19-1621; Rev 2; 2/07
High-Efficiency Step-Up
Current Regulator for LEDs
General Description
The MAX1698 and MAX1698A are efficient drivers for
white or color LEDs. They are ideal for large LED backlit
displays in PDAs and laptop computers. Numerous
benefits include greater simplicity, lower cost, higher
efficiency, longer bulb life, and greater reliability when
compared to fluorescent (CCFL) and electrolumines-
cent (EL) lamps.
The MAX1698/MAX1698A are switch-mode boost con-
trollers in which LED current, rather than output voltage,
is regulated The devices drive series-connected LEDs
with a controlled current that is measured with a typical-
ly 15Ω sense resistor, not an expensive fractional-ohm
value. LED current control and dimming are accom-
plished with an adjust input (ADJ). For larger light out-
put, multiple LED banks can be connected in parallel
with up to 5W total output power.
The MAX1698A has a higher, and more accurately
specified, CS current limit than the MAX1698 for higher-
power applications of 5W or more. Both devices are
supplied in a space-saving 10-pin µMAX package that
occupies half the space of an 8-pin SO. An evaluation
kit (MAX1698EVKIT) is available to speed designs.
♦
Over 90% Efficiency
♦
Lossless, Adjustable LED Brightness
♦
Space-Saving 10-Pin
µMAX
Package
♦
Simpler, Lower Cost, More Reliable Compared
to CCFL or EL Backlights
♦
Up to 5W Output Power
Features
MAX1698/MAX1698A
Ordering Information
PART
MAX1698EUB
MAX1698AEUB
TEMP RANGE
PIN-
PACKAGE
PKG
CODE
U10-2
U10-2
-40°C to +85°C 10µMAX
-40°C to +85°C 10µMAX
Pin Configuration
TOP VIEW
V
CC
1
SHDN
REF
ADJ
GND
2
3
4
5
10
EXT
9
CS
PGND
GND
FB
Applications
Battery-Powered Backlight Applications
Backlight for LCD Panels
Notebook PCs
Handy Terminals
PDAs
MAX1698
MAX1698A
8
7
6
µMAX
Typical Operating Circuit
L
V
BATT
D1
V
OUT
C
OUT
V
CC
V
CC
MAX1698
MAX1698A
SHDN
REF
ADJ
FB
GND
R
FB
R
N
EXT
ON
OFF
CS
PGND
I
LED
________________________________________________________________
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 Step-Up
Current Regulator for LEDs
MAX1698/MAX1698A
ABSOLUTE MAXIMUM RATINGS
V
CC
,
SHDN
to GND ..................................................-0.3V to +6V
EXT, FB, CS, ADJ, REF to GND..................-0.3V to (V
CC
+ 0.3V)
GND to PGND.....................................................................±0.3V
Continuous Power Dissipation (T
A
= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) ............444mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature Range (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,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Supply Voltage
Quiescent Supply Current
Undervoltage Lockout
Undervoltage Hysteresis
FB Regulation Voltage
CS Trip Current
CS Input Current
Minimum Off Time
Maximum On Time
ADJ Start Threshold
ADJ Input Range
FB Input Bias Current
ADJ Input Bias Current
Shutdown Supply Current
REF Output Voltage
REF Load Regulation
REF Short-Circuit Current
REF Power-Supply Rejection
Ratio
EXT Driver Sink/Source Current
EXT Driver On-Resistance
SHDN
Input High Voltage
SHDN
Input Low Voltage
SHDN
Input Bias Current
V
IH
V
IL
I
SHDN
PSRR
V
REF
∆V
REF
V
ADJ
I
FB
I
ADJ
V
FB
= 300mV
ADJ = REF
SHDN
= GND
I
REF
= 0
I
REF
= 0 to 150µA
REF = GND
V
CC
= 2.7V to 5.5V
V
CC
= 5V, EXT = 2V
V
CC
= 5V
V
CC
= 2.7V to 5.5V
V
CC
= 2.7V to 5.5V
V
CC
= 2.7V to 5.5V
-1
2
0.8
1
1.20
I
CS
t
OFF(MIN)
t
ON(MAX)
FB = GND, ADJ = REF
FB = GND, ADJ = REF, CS = GND
0.8
10
30
0.03
-15
-50
0.01
1.25
-2
0.45
+0.3
0.2
8
1.0
15
50
V
FB
ADJ = REF
V
ADJ
= 100mV
FB = GND
MAX1698A
MAX1698
285
18
2.0
0.8
SYMBOL
V
CC
I
CC
V
FB
= 0.3V
Rising edge
2.25
CONDITIONS
MIN
2.7
260
2.4
80
300
24
2.4
1.5
315
30
2.8
2.5
0.8
1.2
20
70
REF
15
50
1
1.30
-25
1
+2
TYP
MAX
5.5
500
2.55
UNITS
V
µA
V
mV
mV
A
A
RMS
µs
µs
mV
V
nA
nA
µA
V
mV
mA
mV/V
A
Ω
V
V
µA
2
_______________________________________________________________________________________
High-Efficiency Step-Up
Current Regulator for LEDs
ELECTRICAL CHARACTERISTICS
(V
CC
= +3.3V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
Supply Voltage
Quiescent Supply Current
Undervoltage Lockout
FB Regulation Voltage
CS Trip Current
Minimum Off Time
Maximum On Time
ADJ Start Threshold
FB Input Bias Current
ADJ Input Bias Current
Shutdown Supply Current
REF Output Voltage
REF Load Regulation
REF Short-Circuit Current
REF Power-Supply Rejection
Ratio
EXT On-Resistance
SHDN
Input High Voltage
SHDN
Input Low Voltage
SHDN
Input Bias Current
V
IH
V
IL
I
SHDN
PSRR
V
REF
∆V
REF
I
FB
I
ADJ
V
FB
= 300mV
ADJ = REF
SHDN
= GND
I
REF
= 0
I
REF
= 0 to 150µA
REF = GND
V
CC
= 2.7V to 5.5V
V
CC
= 5V
V
CC
= 2.7V to 5.5V
V
CC
= 2.7V to 5.5V
V
CC
= 2.7V to 5.5V
-1
2
0.8
1
1.17
t
OFF(MIN)
t
ON(MAX)
V
FB
SYMBOL
V
CC
I
CC
V
FB
= 0.3V
Rising edge
ADJ = REF
V
ADJ
= 100mV
FB = GND
FB = GND, ADJ = REF
FB = GND, ADJ = REF, CS = GND
MAX1698A
MAX1698
2.20
280
13
2.0
0.8
0.6
9
25
-20
-50
CONDITIONS
MIN
2.7
MAX
5.5
500
2.65
320
35
3.0
3.0
1.4
21
75
20
50
1
1.33
-30
1
+2
8
UNITS
V
µA
V
mV
A
µs
µs
mV
nA
nA
µA
V
mV
mA
mV/V
Ω
V
V
µA
MAX1698/MAX1698A
Note 1:
Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
High-Efficiency Step-Up
Current Regulator for LEDs
MAX1698/MAX1698A
Typical Operating Characteristics
(Circuit of Figure 2, V
CC
= V
BATT
= 3.3V, V
ADJ
= V
REF
, T
A
= +25°C, unless otherwise noted.)
OUTPUT CURRENT vs. V
BATT
AND V
CC
MXA1698-01
NORMALIZED OUTPUT CURRENT
vs. ADJ VOLTAGE
MXA1698-02
OUTPUT CURRENT
vs. INPUT VOLTAGE
MXA1698-03
25
vs. V
BATT
20
OUTPUT CURRENT (mA)
vs. V
CC
1.2
NORMALIZED OUTPUT CURRENT
1.0
0.8
0.6
0.4
0.2
22.0
15
OUTPUT CURRENT (mA)
21.5
21.0
10
5
1 CHAIN OF 4 LEDs
0
0
1
2
3
4
5
6
7
8
9
10
V
BATT
, V
CC
(V)
20.5
1 CHAIN OF 4 LEDs
0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
ADJ VOLTAGE (V)
20.0
0
2
4
6
8
10 12 14 16 18 20
INPUT VOLTAGE (V)
BATTERY CURRENT
vs. BATTERY VOLTAGE
MXA1698-04
EXT RISE/FALL TIME vs. C
EXT
MXA1698-05
EFFICIENCY vs. BATTERY VOLTAGE
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
I
OUT
= 80mA
4 CHAINS OF 4 LEDs
0
2
4
6
8
10
MXA1698-06
1000
900
800
4 CHAINS OF 4 LEDs
100
90
80
RISE/FALL TIME (ns)
RISE TIME
100
700
I
OUT,
I
BATT
(mA)
600
500
400
300
200
100
0
0
1
2
I
BATT
70
60
50
40
30
20
FALL TIME
I
OUT
10
0
4
5
6
7
8
9
10
100
400
700
1000 1300 1600 1900 2200
C
EXT
(pF)
3
V
BATT
(V)
BATTERY VOLTAGE (V)
EFFICIENCY vs. OUTPUT CURRENT
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
5
15
25
35
45
55
65
75
85
OUTPUT CURRENT (mA)
V
BATT
= 5V
4 CHAINS OF 4 LEDs
3.3V
0
MXA1698-07
SHUTDOWN/SOFT-START TIMING
MXA1698-08
LED AND INDUCTOR CURRENT
WAVEFORMS
MXA1698-09
100
I
OUT
50mA/div
LED
CURRENT
50mA/div
I
BATT
100mA/div
INDUCTOR
CURRENT
500mA/div
I
OUT
SET TO 80mA, 4 CHAINS OF 4 LEDs
5ms/div
SHDN
5V/div
1µs/div
4
_______________________________________________________________________________________
High-Efficiency Step-Up
Current Regulator for LEDs
Pin Description
PIN
1
2
NAME
V
CC
SHDN
FUNCTION
IC Supply Voltage Input. Power for internal circuitry. Input range is 2.7V to 5.5V.
Active-Low Shutdown Input. In shutdown, the MOSFET turns off, but a current path still exists between the
input and output. The minimum forward voltage of the LED array must exceed the maximum V
BATT
to ensure
that the LEDs are off in shutdown.
1.25V Reference Output. Capable of sourcing 150µA for external loads. This pin is internally compensated.
Do not connect any bypass capacitors at REF.
Adjust Input. Allows dynamic adjustment of the output current. FB regulates to 300mV when ADJ = REF.
Ground
Feedback Input. Connect to the external LED current-sense feedback resistor.
Power Ground
FET Current-Sense Input
Gate Driver Output
MAX1698/MAX1698A
3
4
5, 7
6
8
9
10
REF
ADJ
GND
FB
PGND
CS
EXT
CS
MAX1698
SHDN
UNDERVOLTAGE
LOCKOUT/
SHUTDOWN
V
CC
TRIG
MAX t
ON
Q
V
CC
EXT
ADJ
TRIG
MIN t
OFF
Q
PGND
FB
SOFT-START
1.25V
REFERENCE
REF
GND
Figure 1. Functional Diagram
_______________________________________________________________________________________
5
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