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19-0655; Rev 2; 8/09
KIT ATION EVALU LE B AVAILA
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
General Description
The MAX16807 is an integrated, high-efficiency white or RGB LED driver. It is designed for LCD backlighting and other LED lighting applications with multiple strings of LEDs. The MAX16807 current-mode PWM controller regulates the necessary voltage to the LED array. Depending on the input voltage and LED voltage range, it can be used with boost or buck-boost (SEPIC) topologies. The MAX16807 features an 8V to 26.5V input voltage range. A wide range of adjustable frequency (20kHz to 1MHz) allows design optimization for efficiency and minimum board space. The MAX16807 LED driver includes eight open-drain, constant-current-sinking LED driver outputs rated for 36V continuous operation. The LED current-control circuitry achieves 3% current matching among strings and enables paralleling of outputs for LED string currents higher than 55mA. The output-enable pin is used for simultaneous PWM dimming of all output channels. Dimming frequency range is 50Hz to 30kHz and dimming ratio is up to 5000:1. The constant-current outputs are single resistor programmable and the LED current can be adjusted up to 55mA per output channel. The MAX16807 operates either in stand-alone mode or with a microcontroller (C) using an industry-standard, 4wire serial interface. The MAX16807 includes overtemperature protection, operates over the full -40C to +125C temperature range, and is available in a thermally enhanced, 28-pin TSSOP exposed paddle package.
Features
o Eight Constant-Current Output Channels (Up to 55mA Each) o 3% Current Matching Among Outputs o Paralleling Channels Allows Higher Current per LED String o Output Rated for 36V Continuous Voltage o Output-Enable Pin for PWM Dimming (Up to 30kHz) o One Resistor Sets LED Current for All Channels o Wide Dimming Ratio Up to 5000:1 o Low Current-Sense Reference (300mV) for High Efficiency o 8V to 26.5V Input Voltage or Higher with External Biasing Devices o 4-Wire Serial Interface to Control Individual Output Channels
MAX16807
Applications
LCD White or RGB LED Backlighting: LCD TVs, Desktop, and Notebook Panels Automotive Navigation, Heads-Up, and Infotainment Displays Industrial and Medical Displays Ambient, Mood, and Accent Lighting
Ordering Information
PART MAX16807AUI+ TEMP RANGE -40C to +125C PIN-PACKAGE 28 TSSOP-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad.
Pin Configuration appears at end of data sheet.
Typical Operating Circuits
VIN L VOUT D
Q
COUT
R1
LEDs
RCS CC1
CC2
RC1 R2
3V TO 5.5V
OUT CS AGND VCC CIN
COMP
FB V+ CBYP PGND LE DIN CLK DOUT OE SET REF RSET CREF RT CT RTCT OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7 STAND-ALONE OPERATION
MAX16807
Typical Operating Circuits continued at end of data sheet.
1
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
ABSOLUTE MAXIMUM RATINGS
VCC to AGND..........................................................-0.3V to +30V Current into VCC (VCC > 24V)...........................................30mA V+ to PGND..............................................................-0.3V to +6V OUT to AGND.............................................-0.3V to (VCC + 0.3V) OUT Current (10s duration) .................................................1A FB, COMP, CS, RTCT, REF to AGND.......................-0.3V to +6V COMP Sink Current.............................................................10mA OUT0-OUT7 to PGND............................................-0.3V to +40V DIN, CLK, LE, OE, SET to PGND..................-0.3V to (V+ + 0.3V) DOUT Current...................................................................10mA OUT0-OUT7 Sink Current...................................................60mA Total PGND Current ..........................................................480mA Continuous Power Dissipation (TA = +70C) 28-Pin TSSOP (derate 27mW/C* above +70C) .......2162mW Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C *Per JEDEC51 Standard (Multilayer Board).
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS (PWM CONTROLLER)
(VCC = +15V, V+ = +3V to +5.5V referenced to PGND, RT = 10k, CT = 3.3nF, REF = open, COMP = open, CREF = 0.1F, VFB = 2V, CS = AGND, VAGND = VPGND = 0V; all voltages are measured with respect to AGND, unless otherwise noted. TJ = TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER REFERENCE Output Voltage Line Regulation Load Regulation Total Output-Voltage Variation Output Noise Voltage Output Short-Circuit Current OSCILLATOR Initial Accuracy Voltage Stability Temperature Stability RTCT Ramp Peak-to-Peak RTCT Ramp Valley Discharge Current Frequency Range ERROR AMPLIFIER FB Input Voltage Input Bias Current Open-Loop Gain Unity-Gain Bandwidth Power-Supply Rejection Ratio COMP Sink Current COMP Source Current COMP Output-Voltage High COMP Output-Voltage Low VFB IB(FB) AVOL fGBW PSRR ISINK ISOURCE VOH VOL 12V VCC 25V VFB = 2.7V, VCOMP = 1.1V VFB = 2.3V, VCOMP = 5V VFB = 2.3V, RCOMP = 15k to AGND VFB = 2.7V, RCOMP = 15k to VREF 60 2 0.5 5 2V VCOMP 4V FB shorted to COMP 2.45 2.50 -0.01 100 1 80 6 1.2 5.8 0.1 1.1 1.8 2.55 -0.1 V A dB MHz dB mA mA V V IDIS fOSC VRTCT = 2V, TJ = +25C VRTCT = 2V, -40oC TJ +125C 7.9 7.5 20 TJ = +25C 12V < VCC < 25V 51 54 0.2 1 1.7 1.1 8.3 8.3 8.7 9.0 1000 57 0.5 kHz % % V V mA kHz VREF VLINE VLOAD VREFT VNOISE ISHORT IREF = 1mA, TJ = +25C 12V< VCC < 25V, IREF = 1mA 1mA < IREF < 20mA (Note 2) 10Hz < f < 10kHz VREF = 0V 30 4.875 50 180 4.95 5 0.4 6 5.05 4 50 5.125 V mV mV V V mA SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
ELECTRICAL CHARACTERISTICS (PWM CONTROLLER) (continued)
(VCC = +15V, V+ = +3V to +5.5V referenced to PGND, RT = 10k, CT = 3.3nF, REF = open, COMP = open, CREF = 0.1F, VFB = 2V, CS = AGND, VAGND = VPGND = 0V; all voltages are measured with respect to AGND, unless otherwise noted. TJ = TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER CURRENT-SENSE AMPLIFIER Current-Sense Gain Maximum Current-Sense Signal Power-Supply Rejection Ratio Current-Sense Input Bias Current Current Sense to OUT Delay MOSFET DRIVER OUT Low-Side On-Resistance OUT High-Side On-Resistance Source Current (Peak) Sink Current (Peak) Rise Time Fall Time Startup Voltage Threshold Minimum Operating Voltage After Turn-On Undervoltage-Lockout Hysteresis Maximum Duty Cycle Minimum Duty Cycle SUPPLY CURRENT Startup Supply Current Operating Supply Current VCC Zener Voltage ISTART ICC VZ VCC = 7.5V VFB = VCS = 0V ICC = 25mA 24 32 3 26.5 65 5 A mA V VRDS_ONL VRDS_ONH ISOURCE ISINK tR tF VCC_START VCC_MIN UVLOHYST DMAX DMIN 94.5 ISINK = 200mA ISOURCE = 100mA CLOAD = 10nF CLOAD = 10nF CLOAD = 1nF CLOAD = 1nF 7.98 7.1 TJ = -40C to +85C (Note 2) TJ = -40C to +125C TJ = -40C to +85C (Note 2) TJ = -40C to +125C 4.5 4.5 3.5 3.5 2 1 15 22 8.4 7.6 0.8 96 97.5 0 8.82 8.0 10 12 7.5 10 A A ns ns V V V % % ACS VCS_MAX PSRR ICS tPWM (Notes 3, 4) (Note 3) 12V VCC 25V VCOMP = 0V 50mV overdrive 2.85 0.275 3.00 0.300 70 -1 60 -2.5 3.40 0.325 V/V V dB A ns SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX16807
UNDERVOLTAGE LOCKOUT/STARTUP
PULSE-WIDTH MODULATION (PWM)
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3
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
ELECTRICAL CHARACTERISTICS (LED DRIVER)
(V+ = +3V to +5.5V, VAGND = VPGND = 0V; all voltages are measured with respect to PGND, unless otherwise noted. TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Operating Supply Voltage Output Voltage Standby Current (Interface Idle, All Output Ports High Impedance) Standby Current (Interface Active, All Output Ports High Impedance) Supply Current (Interface Idle, All Output Ports Active Low) INTERFACE (DIN, CLK, DOUT, LE, OE) Input-Voltage High (DIN, CLK, LE, OE) Input-Voltage Low (DIN, CLK, LE, OE) Hysteresis Voltage (DIN, CLK, LE, OE) Input Leakage Current (DIN, CLK) OE Pullup Current to V+ LE Pulldown Current to PGND Output-Voltage High (DOUT) Output-Voltage Low (DOUT) VIH VIL VHYST ILEAK IOE ILE VOH VOL V+ = 5.5V, OE = PGND V+ = 5.5V, LE = V+ ISOURCE = 4mA ISINK = 4mA 0oC TA +125C, VOUT = 1V to 2.5V, RSET = 360 TA = -40C, VOUT = 1V to 2.5V, RSET = 360 OE = V+ 46.5 43 50 -1 0.25 0.25 V+ - 0.5V 0.5 53.5 mA 57 1 A 1.5 1.5 0.8 +1 25.0 25.0 0.7 x V+ 0.3 x V+ V V V A A A V V SYMBOL V+ VOUT_ RSET = 360, DIN, LE, CLK = PGND or V+, OE = V+, DOUT unconnected RSET = 360, fCLK = 5MHz, OE = V+, DIN, LE = PGND or V+, DOUT unconnected RSET = 360, OE = PGND, DIN, LE = V+, DOUT unconnected 3.6 CONDITIONS MIN 3.0 TYP MAX 5.5 36 4.5 UNITS V V mA
3.8
4.8
mA
I+
17
30
mA
OUT_ Output Current
IOUT_
OUT_ Leakage Current
4
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
5V TIMING CHARACTERISTICS
(V+ = +4.5V to +5.5V, VAGND = VPGND = 0V; all voltages are measured with respect to PGND, unless otherwise noted. TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 5)
PARAMETER CLK Clock Period CLK Pulse-Width High CLK Pulse-Width Low DIN Setup Time DIN Hold Time DOUT Propagation Delay DOUT Rise Time DOUT Fall Time LE Pulse-Width High LE Setup Time LE Rising to OUT_ Rising Delay LE Rising to OUT_ Falling Delay CLK Rising to OUT_ Rising Delay CLK Rising to OUT_ Falling Delay OE Rising to OUT_ Rising Delay OE Falling to OUT_ Falling Delay OUT_ Turn-On Fall Time OUT_ Turn-Off Rise Time SYMBOL tCP tCH tCL tDS tDH tDO tDR tDF tLW tLS tLRR tLRF tCRR tCRF tOER tOEF tF tR (Note 6) (Note 6) (Note 6) (Note 6) (Note 6) (Note 6) 80% to 20% (Note 6) 20% to 80% (Note 6) CDOUT = 10pF, 20% to 80% CDOUT = 10pF, 80% to 20% 20 15 110 325 110 325 110 325 210 130 CONDITION MIN 40 19 19 4 8 12 50 10 10 TYP MAX UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
MAX16807
INTERFACE TIMING CHARACTERISTICS
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5
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
3.3V TIMING CHARACTERISTICS
(V+ = +3V to < +4.5V, VAGND = VPGND = 0V; all voltages are measured with respect to PGND, unless otherwise noted. TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 5)
PARAMETERS CLK Clock Period CLK Pulse-Width High CLK Pulse-Width Low DIN Setup Time DIN Hold Time DOUT Propagation Delay DOUT Rise Time DOUT Fall Time LE Pulse-Width High LE Setup Time LE Rising to OUT_ Rising Delay LE Rising to OUT_ Falling Delay CLK Rising to OUT_ Rising Delay CLK Rising to OUT_ Falling Delay OE Rising to OUT_ Rising Delay OE Falling to OUT_ Falling Delay OUT_ Turn-On Fall Time OUT_ Turn-Off Rise Time SYMBOL tCP tCH tCL tDS tDH tDO tDR tDF tLW tLS tLRR tLRF tCRR tCRF tOER tOEF tF tR (Note 6) (Note 6) (Note 6) (Note 6) (Note 6) (Note 6) 80% to 20% (Note 6) 20% to 80% (Note 6) CDOUT = 10pF, 20% to 80% CDOUT = 10pF, 80% to 20% 20 15 140 350 140 350 140 350 275 150 CONDITIONS MIN 52 24 24 4 8 12 70 12 12 TYP MAX UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
INTERFACE TIMING CHARACTERISTICS
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6:
All devices are 100% production tested at TJ = +25C and TJ = +125C. Limits to TA = -40C are guaranteed by design. Guaranteed by design, not production tested. Parameter is measured at trip point of latch with VFB = 0V. Gain is defined as A = VCOMP/VCS, 0.05V VCS 0.25V. See Figures 3 and 4. A 65 pullup resistor is connected from OUT_ to 5.5V. Rising refers to VOUT_ when current through OUT_ is turned off and falling refers to VOUT_ when current through OUT_ is turned on.
6
_______________________________________________________________________________________
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
Typical Operating Characteristics
(VCC = +15V, V+ = 3V to 5.5V, RT = 10k, CT = 3.3nF, VREF = COMP = open, CREF = 0.1F, VFB = 2V, VCS = VAGND = VPGND = 0V. Typical values are at TA = +25C, unless otherwise noted.)
STARTUP CURRENT vs. TEMPERATURE
MAX16807 toc01 MAX16807 toc02
MAX16807
BOOTSTRAP UVLO vs. TEMPERATURE
10 9 8 7 VCC (V) 6 5 4 3 2 1 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) 29 HYSTERESIS 27 25 VCC FALLING ICC (A) VCC RISING 41 39 37 35 33 31
OPERATING SUPPLY CURRENT vs. TEMPERATURE AFTER STARTUP (fOSC = fSW = 300kHz)
CT = 560pF 4.9 4.7 ICC (mA) 4.5 4.3 4.1 3.9 3.7 3.5
MAX16807 toc03
VCC = 7.5V
5.1
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
REFERENCE VOLTAGE vs. TEMPERATURE
MAX16807 toc04
REFERENCE VOLTAGE vs. REFERENCE LOAD CURRENT
MAX16807 toc05
REFERENCE VOLTAGE vs. SUPPLY VOLTAGE
4.998 4.996 4.994 VREF (V) 4.992 4.990 4.988 4.986 IREF = 1mA
MAX16807 toc06
5.08 5.06 5.04 5.02 VREF (V) 5.00 4.98 4.96 4.94 4.92 4.90 IREF = 20mA IREF = 1mA
5.05 5.00 4.95 VREF (V) 4.90 4.85 4.80 4.75 4.70 4.65
5.000
4.984 4.982 4.980 0 10 20 30 40 50 60 70 10 12 14 16 18 VCC (V) 20 22 24 26 IREF (mA)
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
OSCILLATOR FREQUENCY (fOSC) vs. TEMPERATURE
540 OSCILLATOR FREQUENCY (kHz) 530 520 510 500 490 480 470 460 450 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) RT = 3.65k CT = 560pF
MAX16807 toc07
OSCILLATOR RT/CT DISCHARGE CURRENT vs. TEMPERATURE
MAX16807 toc08
CURRENT-SENSE TRIP THRESHOLD vs. TEMPERATURE
0.38 0.36 CS THRESHOLD (V) 0.34 0.32 0.30 0.28 0.26 0.24 0.22 0.20
MAX16807 toc09
550
8.04 VRT/CT = 2V RT/CT DISCHARGE CURRENT (mA) 8.02 8.00 7.98 7.96 7.94 7.92 7.90 7.88
0.40
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
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7
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
Typical Operating Characteristics (continued)
(VCC = +15V, V+ = 3V to 5.5V, RT = 10k, CT = 3.3nF, VREF = COMP = open, CREF = 0.1F, VFB = 2V, VCS = VAGND = VPGND = 0V. Typical values are at TA = +25C, unless otherwise noted.)
TIMING RESISTANCE vs. OSCILLATOR FREQUENCY
MAX16807 toc10
OUT IMPEDANCE vs. TEMPERATURE (RDS_ON PMOS DRIVER)
5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0
MAX16807 toc11
OUT IMPEDANCE vs. TEMPERATURE (RDS_ON NMOS DRIVER)
9 8 7 RDS_ON () 6 5 4 3 2 1 0 ISINK = 200mA
MAX16807 toc12
1000 CT = 1nF 100 RT (k) CT = 560pF CT = 100pF CT = 220pF 10 CT = 10nF CT = 4.7nF CT = 3.3nF CT = 2.2nF 10k 100k 1M
ISOURCE = 100mA
10
1
0.1 10M FREQUENCY (Hz)
RDS_ON ()
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
PROPAGATION DELAY FROM CURRENT-LIMIT COMPARATOR TO OUT vs. TEMPERATURE
MAX16807 toc13
ERROR-AMPLIFIER OPEN-LOOP GAIN AND PHASE vs. FREQUENCY
MAX16807 toc14
COMP VOLTAGE LEVEL TO TURN OFF DEVICE vs. TEMPERATURE
10 -15 2.2 PHASE (DEGREES) 2.1 VCOMP (V) 2.0 1.9 1.8 1.7 1.6 1.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) VCC = 15V
MAX16807 toc15
100 90 PROPAGATION DELAY (ns) 80 70
2.3
140 120 100 GAIN (dB) 80 60 40 20 0 -20 PHASE GAIN
-40 -65 -90 -115 -140 -165 -190 10k 100k 1M 10M 100M
60 50 40 30 20 10 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
0.01 1
10 100 1k
FREQUENCY (Hz)
SUPPLY CURRENT vs. OSCILLATOR FREQUENCY
6.5 6.0 5.5 ICC (mA) 5.0 4.5 4.0 3.5 3.0 2.5 2.0 20 120 220 320 420 520 620 720 820 920 1020 FREQUENCY (kHz) TA = +125C TA = -40C CT = 100pF
MAX16807 toc16
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS OFF, RSET = 720)
TA = +125C
SUPPLY CURRENT (mA) 1.95
TA = +85C
TA = +25C
1.90
TA = -40C
1.85
1.80 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
8
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MAX16807 toc17
7.0
2.00
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
Typical Operating Characteristics (continued)
(VCC = +15V, V+ = 3V to 5.5V, RT = 10k, CT = 3.3nF, VREF = COMP = open, CREF = 0.1F, VFB = 2V, VCS = VAGND = VPGND = 0V. Typical values are at TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS OFF, RSET = 360)
MAX16807 toc18
MAX16807
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS ON, RSET = 720)
TA = +125C TA = +85C 17 SUPPLY CURRENT (mA)
MAX16807 toc19
3.70
20
SUPPLY CURRENT (mA)
3.65
TA = +125C
TA = +85C
14
3.60 TA = +25C 3.55 TA =-40C
11 TA = -40C TA = +25C
8
3.50 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
SUPPLY CURRENT vs. SUPPLY VOLTAGE (INTERFACE IDLE, ALL OUTPUTS ON, RSET = 360)
MAX16807 toc20
OUT_ CURRENT vs. OUT_ VOLTAGE (RSET = 720, V+ = 3.3V)
MAX16807 toc21
25
30 25 OUT_ CURRENT (mA) 20 15 10 5 0 TA = -40C TA = +25C TA = +85C TA = +125C
22 SUPPLY CURRENT (mA)
TA = +125C TA = +85C
19
16
13 TA = -40C 10 3.0 3.5 4.0
TA = +25C
4.5
5.0
5.5
0
0.5
1.0
1.5
2.0
2.5
3.0
SUPPLY VOLTAGE (V)
OUT_ VOLTAGE (V)
OUT_ CURRENT vs. OUT_ VOLTAGE (RSET = 360, V+ = 3.3V)
MAX16807 toc22
OUT_ CURRENT vs. OUT_ VOLTAGE (RSET = 720, V+ = 5.0V)
MAX16807 toc23
60 50 OUT_ CURRENT (mA) 40 30 20 TA = +85C 10 0 0 0.5 1.0 1.5 2.0 2.5 TA = +125C TA = -40C TA = +25C
30 25 OUT_ CURRENT (mA) 20 15 TA = +85C 10 5 0 TA = +125C TA = -40C TA = +25C
3.0
0
0.5
1.0
1.5
2.0
2.5
3.0
OUT_ VOLTAGE (V)
OUT_ VOLTAGE (V)
_______________________________________________________________________________________
9
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
Typical Operating Characteristics (continued)
(VCC = +15V, V+ = 3V to 5.5V, RT = 10k, CT = 3.3nF, VREF = COMP = open, CREF = 0.1F, VFB = 2V, VCS = VAGND = VPGND = 0V. Typical values are at TA = +25C, unless otherwise noted.) OUT_ CURRENT vs. OUT_ VOLTAGE (RSET = 360, V+ = 5.0V)
MAX16807 toc24
OUT_ CURRENT vs. SUPPLY VOLTAGE V+ (RSET = 720, VOUT = 2V)
MAX16807 toc25
60 50 OUT_ CURRENT (mA) 40 30 20 10 0 0 0.5 1.0 1.5 2.0 2.5 TA = -40C TA = +25C TA = +85C TA = +125C
26.0
25.5 OUT_ CURRENT (mA) TA = +125C 25.0
TA = +85C
24.5
TA = +25C TA = -40C
24.0 3.0 3.0 3.5 4.0 4.5 5.0 5.5 OUT_ VOLTAGE (V) SUPPLY VOLTAGE (V)
OUT_ CURRENT vs. SUPPLY VOLTAGE V+ (RSET = 360, VOUT = 2V)
MAX16807 toc26
OUT_ CURRENT vs. SET RESISTANCE (V+ = 5.0V)
MAX16807 toc27
52
50
40 OUT_ CURRENT (mA)
51 OUT_ CURRENT (mA) TA = +125C 50
TA = +85C
30
20
49
TA = +25C TA = -40C
10
48 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
0 0 1 2 3 4 5 RSET (k)
10
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
Pin Description
PIN 1, 13, 28 2 3 4 5 6-9 10 11 12 14 15, 16 17 18 19 20-23 24 25 26 27 -- NAME N.C. AGND OUT VCC REF OUT4-OUT7 OE DOUT SET V+ PGND DIN CLK LE OUT0-OUT3 COMP FB CS RTCT EP Analog Ground MOSFET Driver Output OUT. Connects to the gate of the external n-channel MOSFET. Power-Supply Input. Bypass VCC to AGND with a 0.1F ceramic capacitor or a parallel combination of a 0.1F and a higher value ceramic capacitor. 5V Reference Output. Bypass REF to AGND with a 0.1F ceramic capacitor. LED Driver Outputs. OUT4-OUT7 are open-drain, constant-current-sinking outputs rated for 36V. Active-Low Output Enable Input. Drive OE low to PGND to enable the OUT0-OUT7. Drive OE high to disable OUT0-OUT7. Serial-Data Output. Data is clocked out of the 8-bit internal shift register to DOUT on CLK's rising edge. LED Current Setting. Connect RSET from SET to PGND to set the LED current. LED Driver Positive Supply Voltage. Bypass V+ to PGND with a 0.1F ceramic capacitor. Power Ground Serial-Data Input Serial-Clock Input Latch-Enable Input. Data is loaded transparently from the internal shift register(s) to the output latch(es) while LE is high. Data is latched into the output latch(es) on LE's falling edge, and retained while LE is low. LED Driver Outputs. OUT0-OUT3 are open-drain, constant-current-sinking outputs rated for 36V. Error-Amplifier Output Error-Amplifier Inverting Input PWM Controller Current-Sense Input PWM Controller Timing Resistor/Capacitor Connection. A resistor RT from RTCT to REF and a capacitor CT from RTCT to AGND set the oscillator frequency. Exposed Paddle. Connect to the ground plane for improved power dissipation. Do not use as the only ground connection for the part. FUNCTION No Connection. Not internally connected. Leave unconnected.
MAX16807
Detailed Description
The MAX16807 LED driver includes an internal switchmode controller that can be used as boost or buckboost (SEPIC) converters to generate the voltage necessary to drive the multiple strings of LEDs. This device incorporates an integrated low-side driver, a programmable oscillator (20kHz to 1MHz), an error amplifier, a low-voltage (300mV) current sense for higher efficiency, and a 5V reference to power up external circuitry (see Figures 1a, 1b, and 1c). The MAX16807 LED driver includes a 4-wire serial interface and a current-mode PWM controller to generate the necessary voltage for driving eight open-drain, constant-current-sinking output ports. The driver uses
current-sensing feedback circuitry (not simple current mirrors) to ensure very small current variations over the full allowed range of output voltage (see the Typical Operating Characteristics). The 4-wire serial interface comprises an 8-bit shift register and an 8-bit transparent latch. The shift register is written through a clock input, CLK, and a data input, DIN, and the data propagates to a data output, DOUT. The data output allows multiple drivers to be cascaded and operated together. The contents of the 8-bit shift register are loaded into the transparent latch through a latch-enable input, LE. The latch is transparent to the shift register outputs when high and latches the current state on the falling edge of LE. Each driver output is an open-drain, constant-current sink that should be connected to the cath11
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
ode of a string of LEDs connected in series. The constant-current capability is up to 55mA per output, set for all 8 outputs by an external resistor, R SET . The device can operate in a stand-alone mode (see the Typical Operating Circuits.) The number of channels can be expanded by using the MAX6970 and MAX6971 family in conjunction with the MAX16807.
MAX16807
REFERENCE 2.5V PREREG 5V
UVLO
VOLTAGEDIVIDER VCC 26.5V
THERMAL SHUTDOWN EN_REF BG SNS REG_OK DELAY AGND VCC 300mV ILIM VOLTAGE DIVIDER VDD REF
5V REG
S R CPWM 2R
Q
OUT
CS
VEA FB COMP R
CLK OSC Q RTCT
CLK SERIAL-TO-PARALLEL SHIFT REGISTER DIN D0 D1 D2 D3 D4 D5 D6 D7 DOUT
OUTPUT LATCHES LE D0 D1 D2 D3 D4 D5 D6 D7 POWER-ON RESET V+
OE
V+ CONSTANT-CURRENT SINK THERMAL SHUTDOWN D0 D1 D2 D3 D4 D5 D6 D7 CURRENT REFERENCE SET
PGND OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7
Figure 1a. Internal Block Diagram (MAX16807)
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
V+
68W/L 1.23 REST
W/L
OUT_
1.23V
995R
R
SET
PGND
Figure 1c. OUT_ Driver Internal Diagram
pMOS typically 3.5 and the on-resistance of the nMOS typically 4.5. The driver can source 2A and sink 1A typically. This allows for the MAX16807 to quickly turn on and off high gate-charge MOSFETs. Bypass VCC with one or more 0.1F ceramic capacitors to AGND, placed close to the VCC pin. The average current sourced to drive the external MOSFET depends on the total gate charge (QG) and operating frequency of the converter. The power dissipation in the MAX16807 is a function of the average output drive current (IDRIVE). Use the following equation to calculate the power dissipation in the device due to IDRIVE: IDRIVE = (QG x fSW) PD = (IDRIVE + ICC) x VCC where I CC is the operating supply current. See the Typical Operating Characteristics for the operating supply current at a given frequency.
MAX16807
Switch-Mode Controller
Current-Mode Control Loop
The advantages of current-mode control over voltagemode control are twofold. First, there is the feed-forward characteristic brought on by the controller's ability to adjust for variations in the input voltage on a cycleby-cycle basis. Second, the stability requirements of the current-mode controller are reduced to that of a single pole system unlike the double pole in the voltagemode control scheme. The MAX16807 uses a current-mode control loop where the output of the error amplifier is compared to the current-sense voltage (VCS). When the current-sense signal is lower than the inverting input of the CPWM comparator, the output of the comparator is low and the switch is turned on at each clock pulse. When the current-sense signal is higher than the inverting input of the CPWM comparator, the output is high and the switch is turned off.
Error Amplifier
The MAX16807 includes an internal error amplifier. The inverting input is at FB and the noninverting input is internally connected to a 2.5V reference. Set the output voltage using a resistive divider between output of the converter VOUT, FB, and AGND. Use the following formula to set the output voltage: R1 VOUT = 1 + x VFB R2 where VFB = 2.5V.
Oscillator
The oscillator frequency is programmable using an external capacitor and a resistor at RTCT (see RT and CT in the Typical Operating Circuits). RT is connected from RTCT to the 5V reference (REF), and CT is connected from RTCT to AGND. REF charges CT through RT until its voltage reaches 2.8V. CT then discharges through an 8.3mA internal current sink until CT's voltage reaches 1.1V, at which time CT is allowed to charge through RT again. The oscillator's period is the sum of the charge and discharge times of CT. Calculate the charge time as follows: tC = 0.57 x RT x CT where t C is in seconds, R T in ohms (), and C T in Farads (F). The discharge time is then: tD = (RT x CT x 1000) / [(4.88 x RT) - (1.8 x 1000)] where t D is in seconds, R T in ohms (), and C T in Farads (F).
Undervoltage Lockout (UVLO)
The turn-on supply voltage for the MAX16807 is 8.4V (typ). Once VCC reaches 8.4V, the reference powers up. There is a 0.8V of hysteresis from the turn-on voltage to the UVLO threshold. Once V CC reaches 8.4V, the MAX16807 operates with VCC down to 7.6V (typ). Once VCC goes below 7.6V, the device is in UVLO. When in UVLO, the quiescent supply current into VCC falls back to 32A (typ), and OUT and REF are pulled low.
MOSFET Driver
OUT drives an external n-channel MOSFET and swings from AGND to VCC. Ensure that VCC remains below the absolute maximum VGS rating of the external MOSFET. OUT is a push-pull output with the on-resistance of the
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13
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
The oscillator frequency is then: 1 fOSC = tC + tD) ( RCS = VCS IP - P
Reference Output
REF is a 5V reference output that can source 20mA. Bypass REF to AGND with a 0.1F capacitor.
Current Limit
The MAX16807 includes a fast current-limit comparator to terminate the on cycle during an overload or a fault condition. The current-sense resistor, RCS, connected between the source of the external MOSFET and AGND, sets the current limit. The CS input has a voltage trip level (VCS) of 0.3V. Use the following equation to calculate RCS:
IP-P is the peak current that flows through the MOSFET. When the voltage produced by this current (through the current-sense resistor) exceeds the current-limit comparator threshold, the MOSFET driver (OUT) turns the switch off within 60ns. In most cases, a small RC filter is required to filter out the leading-edge spike on the sense waveform. Set the time constant of the RC filter at 50ns.
Buck-Boost (SEPIC) Operation
Figure 2 shows a buck-boost application circuit using the MAX16807 in a stand-alone mode of operation. SEPIC topology is necessary when the total forward voltage of the LEDs in a string is such that VOUT can be below or above VIN.
VIN
L1
C1
D COUT
VOUT
Q
L2 R1 CC2 CC1 RC1 R2 LEDs
RCS
OUT CS AGND VCC CIN
3V TO 5.5V
COMP FB
V+ CBYP PGND DIN LE EXTERNAL CLOCK INPUT EXTERNAL DIM INPUT CLK DOUT OE SET
MAX16807
OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7
REF RT
RTCT
RSET CREF
CT
Figure 2. Buck-Boost (SEPIC) Configuration
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
LED Driver
4-Wire Interface
The MAX16807 also operates in a stand-alone mode (see the Typical Operating Circuits). For use with a microcontroller, the MAX16807 features a 4-wire serial interface using DIN, CLK, LE, OE inputs and DOUT as a data output. This interface is used to write the LED channels' data to the MAX16807. The serial-interface data word length is 8 bits, D0-D7. See Figure 3. The functions of the five interface pins are as follows: DIN is the serial-data input, and must be stable when it is sampled on the rising edge of CLK. Data is shifted in MSB first. This means that data bit D7 is clocked in first, followed by 7 more data bits, finishing with the LSB, D0. CLK is the serial-clock input that shifts data at DIN into the MAX16807's 8-bit shift register on its rising edge. LE is the latch enable input of the MAX16807 that transfers data from the 8-bit shift register to its 8-bit output latch (transparent latch). The data is latched on the falling edge of LE (Figure 4). The fourth input (OE) provides output-enable control of the output drivers. When OE is driven high, the outputs (OUT0-OUT7) are forced to high impedance without altering the contents of the output latches. Driving OE low enables the outputs to follow the state of the output latches. OE is independent of the operation of the serial interface operation. Data can be shifted into the serial-interface shift register and latched, regardless of the state of OE. DOUT is the serial-data output that shifts data out from the MAX16807's 8-bit shift register on the rising edge of CLK. Data at DIN propagates through the shift register and appears at DOUT eight clock cycles later. Table 1 shows the 4-wire serial-interface truth table.
MAX16807
Selecting External Component RSET to Set LED Output Current
The MAX16807 uses an external resistor, RSET, to set the LED current for outputs OUT0-OUT7. The minimum allowed value of RSET is 330, which sets the output currents to 55mA. The maximum allowed value of RSET is 5k (IOUT_ = 3.6mA) and maximum allowed capacitance at SET is 100pF. Use the following formula to set the output current: RSET = 18, 000 IOUT _
where IOUT_ is the desired output current in milliamps and the value for RSET is in ohms.
Overtemperature Cutoff
The MAX16807 contains an internal temperature sensor that turns off all outputs when the die temperature exceeds +165C. The outputs are enabled again when the die temperature drops below +140C. Register contents are not affected, so when a driver is overdissipating, the external symptom is the load LEDs cycling on and off as the driver repeatedly overheats and cools, alternately turning itself off and then back on again.
Table 1. 4-Wire Serial-Interface Truth Table
BLANKING OUTPUT CONTENTS SERIAL CLOCK SHIFT REGISTER CONTENTS LOAD LATCH CONTENTS INPUT INPUT CURRENT AT OUT_ DATA INPUT INPUT CLK D0 D1 D2 ... Dn-1 Dn LE D0 D1 D2 ... Dn-1 Dn OE D0 D1 D2 ... Dn-1 Dn DIN H L X H L R0 X P0 R0 R1 ... Rn-2 Rn-1 R0 R1 ... Rn-2 Rn-1 R1 R2 ... Rn-1 X P1 X ... X P2 ... Pn-1 Rn X Pn L H R0 R1 R2 P0 X P1 X P2 X ... Rn-1 Rn ... Pn-1 Pn ... X X L H P0 L P1 P2 L L ... ... Pn-1 L Pn L
L = Low Logic Level H = High Logic Level X = Don't Care P = Present State (Shift Register) R = Previous State (Latched) ______________________________________________________________________________________ 15
Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
LE tCL tCH tCP CLK tDH tDS DIN D7 tDO DOUT D7 D0 tLS tLW
OE tOEF
tOEW
tOER 80% 20% tf tr
OUT_
Figure 3. 4-Wire Serial-Interface Timing Diagram
Stand-Alone Operation
In stand-alone operation, the MAX16807 does not use the 4-wire interface (see the Typical Operating Circuits). Connecting DIN and LE to V+ provides at least 8 external clock pulses to CLK to enable 8 outputs. This startup pulse sequence can be provided either using an external clock or the PWM signal. The external clock can also be generated using the signal at RTCT and an external comparator.
LE tLRF OUT_
LE tLRR OUT_
LED Dimming
PWM Dimming
All the output channels can be dimmed simultaneously by applying a PWM signal (50Hz to 30kHz) to OE. This allows for a wide range of dimming up to a 5000:1 ratio. Each channel can be independently turned on and off using a 4-wire serial interface. The dimming is proportional to the PWM duty cycle.
CLK tCRF OUT_
CLK tCRR OUT_
LED Current Amplitude Adjustment
Using an analog or digital potentiometer as RSET allows for LED current amplitude adjustment and linear dimming.
Figure 4. LE and CLK to OUT_ Timing
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
Computing Power Dissipation
Use the following equation to estimate the upper limit power dissipation (PD) for the MAX16807:
i=7 PD = DUTY x (V + x I+) + VOUTi x IOUTi + (VCC x ICC) i=0
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching losses and clean, stable operation. Use a multilayer board whenever possible for better noise immunity. Protect sensitive analog grounds by using a star ground configuration. Minimize ground noise by connecting AGND, PGND, the input bypass-capacitor ground lead, and the output-filter ground lead to a single point (star ground configuration). Also, minimize trace lengths to reduce stray capacitance, trace resistance, and radiated noise. The trace between the output voltage-divider and the FB pin must be kept short, as well as the trace between AGND and PGND.
MAX16807
where: V+ = supply voltage I+ = operating supply current DUTY = PWM duty cycle applied to OE VOUTi = MAX16807 port output voltage when driving load LED(s) IOUTi = LED drive current programmed by RSET PD = power dissipation.
Pin Configuration
PROCESS: BiCMOS
TOP VIEW
N.C. 1 AGND 2 OUT 3 VCC 4 REF 5 OUT4 6 OUT5 7 OUT6 8 OUT7 9 OE 10 DOUT 11 SET 12 N.C. 13 V+ 14
Chip Information
+
28 N.C. 27 RTCT 26 CS
MAX16807
25 FB 24 COMP 23 OUT3 22 OUT2 21 OUT1 20 OUT0 19 LE 18 CLK 17 DIN 16 PGND 15 PGND
TSSOP-EP
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller MAX16807
Typical Operating Circuits (continued)
VIN L D VOUT
COUT Q R1 CC2 CC1 LEDs
RCS
RC1 R2
OUT CS AGND VCC CIN
3V TO 5.5V
COMP FB
V+ CBYP PGND OUT0 OUT1 OUT2 OUT3 OUT4 SCLK C MOSI MISO LOAD ENABLE CLK DIN DOUT LE OE SET RSET OUT5 OUT6 OUT7 OPERATION WITH MICROCONTROLLER
MAX16807
REF RT
RTCT
CREF
CT
Package Information
(For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.) PACKAGE TYPE 28 TSSOP PACKAGE CODE U28ME+1 DOCUMENT NO. 21-0108
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Integrated 8-Channel LED Driver with Switch-Mode Boost and SEPIC Controller
Revision History
REVISION NUMBER 0 1 2 REVISION DATE 10/06 4/07 8/09 Initial release Release of the MAX16808 Removal of the MAX16808 from the data sheet. DESCRIPTION PAGES CHANGED -- 1 1-21
MAX16807
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 19
(c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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