19-0865; Rev 0; 8/07
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
General Description
The MAX8901A/MAX8901B step-up converters drive from
two to six series-connected white LEDs (WLEDs) with
constant current to provide uniform WLED intensity for
LCD backlighting in cell phones, PDAs, and other hand-
held devices. The MAX8901_ operate at a fixed 750kHz
(typ) switching frequency, allowing for tiny external com-
ponents, and are optimized for the highest possible effi-
ciency over the full 1-cell Li+/Li-Poly battery range.
These converters use a single input (ON) to enable the
IC and to control WLED intensity. The MAX8901A
requires a direct PWM input to regulate WLED intensity
with the WLED current proportional to the PWM duty
cycle. The MAX8901B uses single-wire, serial-pulse
dimming that reduces the WLED intensity in 32 linear
steps. Full-scale WLED current for serial-pulse
dimming is 24.75mA (MAX8901B, 0.75mA/step).
The MAX8901_ features an internal soft-start to eliminate
inrush currents during startup, input overvoltage
protection, WLED overvoltage protection, and a shut-
down mode with 0.01µA (typ) shutdown current. No
WLED current is present in shutdown provided the
WLED forward voltage is greater than the input supply
voltage. Additional features include undervoltage lock-
out (UVLO) and thermal shutdown.
The MAX8901_ are available in tiny 8-pin, 2mm x 2mm
TDFN-EP packages (0.8mm max height).
♦
High Efficiency, Up to 91%
♦
2.6V to 5.5V Input Voltage Range
♦
Fixed-Frequency Operation
♦
Supplies from 2 to 6 WLEDs with 1% LED Current
Accuracy
♦
Flexible Dimming Control
Direct PWM Dimming (MAX8901A)
32-Step, 1-Wire Serial Dimming
(MAX8901B)
♦
Input Undervoltage Lockout
♦
Input Overvoltage Lockout
♦
WLED Overvoltage Protection (25V typ)
♦
0.01µA (typ) Shutdown Current
♦
No WLED Current in Shutdown
♦
Internal Soft-Start and Thermal Shutdown
IT
TION K
VALUA
E
BLE
AVAILA
Features
MAX8901A/MAX8901B
Ordering Information
PART
MAX8901AETA+T
MAX8901BETA+T
PIN-PACKAGE
8 TDFN-EP*
2mm x 2mm
8 TDFN-EP*
2mm x 2mm
PKG
CODE
T822-1
T822-1
TOP
MARK
+ABA
+ABB
Applications
Display Backlight (from 2 to 6 WLEDs)
Cellular Phones
PDAs and Smartphones
MP3 and Portable Media Players
Portable Navigation Devices
Digital Cameras
Note:
All devices are specified over the -40°C to +85°C operating
temperature range.
+
Denotes a lead-free package.
*
EP = Exposed paddle.
T = Tape and reel.
Pin Configuration appears at end of data sheet.
Typical Operating Circuits
INPUT
2.6V TO 5.5V
OUTPUT
UP TO 25V
INPUT
2.6V TO 5.5V
3
4
IN
MAX8901A
COMP
LX
3
IN
MAX8901B
LX
4
OUTPUT
UP TO 25V
7
OVP
1
7
COMP
OVP
1
6
PWM DIMMING
CONTROL
2
GND
PGND
5
SERIAL-PULSE
DIMMING
CONTROL
6
GND
PGND
5
ON
EP
CS
8
2
ON
EP
CS
8
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
MAX8901A/MAX8901B
ABSOLUTE MAXIMUM RATINGS
IN to GND .................................................................-0.3V to +7V
CS, COMP, ON to GND ...............................-0.3V to (V
IN
+ 0.3V)
OVP, LX to GND .....................................................-0.3V to +28V
PGND to GND .......................................................-0.3V to +0.3V
LX Current ..................................................................770mA
RMS
Continuous Power Dissipation (multilayer board at +70°C)
8-pin, 2mm x 2mm TDFN
(derate above +70°C by 11.9mW/°C) ..........................953mW
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
IN
= V
ON
= V
OVP
= 3.6V, V
PGND
= V
GND
= 0V, COMP, CS, and LX are unconnected, T
A
= -40°C to +85°C, unless otherwise noted.
Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Input Voltage
Input Undervoltage Lockout
Threshold
Input Overvoltage Lockout
Threshold
Shutdown Input Current
SYMBOL
V
IN
V
IN_UVLO
V
IN
rising
V
IN
falling
V
IN_OVLO
I
SHDN
V
IN
rising
V
IN
falling
V
ON
= 0V
V
CS
= 0.55V, no
load (not
switching)
T
A
= +25°C
T
A
= +85°C
MAX8901A
MAX8901B
V
IN
-
V
DIODE
24
25
20
0.475
1.18
1.3
0.4
T
A
= +25°C
T
A
= +85°C
40
0.5
0.5
500.0
0.01
0.1
1
0.50
1.33
0.525
1.50
CONDITIONS
MIN
2.6
2.25
2.20
6.2
6.0
0.01
0.1
70
115
135
185
V
OV
26
µA
TYP
MAX
5.5
2.50
2.53
6.3
6.3
1
V
µA
UNITS
V
V
Quiescent Current
I
Q
Output Voltage Range
OVP Overvoltage Protection
Threshold
OVP Input Current
CS Regulation Voltage
ON Shutdown Delay
ON High Voltage
ON Low Voltage
ON Input Current
Initial ON High Pulse Width
ON High Pulse Width
ON Low Pulse Width
V
OUT
V
OV
I
OV
V
CS
t
SHDN
V
ON_HI
V
ON_LO
I
ON
t
HI_INIT
t
HI
t
LO
V
DIODE
= external boost diode voltage drop
6 LEDs with 25V OVP option
VOVP = 20V
No dimming
Time V
ON
is below low threshold until
shutdown (Figure 1)
2.6V < V
IN
< 5.5V
2.6V < V
IN
< 5.5V
ON = IN
V
V
µA
V
ms
V
V
µA
µs
µs
µs
First ON high pulse to enable IC
(MAX8901B) (Figure 1)
MAX8901B (Figure 1)
MAX8901B (Figure 1)
2
_______________________________________________________________________________________
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
ON
= V
OVP
= 3.6V, V
PGND
= V
GND
= 0V, COMP, CS, and LX are unconnected, T
A
= -40°C to +85°C, unless otherwise noted.
Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Serial Dimming
Full-Scale LED Current Accuracy
PWM Frequency for PWM
Dimming Control
CS to COMP Transconductance
Soft-Start Interval
Thermal Shutdown
OSCILLATOR
Operating Frequency
Maximum Duty Cycle
n-CHANNEL SWITCH
LX Leakage Current
n-Channel Switch On-Resistance
n-Channel Current Limit
I
LXLKG
R
LX
I
LIM
0.63
V
LX
= 27V
T
A
= +25°C
T
A
= +85°C
0.1
0.1
0.7
0.70
1.4
0.77
5
µA
Ω
A
f
SW
D
MAX
V
CS
= 0.4V
700
90
750
92
800
kHz
%
t
SOFT-
START
MAX8901A/MAX8901B
SYMBOL
CONDITIONS
I
LED
= 24.75mA
(MAX8901B)
T
A
= +25°C
T
A
= -40°C to +85°C
MIN
-1
-3
TYP
MAX
+1
+3
UNITS
%
%
kHz
f
PWM
MAX8901A
40
C
COMP
= 0.022µF (Figure 1)
100
60
10
160
80
µS
ms
°C
Note 1:
Specifications to -40°C are guaranteed by design and characterization and are not production tested.
STEP
t
HI_INIT
> 40μs
0
ON
1
2
3
4
5
28
29
30
31
32
33
t
HI
t
SOFT-START
I
LED_
SHUTDOWN
FULL
32/33 31/33
30/33 29/33
t
LO
500ns TO 500μs
28/33
6/33
5/33
4/33
3/33
2/33
t
SHDN
> 500ns
FULL
32/33 1.33ms (typ)
1/33
SHUTDOWN
Figure 1. MAX8901B Timing Diagram
_______________________________________________________________________________________
3
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
MAX8901A/MAX8901B
Typical Operating Characteristics
(Circuit of Figure 5, I
LED
= 24.75mA, V
IN
= V
ON
= 3.6V, C1 = 1µF, C2 = 1µF, T
A
= +25°C, unless otherwise noted.)
LED EFFICIENCY vs. INPUT VOLTAGE
MAX8901A/B toc01
LED EFFICIENCY vs. INPUT VOLTAGE
4 WLEDs
85
EFFICIENCY (%)
3 WLEDs
80
6 WLEDs
MAX8901A/B toc02
90
90
85
EFFICIENCY (%)
3 WLEDs
80
4 WLEDs
6 WLEDs
75
INDUCTOR: TOKO 1069AS-220M
DIODE: CENTRAL SEMI CMDSH05-4
70
2
3
4
INPUT VOLTAGE (V)
5
75
INDUCTOR: TOKO 1098AS-100M
DIODE: NXP PMEG3005EB
70
6
2
3
4
INPUT VOLTAGE (V)
5
6
LED EFFICIENCY vs. LED CURRENT
(6 WLEDs)
V
IN
= 5V
V
IN
= 5.5V
MAX8901A/B toc03
LED EFFICIENCY vs. LED CURRENT
(6 WLEDs)
V
IN
= 5V V
IN
= 5.5V
85
80
EFFICIENCY (%)
75
70
65
60
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3V
MAX8901A/B toc04
90
85
80
EFFICIENCY (%)
75
70
65
60
55
50
0
5
90
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 3V
INDUCTOR: TOKO 1069AS-220M
DIODE: CENTRAL SEMI CMDSH05-4
10
15
20
25
55
50
0
5
INDUCTOR: TOKO 1098AS-100M
DIODE: NXP PMEG3005EB
10
15
20
25
LED CURRENT (mA)
LED CURRENT (mA)
LED EFFICIENCY vs. LED CURRENT
(4 WLEDs)
V
IN
= 5V
V
IN
= 5.5V
MAX8901A/B toc05
LED EFFICIENCY vs. LED CURRENT
(4 WLEDs)
V
IN
= 5V
85
80
EFFICIENCY (%)
75
70
65
60
V
IN
= 4.2V
V
IN
= 5.5V
MAX8901A/B toc06
90
85
80
EFFICIENCY (%)
75
70
65
60
55
50
0
5
90
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3V
V
IN
= 3.6V
V
IN
= 3V
INDUCTOR: TOKO 1069AS-220M
DIODE: CENTRAL SEMI CMDSH05-4
10
15
20
25
55
50
0
5
INDUCTOR: TOKO 1098AS-100M
DIODE: NXP PMEG3005EB
10
15
20
25
LED CURRENT (mA)
LED CURRENT (mA)
4
_______________________________________________________________________________________
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
Typical Operating Characteristics (continued)
(Circuit of Figure 5, I
LED
= 24.75mA, V
IN
= V
ON
= 3.6V, C1 = 1µF, C2 = 1µF, T
A
= +25°C, unless otherwise noted.)
LED AND BOOST EFFICIENCY
vs. INPUT VOLTAGE
BOOST
90
EFFICIENCY (%)
LED
I
IN
(μA)
85
500
400
300
200
6WLEDs,
INDUCTOR: TOKO A915AY-220M,
DIODE: CENTRAL SEMI CMDSH05-4
2
3
4
INPUT VOLTAGE (V)
5
6
100
0
2
3
4
5
6
7
SUPPLY VOLTAGE (V)
MAX8901A/B toc07
MAX8901A/MAX8901B
IN CURRENT (I
IN
)
vs. SUPPLY VOLTAGE
700
600
MAX8901A
MAX8901B
MAX8901A/B toc08
MAX8901A/B toc10
95
800
80
75
70
SWITCHING WAVEFORMS
V
I
INPUT OVERVOLTAGE
PROTECTION RESPONSE
50mV/div
AC-COUPLED
V
IN
5.4V
V
OUT
6.4V
1V/div
(AC-COUPLED)
MAX8901A/B toc9
V
LX
10V/div
0V
10V/div
0V
V
OUT
I
LX
100mV/div
AC-COUPLED
100mA/div
0mA
1μs/div
I
LEDs
20mA/div
0mA
V
LX
20ms/div
20mA/div
0V
STARTUP AND SHUTDOWN
RESPONSE (MAX8901A)
MAX8901A/B toc11
STARTUP AND SHUTDOWN
RESPONSE (MAX8901B)
MAX8901A/B toc12
C2 = 0.1μF
V
ON
2V/div
0V
V
ON
2V/div
0V
V
OUT
10V/div
0V
V
OUT
10V/div
0V
100mA/div
I
SUPPLY
0mA
20mA/div
0mA
10ms/div
I
SUPPLY
I
LEDs
100mA/div
0mA
20mA/div
0mA
10ms/div
I
LEDs
_______________________________________________________________________________________
5
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