19-2847; Rev 2; 8/05
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
General Description
The MAX1573 fractional charge pump drives up to four
white LEDs with regulated constant current for uniform
intensity. By utilizing proprietary adaptive 1x/1.5x
modes and ultra-low-dropout current regulators, it
maintains the highest possible efficiency over the full
1-cell Li+ battery input voltage range. The 1MHz fixed-
frequency switching allows for tiny external compo-
nents and the regulation scheme is optimized to ensure
low EMI and low input ripple.
An external resistor sets the full-scale LED current, while
two digital inputs control on/off and select amongst three
levels of brightness. A pulse-width modulation (PWM)
signal can also be used to modulate LED brightness,
requiring no additional components.
The MAX1573 is available in the tiny chip-scale UCSP™
(4 x 4 grid) and 16-pin thin QFN packages.
♦
Proprietary Adaptive 1x/1.5x Modes
♦
High Efficiency (P
LEDs
/P
BATT
), Up to 92%
♦
0.2% LED Current Matching
♦
28mA/LED Drive Capability
♦
Low Input Ripple and EMI
♦
Eliminates Ballast Resistors
♦
Logic or PWM Dimming Control
♦
Low 0.1µA Shutdown Current
♦
2.7V to 5.5V Input Voltage Range
♦
Soft-Start Limits Inrush Current
♦
Output Overvoltage Protection
♦
Thermal Shutdown Protection
♦
No External Schottky Diode Required
♦
Tiny UCSP (2.1mm x 2.1mm x 0.6mm) and Thin
QFN (4mm x 4mm) Packages
Features
MAX1573
Applications
Cell Phones, Smart Phones
PDAs, Digital Cameras, Camcorders
MP3 Players
Other Handhelds with Color Displays
Ordering Information
PART
MAX1573EBE-T
MAX1573ETE
MAX1573ETE+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
14 UCSP (4 x 4)
16 Thin QFN
16 Thin QFN
+
Denotes lead-free package.
Typical Operating Circuit
N.C.
Pin Configurations
LED3
10
GND
1μF
1μF
TOP VIEW
12
11
V
IN
2.7V TO 5.5V
1μF
ON/OFF
AND
DIMMING
CONTROL
C1N
IN
C1P C2N
C2P
OUT
V
OUT
UP TO 4 LEDS
1μF
CIN
IN
C2N
C1P
LED4
9
13
14
8
7
LED1
LED2
SET
EN2
EN1
EN2
MAX1573
MAX1573
LED1
LED2
LED3
15
16
1
C2P
2
OUT
3
EN1
4
N.C.
6
5
SET
GND
R
SET
LED4
THIN QFN
4mm
×
4mm
A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.
Pin Configurations continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
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.
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
MAX1573
ABSOLUTE MAXIMUM RATINGS
IN, OUT, EN1, EN2 to GND ...................................-0.3V to +6.0V
SET, LED1, LED2, LED3, LED4 to GND ......-0.3V to (V
IN
+ 0.3V)
C1N, C2N to GND ..........................................-0.3V to (V
IN
+ 1V)
C1P, C2P to GND ............................................-0.3V to greater of
.............................................................(V
OUT
+ 1V) or (V
IN
+ 1V)
OUT Short Circuit to GND ..........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
14-Bump UCSP (derate 7.36mW/°C above +70°C) ....589mW
16-Pin Thin QFN (derate 16.9mW/°C above +70°C) .1349mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°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
EN1
= V
EN2
= 3.6V, C
IN
= C1 = C2 = C
OUT
= 1µF, T
A
= -40°C to +85°C. Typical values are at T
A
= +25°C, unless otherwise
noted.) (Note 1)
PARAMETER
IN Operating Voltage
Undervoltage Lockout Threshold
Supply Current
Shutdown Supply Current
Soft-Start Completion Time
SET Bias Voltage
SET Leakage in Shutdown
SET Current Range
EN1 = EN2 = IN
SET to LED_ Current Ratio (I
LED
/I
SET
)
LED_ Current Accuracy
LED_ Current Matching
Maximum LED_ Sink Current
LED_ Dropout Voltage
LED_ Minimum Regulation Voltage (1.5x Mode)
LED Leakage in Shutdown
Maximum OUT Current
Open-Loop OUT Resistance
Switching Frequency
EN1, EN2 Logic High Voltage
EN1, EN2 Logic Low Voltage
EN1, EN2 Input Current
Thermal-Shutdown Threshold
V
IN
= 2.7V to 5.5V
V
IN
= 2.7V to 5.5V
V
EN
_ = GND or 5.5V, T
A
= +25°C
20°C hysteresis
0.01
160
1.6
0.4
1
I
SET
= 60µA
EN1 = IN, EN2 = GND
EN1 = GND, EN2 = IN
EN1 = EN2 = IN, R
SET
= 4.64kΩ, T
A
= 0°C to +85°C
I
SET
= 130µA, T
A
= 0°C to +85°C (Note 2)
I
SET
= 130µA, EN1 = EN2 = IN
I
SET
= 87µA (Note 3)
EN1 = EN2 = IN, I
SET
= 87µA
EN1 = EN2 = GND, V
LED
= 5.5V, T
A
= +25°C
V
IN
≥
3.4V, V
OUT
≥
3.9V, EN1 = EN2 = IN
1x mode (1 x V
IN
- V
OUT
) / I
OUT
1.5x mode (1.5 x V
IN
- V
OUT
) / I
OUT
1
120
1.5
10
100
25.9
EN1 = EN2 = GND, T
A
= +25°C
40
190
58
19.5
219
66
22
±0.6
±0.2
28
40
150
0.01
80
200
1
0.570
V
IN
rising or falling, 35mV hysteresis
Switching, no load, I
SET
= 130µA
EN1 = EN2 = OUT = GND, T
A
= +25°C
CONDITIONS
MIN
2.7
2.25
2.45
2
0.1
2.1
0.6
0.01
0.630
1
130
245
74
25.0
%
%
mA
mV
mV
µA
mA
Ω
MHz
V
V
µA
°C
A/A
TYP
MAX
5.5
2.60
4
10
UNITS
V
V
mA
µA
ms
V
µA
µA
Note 1:
Specifications to -40°C are guaranteed by design and not production tested.
Note 2:
LED_ current matching is defined as: (I
LED
- I
AVG
) / I
AVG
.
Note 3:
Dropout voltage is defined as the LED_ to GND voltage at which the LED_ current drops 10% from the value at V
LED
= 200mV.
2
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
MAX1573
Typical Operating Characteristics
(V
IN
= 3.6V, EN1 = EN2 = IN, C
IN
= C1 = C2 = C
OUT
= 1µF, R
SET
= 7.50kΩ, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY (P
LEDs
/P
BATT
)
vs. Li+ BATTERY DISCHARGE
MAX1573 toc01
EFFICIENCY (P
LEDs
/P
BATT
)
vs. SUPPLY VOLTAGE
MAX1573 toc02
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1573 toc03
100
100
1/10
90
EFFICIENCY (%)
3/10
FULL
120
100
BATTERY CURRENT (mA)
80
60
40
3/10
20
0
1/10
3.0
3.2
3.4
3.6
3.8
4.0
FULL
90
EFFICIENCY (%)
FULL
3/10
1/10
80
80
70
70
60
60
50
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
Li+ BATTERY VOLTAGE, TIME-WEIGHTED (V)
50
3.0
3.2
3.4
3.6
3.8
4.0
4.2
SUPPLY VOLTAGE (V)
4.2
SUPPLY VOLTAGE (V)
INPUT RIPPLE vs. SUPPLY VOLTAGE
MAX1573 toc04
LED CURRENT vs. SUPPLY VOLTAGE
MAX1573 toc05
LED CURRENT vs. TEMPERATURE
17.4
17.3
LED CURRENT (mA)
17.2
17.1
17.0
16.9
16.8
16.7
16.6
16.5
MAX1573 toc06
9
8
INPUT RIPPLE (mV
RMS
)
7
6
5
4
3
2
1/10
1
0
3.0
3.2
3.4
3.6
3.8
4.0
3/10
FULL
20
19
18
LED CURRENT (mA)
17
16
15
14
13
12
11
10
LED3
LED1
LED4
LED2
17.5
4.2
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
LED CURRENT vs. R
SET
MAX1573 toc07
TYPICAL OPERATING WAVEFORMS
IN 1x MODE
30
25
LED CURRENT (mA)
20
15
3/10
10
1/10
5
0
5
6
7
8
9
FULL
MAX1573 toc08
TYPICAL OPERATING WAVEFORMS
IN 1.5x MODE
20mV/
div
MAX1573 toc09
3.6V Li+ BATTERY INPUT
V
IN
3.4V Li+ BATTERY INPUT
V
IN
20mV/
div
I
IN
10mA/
div
I
IN
10mA/
div
V
OUT
20mV/
V
OUT
div
20mV/
div
500ns/div
10 11 12 13 14 15
500ns/div
R
SET
(kΩ)
_______________________________________________________________________________________
3
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
MAX1573
Typical Operating Characteristics (continued)
(V
IN
= 3.6V, EN1 = EN2 = IN, C
IN
= C1 = C2 = C
OUT
= 1µF, R
SET
= 7.50kΩ, T
A
= +25°C, unless otherwise noted.)
STARTUP AND SHUTDOWN RESPONSE
MAX1573 toc10
DIMMING RESPONSE
MAX1573 toc11
V
EN_
5V/
div
V
ENI1
2V/
div
I
IN
50mA/
div
V
OUT
LED_ = 4
✕
17mA
EN1 = EN2
500μs/div
2V/
div
I
OUT
EN2 = IN
5μs/div
50mA/
div
Pin Description
PIN
NAME
TQFN
1
2
3
4
5
6
UCSP
B2
A2
A3
—
A4
B4
C2P
OUT
EN1
N.C.
EN2
SET
Transfer Capacitor 2 Positive Connection. See the
Component Selection
section for capacitor value.
Output. Bypass to GND with a 1µF ceramic capacitor. Connect to the anodes of all the LEDs. OUT is
high impedance during shutdown.
Enable, Dimming Control Input 1. EN1 and EN2 control shutdown and the LED current. See Table 1.
No Connection
Enable, Dimming Control Input 2. EN1 and EN2 control shutdown and the LED current. See Table 1.
Bias-Current Set Input. Connect a resistor from SET to GND to set the LED bias current (I
SET
). I
SET
=
600mV/R
SET
.
LED2 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest
voltage on any of the LED_ inputs. Connect LED2 to the cathode of one output LED. Connect LED2 to
IN if this LED is not populated.
LED1 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest
voltage on any of the LED_ inputs. Connect LED1 to the cathode of one output LED. Connect LED1 to
IN if this LED is not populated.
LED4 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest
voltage on any of the LED_ inputs. Connect LED4 to the cathode of one output LED. Connect LED4 to
IN if this LED is not populated.
LED3 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest
voltage on any of the LED_ inputs. Connect LED3 to the cathode of one output LED. Connect LED3 to
IN if this LED is not populated.
Ground
No Connection
FUNCTION
7
C4
LED2
8
D4
LED1
9
C3
LED4
10
11
12
D3
D2
—
LED3
GND
N.C.
4
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
Pin Description (continued)
PIN
NAME
TQFN
13
14
15
16
UCSP
D1
C1
B1
A1
C1N
IN
C2N
C1P
Transfer Capacitor 1 Negative Connection. See the
Component Selection
section for capacitor value.
Supply Voltage Input. IN supplies power for the IC. Bypass IN to GND with a 1µF ceramic capacitor.
Transfer Capacitor 2 Negative Connection. See the
Component Selection
section for capacitor value.
Transfer Capacitor 1 Positive Connection. See the
Component Selection
section for capacitor value.
FUNCTION
MAX1573
Block Diagram
C1P C1N
IN
C2P C2N
OUT
1x/1.5x REGULATED CHARGE PUMP
The MAX1573 utilizes a proprietary 1x/1.5x fractional
charge-pump topology to drive up to four white LEDs
with regulated constant current for uniform intensity.
The MAX1573 operates with a 1MHz fixed frequency.
An external resistor (R
SET
) programs the full-scale LED
current, while two digital inputs control on/off and pro-
vide brightness control.
Output Regulation
EN1
0.15V
BRIGHTNESS
CONTROL
0.6V
MINIMUM
SELECT
P
P
1.25V
EN2
LDO CURRENT
REGULATOR
N
LDO CURRENT
REGULATOR
LED1
LED2
SET
The MAX1573 operates in 1x mode until just above
dropout. Then the MAX1573 switches to 1.5x charge-
pump mode to regulate the lowest of LED1–LED4 to
150mV and maintain constant LED brightness even at
very low battery voltages. Using this topology, there is
no LED brightness change during the 1x/1.5x switchover,
which guarantees no flicker on the display. The
switchover scheme has low hysteresis, minimizing
operation in the less-efficient 1.5x mode. The 1x mode
produces almost no ripple, while the 1.5x mode regu-
lates the output voltage by controlling the rate at which
the transfer capacitors are charged. In this way, the
switching frequency remains constant for reduced input
ripple and stable noise spectrum.
Soft-Start
LDO CURRENT
REGULATOR
LED3
MAX1573
LDO CURRENT
REGULATOR
LED4
GND
Detailed Description
The MAX1573 is a complete charge-pump buck-boost
converter requiring only four small ceramic capacitors.
The MAX1573 includes soft-start circuitry to limit inrush
current at turn-on. When starting up with an output
voltage that is not near the input voltage, the output
capacitor is charged directly from the input with a DAC-
ramped current source (with no charge-pump action)
until the output voltage is near the input voltage. Once
this occurs, the charge pump determines if 1x or 1.5x
mode is required. In the case of 1x mode, the soft-start
is terminated and normal operation begins. In the case
of 1.5x mode, soft-start operates until the lowest of
LED1–LED4 reaches regulation. If an overload condi-
tion occurs, soft-start repeats every 2.1ms. If the output
is shorted to ground, the output current is limited by
the MAX1573 fractional-switching technique.
_______________________________________________________________________________________
5
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