MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
________________________________________________________________ Maxim Integrated Products 1
19-2067; Rev 0; 7/01
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.
General Description
The MAX1916 low-dropout bias supply for white LEDs
is a high-performance alternative to the simple ballast
resistors used in conventional white LED designs. The
MAX1916 uses a single resistor to set the bias current
for three LEDs, which are matched to 0.3%. The
MAX1916 consumes only 40µA of supply current when
enabled and 0.05µA when disabled.
The MAX1916’s advantages over ballast resistors
include significantly better LED-to-LED bias matching,
much lower bias variation with supply voltage variation,
significantly lower dropout voltage, and in some appli-
cations, significantly improved efficiency. The MAX1916
requires a 200mV dropout at a 9mA load on each out-
put to match the LED brightness.
The MAX1916 is available in a space-saving 6-pin Thin
SOT23 package.
Applications
Next-Generation Wireless Handsets
PDAs, Palmtops, and Handy Terminals
Digital Cameras, Camcorders
Battery-Powered Equipment
Features
♦Low 200mV Dropout at 9mA
♦Up to 60mA/LED Bias Current
♦0.3% LED Current Matching
♦Simple LED Brightness Control
♦Low 40µA Supply Current
♦Low 0.05µA Shutdown Current
♦2.5V to 5.5V Supply Voltage Range
♦Thermal Shutdown Protection
♦Tiny 6-Pin Thin SOT23 Package (1mm High)
GND
LED3SET
16LED1
5LED2
EN
MAX1916
THIN SOT23-6
TOP VIEW
2
34
Pin Configuration
MAX1916
ON
EN
OFF
GND
SET LED1 LED2 LED3
VCTRL
V+
Typical Operating Circuit
Ordering Information
PART TEMP. RANGE PIN-
PACKAGE
TOP
MARK
MAX1916EZT -40°C to +85°C 6 Thin SOT23 AAAG
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
Note 1: Limits are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed through
correlation using statistical quality control (SQC) methods.
Note 2: Dropout Voltage is defined as the LED_ to GND voltage at which current sink into LED_ drops 20% from the value at
VLED = 1V.
Note 3: Dropout Voltage is defined as the LED_ to GND voltage at which current sink into LED_ drops 10% from the value at
VLED = 1V.
EN, SET, LED1, LED2, LED3 to GND ..................... -0.3V to +6V
Continuous Power Dissipation (TA= +70°C)
6-Pin Thin SOT23 (derate 9.1mW/°C above +70°C) ... 727mW
Operating Temperature Range ......................... -40°C to +85°C
Storage Temperature Range ........................... -65°C to +150°C
Lead Temperature (soldering, 10s)................................... 300°C
ELECTRICAL CHARACTERISTICS
(VEN = 3.3V, VLED1 = VLED2 = VLED3 = 1V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Voltage Range VEN EN is the power-supply input 2.5 5.5 V
VEN rising 2.2 2.47 V
Undervoltage Lockout
Threshold VUVLO Hysteresis 85 mV
SET Input Current Range ISET 5 260 µA
SET to LED_ Current Ratio ILED/ISET, ISET = 42µA 207 230 253 A/A
SET Bias Voltage VSET ISET = 42µA 1.154 1.215 1.276 V
TA = -40°C to +25°C 0.01 1
SET Leakage Current
in Shutdown
EN = GND,
VSET = 3.3V TA = -40°C to +85°C5
µA
LED_-to-LED_ Current Matching ISET = 42µA0.35%
Maximum LED_ Sink Current ILED_Each LED_ 60 mA
ISET = 22µA (Note 2) 100 180
ISET = 42µA (Note 3) 200 360
LED_ Dropout Voltage
ISET = 84µA (Note 3) 230 410
mV
LED_ Leakage Current
in Shutdown
VLED1 = VLED2 =
VLED3 = 5.5V, EN =
GND, each LED_
TA = +25°C 0.01 1 µA
Input High Voltage VIH VEN > VIH for enable 2.5
Input Low Voltage VIL VEN < VIL for disable 2.2 V
VEN = 2.5V to 5.5V, EN is the power-supply
input 40 100
EN Input Bias Current IEN
VEN = 0.4V TA = +25°C 0.05 1
µA
Thermal Shutdown Temperature 170 °C
Thermal Shutdown Hysteresis 10 °C
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
_______________________________________________________________________________________ 3
0
5
15
10
20
25
LED CURRENT vs.
V+ BIAS VOLTAGE
MAX1916 toc01
V+ BIAS VOLTAGE (V)
LED CURRENT (mA)
24356
LED3
LED2
LED1
UNMATCHED LEDS
0
5
15
10
20
2.0 2.5 4.0 4.53.0 3.5 5.0 5.5 6.0
OUTPUT CURRENT
vs. VEN SUPPLY VOLTAGE
MAX1916 toc02
VEN SUPPLY VOLTAGE (V)
OUTPUT CURRENT (mA)
19.5
19.6
19.8
19.7
19.9
20.0
-40 10-15 35 60 85
LED CURRENT vs.
TEMPERATURE
MAX1916 toc03
TEMPERATURE (°C)
LED CURRENT (mA)
100
10
1
10 100
LED CURRENT
vs. RSET
MAX1916 toc04
RSET (kΩ)
LED CURRENT (mA)
VCTRL = 5.0V
VCTRL = 3.3V
VCTRL = 2.5V
VCTRL = 1.8V
0
10
20
30
40
50
60
1.5 2.52.0 3.0 3.5 4.0 4.5 5.0 5.5
LED CURRENT (ILED)
vs. VCTRL
MAX1916 toc05
VCTRL (V)
LED CURRENT (mA)
A
B
C
D
E
F
G
A: RSET = 10kΩ
B: RSET = 15kΩ
C: RSET = 22kΩ
D: RSET = 33kΩ
E: RSET = 47kΩ
F: RSET = 68kΩ
G: RSET = 100kΩ
0
50
100
150
200
250
300
0105 152025303540
LED DROPOUT VOLTAGE
vs. CURRENT
MAX1916 toc06
LED CURRENT (mA)
LED DROPOUT VOLTAGE (mV)
Typical Operating Characteristics
(VEN = 3.3V, VCTRL = 3.3V, RSET = 24.9kΩ, V+ = 5V, TA= +25°C, unless otherwise noted.) (Circuit of Figure 1)
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
4 _______________________________________________________________________________________
ENABLE AND SHUTDOWN RESPONSE
MAX1916 toc08
0
20mA
0
ILED
20mA/div
VEN
2V/div
40µs/div
0
10
5
25
20
15
40
35
30
45
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5 6.0
IEN SUPPLY CURRENT
vs. VEN SUPPLY VOLTAGE
MAX1916 toc07
VEN SUPPLY VOLTAGE (V)
IEN SUPPLY CURRENT (µA)
VCTRL TRANSIENT RESPONSE
MAX1916 toc09
3V
20mA
10mA
ILED
10mA/div
VCTRL
1V/div
10µs/div
V+ TRANSIENT RESPONSE
MAX1916 toc10
4V
20mA
10mA
ILED
10mA/div
V+
1V/div
20µs/div
Typical Operating Characteristics (continued)
(VEN = 3.3V, VCTRL = 3.3V, RSET = 24.9kΩ, V+ = 5V, TA= +25°C, unless otherwise noted.) (Circuit of Figure 1)
Detailed Description
The MAX1916 provides constant-current bias supply
for white LED designs. The MAX1916 uses a single
resistor to set the bias current for up to three LEDs.
LED bias currents are matched to 0.3% by the
MAX1916’s unique current-matching architecture
(Figure 1). Supply current (IEN) is a low 40µA in normal
operation and 0.05µA when disabled.
The MAX1916 offers several advantages over using
ballast resistors, such as improved LED-to-LED bright-
ness matching, lower bias variation with supply voltage
changes, significantly lower dropout voltage, and in
some applications, significantly improved efficiency.
The MAX1916 achieves a 200mV dropout with a 9mA
load on each output.
For circuits requiring only one or two LEDs, leave
unused LED outputs unconnected.
Enable Input
EN powers the input of the MAX1916. Drive EN high
(> 2.5V) to enable the device; drive EN low (< 2.2V) to
disable the device. When driven high, EN draws 40µA
to power the IC. Driving EN low forces LED1, LED2,
LED3, and SET into a high-impedance state.
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
_______________________________________________________________________________________ 5
PIN NAME FUNCTION
1EN
Enable Input/Power Input. Drive high (> 2.5V) to enable; drive low (< 2.2V) to disable. When
disabled, SET, LED1, LED2, and LED3 are high impedance. When enabled, EN is the power input
for the MAX1916.
2 GND Ground
3 SET Bias Current Set Input. The current flowing into SET sets the bias current into each LED by
ILED_= 230 x ISET. VSET is internally biased to 1.215V. SET is high impedance when EN is low.
4 LED3 LED 3 Cathode Connection. Current flowing into LED3 is 230 times the current flowing into SET.
LED3 is high impedance when EN is low.
5 LED2 LED 2 Cathode Connection. Current flowing into LED2 is 230 times the current flowing into SET.
LED2 is high impedance when EN is low.
6 LED1 LED 1 Cathode Connection. Current flowing into LED1 is 230 times the current flowing into SET.
LED1 is high impedance when EN is low.
Pin Description
MAX1916
ON
EN
OFF
THERMAL
SHUTDOWN
GND
SET LED1 LED2 LED3
VCTRL V+
230X230X
1.215V
1X
RSET
UVLO REF
230X
Figure 1. MAX1916 Simplified Functional Diagram
MAX1916
Setting the Output Current
SET controls the LED bias current. Current flowing into
LED1, LED2, and LED3 is 230 times greater than the
current flowing into SET. Set the output current as fol-
lows:
where VSET = 1.215V, VCTRL is an external voltage
between 1.8V and 5.5V, and RSET is the resistor con-
nected between VCTRL and SET (Figure 1).
Applications Information
1) Very Low-Cost, High-Efficiency Solution (Figure 2).
A battery (single Li+ or three NiMH cells) powers
the LEDs directly. This is the least expensive and
most efficient architecture. Due to the high forward
voltage of white LEDs (3.3V), the LED brightness
may dim slightly at the end of battery life. The
MAX1916’s current-regulating architecture and low
dropout greatly minimize this effect compared to
using simple ballast resistors. The enable function
of the MAX1916 turns on and off the LEDs. An exist-
ing low-dropout regulator is used as VCTRL.
2) Brightness Adjustment Using a DAC (Figure 3). A
DAC is used as VCTRL such that the LED brightness
may be dynamically adjusted to eliminate factory
calibration. A battery (single Li+ or three NiMH
cells) or a regulated power source drives the LEDs.
3) Existing 5V Supply (Figure 4). Use an existing sys-
tem regulator, such as the MAX684, to provide the
required LED voltage and provide power to other
circuits. Due to the high forward voltage of white
LEDs (3.3V), use a 3.6V to 5.5V regulated supply to
provide enough voltage headroom such that the
LEDs will maintain constant brightness for any bat-
tery voltage. Use the existing regulated supply as
VCTRL.
Chip Information
TRANSISTOR COUNT: 220
PROCESS: BiCMOS
IVV
R
LED CTRL SET
SET
_
()
=−
230
Low-Dropout, Constant-Current
Triple White LED Bias Supply
6 _______________________________________________________________________________________
MAX1916
ON
EN
OFF
EXISTING
LDO
GND
SET LED1 LED2 LED3
VCTRL
V+
TO OTHER
CIRCUITS
Figure 2. Very Low-Cost, High-Efficiency Solution
MAX1916
ON
EN
OFF
DAC
GND
SET LED1 LED2 LED3
VCTRL
V+
Figure 3. Brightness Adjust Using DAC
MAX1916
ON
EN
OFF
EXISTING
REGULATOR
GND
SET LED1 LED2 LED3
VBATT
V+
5.0V TO OTHER
CIRCUITS
Figure 4. Existing 5V Supply Circuit
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
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 _____________________ 7
© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
