19-2067; Rev 0; 7/01
Low-Dropout, Constant-Current
Triple White LED Bias Supply
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 applications, significantly improved efficiency. The MAX1916
requires a 200mV dropout at a 9mA load on each output to match the LED brightness.
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)
The MAX1916 is available in a space-saving 6-pin Thin
SOT23 package.
Applications
Ordering Information
Next-Generation Wireless Handsets
PDAs, Palmtops, and Handy Terminals
Digital Cameras, Camcorders
PART
TEMP. RANGE
PINPACKAGE
TOP
MARK
MAX1916EZT
-40°C to +85°C
6 Thin SOT23
AAAG
Battery-Powered Equipment
Pin Configuration
Typical Operating Circuit
VCTRL
TOP VIEW
V+
EN 1
SET
LED1 LED2
LED3
GND 2
MAX1916
6
LED1
5
LED2
4
LED3
ON
OFF
EN
MAX1916
SET 3
GND
THIN SOT23-6
________________________________________________________________ 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
MAX1916
General Description
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
ABSOLUTE MAXIMUM RATINGS
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
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
(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
Operating Voltage Range
Undervoltage Lockout
Threshold
SET Input Current Range
SYMBOL
VEN
VUVLO
VEN rising
2.2
Hysteresis
VSET
ISET = 42µA
LED_ Dropout Voltage
260
µA
253
A/A
1.154
1.215
1.276
V
0.01
1
µA
0.3
5
5
TA = -40°C to +85°C
60
100
180
ISET = 42µA (Note 3)
200
360
ISET = 84µA (Note 3)
230
410
0.01
1
TA = +25°C
Input High Voltage
VIH
VEN > VIH for enable
Input Low Voltage
VIL
VEN < VIL for disable
EN Input Bias Current
IEN
VEN = 2.5V to 5.5V, EN is the power-supply
input
VEN = 0.4V
%
mA
ISET = 22µA (Note 2)
VLED1 = VLED2 =
VLED3 = 5.5V, EN =
GND, each LED_
LED_ Leakage Current
in Shutdown
V
mV
230
TA = -40°C to +25°C
Each LED_
UNITS
V
207
ISET = 42µA
ILED_
MAX
5.5
2.47
5
EN = GND,
VSET = 3.3V
LED_-to-LED_ Current Matching
TYP
85
ILED/ISET, ISET = 42µA
SET Leakage Current
in Shutdown
Maximum LED_ Sink Current
MIN
2.5
ISET
SET to LED_ Current Ratio
SET Bias Voltage
CONDITIONS
EN is the power-supply input
mV
µA
2.5
V
2.2
TA = +25°C
40
100
0.05
1
µA
Thermal Shutdown Temperature
170
°C
Thermal Shutdown Hysteresis
10
°C
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.
2
_______________________________________________________________________________________
Low-Dropout, Constant-Current
Triple White LED Bias Supply
OUTPUT CURRENT
vs. VEN SUPPLY VOLTAGE
LED3
LED2
10
LED1
20.0
19.9
LED CURRENT (mA)
15
OUTPUT CURRENT (mA)
LED CURRENT (mA)
20
20
15
10
5
5
MAX1916 toc03
MAX1916 toc01
25
LED CURRENT vs.
TEMPERATURE
MAX1916 toc02
LED CURRENT vs.
V+ BIAS VOLTAGE
19.8
19.7
19.6
UNMATCHED LEDS
0
0
3
4
5
19.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
-40
-15
10
35
60
V+ BIAS VOLTAGE (V)
VEN SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
LED CURRENT
vs. RSET
LED CURRENT (ILED)
vs. VCTRL
LED DROPOUT VOLTAGE
vs. CURRENT
50
LED CURRENT (mA)
VCTRL = 3.3V
A
10
VCTRL = 2.5V
B
40
C
30
D
20
E
F
10
300
250
200
150
100
50
G
VCTRL = 1.8V
0
1
10
85
MAX1916 toc06
VCTRL = 5.0V
LED DROPOUT VOLTAGE (mV)
60
MAX1916 toc04
100
LED CURRENT (mA)
6
MAX1916 toc05
2
100
0
1.5
2.0
2.5
3.0
3.5
4.0
VCTRL (V)
RSET (kΩ)
4.5
5.0
5.5
0
5
10
15
20
25
30
35
40
LED CURRENT (mA)
A: RSET = 10kΩ
B: RSET = 15kΩ
C: RSET = 22kΩ
D: RSET = 33kΩ
E: RSET = 47kΩ
F: RSET = 68kΩ
G: RSET = 100kΩ
_______________________________________________________________________________________
3
MAX1916
Typical Operating Characteristics
(VEN = 3.3V, VCTRL = 3.3V, RSET = 24.9kΩ, V+ = 5V, TA = +25°C, unless otherwise noted.) (Circuit of Figure 1)
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)
IEN SUPPLY CURRENT
vs. VEN SUPPLY VOLTAGE
ENABLE AND SHUTDOWN RESPONSE
MAX1916 toc08
MAX1916 toc07
45
40
IEN SUPPLY CURRENT (µA)
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
35
VEN
2V/div
0
30
25
20
20mA
15
ILED
20mA/div
0
10
5
0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
40µs/div
VEN SUPPLY VOLTAGE (V)
VCTRL TRANSIENT RESPONSE
V+ TRANSIENT RESPONSE
MAX1916 toc09
3V
VCTRL
1V/div
20mA
ILED
10mA/div
10mA
4V
V+
1V/div
20mA
ILED
10mA/div
10mA
10µs/div
4
MAX1916 toc10
20µs/div
_______________________________________________________________________________________
Low-Dropout, Constant-Current
Triple White LED Bias Supply
PIN
NAME
FUNCTION
1
EN
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.
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.
VCTRL
ON
V+
OFF
RSET
EN
SET
THERMAL
SHUTDOWN
1X
UVLO
REF
1.215V
LED1
230X
LED2
230X
LED3
230X
MAX1916
GND
Figure 1. MAX1916 Simplified Functional Diagram
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 brightness 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.
_______________________________________________________________________________________
5
MAX1916
Pin Description
MAX1916
Low-Dropout, Constant-Current
Triple White LED Bias Supply
Setting the Output Current
V+
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 follows:
TO OTHER
CIRCUITS
EXISTING VCTRL
LDO
SET
ILED _ = 230
LED1 LED2 LED3
ON
EN
OFF
(VCTRL − VSET )
RSET
where V SET = 1.215V, V CTRL is an external voltage
between 1.8V and 5.5V, and RSET is the resistor connected between VCTRL and SET (Figure 1).
MAX1916
GND
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 existing low-dropout regulator is used as VCTRL.
Figure 2. Very Low-Cost, High-Efficiency Solution
V+
VCTRL
DAC
SET
LED1 LED2
LED3
ON
OFF
EN
MAX1916
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.
GND
Figure 3. Brightness Adjust Using DAC
VBATT
V+
EXISTING 5.0V
REGULATOR
SET
LED1 LED2
TO OTHER
CIRCUITS
3) Existing 5V Supply (Figure 4). Use an existing system 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 battery voltage. Use the existing regulated supply as
VCTRL.
LED3
Chip Information
ON
OFF
EN
MAX1916
GND
TRANSISTOR COUNT: 220
PROCESS: BiCMOS
Figure 4. Existing 5V Supply Circuit
6
_______________________________________________________________________________________
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.
MAX1916
Package Information
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