19-2875; Rev 1; 12/03
KIT
ATION
EVALU
BLE
AVAILA
High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
General Description
Features
♦
Constant-Current Regulation for Even LED
Illumination
♦
Internal 40V MOSFET Switch Capable of Driving
10 LEDs
♦
Small, Low-Profile External Components
♦
2.7V to 5.5V Input Range
♦
Up to 88% Efficiency Driving 6 LEDs
♦
Up to 82% Efficiency Driving 9 LEDs
(20mA, V
CC
= 3.6V)
♦
Analog or PWM Control of LED Intensity
♦
Optimized for Low Input Ripple
♦
Soft-Start to Minimize Inrush Current
♦
3mm x 3mm 8-Pin TDFN Package
MAX1553/MAX1554
The MAX1553/MAX1554 drive white LEDs in series with
a constant current to provide efficient display backlight-
ing in cellular phones, PDAs, and other hand-held
devices. The step-up converter includes an internal
40V, low R
DSON
, N-channel MOSFET switch for high
efficiency and maximum battery life. The MAX1553 has
a current limit of 480mA for driving two to six white
LEDs, while the MAX1554 has a current limit of 970mA
for driving up to 10 white LEDs.
A single analog/PWM Dual Mode input provides two
simple means of brightness adjustment. A separate
enable input provides on/off control. Soft-start minimizes
inrush current during startup.
The MAX1553/MAX1554 are available in space-saving
8-pin TDFN 3mm x 3mm packages.
Applications
Cellular Phones
PDA, Palmtop, and Wireless Handhelds
Color Display Backlight
PART
MAX1553
ETA
MAX1554
ETA
Ordering Information
TEMP RANGE
PIN-PACKAGE
TOP
MARK
AGX
AGY
-40°C to +85°C 8 TDFN 3mm x 3mm
-40°C to +85°C 8 TDFN 3mm x 3mm
Dual Mode is a trademark of Maxim Integrated Products, Inc.
Typical Operating Circuit
TOP VIEW
2.7V TO 5.5V
INPUT
V
CC
ON
OFF
EN
LX
OV
WHITE
LEDS
Pin Configuration
GND
V
CC
1
2
3
4
8
7
LX
0V
SS
PWM
OR
DC CONTROL
MAX1553
MAX1554
BRT
SS
FB
GND
EN
BRT
MAX1553
MAX1554
6
5
FB
TDFN
3mm x 3mm
________________________________________________________________
Maxim Integrated Products
1
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.
High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
MAX1553/MAX1554
ABSOLUTE MAXIMUM RATINGS
V
CC
, FB, OV to GND..............................................-0.3V to +6.0V
LX to GND ..............................................................-0.3V to +45V
EN, BRT, SS to GND...................................-0.3V to (V
CC
+ 0.3V)
I
LX
...................................................................................0.9A
RMS
Continuous Power Dissipation (T
A
= +70°C)
8-Pin 3mm x 3mm TDFN
(derate 24.4mW/°C above +70°C) .............................1951mW
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
(V
CC
= 3.3V, V
OV
= 0V, C
OUT
= 1µF, R
SENSE
= 10Ω,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Supply Voltage
Undervoltage Lockout Threshold
Quiescent Current
Shutdown Supply Current
OV Threshold
OV Input Bias Current
BRT Input Resistance
TIMING CONTROL
Maximum On-Time
On-Time Constant (K)
Minimum Off-Time
ERROR AMPLIFIER
FB Threshold
FB Input Bias Current
N-CHANNEL SWITCH
LX On-Resistance
0.8
1.4
Ω
V
BRT
= 1.25V
V
BRT
= 3.3V
V
FB
= 1.0V
T
A
= +25°C
T
A
= +85°C
192
203
280
15
100
200
212
mV
nA
V
CC
= 3.3V
t
ON
= K / V
CC
150
2.0
3.4
6.3
250
350
4.8
µs
µs-V
ns
MAX1553
MAX1554
V
CC
rising or falling, 35mV hysteresis typical
Not switching
Switching
V
EN
= 0V
Rising edge
V
OV
= 1V
T
A
= +25°C
T
A
= +85°C
200
T
A
= +25°C
T
A
= +85°C
1.18
CONDITIONS
MIN
2.7
3.15
2.35
2.5
0.33
0.44
0.1
1
1.25
1
10
400
600
1.33
200
TYP
MAX
5.5
5.50
2.65
0.65
0.9
1
UNITS
V
V
mA
µA
V
nA
kΩ
0 < V
BRT
< 1.5V, EN = V
CC
2
_______________________________________________________________________________________
High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 3.3V, V
OV
= 0V, C
OUT
= 1µF, R
SENSE
= 10Ω,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
LX Current Limit
LX Leakage Current
SHUTDOWN CONTROL
EN Logic-Level High
EN Logic-Level Low
EN Input Current
V
EN
= 0V or 5.5V
T
A
= +25°C
T
A
= +85°C
0.01
0.1
1.8
0.4
1
V
V
µA
MAX1553
MAX1554, V
CC
= 4.2V
V
LX
= 38V,
V
EN
= 0V
T
A
= +25°C
T
A
= +85°C
CONDITIONS
MIN
300
600
TYP
480
970
0.1
1
MAX
600
1200
5
UNITS
mA
µA
MAX1553/MAX1554
ELECTRICAL CHARACTERISTICS
(V
CC
= 3.3V, V
OV
= 0V, C
OUT
= 1µF, R
SENSE
= 10Ω,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
Supply Voltage
Undervoltage Lockout Threshold
Quiescent Current
OV Threshold
BRT Input Resistance
TIMING CONTROL
Maximum On-Time
Minimum Off-Time
ERROR AMPLIFIER
FB Threshold
N-CHANNEL SWITCH
LX On-Resistance
LX Current Limit
SHUTDOWN CONTROL
EN Logic-Level High
EN Logic-Level Low
1.8
0.4
V
V
MAX1553
MAX1554, V
CC
= 4.2V
300
600
1.4
600
1200
Ω
mA
V
BRT
= 1.25V
192
217
mV
V
CC
= 3.3V
2.0
150
4.8
350
µs
ns
MAX1553
MAX1554
V
CC
rising or falling, 35mV hysteresis typical
Not switching
Switching
Rising edge
0 < V
BRT
< 1.5V, EN = V
CC
1.18
200
CONDITIONS
MIN
2.7
3.15
2.35
MAX
5.5
5.50
2.65
0.65
0.9
1.33
600
UNITS
V
V
mA
V
kΩ
Note 1:
Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
MAX1553/MAX1554
Typical Operating Characteristics
(MAX1553 driving six white LEDs, V
CC
= V
EN
= 3.6V, Circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
DRIVING 6 WHITE LEDS
MAX1553/54 toc01
EFFICIENCY vs. LOAD CURRENT
DRIVING 6 WHITE LEDS
MAX1553/54 toc02
EFFICIENCY vs. LOAD CURRENT
DRIVING 6 WHITE LEDS
V
CC
= 4V
90
EFFICIENCY (%)
V
CC
= 5V
MAX1553/54 toc03
100
V
CC
= 5V
90
EFFICIENCY (%)
V
CC
= 4V
100
V
CC
= 4V
90
EFFICIENCY (%)
V
CC
= 5V
100
80
V
CC
= 3.6V
80
V
CC
= 3.6V
V
CC
= 3V
70
80
V
CC
= 3.6V
70
V
CC
= 3V
70
V
CC
= 3V
60
L1 = 22µH
NO CAPACITOR ACROSS LEDs
50
0
5
10
LOAD CURRENT (mA)
15
20
60
L1 = 33µH
4700pF ACROSS LEDs
50
0
5
10
LOAD CURRENT (mA)
15
20
60
L1 = 47µH
4700pF ACROSS LEDs
50
0
5
10
LOAD CURRENT (mA)
15
20
EFFICIENCY vs. LOAD CURRENT
WITH MAX1554 DRIVING 9 WHITE LEDS
V
CC
= 5V
MAX1553/54 toc04
LED CURRENT
vs. INPUT VOLTAGE
MAX1553/54 toc05
LED CURRENT
vs. INPUT VOLTAGE
MAX1553/54 toc06
100
V
CC
= 4V
26
26
90
EFFICIENCY (%)
23
LED CURRENT (mA)
L1 = 22µH, NO CAPACITOR ACROSS LEDs
23
LED CURRENT (mA)
L1 = 22µH, NO CAPACITOR ACROSS LEDs
80
V
CC
= 3.6V
20
L1 = 47µH,
4700pF ACROSS LEDs
L1 = 33µH, 4700pF ACROSS LEDs
20
L1 = 47µH,
4700pF ACROSS LEDs
L1 = 33µH, 4700pF ACROSS LEDs
14
R1 = 14Ω, V
BRT
= 3.3V
11
70
17
17
60
CIRCUIT OF FIGURE 3
50
0
5
10
LOAD CURRENT (mA)
15
20
14
R1 = 10Ω, V
BRT
= 1.25V
11
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
LED CURRENT vs. INPUT VOLTAGE
WITH MAX1554 DRIVING 9 LEDS
MAX1553/54 toc07
LED CURRENT
vs. BRT VOLTAGE
MAX1553/54 toc08
LED CURRENT
vs. BRT DUTY CYCLE
MAX1553/54 toc09
26
35
30
LED CURRENT (mA)
25
20
15
10
30
25
LED CURRENT (mA)
20
15
10
5
0
23
LED CURRENT (mA)
20
17
14
5
CIRCUIT OF FIGURE 3
11
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
0
0
0.6
1.2
1.8
2.4
3.0
3.6
BRT VOLTAGE (V)
0
20
40
60
80
100
BRT DUTY CYCLE (%)
4
_______________________________________________________________________________________
High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
MAX1553/MAX1554
Typical Operating Characteristics (continued)
(MAX1553 driving six white LEDs, V
CC
= V
EN
= 3.6V, Circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
SWITCHING WAVEFORMS
(CONTINUOUS OPERATION,
3.75V Li+ BATTERY, 18mA OUTPUT)
MAX1553/54 toc10
SWITCHING WAVEFORMS
(DISCONTINUOUS OPERATION,
3.75V Li+ BATTERY, 10mA OUTPUT)
MAX1553/54 toc11
V
LX
10V/div
V
LX
10V/div
V
OUT
200mV/div
V
OUT
200mV/div
I
L
200mA/div
I
L
200mA/div
2µs/div
L1 = 47µH, 4700pF CAPACITOR ACROSS LEDs
2µs/div
L1 = 47µH, 4700pF CAPACITOR ACROSS LEDs
STARTUP/SHUTDOWN WAVEFORMS
MAX1553/54 toc12
BRT STEP RESPONSE
MAX1553/54 toc13
V
EN
5V/div
V
BRT
1V/div
V
FB
200mV/div
V
FB
200mV/div
V
OUT
V
OUT
10V/div
2V/div
40ms/div
L1 = 22µH
20ms/div
L1 = 22µH,
V
BRT
= 0.5V TO 1.25V TO O.5V
_______________________________________________________________________________________
5
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