of the MOSFET at up to VIN - 2V. Select a MOSFET with a maximum drain-source voltage of at least 20% above:
R TOP
V fb  -----------------------+ 1 + 340A  R TOP
R

BOTTOM
where 340µA is the maximum FBO full scale current.
11.5
Selecting the Drain Resistor – RD
The drain resistor, RD, connects the MSL2021 to the drain of the main string external MOSFET. Use a 100k for RD.
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11.6
Selecting the Color-Adjust String Floating Buck Components
Figure 11-1. Floating buck LED driver
VLED
WHITE LEDS
(MAIN STRING)
COLOR LEDS
(COLOR-ADJUST STRING)
Ci
+
IAVE
VBUCK
-
Co
Lo
D1
MSL2021
LED Driver
Q
TOFF
DRV
CS
RCS
RTOFF
PGND
The MSL2021 includes a driver for a constant off-time floating buck topology, shown in Figure 11-1, to convert the main
string voltage to a value appropriate for the color-adjust LED string. The buck is operated in continuous conduction
mode.
Continuous conduction operation is assured when the peak-to-peak ripple current in the inductor, ∆iL, is less than twice
the average LED current. A peak-to-peak ripple current magnitude of 15% of the average LED on-current is suggested,
i.e.
i L  0.15I AVE A
where IAVE is the average color-adjust LED string on-current. Choose IAVE appropriate for the color-adjust LEDs (Figure
11-1 on page 17 and Figure 11-2 on page 18) and calculate the peak string on-current using
i
I PEAK = I AVE + -------L- A
2
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Figure 11-2. Color-adjust string LED on-current details.
I
INDUCTOR CURRENT
IPEAK
? iL
IAVE
LED CURRENT
(WHEN USING CO)
tOFF
t
The color-adjust string LED on-current regulates by monitoring the voltage at CS, the color-adjust string FET source
resistor connection. The reference voltage VCSFB for CS is 200mV (VCSFB is 200mV by default, and is adjustable through
the serial interface; see the register definitions for details about changing VCSFB). Choose the current sense resistor RCS
using
V CSFB
R CS = ---------------- 
I PEAK
Determine VBUCK, the voltage across the color-adjust LEDs, using
V BUCK = NV f V
where N is the number of LEDs in the string and VF is the forward voltage drop of the LEDs at IPEAK.
The duty ratio of MOSFET Q is
V BUCK
D = ---------------V LED
where VLED is the main string voltage, Figure 11-1 on page 17. The constant off-time of the MOSFET is toff and calculated
in seconds using
– Dt off = 1
-----------s
fs
where fS is the selected switching frequency in Hz. Use 100kHz to 1MHz for fS. Set toff with resistor RTOFF from TOFF to
GND (Figure 11-1 on page 17), whose value is
Rt
Choose the inductor value using
9
off
= t off  90.9  10 
V BUCK  t off
L O = -----------------------------H
i L
Use a ferrite inductor with a saturation current at least 50% higher than the peak current flowing in it:
IL
SAT
 1.5  I PEAK A
Note here a particular advantage of constant off-time operation of the buck converter is that ripple current is independent
of the input voltage. The circuit provides a constant average LED current, IAVE, but the buck converter actually regulates
the peak inductor current, IPEAK (Figure 11-1 on page 17 and Figure 11-2 on page 18). From the equation for the inductor
value L0 above, we see that because toff is constant, and VBUCK is relatively constant, the ripple current ∆iL is also
constant, so that IAVE is a constant, as desired. If the main string voltage changes, the switching frequency changes to
keep the on-time constant, thus the ripple current is independent of the input voltage.
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This topology does not require an output capacitor, Co in Figure 11-1 on page 17. When used, Co steers the inductor’s
ripple current away from the LEDs but reduces the accuracy of PWM dimming because the voltage across it cannot
change quickly. When using Co, a ceramic capacitor of between 1.0µF and 10µF is adequate, with a voltage rating higher
than VBUCK.
The output capacitor of the AC/DC converter that produces the main string voltage, Ci in Figure 11-1 on page 17, doubles
as the buck’s input capacitor. The capacitor’s function is to provide a smooth voltage to the buck converter. It should be
able to handle the R.M.S. ripple current of the buck converter, which is approximately equal to
I C = I AVE D  1 – D  A
i
This ripple current peaks at a duty ratio of D = 0.5.
Select an N-channel MOSFET for Q with a maximum drain-source voltage at least 25% above VLED. The R.M.S. current
in the MOSFET is approximately equal to
I Q = I AVE D A
The MOSFET conduction power loss due to this current is
2
PCON  I Q2 RDS  I AVE
RDS D
W
where RDS is the hot on-resistance of the MOSFET, which can be found in the MOSFET datasheet, and is typically 1.5 to
1.8 times greater than the cold resistance. The MOSFET will also incur switching losses, which can be difficult to
calculate exactly. A good rule-of-thumb is to choose a MOSFET in a package that dissipates at least four times PCON.
The average current in the output rectifier D1 is
I D = I AVE  1 – D  A
i
and the power dissipated in the rectifier due to conduction is
P CON
D1
= I D V on W
1
where Von is the voltage drop across the rectifier at the forward current of ID1. Pick a rectifier with an average current
rating at least 50% higher than ID1. Use a Schottky rectifier if the LED voltage is less than 50V. The Schottky rectifier’s
voltage rating should be at least 25% higher than VLED. Schottky rectifiers have very low on-state voltage and very fast
switching speed, but at high voltage and high temperatures their leakage current becomes significant. The power
dissipated in the Schottky rectifier due to the leakage current at any temperature and duty ratio is
P lkg = V LED I r D W
where Ir is the reverse leakage current, found in the diode’s datasheet. This power must be added to the conduction
power loss.
P D = P CON + P lkg W
1
D
Make sure that the rectifier’s total power dissipation is within the rectifier’s specifications.
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11.7
PWM and LED Brightness
The “Block Diagram” on page 11 shows how the MSL2021 controls the brightness of the LEDs. The duty cycle of the
main string equals the duty cycle of the input signal at PWM. The PWM input accepts an input signal frequency of 60Hz
to 10kHz, while the LED dimming frequency, of both the main and color-adjust strings, is 400Hz. The duty cycle of the
color-adjust string is based on the duty cycle of the signal at the PWM input, but compensated for temperature based on
a programmable look-up table, whose defaults are presented in Table 11-2 on page 21. See “Light Color and the THM
Input” on page 20 for temperature adjustment information.
Figure 11-3. LED current and duty cycle control.
MSL2021
D
DAC
0x20
400Hz CLOCK
+
-
RD
G
EN
S
RS
PWM
THM
PWM ENGINE
THERMAL
MONITOR
DAC
0x21
+
-
EN
DRV
CS
RCS
11.8
Light Color and the THM Input
The overall color of the light generated by the two LED strings is a blend of the main string’s white LEDs and the coloradjust string’s color LEDs. Brightness is primarily controlled by the duty cycles of the PWM signals driving the LEDs. The
brightness of white LEDs is relatively constant over temperature, but the brightness of color LEDs may drop significantly
as temperature increases. The main string’s PWM duty cycle is fixed at the duty cycle of the input PWM signal, but the
duty cycle of the color-adjust string is changed as the LED temperature changes, to keep the blended light color
constant.
The thermistor input, THM, monitors the temperature of an external thermistor connected from THM to ground. A fixed
current is forced out THM to generate a voltage that is proportional to the thermistor’s temperature. The THM voltage is
measured by a 8-bit ADC internal to the MSL2021. When used with the suggested thermistor (ERT-J0EG103FA or
equivalent) in series with a 1.5kΩ resistor, THM measures temperatures from 18oC to 80oC with 2oC resolution, for 32
different temperature values. When the temperature is below 18oC, 18oC is returned by the temperature monitor circuit.
When the temperature is above 80oC, 80oC is returned by the temperature monitor circuit. The temperature information
is fed to the color-adjust string’s duty cycle circuit.
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The MSL2021 modifies the color-adjust string duty cycle using a look-up table. Default values are presented in Table 111; each location in the table corresponds to one temperature. The modification value is stored in the table as an 8-bit
color-adjust duty cycle ratio (SDCR). The SDCR, a number from 0 to 255, is divided by 255, and multiplied by the duty
cycle of the incoming PWM signal. The result is the duty cycle of the color-adjust string. The table is programmable
through the serial interface when values different from the defaults are desired.
Table 11-1. Temperature based duty cycle modification of the color-adjust string
COLOR-ADJUST DUTY CYCL
TEMPERATURE ADJUSTMENT
Part
Limits
SDCRxx = VALUE IN LOOK-UP TABLE 0x00 THRU 0x1F
MSL2021
SDCRxx
DC CA = ----------------------  DC PWM
255
SDCRxx = 0xFF RETURNS 100% OF THE PWM DUTY CYCLE
SDCRxx = 0x00 RETURNS 0% OF THE PWM DUTY CYCLE
Table 11-2. Temperature Look-Up Table Defaults(1)
Register
Multiplication factor
Temperature (°C)
SDCRxx
---------------------255
Address
Name
Default Value
≤18
0x00
SDCR18
0x4C
0.300
20
0x01
SDCR20
0x4D
0.303
22
0x02
SDCR22
0x4E
0.307
24
0x03
SDCR24
0x4F
0.311
26
0x04
SDCR26
0x50
0.314
28
0x05
SDCR28
0x51
0.318
30
0x06
SDCR30
0x52
0.322
32
0x07
SDCR32
0x53
0.327
34
0x08
SDCR34
0x54
0.331
36
0x09
SDCR36
0x55
0.336
38
0x0A
SDCR38
0x56
0.340
40
0x0B
SDCR40
0x58
0.345
42
0x0C
SDCR42
0x59
0.350
44
0x0D
SDCR44
0x5A
0.355
46
0x0E
SDCR46
0x5C
0.361
48
0x0F
SDCR48
0x5D
0.367
50
0x10
SDCR50
0x5E
0.373
52
0x11
SDCR52
0x60
0.379
54
0x12
SDCR54
0x62
0.385
56
0x13
SDCR56
0x63
0.392
58
0x14
SDCR58
0x65
0.399
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Register
Multiplication factor
Temperature (°C)
Note:
1.
SDCRxx
---------------------255
Address
Name
Default Value
60
0x15
SDCR60
0x67
0.406
62
0x16
SDCR62
0x69
0.414
64
0x17
SDCR24
0x6B
0.422
66
0x18
SDCR66
0x6D
0.431
68
0x19
SDCR68
0x70
0.440
70
0x1A
SDCR70
0x72
0.450
72
0x1B
SDCR72
0x72
0.460
74
0x1C
SDCR74
0x72
0.460
76
0x1D
SDCR76
0x72
0.460
78
0x1E
SDCR78
0x72
0.460
≥80
0x1F
SDCR70
0x72
0.460
Change SDCRxx values through the serial interface
Figure 11-4. MSL2021 default look-up Table color correction vs. temperature.
DUTY CYCLE MULTIPLICATION FACTOR
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
TEMPERATURE (ºC)
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11.9
MSL2021 Look-Up Table Lockout Procedure
The MSL2021 features a lock for the look-up table. When locked, the table’s registers (0x00 through 0x1F) become readonly. A locked table cannot be unlocked; changing the table’s registers is no longer possible. Reads of a locked table’s
registers return 0x00, unless the password (chosen when locking the table) is first entered to make the registers visible.
Locking the table requires use of the I2C interface to enter data, read data and program the EEPROM. For information
about using the I2C interface, see “I²C Serial Interface ” on page 31. For information about programming the EEPROM
see “EEPROM Address and Control/Status Registers” on page 26.
Lock the table by performing the following sequence; an example is presented below:
1.
Fill the look-up table with data.
2.
Commit the look-up table to EEPROM.
3.
Cycle power, then verify the contents of the look-up table.
4.
Choose a 16-bit password.
5.
Enter the password into Password Registers 0x68 and 0x69.
6.
Enter the password into Password Verification Registers 0x38 and 0x39.
7.
Commit the password to EEPROM.
8.
Set the lock bit.
9.
Commit the lock bit to EEPROM.
10. Cycle power to the MSL2021.
11.9.1 Example:
The Look-Up Table is four pages long (each page is 8-bytes). When the look-up table is filled with the proper data,
commit the data to the EEPROM, one page at a time, by sending the following commands to the MSL2021 through its
I2C interface:
0x60 0x00 {to register 0x60 write 0x00: sets the EEPROM write pointer to 0x00}
0x61 0x04 {to register 0x61 write 0x04: writes the first page (8 bytes) of data to the EEPROM}
Wait 5ms.
0x61 0x00 {to register 0x61 write 0x00 : disables EEPROM writing}
0x60 0x08 {sets the EEPROM write pointer to 0x08}
0x61 0x04 {writes the second page of data to the EEPROM}
Wait 5ms.
0x61 0x00 {disables EEPROM writing}
0x60 0x10 {sets the EEPROM write pointer to 0x10}
0x61 0x04 {writes the third page of data to the EEPROM}
Wait 5ms.
0x61 0x00 {disables EEPROM writing}
0x60 0x18 {sets the EEPROM write pointer to 0x18}
0x61 0x04 {writes the final page of data to the EEPROM}
Wait 5ms.
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0x61 0x00 {disables EEPROM writing}
The EEPROM is now programmed with the data that are in registers 0x00 through 0x1F (the look-up table). Although not
required, now is a good time to cycle power to the MSL2021, then read registers 0x00 through 0x1F to verify that the
EEPROM was properly programmed (at power-up the EEPROM automatically programs registers 0x00 through 0x40).
Next, choose a 16-bit password and write it into the Password Registers, and into the Password Verification Registers.
For this example the password is 0xAA55:
0x68 0xAA
0x69 0x55 {writes the password into the password registers 0x68 and 0x69}
0x38 0xAA
0x38 0x55 {writes the same password into the password verification registers 0x38 and 0x39}
Now commit the password to EEPROM.
0x60 0x68 {sets the EEPROM write pointer to 0x68}
0x61 0x03 {writes the first byte of the password to the EEPROM}
Wait 5ms.
0x61 0x00 {disables EEPROM writing}
0x60 0x69 {sets the EEPROM write pointer to 0x69}
0x61 0x03 {writes the second byte of the password to the EEPROM}
Wait 5ms.
0x61 0x00 {disables EEPROM writing}
Next, set the lock bit and commit it to EEPROM.
0x3A 0x02 {sets the lock bit (bit D1) in register 0x3A}
0x60 0x3A {sets the EEPROM write pointer to 0x3A}
0x61 0x03 {writes the contents of register 0x3A to the EEPROM}
Wait 5ms.
0x61 0x00 {disables EEPROM writing}
Now cycle power to the MSL2021. All reads of the Look-Up Table now return 0x00.
To read the Table, enter the password into the password verification registers:
0x38 0xAA
0x39 0x55 {writes the password into registers 0x38 and 0x39}
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Reads of the Look-Up Table now return its true contents, until the password register is changed, power is cycled or
enable input EN is toggled.
12.
Control Registers
Table 12-1. Register map(1)
Address and
Register name
Function
Default
value(2)
Bit functions
D7
D6
D5
D4
D3
0x00
SDCR18
Look up for 18C
0x4C
Look up table
0x01
SDCR20
Look up for 20C
0x4D
Look up table
…thru…
D2
D1
D0
…thru…
0x1E
SDCR78
Look up for 78C
0x72
Look up table
0x1F
SDCR80
Look up for 80C
0x72
Look up table
0x20
MREF
Main String
Feedback
Reference
Voltage
0x64
MSREF = 2mV per LSB
0x21
CAREF
Color-Adjust
String Reference
Feedback Voltage
0x64
VCAREF = 2mV per LSB
0x22
FAULT
DISABLE
Color-Adjust Fault
Disable
0x00
-
-
-
-
-
TSDMASK
OCDIS
SCDIS
0x23
FAULTSTAT
Fault Status
Read
Only
-
-
-
-
-
TSD
OCFLT
SCFLT
0x24
SLEEP
Configuration
0x00
-
-
-
-
-
-
-
SLEEP
0x31
TEMP
Temperature
Read
Only
Thermistor temperature
0x38
PWV(HIGH)
Look-Up Table
Password
Verification High
Byte
0xFF
Look-Up Table Password Verification [15:8]
0x39
PWV(LOW)
Look-Up Table
Password
Verification Low
Byte
0xFF
Look-Up Table Password Verification [7:0]
0x3A
LUT LOCK
Look-Up Table
Lock
0x83
-
-
-
-
0x40
EOCTRL
Efficiency
Optimizer
0xE5
-
-
-
-
0x60
E2ADDR
EEPROM
Address
0x00
-
0x61
E2CTRL
EEPROM Control
0x00
-
0x68
PW(HIGH)
Look-Up Table
Password High
Byte
0xFF
Look-Up Table Password [15:8]
0x69
PW(LOW)
Look-Up Table
Password Low
Byte
0xFF
Look-Up Table Password [7:0]
Notes:
1.
2.
-
-
LOCK[1:0]
DThresh[3:0]
EEPROM Address Pointer
-
-
-
-
RWCTRL[2:0]
Do not change the contents of undefined bits or unlisted registers.
Unless changed through the EEPROM, these default values load at power-up, and when EN is taken from low to high.
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12.1
EEPROM and Power-Up Defaults
An on-chip EEPROM holds all the default register values. At power-up the data in the EEPROM is transferred directly to
control registers 0x00 thru 0x51, setting up the device for operation.
Any changes made to registers 0x00 thru 0x69 after power-up are not reflected in the EEPROM and are lost when power
is removed from the device, or when the enable input EN is forced low. If a different power-up condition is desired
program the values into the EEPROM via the serial interface as explained in the next section, or contact the factory to
inquire about ordering a customized power-up setting.
12.2
EEPROM Address and Control/Status Registers
The EEPROM can be visualized as an image of the control registers from 0x00 thru 0x69. Change an EEPROM register
value by writing the new value into the associated control register, and then instructing the device to program that value
into the EEPROM. Two control registers facilitate this process, the EEPROM address register E2ADDR (0x60), and the
EEPROM control register E2CTRL (0x61). Into E2ADDR write the location of the data that is to be programmed into the
EEPROM, and write 0x03 to E2CTRL to command the device to program that data into the EEPROM. Programming the
EEPROM takes a finite amount of time; after sending a command to E2CTRL wait 5ms, then end the write cycle by
writing 0x00 to E2CTRL.
Example: Change the string current feedback voltage MREF to 100mV.
Commands: To register 0x20 (MREF) write 0x32 (the new value for MREF). To register 0x60 (E2ADDR) write 0x20 (the
address of the MREF register). To register 0x61 (E2CTRL) write 0x03 (the command to copy the value to EEPROM).
Wait 5ms. To register 0x61 (E2CTRL) write 0x00, to turn off EEPROM access.
Result: The value 0x32, located in the MREF register, is programmed into the EEPROM and becomes the new powerup default value for MREF.
Summary:
0x20 32
0x60 20
0x61 03
Wait 5ms
0x61 00
E2CTRL provides additional functions beyond simply programming a register’s value into the EEPROM. Data may be
transferred in either direction, from the registers to the EEPROM, or from the EEPROM to the registers. Register data
may be transferred into or out of the EEPROM in groups of eight, a page at a time. The page address boundaries are
predefined, and E2ADDR must be loaded with the address of the first byte of the page that is to be copied. Page
addresses begin at 0x00 and increment by eight, with the second page beginning at 0x08, the third at 0x10, etc. To
program a full page of data into the EEPROM, write the address of the page’s first byte to E2ADDR, and write 0x04 to
E2CTRL. Wait 5ms, and then end the write cycle by writing 0x00 to E2CTRL. When finished accessing the EEPROM
always write 0x00 to E2CTRL to block inadvertent EEPROM read/writes. Table 12-2 on page 26 details the functions
available through E2CTRL.
Table 12-2. EEPROM Address Register (E2ADDR, 0x60), defaults highlighted.
Register data
Register
Address
D7
E2ADDR
0x60
D6
D5
D4
-
D3
D2
D1
D0
E2ADDR[6:0]
DEFAULT
0
0
0
0
0
0
0
0
EEPROM Minimum Address 0x00
-
0
0
0
0
0
0
0
EEPROM Maximum Address 0x51
-
1
0
1
0
0
0
1
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Table 12-3. EEPROM Status Register (E2CTRL, 0x61), defaults highlighted.
Register data
Register
Address
D7
D6
D5
D4
D3
-
-
-
-
-
DEFAULT
0
0
0
0
0
0
0
0
EEPROM Read / Write Disabled
x
x
x
x
x
0
0
0
Read 1 Byte from EEPROM
x
x
x
x
x
0
0
1
Read 8 Bytes from EEPROM
x
x
x
x
x
0
1
0
Write 1 Byte to EEPROM
x
x
x
x
x
0
1
1
Write 8 Bytes to EEPROM
x
x
x
x
x
1
0
0
x
x
x
x
x
1
0
1
x
x
x
x
x
1
1
x
E2CTRL
0x61
Unused
13.
D2
D1
D0
RWCTRL[2:0]
Detailed Register Descriptions
The MSL2021 registers are summarized in “Control Registers” on page 25. Detailed register information follows.
13.1
String Duty Cycle Control Registers (SDCR18 through SDCR80, 0x00 through 0x1F)
Holds the look-up table for the thermistor color-adjust string duty cycle correction. See “Light Color and the THM Input”
on page 20 for information. Put the device to sleep using SLEEP register 0x24 before modifying the SDCR values to
avoid undesired changes in the light output of the LEDs.
Table 13-1. String Duty Cycle Control Registers (SDCR18 through SDCR80, 0x00 through 0x1F), defaults highlighted
Register data
Register name
Address
D7
SDCR18 through SDCR80
13.2
D6
D5
0x00 – 0x1F
D4
D3
D2
D1
D0
SDCR[7:0]
DEFAULT (See Table 11-2 on page 21)
X
X
X
X
X
X
X
X
Correction factor = 0
0
0
0
0
0
0
0
0
Correction factor = 1
1
1
1
1
1
1
1
1
Main String Reference Voltage register (MREF, 0x20)
Holds the DAC value that controls the reference voltage for the main string FET source feedback voltage. The reference
voltage equals decimal value of this register times 2mV. The default value for MSREF is 0x64, which equates to MSREF =
200mV.
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Table 13-2. Main String Reference register (MREF, 0x20), defaults highlighted
Register data
Register name
Address
D7
MREF
13.3
D6
D5
D4
0x20
D3
D2
D1
D0
MREF[7:0]
DEFAULT: MREF = 100 * 2mV = 200mV
0
1
1
0
0
1
0
0
MREF = 0  2mV = 0V
0
0
0
0
0
0
0
0
MREF = 255 * 2mV = 510mV
1
1
1
1
1
1
1
1
Color-Adjust String Reference Voltage register (CAREF, 0x21)
Holds the DAC value that controls the reference voltage for the color-adjust string FET source feedback voltage. The
reference voltage equals decimal value of this register times 2mV. The default value for CASREF is 0x64, which equates
to CAREF = 200mV.
Table 13-3. Color-Adjust String Reference register (CAREF, 0x21), defaults highlighted
Register data
Register name
Address
D7
CAREF
13.4
D6
D5
D4
0x21
D3
D2
D1
D0
CAREF[7:0]
DEFAULT: VCAREF = 100 * 2mV = 200mV
0
1
1
0
0
1
0
0
VCAREF = 0  2mV = 0mV
0
0
0
0
0
0
0
0
VCAREF = 255  2mV = 510mV
1
1
1
1
1
1
1
1
Fault Disable register (FAULT, 0x22)
Bits D0 and D1 control the fault response for the color-adjust string. For fault response behavior see “Fault Conditions”
on page 15. Bit D2 prevents the thermal shutdown fault from pulling FLTB low. Write 0x03 to this register to clear faults;
write 0x00 to re-enable fault response.
Table 13-4. Fault Disable register (FAULT, 0x22), defaults highlighted
Register data
Register name
Address
D7
D6
D5
D4
D3
D2
D1
D0
-
-
-
-
-
TSDMASK
OCDIS
SCDIS
DEFAULT
0
0
0
0
0
0
1
1
Act on faults
x
x
x
x
x
0
0
0
Disable LED Short Circuit Fault
x
x
x
x
x
x
x
1
Disable String Open Circuit Fault
x
x
x
x
x
x
1
x
Do Not Allow Thermal Shutdown Fault to
Pull FLTB Low
x
x
x
x
x
1
x
x
FAULT
0x22
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13.5
Fault Status register (FAULTSTAT, 0x23), Read Only
Reports the fault status for the color-adjust string. When a fault is reported in this register, the fault output FLTB pulls low.
Toggle EN low, then high to clear the faults. Faults recur if the fault persists.
Table 13-5. Fault Status register (FAULTSTAT, 0x23), defaults highlighted
Register data
Register name
Address
D7
D6
D5
D4
D3
D2
D1
D0
-
-
-
-
-
TSD
OCFLT
SSFLT
No Faults Detected
x
x
x
x
x
x
0
0
LED Short Circuit Fault Detected
x
x
x
x
x
x
x
1
String Open Circuit Fault Detected
x
x
x
x
x
x
1
x
The MSL2021 is in Thermal Shutdown
x
x
x
x
x
1
x
x
FAULTSTAT
13.6
0x23
Sleep register (SLEEP, 0x24)
Puts the device to sleep (the serial interface remains awake). When asleep, device supply current reduces to 7mA
(typical), the gate drive outputs stop switching, and the LEDs turn off.
Table 13-6. Sleep register (SLEEP, 0x24), defaults highlighted
Register data
Register name
D7
D6
D5
D4
D3
D2
D1
D0
-
-
-
-
-
-
-
SLEEP
DEFAULT
0
0
0
0
0
0
0
0
Device is Awake
x
x
x
x
x
x
x
0
Device is Asleep
x
x
x
x
x
x
x
1
SLEEP
13.7
Address
0x24
Thermistor Temperature register (TEMP, 0x31), Read Only
Reports the thermistor temperature at 2C per LSB. When the thermistor temperature is equal to or below 18C, this
register returns 0x12, or 18C. When the thermistor temperature is equal to or above 80C, this register returns 0x50, or
80C.
Table 13-7. Thermistor Temperature register (TEMP, 0x31), defaults highlighted
Register name
Register name
Address
D7
TEMP
D6
D5
0x31
D4
D3
D2
D1
D0
TEMP[7:0]
Minimum Value: 0x12 = 18C
0
0
0
1
0
0
1
0
Maximum Value: 0x50 = 80C
0
1
0
1
0
0
0
0
MSL2021 [DATASHEET]
42062A–LED–02/2013
29
13.8
Password Verification registers
(PWV(HIGH) and PWV(LOW), 0x38 and 0x39)
Use these registers when locking the look-up table of the MSL2021. Also, enter the password (chosen when the Look-Up
Table was locked) into these registers to allow reading the contents of a locked look-up table. See section “MSL2021
Look-Up Table Lockout Procedure” on page 23 for details about locking the look-up table.
Table 13-8. Password Verification registers
(PWV(HIGH and PWV(LOW), 0x38 and 0x39), defaults highlighted
Register name
Register name
Address
D7
D5
D4
D3
D2
PWV(HIGH)
0x38
Password Verification High Byte [15:8]
PWV(LOW)
0x39
Password Verification Low Byte [7:0]
DEFAULT
13.9
D6
1
1
1
1
1
1
D1
D0
1
1
Look-Up Table Lock register (LUT LOCK, 0x3A)
Use this register to lock the look-up table of the MSL2021. See section “MSL2021 Look-Up Table Lockout Procedure” on
page 23 for details about locking the look-up table. At power-up, this register returns 0x02 when the look-up table is
locked, and returns 0x83 when the table is unlocked.
Table 13-9. Look-Up Table Lock register (LUT LOCK, 0x3A), defaults highlighted
Register data
Register name
Address
D7
D6
D5
D4
D3
D2
-
-
-
-
-
-
DEFAULT
1
0
0
0
0
0
1
1
Locks the Look-Up Table when committed to
EEPROM
0
0
0
0
0
0
1
0
LUT LOCK
0x3A
D1
D0
LOCK
13.10 Efficiency Optimizer Control Register (EOCTRL, 0x40)
Configures voltage feedback threshold for D. It is recommended that SLEEP = 1 (bit D0 in the configuration register
0x24) while changing this register to avoid perturbations of the string power supply. The MSL2021 always performs a
power supply voltage calibration when power is applied, EN is taken high, or SLEEP is reset to 0. Do not change bits D4
through D7.
DThresh sets the voltage feedback threshold for D, The Main string FET drain connection.
D Threshold = (DThresh  150mV) + 250mV.
Table 13-10. Efficiency Optimizer Control Register (FBOCTRL, 0x40), default highlighted
Register name
Address /
Default
Register data
D7
D6
D5
D4
-
-
-
-
DEFAULT = 0xE5
1
1
1
0
0
1
0
1
D Threshold = (0  150mV) + 250mV = 0.25V
1
1
1
0
0
0
0
0
FBOCTRL
0x40
D3
D2
D1
D0
DThresh[3:0]
MSL2021 [DATASHEET]
42062A–LED–02/2013
30
Address /
Default
Register name
Register data
D7
D6
D5
D4
•••
D3
D2
D1
D0
0
1
0
1
1
0
1
1
•••
D Threshold = (5  150mV) + 250mV = 1V
1
1
1
0
•••
•••
D Threshold = (15  150mV) + 250mV = 2.5V
x
1
1
0
13.11 Registers 0x60 and 0x61, EEPROM Access
These registers control access to the EEPROM. See “EEPROM and Power-Up Defaults” and “EEPROM Address and
Control/Status Registers” on page 26 for information.
13.12 Password registers (PW(HIGH) and PW(LOW), 0x68 and 0x69)
Use these registers to enter the password when locking the look-up table of the MSL2021. See section “MSL2021 LookUp Table Lockout Procedure” on page 23 for details about locking the look-up table.
Table 13-11. Password registers
(PW(HIGH) and PW(LOW), 0x68 and 0x69), defaults highlighted
Register data
Register name
Address
D7
D5
D4
D3
D2
PWV(HIGH)
0x68
Password High Byte [15:8]
PWV(LOW)
0x69
Password Low Byte [7:0]
DEFAULT
14.
D6
1
1
1
1
1
1
D1
D0
1
1
I²C Serial Interface
The MSL2021 operates as a slave that sends and receives data through an I²C/SMBus compatible 2-wire serial
interface. The interface is not needed for operation, but is provided to allow control and monitoring of device functions.
These functions include changing the Look-Up Table and equation parameters, changing the string current reference
feedback voltages, reading and adjusting the fault response behavior and status, putting the device to sleep without
losing the register settings, and programming the EEPROM. The I²C/SMBus compatible interface is suitable for 100kHz,
400kHz and 1MHz communication. The interface uses data I/O SDA and clock input SCL to achieve bidirectional
communication between master and slaves. Fault output FLTB optionally alerts the host system to faults detected by the
MSL2021 (Figure 14-1 on page 32 and “Fault Conditions” on page 15). During over temperature shutdown (TSD) the
serial interface remains active.
The master, typically a microcontroller, initiates all data transfers, and generates the clock that synchronizes the
transfers. SDA operates as both an input and an open-drain output. SCL operates only as an input, and does not perform
clock-stretching. Pull-up resistors are required on SDA, SCL and FLTB.
MSL2021 [DATASHEET]
42062A–LED–02/2013
31
Figure 14-1. I2C Interface Connections
VI2C
2 x 2.2k
TYPICAL
100k
MASTER SDA
SCL
INT
(µC)
SDA
SCL
FLTB
MSL2021
A transmission consists of a START condition sent by a master, a 7-bit slave address plus one R/W bit, an acknowledge
bit, none or many data bytes each separated by an acknowledge bit, and a STOP condition (Figure 14-2, Figure 14-4 and
Figure 14-5 on page 33).
Figure 14-2. I2C Serial Interface Timing Details
SDA
tBUF
tSU:DAT
tSU:STA
tHD:STA
tHD:DAT
tSU:STO
tLOW
SCL
tHIGH
tHD:STA
tR
START
CONDITION
14.1
tF
REPEATED START
CONDITION
START
STOP
CONDITION CONDITION
I2C Bus Timeout
The bus timeout feature allows the MSL2021 to reset the serial bus interface if a communication ceases before a STOP
condition is sent. If SCL or SDA is low for more than 25ms (typical), then the MSL2021 terminates the transaction,
releases SDA and waits for another START condition.
14.2
I2C Bit Transfer
One data bit is transferred during each clock pulse. SDA must remain stable while SCL is high.
Figure 14-3. I2C Bit Transfer
SDA
SCL
SDA LEVEL STABLE
SDA DATA VALID
SDA ALLOWED TO
CHANGE LEVEL
MSL2021 [DATASHEET]
42062A–LED–02/2013
32
14.3
I2C START and STOP Conditions
Both SCL and SDA remain high when the interface is free. The master signals a transmission with a START condition (S)
by transitioning SDA from high to low while SCL is high. When the master has finished communicating with the slave, it
issues a STOP condition (P) by transitioning SDA from low to high while SCL is high. The bus is then free.
Figure 14-4. I2C START and STOP Conditions
SDA
S
P
START
CONDITION
STOP
CONDITION
SCL
14.4
I2C Acknowledge Bit
The acknowledge bit is a clocked 9th bit which the recipient uses to handshake receipt of each byte of data. The master
generates the 9th clock pulse, and the recipient holds SDA low during the high period of the clock pulse. When the
master is transmitting to the MSL2021, the MSL2021 pulls SDA low because the MSL2021 is the recipient. When the
MSL2021 is transmitting to the master, the master pulls SDA low because the master is the recipient.
Figure 14-5. I2C Acknowledge
SCL
1
2
8
9
1
SDA
TRANSMITTER
S
A
START
CONDITION
ACKNOWLEDGE
BY RECEIVER
SDA
RECEIVER
14.5
I2C Slave Address
The MSL2021 has a 7-bit long slave address, 0b0100000, followed by an eighth bit, the R/W bit. The R/W bit is low for a
write to the MSL2021, high for a read from the MSL2021. All MSL2021 devices have the same slave address; when
using multiple devices and communicating with them through their serial interfaces, make external provision to route the
serial interface to the appropriate device. Note that development systems that use I2C often left-shift the address one
position before they insert the R/W bit, and so expect a default address of 0x20 (not 0x40).
MSL2021 [DATASHEET]
42062A–LED–02/2013
33
Figure 14-6. I2C Slave Address
SDA
A7 = 0
A6 = 1
A5 = 0
A4 = 0
A3 =0
A2 = 0
A1 = 0
R/W
A
2
3
4
5
6
7
8
9
MSB
SCL
14.6
1
I2C Message Format for Writing to the MSL2021
A write to the MSL2021 contains the MSL2021’s slave address, the R/W bit cleared to 0, and at least 1 byte of
information (Figure 14-7 on page 34). The first byte of information is the register address byte. The register address byte
is stored as a register pointer, and determines which register the following byte is written into. If a STOP condition is
detected after the register address byte is received, then the MSL2021 takes no further action beyond setting the register
pointer.
Figure 14-7. I2C Writing a Register Pointer
ACKNO W LED GE
FRO M M SL202x
START
SD A
0
1
0
0
0
0
0
0
A
D7
ACKNO W LEDG E
FRO M M SL202x
.
SLAVE AD DR ESS ,
W R ITE AC CESS
.
.
.
.
.
STO P
D0
A
SET REG ISTER
PO IN TER TO X
TH E R EG ISTER PO IN TER N OW POINTS TO X ; A SUBSEQ UEN T READ
ACCESS R EAD S FRO M R EG ISTER ADD RESS X
When no STOP condition is detected, the byte transmitted after the register address byte is a data byte, and is placed
into the register pointed to by the register address byte (Figure 14-8). To simplify writing to multiple consecutive registers,
the register pointer auto-increments during each following acknowledge period. Further data bytes transmitted before a
STOP condition fill subsequent registers.
Figure 14-8. I2C Writing Two Data Bytes
ACKNOWLEDGE
FROM MSL202x
START
SDA
0
1
0
0
0
0
SLAVE ADDRESS,
WRITE ACCESS
0
0
A
D7
.
ACKNOWLEDGE
FROM MSL202x
.
.
.
.
.
D0
SET REGISTER
POINTER TO X
A
D7
.
ACKNOWLEDGE
FROM MSL202x
.
.
.
.
.
DATA WRITES TO
REGISTER X
D0
A
D7
.
ACKNOWLEDGE
FROM MSL202x
.
.
.
.
.
D0
STOP
A
DATA WRITES TO
REGISTER X + 1
THE REGISTER POINTER NOW POINTS TO X + 2; A SUBSEQUENT READ
ACCESS BEGINS READING FROM REGISTER ADDRESS X + 2
14.7
I2C Message Format for Reading from the MSL2021
Read the MSL2021 registers using one of two techniques.
The first technique begins the same way as a write, by setting the register address pointer as shown in Figure 14-7,
including the STOP condition (note that even though the final objective is to read data, the R/W bit is first sent as a write
because the address pointer byte is being written into the device). Follow the Figure 14-7 transaction by what shown in
Figure 14-9, with a new START condition and the slave address, this time with the R/W bit set to 1 to indicate a read.
Then, after the slave initiated acknowledge bit, clock out as many bytes as desired, separated by master initiated
MSL2021 [DATASHEET]
42062A–LED–02/2013
34
acknowledges. The pointer auto-increments during each master initiated acknowledge period. End the transmission with
a not-acknowledge followed by a stop condition.
Figure 14-9. I2C Reading Register Data with Preset Register Pointer
ACKNOWLEDGE
FROM MSL202x
START
SDA
0
1
0
0
0
0
0
1
A
ACKNOWLEDGE
FROM MASTER
.
D7
SLAVE ADDRESS,
READ ACCESS
.
.
.
.
.
D0
A
NOT ACKNOWLEDGE
FROM MASTER
.
D7
READ REGISTER
ADDRESS X
.
.
.
.
.
D0
STOP
A
READ REGISTER
ADDRESS X + 1
THE REGISTER POINTER NOW POINTS TO X + 2; A SUBSEQUENT
READ ACCESS READS FROM REGISTER ADDRESS X + 2
The second read technique is illustrated in Figure 14-10. Write to the MSL2021 to set the register pointer, send a
repeated START condition after the second acknowledge bit, then send the slave address again with the R/W bit set to 1
to indicate a read. Then clock out the data bytes separated by master initiated acknowledge bits. The register pointer
auto-increments during each master initiated acknowledge period. End the transmission with a not-acknowledge
followed by a stop condition. This technique is recommended for buses with multiple masters, because the read
sequence is performed in one uninterruptible transaction.
Figure 14-10. I2C Reading Register Data Using a Repeated START
ACKNOWLEDGE
FROM MSL202x
START
SDA
0
1
0
0
0
0
SLAVE ADDRESS
WRITE ACCESS
14.8
0
0
A
D7
ACKNOWLEDGE
FROM MSL202x
.
.
.
.
.
.
SET REGISTER
POINTER
REPEATED
START
D0
A
1
ACKNOWLEDGE
FROM MSL202x
0
1
0
0
0
0
SLAVE ADDRESS
READ ACCESS
1
A
D7
NOT ACKNOWLEDGE
STOP
FROM MASTER
.
.
.
.
.
.
D0
A
READ REGISTERS
I2C Message Format for Broadcast Writing to Multiple devices
With a broadcast write to MSL2021, a master broadcasts the same register data to all MSL2021s on the bus. First send
the broadcast write slave address of 0x00, followed by the MSL2021 broadcast device ID of 0x42. These two bytes are
followed by the register address in the MSL2021s that the following data are to be written into, and finally the data byte(s)
to be written into all devices.
A broadcast write example is shown in Figure 14-11. Here, the same register address in every MSL2021 is written to with
identical data. If further data bytes are transmitted before the STOP condition, they are stored in subsequent internal
registers of each MSL2021.
MSL2021 [DATASHEET]
42062A–LED–02/2013
35
Figure 14-11. I2C Broadcast Writing a Data Byte
ACKNOWLEDGE
FROM MSL202x
START
SDA
0
0
0
0
0
0
0
0
A
BROADCAST WRITE
SLAVE ADDRESS
0
1
ACKNOWLEDGE
FROM MSL202x
0
0
0
0
1
0
A
D7
.
ACKNOWLEDGE
FROM MSL202x
.
.
.
.
.
D0
A
D7
SETS ALL REGISTER
POINTERS TO X
MSL202x BROADCAST ID
.
ACKNOWLEDGE
FROM MSL202x
.
.
.
.
.
D0
STOP
A
DATA WRITES TO ALL
REGISTER Xs
ALL REGISTER POINTERS NOW POINT TO X + 1; THE FIRST SUBSEQUENT READ
ACCESS OF EACH MSL202x READS FROM REGISTER ADDRESS X + 1
There is no broadcast read. However, a broadcast write may be used to set up the internal register pointers of all the
MSL2021s in a system to speed up the subsequent individual reading of, for example, all the status registers. Figure 1412 illustrates a broadcast write that sets all the register pointers, and issues a STOP.
Figure 14-12. I2C Broadcast Writing a Register Pointer
ACKNOWLEDGE
FROM MSL202x
START
SDA
0
0
0
0
0
0
0
BROADCAST WRITE
SLAVE ADDRESS
0
A
0
1
ACKNOWLEDGE
FROM MSL202x
0
0
0
0
1
0
MSL202x BROADCAST ID
A
D7
.
ACKNOWLEDGE
FROM MSL202x
.
.
.
.
.
D0
STOP
A
SETS ALL REGISTER
POINTERS TO X
ALL REGISTER POINTERS NOW POINT TO X; THE FIRST SUBSEQUENT READ ACCESS
OF EACH MSL202x BEGINS READING FROM REGISTER ADDRESS X
MSL2021 [DATASHEET]
42062A–LED–02/2013
36
d 0.1 C
Packaging Information
d 0.1 C
(TOP VIEW)
D
24
(SIDE VIEW)
d 0.08
SEATING PLANE
d 0.1 C
1
2
PIN 1 ID
E
A
A1
(A3)
D2
e/2
E2
COMMON DIMENSIONS
(UNIT OF MEASURE=MM)
e
SYMBOL
24X L
24X b
K
15.
(BOTTOM VIEW)
MIN
NOM
MAX
A
-
0.85
0.90
A1
0.00
-
0.05
0.203 REF
A3
b
0.20
D
D2
NOTES:
2. Dimension "b" applies to metalized terminal and is measured between
0.15mm and 0.30mm from the terminal tip. If the terminal has the optional
radius on the other end of the terminal, the dimension should not be
measured in that radius area.
E2
0.25
0.30
2
4.00 BSC
2.35
E
1. Refer to JEDEC Drawing MO-220 (SAW SINGULATION)
NOTE
2.45
2.55
4.00 BSC
2.35
e
2.45
2.55
0.50 BSC
L
0.35
0.40
0.45
K
0.20
-
-
1/10/13
Package Drawing Contact:
[email protected]
TITLE
24M1, 24-lead, 4.0x4.0x0.9mm Body, 0.50mm
Pitch, 2.45mm sq exposed pad, Very Thin Fine
Pitch, Quad Flat No Lead Package (VQFN)
GPC
DRAWING NO.
REV.
ZUH
24M1
B
No representation or warranties are made concerning third-party patents with regard to the use of Atmel® products. The
mixing of red LEDs with phosphor-converted LEDs may be protected by certain third-party patents, such as U.S. Patent
No. 7,213,940 and related patents of Cree, Inc.
MSL2021 [DATASHEET]
42062A–LED–02/2013
37
16.
Datasheet Revision History
16.1
42062A – 02/2013
1.
Initial revision.
MSL2021 [DATASHEET]
42062A–LED–02/2013
38
Table of Contents
Features 1
Typical Applications 1
1. Introduction 2
2. Ordering Information 2
3. Application Circuit 2
4. Absolute Maximum Ratings 3
5. Electrical Characteristics 4
6. Block Diagram 11
7. Pinout and Pin Description 12
7.1
7.2
Pinout MSL2021 12
Pin Descriptions 12
8. Typical Application Circuit 14
9. Detailed Description 14
10. Fault Conditions 15
11. Applications Information 15
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
11.9
Turn-On Sequence 15
Setting the Main String Current with RS 15
Setting AC/DC Output Voltage 16
Selecting the Main String MOSFET 16
Selecting the Drain Resistor – RD 16
Selecting the Color-Adjust String Floating Buck Components 17
PWM and LED Brightness 20
Light Color and the THM Input 20
MSL2021 Look-Up Table Lockout Procedure 23
11.9.1 Example: 23
12. Control Registers 25
12.1
12.2
EEPROM and Power-Up Defaults 26
EEPROM Address and Control/Status Registers 26
13. Detailed Register Descriptions 27
13.1
13.2
13.3
13.4
13.5
13.6
13.7
13.8
13.9
String Duty Cycle Control Registers (SDCR18 through SDCR80, 0x00 through 0x1F) 27
Main String Reference Voltage register (MREF, 0x20) 27
Color-Adjust String Reference Voltage register (CAREF, 0x21) 28
Fault Disable register (FAULT, 0x22) 28
Fault Status register (FAULTSTAT, 0x23), Read Only 29
Sleep register (SLEEP, 0x24) 29
Thermistor Temperature register (TEMP, 0x31), Read Only 29
Password Verification registers
(PWV(HIGH) and PWV(LOW), 0x38 and 0x39) 30
Look-Up Table Lock register (LUT LOCK, 0x3A) 30
MSL2021 [DATASHEET]
42062A–LED–02/2013
i
13.10 Efficiency Optimizer Control Register (EOCTRL, 0x40) 30
13.11 Registers 0x60 and 0x61, EEPROM Access 31
13.12 Password registers (PW(HIGH) and PW(LOW), 0x68 and 0x69) 31
14. I²C Serial Interface 31
14.1
14.2
14.3
14.4
14.5
14.6
14.7
14.8
I2C Bus Timeout 32
I2C Bit Transfer 32
I2C START and STOP Conditions 33
I2C Acknowledge Bit 33
I2C Slave Address 33
I2C Message Format for Writing to the MSL2021 34
I2C Message Format for Reading from the MSL2021 34
I2C Message Format for Broadcast Writing to Multiple devices 35
15. Packaging Information 37
16. Datasheet Revision History 38
16.1
42062A – 01/2013 38
Table of Contents i
MSL2021 [DATASHEET]
42062A–LED–02/2013
ii
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© 2013 Atmel Corporation. All rights reserved. / Rev.: 42062A–LED–02/2013
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automotive applications. Atmel products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life.