MAXIM MAX1985ETP

19-2761; Rev 0; 1/03
KIT
ATION
EVALU
E
L
B
A
AVAIL
Ultra-High-Efficiency White
LED Drivers
Features
♦ Synchronous Step-Up Regulator
Achieves >95% Efficiency
Internal Switch and Synchronous Rectifier
Eliminates External MOSFETs and Diodes
1MHz Fixed Frequency Minimizes Component
Sizes
The brightness can be easily adjusted using a multimode dimming interface, which allows brightness control
through a DPWM signal, a 2- or 3-bit parallel control
interface, or an analog signal. The DPWM signal can be
connected directly to the control pin without the need for
an external RC filter if its frequency is 10kHz or above.
The MAX1984 drives up to eight LEDs, the MAX1985
drives up to six LEDs, and the MAX1986 drives up to
four LEDs. Each device has an LED select pin (SEL)
that allows one subset, the other subset, or all LEDs to
be illuminated. All three devices are available in a
4mm ✕ 4mm thin QFN package.
♦ Open-LED Detection
♦
♦
♦
♦
Up to 90% Total LED Efficiency
Accurate LED Current Matching (8% max)
Adjustable Maximum LED Current
Multimode Dimming Control
Digital Pulse-Width Modulation Control
2-Bit Parallel Control
3-Bit Parallel Control
Analog Control
♦ Selectively Enable LEDs
♦ Unique 0.5mA LED Test Mode
♦ 2.7V to 5.5V Input Supply Range
♦ Small 4mm x 4mm 20-Pin Thin QFN Package
Ordering Information
PART
Applications
PDAs and Hand-Held PCs
TEMP RANGE
PIN-PACKAGE
NO. OF
LEDs
MAX1984ETP
-40°C to +85°C
20 Thin QFN
8
MAX1985ETP
-40°C to +85°C
20 Thin QFN
6
MAX1986ETE
-40°C to +85°C
16 Thin QFN
4
Cellular Phones
Digital Cameras
15 BITB
LX 2
14 REF
LX 2
14 REF
13 SETI
GND 3
12 LD8
N.C. 4
8
9
10
6
LD6
LD2
4mm x 4mm
THIN QFN
BITC
12 BITA
LX 2
11 BITB
MAX1986
GND 3
10 REF
LD1 4
9 SETI
7
8
9
10
5
LD2
7
LD5
11 LD6
LDG
LD3
6
LD1 5
LD4
11 LD7
OUT 1
LD5
LD2 5
12 N.C.
13
LD4
LD1 4
13 SETI
MAX1985
14
LD3
MAX1984
15
LDG
GND 3
16
4mm x 4mm
THIN QFN
6
7
8
LD4
16
IN
17
LD3
18
OUT 1
MODE
19
15 BITB
SEL
20
OUT 1
LDG
16
BITA
17
BITC
BITA
18
IN
BITC
19
MODE
IN
20
SEL
MODE
TOP VIEW
SEL
Pin Configurations
4mm x 4mm
THIN QFN
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX1984/MAX1985/MAX1986
General Description
The MAX1984/MAX1985/MAX1986 are white light-emitting diode (LED) drivers that use individual regulators to
control the current of up to eight LEDs. A high-efficiency
step-up regulator generates just enough voltage to keep
all the current regulators in regulation. A versatile dimming interface accommodates analog, digitally adjusted
pulse-width modulation (DPWM), or parallel control.
The individual current regulators allow good current
matching between LEDs. Open or shorted LEDs cannot
affect the performance of other LEDs.
The step-up regulator achieves high efficiency by using
synchronous rectification. The internal N-channel switch
and P-channel synchronous rectifier eliminate the need
for external MOSFETs and diodes. The 1MHz switching
frequency allows the use of low-profile inductors and
ceramic capacitors.
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
ABSOLUTE MAXIMUM RATINGS
OUT, IN, BITA, BITB, BITC, LD1, LD2, LD3, LD4,
LD5, LD6, LD7, LD8 to GND ................................-0.3V to +6V
LDG to GND........................................................................±0.3V
LX to GND ................................................-0.3V to (VOUT + 0.3V)
SETI, REF, MODE, SEL to GND ...................-0.3V to (VIN + 0.3V)
Continuous Power Dissipation (TA = +70°C)
16-Pin Thin QFN (derate 16.9mW/°C above +70°C) ...1349mW
20-Pin Thin QFN (derate 16.9mW/°C above +70°C) ...1349mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
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
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = 0°C to +85°C,
unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
IN Supply Range
MIN
TYP
2.7
UNITS
5.5
V
IN Undervoltage Lockout Threshold
50mV typical hysteresis
2.4
2.6
V
IN Quiescent Current
BITA = BITB = BITC = IN, LD1 to LD8 = GND
400
600
µA
IN Shutdown Current
BITA = BITB = BITC = GND
0.1
1
µA
1.250
1.270
V
0.2
5
mV
REF Output Voltage
IREF = 0
REF Line Regulation
2.7V < VIN < 5.5V
REF Load Regulation
-1µA < IREF < +50µA
Oscillator Frequency
2.2
MAX
1.230
0.8
Oscillator Maximum Duty Cycle
OUT Overvoltage Protection (OVP)
Threshold
5
15
mV
1
1.2
MHz
85
VLD1 to VLD8 = 50mV, OUT rising, 100mV typical
hysteresis
5.1
%
5.3
5.5
V
INTERNAL MOSFET SWITCHES
N-Channel MOSFET On-Resistance
ILX = 200mA
0.4
0.8
Ω
N-Channel MOSFET Leakage Current
VLX = 5.5V, BITA = BITB = BITC = GND
0.1
1
µA
P-Channel MOSFET On-Resistance
ILX = 200mA
0.5
1
Ω
P-Channel MOSFET Leakage Current
LX = GND, VOUT = 5.5V, BITA = BITB = BITC = GND
0.1
1
µA
0.65
0.81
MAX1984
N-Channel MOSFET Current Limit
0.50
MAX1985
0.40
0.52
0.65
MAX1986
0.30
0.39
0.52
A
CONTROL INPUTS
BITA, BITB, BITC Input Logic Low
Level
2.7V < VIN < 5.5V
BITA, BITB, BITC Input Logic High
Level
2.7V < VIN < 5.5V
MODE Input Logic Low Level
2.7V < VIN < 5.5V
MODE Input Logic High Level
2.7V < VIN < 5.5V
MODE, BITA, BITB, BITC Input Bias
Current
2.7V < VIN < 5.5V
2
0.4
1.6
V
V
0.4
VIN - 0.4
V
V
0.01
_______________________________________________________________________________________
1
µA
Ultra-High-Efficiency White
LED Drivers
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = 0°C to +85°C,
unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
SEL Input Logic Low Level
2.7V < VIN < 5.5V
SEL Input Logic Midlevel
2.7V < VIN < 5.5V
0.50
SEL Input Logic High Level
2.7V < VIN < 5.5V
2.05
SEL Input Bias Current
TYP
MAX
UNITS
0.4
V
1.85
V
V
SEL = GND, current out of the pin
5
SEL = IN, current into the pin
10
µA
FULL-SCALE LED CURRENT ADJUSTMENT
LD1 to LD8 Output Current
VLD_ = 80mV, SETI = BITA = BITB = BITC = IN
16.5
18
19.5
VLD_ = 80mV, RSETI = 278kΩ ±0.1%, BITA = BITB =
BITC = IN
22.5
25
27.5
VLD_ = 80mV, RSETI = 1.8MΩ ±0.1%, BITA = BITB =
BITC = IN
12.5
14
15.5
VLD_ = 80mV, RSETI = 597kΩ ±0.1%, BITA = BITB =
BITC = IN
16.5
18
19.5
0.42
0.50
0.60
80
100
120
VLD1 = 1V, RSETI = 10kΩ, BITA = BITB = BITC = IN
SETI = GND
mA
26
LD1 to LD8 Regulation Voltage
SETI = IN, ILX = 120mA (MAX1984),
110mA (MAX1985), 98mA (MAX1986)
SETI High-Level Threshold
(18mA LED Default Current)
2.7V < VIN < 5.5V
VIN - 0.4
SETI Low-Level Threshold
(0.5mA LED Default Current)
2.7V < VIN < 5.5V
50
SETI Output Current
SETI = GND
40
mV
V
125
mV
70
100
µA
3
4
Ω
OUTPUT CURRENT SOURCE
LD1 to LD8 On-Resistance
VLD_ = 50mV, VOUT = 3.5V
LD1 to LD8 Current-Source
Compliance
BITA = BITB = BITC = IN, 80mV < VLD_ < 1V
(Note 1)
0.3
5
%
LD1 to LD8 Leakage Current
BITA = BITB = BITC = GND
0.01
1
µA
DIGITAL BRIGHTNESS CONTROL
2-Bit Control DAC LSB
MODE = SETI = BITB = IN, BITA = BITC = GND
(Note 2)
26
33
39
%
3-Bit Control DAC LSB
SETI = BITC = IN, MODE = BITA = BITB = GND
(Note 2)
7
14
21
%
5.5
V
7
%
DPWM BRIGHTNESS CONTROL
DPWM Input Supply Range
MODE = BITC = IN
DPWM Shutdown Duty Cycle
BITC = GND
2.3
3
5
_______________________________________________________________________________________
3
MAX1984/MAX1985/MAX1986
ELECTRICAL CHARACTERISTICS (continued)
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = -40°C to
+85°C, unless otherwise noted.) (Note 3)
PARAMETER
CONDITIONS
IN Supply Range
IN Undervoltage Lockout Threshold
50mV typical hysteresis
IN Quiescent Current
BITA = BITB = BITC = IN, LD1 to LD8 = GND
REF Output Voltage
IREF = 0
REF Line Regulation
2.7V < VIN < 5.5V
REF Load Regulation
-1µA < IREF < +50µA
Oscillator Frequency
MIN
MAX
UNITS
2.7
TYP
5.5
V
2.2
2.6
V
600
µA
1.230
1.270
V
5
mV
15
mV
0.8
1.2
MHz
5.1
5.5
V
OUT Overvoltage Protection
Threshold
VLD1 to VLD8 = 50mV, OUT rising, 100mV typical
hysteresis
INTERNAL MOSFET SWITCHES
N-Channel MOSFET On-Resistance
ILX = 200mA
0.8
Ω
P-Channel MOSFET On-Resistance
ILX = 200mA
1.0
Ω
N-Channel MOSFET Current Limit
MAX1984
0.50
MAX1985
0.40
0.81
0.65
MAX1986
0.30
0.52
A
CONTROL INPUTS
BITA, BITB, BITC Input Logic Low
Level
2.7V < VIN < 5.5V
BITA, BITB, BITC Input Logic High
Level
2.7V < VIN < 5.5V
MODE Input Logic Low Level
2.7V < VIN < 5.5V
MODE Input Logic High Level
2.7V < VIN < 5.5V
SEL Input Logic Low Level
2.7V < VIN < 5.5V
SEL Input Logic Midlevel
2.7V < VIN < 5.5V
SEL Input Logic High Level
2.7V < VIN < 5.5V
FULL-SCALE LED CURRENT ADJUSTMENT
VLD_ = 80mV, SETI = BITA = BITB = BITC = IN
LD1 to LD8 Output Current
4
0.4
1.6
V
0.4
VIN - 0.4
0.50
V
V
0.4
V
1.85
V
2.05
V
16
20
VLD_ = 80mV, RSETI = 278kΩ ±1%, BITA = BITB =
BITC = IN
22
28
VLD_ = 80mV, RSETI = 1.8MΩ ±1%, BITA = BITB =
BITC = IN
11.5
16.0
VLD_ = 80mV, RSETI = 697kΩ ±1%, BITA = BITB =
BITC = IN
15.5
20.0
SETI = GND
0.42
0.60
_______________________________________________________________________________________
V
mA
Ultra-High-Efficiency White
LED Drivers
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = -40°C to
+85°C, unless otherwise noted.) (Note 3)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
120
mV
LD1 to LD8 Regulation Voltage
SETI = IN, ILX = 120mA (MAX1984),
110mA (MAX1985), 98mA (MAX1986)
SETI High-Level Threshold
(18mA LED Default Current)
2.7V < VIN < 5.5V
VIN - 0.4
SETI Low-Level Threshold
(0.5mA LED Default Current)
2.7V < VIN < 5.5V
50
125
mV
SETI Output Current
SETI = GND
40
100
µA
80
V
OUTPUT CURRENT SOURCE
LD1 to LD8 On-Resistance
LD1 to LD8 Current-Source
Compliance
DIGITAL BRIGHTNESS CONTROL
ILD_ = 25mA, VOUT = 3.5V
4
Ω
BITA = BITB = BITC = IN, 80mV < VLD_ < 1V (Note 1)
8
%
2-Bit Control DAC LSB
MODE = SETI = BITB = IN, BITA = BITC = GND
26
39
%
3-Bit Control DAC LSB
SETI = BITC = IN, MODE = BITA = BITB = GND
(Note 2)
7
21
%
2.3
5.5
V
3
7
%
DPWM BRIGHTNESS CONTROL
DPWM Input Supply Range
MODE = BITC = IN
DPWM Shutdown Duty Cycle
BITC = GND
Note 1: Current variation is caused by the current source voltage changes.
Note 2: Measurement is with respect to 100% of the programmed LED output current.
Note 3: Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
5
MAX1984/MAX1985/MAX1986
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(Circuit of Figure 1; VIN = 3.3V, SETI = IN, MODE = IN, TA = +25°C, unless otherwise noted.)
VIN = 4.2V
VIN = 3.0V
70
60
VIN = 4.2V
VIN = 3.0V
80
90
VIN = 3.6V
70
5
10
15
20
25
VIN = 4.2V
VIN = 3.0V
70
50
50
0
80
60
60
50
0
5
10
15
20
0
25
5
10
20
LED CURRENT (mA)
LED CURRENT (mA)
STEP-UP REGULATOR EFFICIENCY
vs. INPUT VOLTAGE (25mA LED CURRENT)
STEP-UP REGULATOR EFFICIENCY
vs. INPUT VOLTAGE (4mA LED CURRENT)
TOTAL EFFICIENCY
vs. LED CURRENT (8 LEDs)
90
8 LEDs
8 LEDs
80
6 LEDs
70
MAX1984/85/86 toc06
90
EFFICIENCY (%)
EFFICIENCY (%)
90
80
70
6 LEDs
85
4 LEDs
VIN = 3.0V
4 LEDs
60
60
η
Σ VLEDi x ILEDi
VIN = 3.6V
ηTOTAL =
VIN = 4.2V
80
3.0
3.5
4.0
4.5
5.0
2.5
3.0
3.5
4.0
4.5
5.0
5
10
15
20
25
INPUT VOLTAGE (V)
LED CURRENT (mA)
TOTAL EFFICIENCY
vs. LED CURRENT (6 LEDs)
TOTAL EFFICIENCY
vs. LED CURRENT (4 LEDs)
TOTAL EFFICIENCY vs. INPUT VOLTAGE
(25mA LED CURRENT)
70
VIN = 4.2V
60
Σ VLEDi x ILEDi
VIN = 4.2V
80
70
i =1
ηTOTAL =
INPUT_POWER
15
LED CURRENT (mA)
20
8 LEDs
70
6 LEDs
60
i =1
INPUT_POWER
50
50
10
80
4 LEDs
Σ VLEDi x ILEDi
60
50
5
90
η
η
ηTOTAL =
MAX1984/85/86 toc09
VIN = 3.6V
EFFICIENCY (%)
80
VIN = 3.0V
90
EFFICIENCY (%)
VIN = 3.0V
100
MAX1984/85/86 toc08
100
MAX1984/85/86 toc07
VIN = 3.6V
0
0
5.5
INPUT VOLTAGE (V)
100
90
5.5
i =1
INPUT_POWER
50
50
2.5
25
100
MAX1984/85/86 toc05
100
MAX1984/85/86 toc04
95
6
15
LED CURRENT (mA)
100
EFFICIENCY (%)
VIN = 3.6V
EFFICIENCY (%)
80
90
100
MAX1984/85/86 toc02
VIN = 3.6V
EFFICIENCY (%)
EFFICIENCY (%)
90
100
MAX1984/85/86 toc01
100
STEP-UP REGULATOR EFFICIENCY
vs. LED CURRENT (4 LEDs)
STEP-UP REGULATOR EFFICIENCY
vs. LED CURRENT (6 LEDs)
MAX1984/85/86 toc03
STEP-UP REGULATOR EFFICIENCY
vs. LED CURRENT (8 LEDs)
EFFICIENCY (%)
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
25
0
5
10
15
LED CURRENT (mA)
20
25
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5.0
5.5
Ultra-High-Efficiency White
LED Drivers
TOTAL EFFICIENCY vs. INPUT VOLTAGE
(4mA LED CURRENT )
60
8 LEDs
MAX9184/85/86 toc12
MAX9184/85/86 toc11
25.0
26
25
LED CURRENT (mA)
70
25.5
LED CURRENT (mA)
80
26.0
24
LD1 TO LD8
23
24.5
6 LEDs
50
4 LEDs
RSETI = 278kΩ
RSETI = 278kΩ
22
24.0
40
3.0
3.5
4.0
4.5
5.0
2.5
5.5
3.0
3.5
4.0
4.5
5.0
0
5.5
50
100
150
200
INPUT VOLTAGE (V)
LD_VOLTAGE (mV)
STARTUP WAVEFORMS
LED CURRENT vs. DPWM DUTY
MAXIMUM LED CURRENT
vs. SETI RESISTANCE
0
20
4V
B
2V
0
100mA
0
C
THEORETICAL
15
ACTUAL
10
50kHz DPWM FREQUENCY
5
30
MAX9184/85/86 toc15
25
5V
MAXIMUM LED CURRENT (mA)
MAX1984/85/86 toc13
A
300
250
INPUT VOLTAGE (V)
MAX9184/85/86 toc14
2.5
LED CURRENT (mA)
EFFICIENCY (%)
90
LED CURRENT MATCHING
LED CURRENT vs. INPUT VOLTAGE
MAX1984/85/86 toc10
100
THEORETICAL
25
20
ACTUAL
15
20mA
D
0
100µs/div
A: BITA VOLTAGE, 5V/div
B: OUT VOLTAGE, 2V/div
C: INDUCTOR CURRENT, 100mA/div
D: LD_ CURRENT, 20mA/div
RSETI = 278kΩ
0
10
0
20
40
60
DPWM DUTY (%)
80
100
0
500
1000
1500
2000
SETI RESISTANCE (kΩ)
_______________________________________________________________________________________
7
MAX1984/MAX1985/MAX1986
Typical Operating Characteristics (continued)
(Circuit of Figure 1; VIN = 3.3V, SETI = IN, MODE = IN, TA = +25°C, unless otherwise noted.)
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
Pin Description
PIN
NAME
MAX1984
MAX1985
MAX1986
1
1
1
OUT
2
2
2
LX
Step-Up Regulator Output. Bypass OUT to GND with a 4.7µF capacitor.
Inductor Connection. LX is connected to the drains of the internal N-channel and
P-channel MOSFETs.
3
3
3
GND
Ground
—
4, 12
—
N.C.
No Connection. Not internally connected.
4
5
4
LD1
LED1 Cathode Connection. LD1 is the open-drain output of an internal current
regulator for controlling the current through LED1. It is able to sink up to 25mA.
If not used, connect LD1 to GND.
5
6
5
LD2
LED2 Cathode Connection. LD2 is the open-drain output of an internal current
regulator for controlling the current through LED2. It is able to sink up to 25mA.
If not used, connect LD2 to GND.
6
7
7
LD3
LED3 Cathode Connection. LD3 is the open-drain output of an internal current
regulator for controlling the current through LED3. It is able to sink up to 25mA.
If not used, connect LD5 to GND.
7
9
8
LD4
LED4 Cathode Connection. LD4 is the open-drain output of an internal current
regulator for controlling the current through LED4. It is able to sink up to 25mA.
If not used, connect LD4 to GND.
8
8
6
LDG
Common Ground Connection for Internal Current Regulators. Connect LDG to
GND.
9
10
—
LD5
LED5 Cathode Connection. LD5 is the open-drain output of an internal current
regulator for controlling the current through LED5. It is able to sink up to 25mA.
If not used, connect LD5 to GND.
10
11
—
LD6
LED6 Cathode Connection. LD6 is the open-drain output of an internal current
regulator for controlling the current through LED6. It is able to sink up to 25mA.
If not used, connect LD6 to GND.
11
—
—
LD7
LED7 Cathode Connection. LD7 is the open-drain output of an internal current
regulator for controlling the current through LED7. It is able to sink up to 25mA.
If not used, connect LD7 to GND.
12
—
—
LD8
LED8 Cathode Connection. LD8 is the open-drain output of an internal current
regulator for controlling the current through LED8. It is able to sink up to 25mA.
If not used, connect LD8 to GND.
13
13
9
SETI
Maximum LED Current Set Input. SETI sets the maximum current through each
LED. Connect SETI to IN for a default maximum current of 18mA; connect SETI to
GND for the 0.5mA LED test mode. Connect a resistor from SETI to GND to adjust
the maximum current between 12mA to 25mA (see the Setting the Maximum LED
Current section).
14
14
10
REF
1.25V Reference Output. Bypass REF to GND with a minimum 0.22µF ceramic
capacitor.
BITB
Brightness Control Input (Multimode):
DPWM Mode: Leave unconnected for greater than 50kHz operation. Add a
capacitor from BITB to ground for lower frequency operation.
Analog Mode: Analog control signal input.
2- or 3-Bit Parallel Mode: Digital input. Least significant bit (LSB) for 2-bit mode.
15
8
FUNCTION
15
11
_______________________________________________________________________________________
Ultra-High-Efficiency White
LED Drivers
PIN
MAX1984
MAX1985
16
NAME
MAX1986
16
12
BITA
Brightness Control Input (Multimode):
DPWM Mode: DPWM control signal input.
Analog Mode: Connect to IN.
2- or 3-Bit Parallel Mode: Digital input. Most significant bit (MSB).
Brightness Control Input:
DPWM Mode: Connect to IN.
Analog Mode: Connect to IN.
2-Bit Parallel Mode: Connect to GND.
3-Bit Parallel Mode: Digital input (LSB).
17
17
13
BITC
18
18
14
IN
19
19
20
15
20
16
FUNCTION
Input Supply. IN provides power to the internal control circuitry and MOSFET
drivers. Bypass IN to GND with a minimum 0.1µF ceramic capacitor.
MODE
Brightness Control Mode Selection Input. Connect MODE and BITC to IN for
DPWM control. Connect MODE, BITA, and BITC to IN for analog control. For 2-bit
parallel control, connect MODE to IN and BITC to ground. For 3-bit parallel control,
connect MODE to GND.
SEL
LED Selection Input. Connect SEL to IN to turn on all LEDs. Connect SEL to ground
to turn on only LED1–LED5 (MAX1984), LED1–LED4 (MAX1985), or LED1 to LED3
(MAX1986). Leave SEL unconnected or force to VIN/2 to turn on only LED6 to LED8
(MAX1984), LED3–LED6 (MAX1985), or LED4 (MAX1986).
VIN
2.7V TO 5.5V
C2
0.1µF
C1
2 x 2.2µF
14
C3
0.22µF
VIN
13
L1
10µH
3
GND
2
LX
REF
SETI
18
IN
OUT
MAX1984
LD1
LD2
16
15
BRIGHTNESS
CONTROL
17
19
LED SELECT
20
8
BITA
LD3
BITB
LD4
BITC
LD5
MODE
LD6
SEL
LD7
LDG
LD8
1
4
D1
5
D2
6
D3
7
D4
9
D5
10
D6
11
D7
12
D8
C4
2 x 2.2µF
Figure 1. Standard Application Circuit of the MAX1984
_______________________________________________________________________________________
9
MAX1984/MAX1985/MAX1986
Pin Description (continued)
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
L
VIN
CIN
IN
LX
OUT
FB
STEP-UP
CONTROLLER
MAX1984
MAX1985
MAX1986
GND
CURRENT
SENSE
MIN
UVLO
COMP
2.4V
CREF
COUT
REF AND
BIAS
BLOCK
REF
EN1
IREF
LD1
LDG
EN2
IREF
LD2
LDG
EN3
IREF
LD3
LDG
EN4
IREF
LD4
LDG
EN5
IREF
LD5
LDG
EN6
IREF
LD6
LDG
EN7
IREF
LD7
LDG
EN8
IREF
LD8
LDG
LD1
LD2
LD3
LD4
SHUTDOWN
MODE
DIMMING
CONTROL
BITA
BITB
DIMMING
CONTROL
BLOCK
IREF
BITC
LD5*
LD6*
SETI
RSETI
LED SELECT
SEL
LOGIC
EN [8:1]
LD7**
LD8**
LDG
*MAX1984 AND MAX1985 ONLY.
**MAX1984 ONLY.
Figure 2. System Functional Diagram
10
______________________________________________________________________________________
Ultra-High-Efficiency White
LED Drivers
The standard application circuit of the MAX1984 drives
eight white LEDs (Figure 1). The standard application circuit of the MAX1985 drives six white LEDs (Figure 6). The
standard application circuit of the MAX1986 drives four
white LEDs (Figure 7). The input voltage range is from
2.7V to 5.5V. Table 1 lists the recommended component
options and Table 2 lists the component suppliers.
Detailed Description
The MAX1984/MAX1985/MAX1986 are white LED drivers that use individual regulators to control the current
of up to eight LEDs. A high-efficiency step-up regulator
generates just enough voltage to keep all the current
regulators in regulation. A versatile dimming interface
accommodates analog, DPWM, or parallel control.
LED Current Regulators
Good LED current matching is achieved using individual current regulators for each LED (Figure 3). The regulator is an analog gain block with an open-drain
N-channel MOSFET output stage and can sink up to
25mA LED current. The LED current is sensed using an
internal 1Ω resistor connected between the source of
the MOSFET and ground. The regulator controls the
output current by comparing the voltage across the
current-sense resistor with a reference voltage (IREF)
set by the dimming control circuitry.
Startup and Feedback
The step-up converter is regulated at a voltage just
high enough to power the LEDs. Since the forward voltage is different for each LED, the LED with the largest
forward voltage sets the regulation voltage. Each current regulator’s voltage drop (from LD_ to LDG) is monitored and the lowest voltage drop is used as the
step-up regulator’s feedback.
At startup, it is important to ensure the output voltage
rises high enough to forward bias all LEDs and allow their
current regulators to detect their presence. Therefore,
before the current regulators are enabled the step-up
regulator output is made to rise up to the OUT OVP
threshold (5.3V, typ). Then, the step-up regulator stops
switching and each current regulator output is tested
Table 1. Component List
DESCRIPTION
DESIGNATION
MAX1984
2 x 2.2µF, 6.3V X5R ceramic
capacitors (0603)
Taiyo Yuden JMK107BJ225MA
TDK C1608X5ROJ225K
C1, C4
D1–D4, D5*, D6*,
D7**, D8**
MAX1985
MAX1986
2 x 2.2µF, 6.3V X5R ceramic
capacitors (0603)
Taiyo Yuden JMK107BJ225MA
TDK C1608X5ROJ225K
2.2µF, 6.3V X5R ceramic
capacitors (0603)
Taiyo Yuden JMK107BJ225MA
TDK C1608X5ROJ225K
15µH, 0.85A inductor
Sumida CLS5D11HP-150NC
22µH, 0.65A inductor
Sumida CLS5D11HP-220NC
Surface-mount white LEDs
Nichia NSCW215T
10µH, 1A inductor
Sumida CLS5D11HP-100NC
L1
*MAX1984 and MAX1985 only.
**MAX1984 only.
Table 2. Component Suppliers
PHONE
FAX
Nichia
SUPPLIER
717-285-2323
717-285-9378
www.nichia.com
WEBSITE
Sumida
847-545-6700
847-545-6720
www.sumida.com
Taiyo Yuden
800-348-2496
847-925-0899
www.t-yuden.com
TDK
847-803-6100
847-390-4405
www.component.tdk.com
______________________________________________________________________________________
11
MAX1984/MAX1985/MAX1986
Standard Application Circuits
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
THRESHOLD
EN_
LD_
CURRENT
SENSE
IREF
SLOPE
COMP
OC COMP
OSCILLATOR
OSC
SUMMING
COMPARATOR
LOGIC
GATE
DRIVERS
FB
1Ω
100mV
LDG
OV COMP
5.3V
OUT
Figure 3. Current Regulator Functional Diagram
Figure 4. Step-Up Regulator Functional Diagram
for an LED’s presence. The current regulators are
enabled and any regulator with an output voltage less
than 45mV is detected and is ignored, preventing outputs left open or shorted to ground from dominating the
step-up regulation loop. Outputs shorted to IN, OUT, or
any voltage above 45mV resemble valid LEDs and are
regulated at the current set point.
MOSFET and turns on the P-channel MOSFET when
one of the following three conditions occurs: the summing comparator output becomes high, the switch current exceeds the overcurrent threshold, or the falling
edge of the oscillator occurs.
As the LEDs draw current, the step-up regulator’s output voltage gradually falls and the voltage drop across
each of the current regulators reduces. Eventually, the
voltage drop across whichever current regulator drives
the LED with the highest forward voltage reaches the
step-up regulator’s threshold (100mV, typ) and step-up
switching starts again (see the Startup Waveform in the
Typical Operating Characteristics).
Step-Up Regulator
The step-up regulator employs a fixed-frequency current-mode control method to generate the bias voltage
for the white LEDs. The regulator takes the minimum
value of all the LD_ pin voltages as the feedback signal
to ensure that the output voltage is high enough to
drive all the LEDs. The heart of the controller is a multiinput, open-loop comparator that sums three signals:
the feedback error signal with respect to the 100mV reference, the current-sense signal, and the slope compensation ramp (Figure 4).
In normal operation, the controller starts a new cycle by
turning on the N-channel MOSFET and turning off the
P-channel MOSFET on the rising edge of the internal
oscillator if all of the following three conditions are satisfied: the summing comparator output is low, the switch
current does not exceed the overcurrent threshold, and
the output voltage does not exceed the overvoltage
threshold. The controller turns off the N-channel
12
Both the N-channel MOSFET and the P-channel
MOSFET turn off if the output voltage exceeds the overvoltage rising threshold. Both switches stay off until all
of the following three conditions are satisfied: the output voltage is below the overvoltage falling threshold,
the summing comparator output is low, and the next rising edge of the oscillator occurs.
Brightness Control Interface
The light intensity of the white LEDs can be easily
adjusted from 15% to 100% of the full-scale LED current
chosen by SETI. The MAX1984/MAX1985/MAX1986
support DPWM control, analog control, and 2-bit or 3-bit
parallel control.
DPWM Control
To use the DPWM control mode, connect MODE and
BITC to IN, leave BITB unconnected, and connect the
DPWM signal to BITA. The LED current is given by the
following equation:
ILED = D ✕ ILED(FS)
where ILED(FS) is the full-scale LED current set by SETI,
and D is the duty cycle of the DPWM signal. The average voltage of the DPWM signal is obtained through an
internal RC filter (Figure 5). The 0.1ms filter time constant allows the use of DPWM frequencies from 10kHz
to 2MHz. If lower frequencies are preferred, an external
______________________________________________________________________________________
Ultra-High-Efficiency White
LED Drivers


VBITB
× ILED(FS)
ILED =  K1 + K2 ×
0.75 × VREF 

τ = 0.2MΩ ✕ CEXT + 0.098ms
where K1 = 0.0465, K2 = 0.953, VBITB is the voltage at
the BITB pin, VREF is the 1.25V internal reference voltage,
and ILED(FS) is the full-scale LED current set by SETI.
In analog mode, the MAX1984/MAX1985/MAX1986
enter shutdown mode when both VBITA and VBITB are
logic low.
where CEXT is the external capacitance.
The recommended DPWM duty-factor range is from
20% to 100% for DPWM frequencies between 20kHz
and 2MHz, using the internal 0.1ms filter. For lower
DPWM operating frequencies, use CEXT and ensure the
voltage on C EXT (BITB), including ripple, remains
above DFMIN ✕ 0.75 ✕ VREF, where DFMIN is the minimum reliable DPWM duty factor of 15%.
Parallel Control
The MAX1984/MAX1985/MAX1986 also support 2-bit or
3-bit parallel control. To use the 3-bit parallel control
mode, connect MODE to ground. BITA is the most significant bit and BITC is the least significant bit. To use
the 2-bit parallel control, connect MODE to IN and BITC
to ground. BITA is the most significant bit and BITB is
the least significant bit. In parallel mode, the
MAX1984/MAX1985/MAX1986 enter shutdown mode
when BITA, BITB, and BITC are logic low. Tables 3 and
4 are the truth tables.
In DPWM mode, the MAX1984/MAX1985/MAX1986
enter shutdown mode when the DPWM duty cycle is
below 5% (typ) and BITC is a logical low level.
Analog Control
To use the analog control mode, connect MODE, BITA,
and BITC to IN. Connect BITB to a DC voltage that sets
the LED current. The operational range for the analog
SHUTDOWN
THRESHOLD
SHUTDOWN
VIN
MODE
0.75 x VREF
BITA
1
DECODER
BITB
100
DAC
3-BIT
BITC
IREF
0.75 x VREF
LEVEL
SHIFT
200kΩ
9.8MΩ
TO CURRENT
REGULATORS
38Ω
10pF
SETI
18mA DEFAULT
RSETI
0.5mA TEST
SETI
SETI
VIN - 0.7V
0.045V
300kΩ
200kΩ
7.2MΩ
Figure 5. Brightness Control Equivalent Functional Diagram
______________________________________________________________________________________
13
MAX1984/MAX1985/MAX1986
control is from 140mV (15%) to 0.75 ✕ VREF (100%).
The LED current is given by the following equation:
capacitor can be connected from BITB to ground to
increase the total time constant. Use the following
equation to calculate the total time constant:
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
LED Selection
Shutdown
The MAX1984/MAX1985/MAX1986 provide a control
input (SEL) to selectively turn on one subset, the other
subset, or all of the LEDs. SEL is a three-level logic
input that can be connected to logic low, logic high, or
left unconnected. Table 5 is the truth table.
As soon as the input voltage rises above the UVLO
threshold and the internal reference is ready, the stepup regulator starts unless the device is in shutdown. If a
2-bit or 3-bit parallel control is used, the MAX1984/
MAX1985/MAX1986 enter shutdown mode when BITA,
BITB, and BITC are logic low. The parts come out of
shutdown if at least 1 bit is logic high. If DPWM control
is used, the parts enter shutdown mode when the duty
cycle of BITA is less than 5% (typ) and BITC is logic
low. If analog control is used, the parts enter shutdown
when the voltages on both BITA and BITB are logic low.
LED Test Mode
Connecting SETI to ground enables the LED test mode.
In this mode, the LED current is set to 0.5mA and
DC-to-DC switching is inhibited. OUT is powered from
IN through an internal silicon diode.
Forcing 0.5mA through the LED is a simple way to
determine whether the diode has suffered any ESD
damage. LEDs that do not light in this mode usually
have suffered ESD or other damage. The dimming control inputs are ignored in the test mode.
Table 3. 3-Bit Parallel Control Truth Table
BITA
BITB
BITC
BRIGHTNESS (%)
COMMENTS
0
0
0
0
Shutdown
0
0
1
14.3
Minimum current
0
1
0
26.6
—
0
1
1
42.9
—
1
0
0
57.1
—
1
0
1
71.4
—
1
1
0
85.7
—
1
1
1
100
Full-scale current
set by SETI
Table 4. 2-Bit Parallel Control Truth Table
BITA
BITB BITC
BRIGHTNESS (%)
COMMENTS
0
0
0
0
Shutdown
0
1
0
33.3
Minimum current
1
0
0
66.7
—
1
1
0
100
Full-scale current
set by SETI
Overvoltage Protection
Output OVP prevents the internal switches from being
damaged if all LEDs are open. If the output voltage
rises above OUT OVP rising threshold, the
MAX1984/MAX1985/MAX1986 turn off the step-up regulator. Once the output voltage falls below OVP falling
threshold, the step-up regulator turns on again.
Applications Information
Inductor Selection
The MAX1984/MAX1985/MAX1986’s 1MHz switching
frequency allows the use of low-profile surface-mount
inductors. The MAX1984 works well with a 10µH inductor, the MAX1985 works well with a 15µH inductor, and
the MAX1986 works well with a 22µH inductor. The
inductor saturation current rating should be higher than
the N-channel switch current limit. For high efficiency,
choose an inductor made of high-frequency core material to reduce core losses. Using a shielded inductor
reduces radiated EMI.
Output Capacitor Selection
The output capacitor affects the circuit’s stability and
output-voltage ripple. The MAX1984 works well with a
4.7µF ceramic output capacitor, the MAX1985 works
well with a 3.3µF ceramic output capacitor, and the
MAX1986 works well with a 2.2µF ceramic output
capacitor. Always use capacitors with working voltage
ratings higher than the output OVP rising threshold
(5.5V max).
Table 5. SEL Control Truth Table
SEL
MAX1984
MAX1985
MAX1986
Low (VSEL < 0.4V)
LED1 to
LED5 ON
LED1 to
LED4 ON
LED1 to
LED3 ON
Mid (SEL unconnected
or 0.5V < VSEL < 1.8V)
LED6 to
LED8 ON
LED5 to
LED6 ON
LED4 ON
High (VSEL > 2.05V)
14
All LEDs ON
______________________________________________________________________________________
Ultra-High-Efficiency White
LED Drivers
PC Board Layout and Grounding
Careful PC board layout is very important for proper
operation. Use the following guidelines for good PC
board layout:
To prevent noise from coupling into the device, connect
an additional 0.1µF ceramic capacitor from the IN pin to
the GND pin. Place that capacitor within 5mm of the pins.
Setting the Maximum LED Current
The full-scale current through each LED can be set
using SETI. When SETI is connected to IN, the full-scale
LED current is set to the default value of 18mA. When
SETI is connected to GND, the LED current is set to
0.5mA LED test mode. If SETI is connected with a resistor to GND, the full-scale LED current can be adjusted
from 14mA to 25mA:
ILED(FS) = 12mA + K ×
0.75 × VREF
RSETI
where K = 3851, and VREF is the internal reference
voltage.
1) Minimize the area of high-current loops by placing
the input capacitors, inductor, and output capacitors less than 0.2in (5mm) from the LX and GND
pins. Connect these components with wide traces.
Avoid using vias in the high-current paths. If vias
are unavoidable, use many vias in parallel to
reduce resistance and inductance.
2) Create islands for the analog ground and power
ground. The analog ground island includes the
exposed backside pad of the device, the REF
bypass capacitor ground, and the SETI resistor
ground. The power ground island includes the GND
pin, the common ground for the current regulators
(LDG), and the step-up regulator’s input/output
capacitor grounds. The analog ground and power
ground islands are connected together at only one
location using a short trace between the GND pin
and the exposed backside pad underneath the
device.
3) Maximize the width of the power ground traces to
improve efficiency, and reduce output-voltage ripple and noise spikes.
4) Place the IN pin and REF pin bypass capacitors
within 5mm to the device.
5) Minimize the size of LX node while keeping it wide
and short to reduce radiated EMI.
Refer to the MAX1985 evaluation kit for an example of
proper board layout.
Chip Information
TRANSISTOR COUNT: 3016
______________________________________________________________________________________
15
MAX1984/MAX1985/MAX1986
Input Capacitor Selection
The input capacitor reduces the current peaks drawn
from the input supply and reduces noise injection into
all devices running from that supply. The input voltage
source impedance determines the required size of the
input capacitor. The standard application circuits
(Figures 1, 6, and 7) use an input capacitor equal to the
output capacitor to accommodate the high impedance
seen in a typical lab environment. Actual applications
usually have much lower source impedance since the
step-up regulator typically runs directly from a lowimpedance battery. Often, the input capacitor can be
reduced by 50% or more of the output capacitor value.
MAX1984/MAX1985/MAX1986
Ultra-High-Efficiency White
LED Drivers
VIN
2.7V TO 5.5V
L1
15µH
3
GND
14
C3
0.22µF
VIN
13
2
LX
SETI
MAX1985
BITA
LD1
1
3
GND
5
D1
6
D2
10
LD3
7
C3
0.22µF
BRIGHTNESS
CONTROL
BITB
LD4
D4
10
D5
9
12
17
BITC
LD5
11
19
LED SELECT
20
MODE
SEL
LD6
N.C.
11
4
D6
C4
2 x 2.2µF
BRIGHTNESS
CONTROL
13
15
8
LDG
N.C.
14
IN
OUT
LD1
SETI
LD2
BITA
LD3
BITB
LD4
BITC
LDG
MODE
SEL
1
4
D1
5
D2
7
D3
8
D4
C4
2 x 2.2µF
6
16
LED SELECT
12
Figure 6. Standard Application Circuit of the MAX1985
16
REF
D3
9
2
LX
MAX1986
VIN
15
L1
22µH
18
IN
OUT
REF
C2
0.1µF
C1
2 x 2.2µF
LD2
16
VIN
2.7V TO 5.5V
C2
0.1µF
C1
2 x 2.2µF
Figure 7. Standard Application Circuit of the MAX1986
______________________________________________________________________________________
Ultra-High-Efficiency White
LED Drivers
24L QFN THIN.EPS
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
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 ____________________ 17
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX1984/MAX1985/MAX1986
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)