General Description
The MAX1561/MAX1599 step-up converters drive up to
six white LEDs with a constant current to provide back-
light in cell phones, PDAs, and other hand-held
devices. The step-up converter topology allows series
connection of the white LEDs so the LED currents are
identical for uniform brightness. This configuration elim-
inates the need for ballast resistors and expensive fac-
tory calibration.
The MAX1561/MAX1599 include an internal, high-volt-
age, low-RDS(ON) N-channel MOSFET switch for high
efficiency and maximum battery life. A single Dual
Mode™ input provides a simple means of brightness
adjustment and on/off control. Fast 1MHz (500kHz for
the MAX1599) current-mode, pulse-width modulated
(PWM) operation allows for small input and output
capacitors and a small inductor while minimizing ripple
on the input supply/battery. Programmable soft-start
eliminates inrush current during startup.
Both devices are available in a space-saving, 8-pin 3mm
x 3mm thin DFN package with exposed paddle (EP).
Applications
Cell Phones and Smart Phones
PDAs, Palmtops, and Wireless Handhelds
e-Books and Subnotebooks
White LED Display Backlighting
Features
♦Accurate Current Regulation for Uniform
Illumination
♦High Efficiency Up to 87%
♦Flexible Analog or PWM Dimming Control
♦Up to 900mW Output Power with Internal 30V
MOSFET Switch
♦Fast 1MHz (MAX1561) or 500kHz (MAX1599) PWM
Operation
♦Small, Low-Profile External Components
♦2.6V to 5.5V Input Range
♦26V (max) Output with Overvoltage Protection
♦Optimized for Low 15mVP-P Input Ripple
♦Soft-Start with Zero Inrush Current
♦0.3µA Shutdown Current
♦Tiny 8-Pin 3mm x 3mm Thin DFN Package
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
________________________________________________________________ Maxim Integrated Products 1
3mm × 3mm
THIN DFN
TOP VIEW
1
2
8
7
3
4
6
5
GND
COMP
CS
LX
PGND
IN
CTRL
OUT
MAX1561
MAX1599
PART TEMP RANGE PIN-PACKAGE TOP
MARK
MAX1561ETA -40°C to +85°C8 TDFN-EP* ACS
MAX1599ETA -40°C to +85°C8 TDFN-EP* AHG
Pin Configuration
Ordering Information
MAX1561
MAX1599
LX
OUT
PGND
CSCOMP
IN
GND
INPUT 2.6V TO 5.5V
PWM OR
ANALOG
DIMMING
CTRL
OUTPUT UP TO 6 LEDs
Typical Operating Circuit
19-2731; Rev 1; 10/03
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.
EVALUATION KIT
AVAILABLE
Dual Mode is a trademark of Maxim Integrated Products, Inc.
*EP = Exposed paddle.
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = 3V, VOUT = 20V, COUT = 0.1µF, CCOMP = 0.15µF, RSENSE = 7.5Ω, VCTRL = 1.5V, Figure 1, TA = 0°C to +85°C, unless other-
wise noted. Typical values are at TA= +25°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.
IN to GND .................................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
LX, OUT to GND .....................................................-0.3V to +30V
CTRL to GND...................-0.3V to the lower of +6V or (VIN + 2V)
COMP, CS to GND.........................................-0.3 to (VIN + 0.3V)
ILX.............................................................................................1A
Continuous Power Dissipation (TA = +70°C)
3mm x 3mm 8-Pin TDFN
(derate 24.4mW/°C above +70°C).............................1950mW
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
PARAMETER CONDITIONS MIN TYP MAX UNITS
Supply Voltage 2.6 5.5 V
UVLO Threshold VIN rising or falling 2.10 2.38 2.55 V
UVLO Hysteresis 40 mV
Quiescent Current No switching 0.38 0.55 mA
TA = +25°C 0.3 2
Shutdown Supply Current CTRL = GND, VOUT = VIN TA = +85°C1
µA
OVLO Threshold VOUT rising 26 27 29 V
OVLO Hysteresis 2V
VOUT = 26V, VCTRL > 0.24V 10 20 30
OUT Input Bias Current VOUT = VIN, CTRL = GND 0.01 1 µA
Output Voltage Range (Note 1) (VIN - VD1) 25.5 V
ERROR AMPLIFIER
CTRL to CS Regulation VCTRL = 1V, VIN = 2.6V to 5.5V 0.095 0.100 0.105 V
TA = +25°C 0.01 1
CS Input Bias Current VCS = VCTRL/10 TA = +85°C 0.03 µA
CTRL Input Resistance VCTRL ≤ 1.0V 290 500 780 kΩ
CTRL Dual-Mode Threshold 100 170 240 mV
CTRL Dual-Mode Hysteresis 5mV
MAX1561 6.5 8.2 10.5
CTRL Shutdown Enable Delay (Note 2) MAX1599 13.6 16.4 21.0 ms
CS-to-COMP Transconductance VCOMP = 1.0V 32 50 82 µS
OSCILLATOR
MAX1561 0.80 1.0 1.25
Operating Frequency MAX1599 0.4 0.5 0.6 MHz
PWM mode 12
Minimum Duty Cycle Pulse skipping 0 %
Maximum Duty Cycle CTRL = IN, CS = GND 91 94 %
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3V, VOUT = 20V, COUT = 0.1µF, CCOMP = 0.15µF, RSENSE = 7.5Ω, VCTRL = 1.5V, Figure 1, TA = 0°C to +85°C, unless other-
wise noted. Typical values are at TA= +25°C.)
Note 1: VD1 is the diode forward-voltage drop of diode D1 in Figure 1.
Note 2: Time from CTRL going below the dual-mode threshold to IC shutdown.
Note 3: Specifications to -40°C are guaranteed by design and not production tested.
PARAMETER CONDITIONS MIN TYP MAX UNITS
N-CHANNEL SWITCH
LX On-Resistance ILX = 190mA 1.45 2.25 Ω
TA = +25°C 0.01 5
LX Leakage Current VLX = 28V, CTRL = GND TA = +85°C1
µA
LX Current Limit Duty cycle = 90% 450 700 950 mA
ELECTRICAL CHARACTERISTICS
(VIN = 3V, VOUT = 20V, COUT = 0.1µF, CCOMP = 0.15µF, RSENSE = 7.5Ω, VCTRL = 1.5V, Figure 1, TA = -40°C to +85°C, unless other-
wise noted.) (Note 3)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Supply Voltage 2.6 5.5 V
UVLO Threshold VIN rising or falling 2.10 2.55 V
Quiescent Current No switching 0.55 mA
OVLO Threshold VOUT rising 26 29 V
VOUT = 26V, VCTRL > 0.24V 10 30
OUT Input Bias Current VOUT = VIN, CTRL = GND 1 µA
Output Voltage Range (Note 1) (VIN - VD1) 25.5 V
ERROR AMPLIFIER
CTRL to CS Regulation VCTRL = 1V, VIN = 2.6V to 5.5V 0.093 0.107 V
CTRL Input Resistance VCTRL ≤ 1.0V 240 780 kΩ
CTRL Dual-Mode Threshold 100 240 mV
MAX1561 6 11
CTRL Shutdown Enable Delay (Note 2) MAX1599 13 22 ms
CS-to-COMP Transconductance VCOMP = 1.0V 32 85 µS
OSCILLATOR
MAX1561 0.75 1.25
Operating Frequency MAX1599 0.37 0.63 MHz
Maximum Duty Cycle CTRL = IN, CS = GND 91 %
N-CHANNEL SWITCH
LX On-Resistance 2.25 Ω
LX Current Limit Duty cycle = 90% 450 950 mA
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
4 _______________________________________________________________________________________
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 3.6V, ILED = 15mA, L1 = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 7.5Ω, 4 LEDs,
TA= +25°C, unless otherwise noted.)
40
60
50
80
70
90
100
01051520
MAX1561
EFFICIENCY vs. LED CURRENT
(vs. NUMBER of LEDs)
MAX1561 toc01
LED CURRENT (mA)
EFFICIENCY (%)
2 LEDs
4 LEDs
6 LEDs
40
60
50
80
70
90
100
01051520
MAX1561
EFFICIENCY vs. LED CURRENT
(vs. INPUT VOLTAGE)
MAX1561 toc02
LED CURRENT (mA)
EFFICIENCY (%)
4.2VIN
3.6VIN
2.7VIN
40
60
50
80
70
90
100
01051520
MAX1561
EFFICIENCY vs. LED CURRENT
(vs. INDUCTANCE)
MAX1561 toc03
LED CURRENT (mA)
EFFICIENCY (%)
10µH
4.7µH
47µH
22µH
40
60
50
80
70
90
100
01051520
MAX1599 EFFICIENCY vs. LED CURRENT
(vs. NUMBER OF LEDs)
MAX1561 toc04
LED CURRENT (mA)
EFFICIENCY (%)
6 LEDs
2 LEDs
4 LEDs
40
60
50
80
70
90
100
01051520
MAX1599 EFFICIENCY vs. LED CURRENT
(vs. INPUT VOLTAGE)
MAX1561 toc05
LED CURRENT (mA)
EFFICIENCY (%)
2.7VIN
3.6VIN
4.2VIN
40
60
50
80
70
90
100
01051520
MAX1599 EFFICIENCY vs. LED CURRENT
(vs. INDUCTANCE)
MAX1561 toc06
LED CURRENT (mA)
EFFICIENCY (%)
47µH
22µH
0
5
10
20
15
25
0 2030405010 60 70 80 90 100
LED CURRENT vs. DIRECT-PWM
DIMMING DUTY CYCLE
MAX1561 toc09
DIRECT-PWM DIMMING DUTY CYCLE (%)
LED CURRENT (mA)
VCTRL = SQUARE WAVE
200Hz < FREQ < 200kHz
0
10
5
15
30
35
25
20
40
0 101520255 3035404550
INPUT RIPPLE vs. INDUCTANCE
MAX1561 toc07
INDUCTANCE (µH)
INPUT RIPPLE (mVP-P)
0
1
2
4
5
3
6
0 23451 678910
INPUT RIPPLE SPECTRUM
MAX1561 toc08
FREQUENCY (MHz)
INPUT RIPPLE (mVRMS)
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 3.6V, ILED = 15mA, L1 = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 7.5Ω, 4 LEDs,
TA= +25°C, unless otherwise noted.)
SWITCHING WAVEFORMS
MAX1561 toc10
VIN
10mV/div
VOUT
100mV/div
VLX
10V/div
500ns/div
SOFT-START AND SHUTDOWN
MAX1561 toc11
VCTRL
1V/div
IIN
50mA/div
VIN
50mV/div
VOUT
5V/div
0mA
0V
0V
20ms/div
VIN = 3.8V Li+ BATTERY
DIRECT-PWM DIMMING
MAX1561 toc13
VCTRL
32kHz
1V/div
IIN
50mA/div
VIN
50mV/div
VOUT
5V/div
0mA
0V
0V
50µs/div
VIN = 3.8V Li+ BATTERY
LINE-TRANSIENT RESPONSE
MAX1561 toc14
VIN
500mV/div
IIN
50mA/div
VCS
100mV/div
0V
3.5V
4V
0mA
50µs/div
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
6 _______________________________________________________________________________________
Detailed Description
The MAX1561/MAX1599s’ high efficiency and small size
make them ideally suited to drive up to six series-con-
nected LEDs. The device operates as a boost DC-DC
converter that regulates output current rather than volt-
age. The MAX1561/MAX1599 provide even illumination
by sourcing the same output current through each LED,
eliminating the need for expensive factory calibration.
The fast 1MHz (500kHz for the MAX1599) internal oscil-
lator allows for a small inductor and small input and out-
put capacitors while minimizing input and output ripple.
The single analog control input allows easy adjustment
of LED brightness and on/off control. This allows either
simple logic-level on/off control, analog voltage control,
or PWM duty-cycle control of both brightness and shut-
down. In shutdown, supply current is reduced to a low
0.3µA. A soft-start gradually illuminates the LEDs, elimi-
nating the inrush current during startup.
Soft-Start
The MAX1561/MAX1599 attain soft-start by charging
CCOMP gradually with a current source. When VCOMP
rises above 1.25V, the internal MOSFET begins switch-
ing at a reduced duty cycle. When VCOMP rises above
2.25V, the duty cycle is at its maximum. See the Typical
Operating Characteristics for an example of soft-start
operation.
Shutdown
The MAX1561/MAX1599 enter shutdown when VCTRL is
less than 100mV for more than 8.2ms (16.4ms for the
MAX1599). In shutdown, supply current is reduced to
0.3µA by powering down the entire IC except for the
CTRL voltage-detection circuitry. CCOMP is discharged
during shutdown, allowing the device to reinitiate soft-
start when it is enabled. Although the internal N-chan-
nel MOSFET does not switch in shutdown, there is still
a DC current path between the input and the LEDs
through the inductor and Schottky diode. The minimum
forward voltage of the LED array must exceed the max-
imum input voltage to ensure that the LEDs remain off
in shutdown. However, with two or more LEDs, the for-
ward voltage is large enough to keep leakage current
low, less than 1µA (typ). Typical shutdown timing char-
acteristics are shown in the Typical Operating
Characteristics.
Overvoltage Protection
Overvoltage lockout (OVLO) occurs when VOUT is
above 27V. The protection circuitry stops the internal
MOSFET from switching and causes VCOMP to decay
to 0V. The device comes out of OVLO and into soft-
start when VOUT falls below 25V.
PIN
NAME
FUNCTION
1 OUT Overvoltage Sense. When VOUT is greater than 27V, the internal N-channel MOSFET turns off until VOUT
drops below 25V, then the IC reenters soft-start. Connect a 0.1µF capacitor from OUT to PGND.
2 IN Input Voltage Supply. Input voltage range is 2.6V to 5.5V. Connect a 2.2µF capacitor from IN to PGND.
3 CTRL
Brightness Control Input. LED brightness is controlled by the voltage applied to CTRL. Varying the voltage
from 0.24V to 1.62V adjusts the brightness from dim to bright, respectively. Any voltage above 1.62V does
not increase brightness. If CTRL is held below 100mV for more than 8.2ms (16.4ms for the MAX1599), the
IC shuts down.
4CS
Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias current. The
voltage at CS regulates to VCTRL / 10 or 0.162V, whichever is lower.
5
COMP
Compensation Input. Connect a 0.1µF capacitor (CCOMP) from COMP to GND. CCOMP stabilizes the
converter and controls soft-start. CCOMP discharges to GND when in shutdown.
6 GND Ground. Connect to PGND and the exposed pad directly under the IC.
7 PGND Power Ground. Connect to GND and the exposed pad directly under the IC.
8 LX Inductor Connection. This pin is high impedance during shutdown.
Exposed
Pad EP Ground. Connect directly to GND and PGND under the IC.
Pin Description
Design Procedure
Adjusting LED Current
Adjusting the MAX1561/MAX1599s’ output current
changes the brightness of the LEDs. An analog input
(CTRL) and the sense-resistor value set the output cur-
rent. Output current is given by:
The VCTRL voltage range for adjusting output current is
0.24V to 1.62V. To set the maximum current, calculate
RSENSE when VCTRL is at its maximum as follows:
Power dissipation in RSENSE is typically less than 5mW,
making a standard chip resistor sufficient.
PWM Dimming Control
CTRL is also used as a digital input allowing LED bright-
ness control with a logic-level PWM signal applied direct-
ly to CTRL. The frequency range is from 200Hz to
200kHz, while 0% duty cycle corresponds to zero cur-
rent and 100% duty cycle corresponds to full current.
The error amplifier and compensation capacitor form a
lowpass filter so PWM dimming results in DC current to
the LEDs without the need for any additional RC filters;
see the Typical Operating Characteristics.
Capacitor Selection
The exact values of input and output capacitors are not
critical. The typical value for the input capacitor is
2.2µF and the typical value for the output capacitor is
0.1µF. Larger value capacitors can be used to reduce
RV
I
SENSE LED MAX
=×
162
10
.
()
IV
R
LED CTRL
SENSE
=×10
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
_______________________________________________________________________________________ 7
SLOPE COMP
CURRENT SENSE
fOSC OVERVOLTAGE
PROTECTION
gm
170mV
450kΩ
50kΩ
CTRL
SHUTDOWN TIMER SHUTDOWN
GND
PWM CONTROL
OUT
COMP
CS
PGND
IN LX
INPUT
2.6V TO 5.5V
L1
2.2µF
COUT
0.1µF
CCOMP
0.1µF
UP TO 26V
2 TO 6 LEDS
RSENSE
7.5Ω
PWM OR
ANALOG
DIMING
MAX1561
MAX1599
Figure 1. Functional Diagram
MAX1561/MAX1599
input and output ripple, but at the expense of size and
higher cost. CCOMP stabilizes the converter and con-
trols soft-start. Connect a 0.1µF capacitor from COMP
to GND. For stable operation, COUT must not exceed
10 times CCOMP.
Inductor Selection
Inductor values range from 10µH to 47µH. A 22µH
(47µH for the MAX1599) inductor optimizes the efficien-
cy for most applications while maintaining low 15mVP-P
input ripple. With input voltages near 5V, a larger value
of inductance can be more efficient. To prevent core
saturation, ensure that the inductor-saturation current
rating exceeds the peak inductor current for the appli-
cation. Calculate the peak inductor current with the fol-
lowing formula:
Schottky Diode Selection
The MAX1561/MAX1599s’ high switching frequency
demands a high-speed rectification diode (D1) for opti-
mum efficiency. A Schottky diode is recommended due
to its fast recovery time and low forward-voltage drop.
Ensure that the diode’s average and peak current rating
exceed the average output current and peak inductor
current. In addition, the diode’s reverse breakdown volt-
age must exceed VOUT. The RMS diode current can be
calculated from:
Applications Information
PC Board Layout
Due to fast switching waveforms and high-current
paths, careful PC board layout is required. An evalua-
tion kit (MAX1561EVKIT) is available to speed design.
Order MAX1599 samples separately.
When laying out a board, minimize trace lengths between
the IC and RSENSE, the inductor, the diode, the input
capacitor, and the output capacitor. Keep traces short,
direct, and wide. Keep noisy traces, such as the LX node
trace, away from CS. The IN bypass capacitor (CIN)
should be placed as close to the IC as possible. PGND
and GND should be connected directly to the exposed
paddle underneath the IC. The ground connections of
CIN and COUT should be as close together as possible.
The traces from IN to the inductor and from the Schottky
diode to the LEDs may be longer.
Chip Information
TRANSISTOR COUNT: 2895
PROCESS: BiCMOS
III
DIODE RMS OUT PEAK()
≅×
IVI
V
Vs
L
PEAK
OUT MAX LED MAX
IN MIN
IN MIN
=×
×+×µ
×
() ()
()
()
.
.
08
08
2
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
8 _______________________________________________________________________________________
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
_______________________________________________________________________________________ 9
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.)
6, 8, &10L, DFN THIN.EPS
PROPRIETARY INFORMATION
TITLE:
APPROVAL DOCUMENT CONTROL NO. REV.
2
1
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137 D
L
CL
C
SEMICONDUCTOR
DALLAS
A2
A
PIN 1
INDEX
AREA
D
E
A1
D2
b
E2 [(N/2)-1] x e
REF.
e
k
1N1
L
e
L
A
L
PIN 1 ID
C0.35
DETAIL A
e
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
MAX1561/MAX1599
High-Efficiency, 26V Step-Up Converters
for Two to Six White LEDs
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information (continued)
(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.)
DOCUMENT CONTROL NO.APPROVAL
TITLE:
PROPRIETARY INFORMATION
REV.
2
2
COMMON DIMENSIONS
SYMBOL MIN. MAX.
A0.70 0.80
D2.90 3.10
E2.90 3.10
A1 0.00 0.05
L0.20 0.40
PKG. CODE
6
N
T633-1 1.50–0.10
D2
2.30–0.10
E2
0.95 BSC
e
MO229 / WEEA
JEDEC SPEC
0.40–0.05
b
1.90 REF
[(N/2)-1] x e
1.50–0.10 MO229 / WEEC 1.95 REF0.30–0.05
0.65 BSC
2.30–0.10T833-1 8
PACKAGE VARIATIONS
21-0137
0.25–0.05 2.00 REFMO229 / WEED-30.50 BSC1.50–0.10 2.30–0.1010T1033-1
0.25 MIN.
k
A2 0.20 REF.
D
SEMICONDUCTOR
DALLAS
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm