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 chip-scale package
(UCSPTM) (4 x 4 grid) to minimize PC board area.
Applications
Cell Phones, Smart Phones
PDAs, Digital Cameras, Camcorders
MP3 Players
Other Handhelds with Color Displays
Features
o Proprietary Adaptive 1x/1.5x Modes
o High Efficiency (P
LEDs
/P
BATT
), Up to 92%
o 2% LED Current Matching and Accuracy
o 28mA/LED Drive Capability
o Low Input Ripple and EMI
o Eliminates Ballast Resistors
o Logic or PWM Dimming Control
o Low 0.1µA Shutdown Current
o 2.7V to 5.5V Input Voltage Range
o Soft-Start Limits Inrush Current
o Output Overvoltage Protection
o Thermal Shutdown Protection
o No External Schottky Diode Required
o Tiny 2.1mm x 2.1mm x 0.6mm UCSP Package
MAX1573
White LED 1x/1.5x Charge Pump in UCSP
________________________________________________________________ Maxim Integrated Products
1
UCSP 4
4
OUT
EN1
EN2
C1P
1
A
B
C
D
2
3
4
C2N
C2P
SET
IN
LED4
LED2
C1N
GND
LED3
LED1
TOP VIEW
Pin Configuration
Ordering Information
MAX1573
V
IN
2.7V TO 5.5V
R
SET
ON/OFF
AND
DIMMING
CONTROL
SET
GND
C1N
C1P
C2N
C2P
OUT
LED1
LED2
LED3
LED4
IN
EN1
1
µF
1
µF
1
µF
1
µF
V
OUT
UP TO 4 LEDS
EN2
Typical Operating Circuit
19-2847; Rev 0; 4/03
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.
PART
TEMP RANGE
PIN-PACKAGE
MAX1573EBE-T
-40°C to +85°C
14 UCSP (4 x 4)
UCSP is a trademark of Maxim Integrated Products, Inc.
MAX1573
White LED 1x/1.5x Charge Pump in UCSP
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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)
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, 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
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
IN Operating Voltage
2.7
5.5
V
Undervoltage Lockout Threshold
V
IN
rising or falling, 35mV hysteresis
2.25
2.45
2.60
V
Supply Current
Switching, no load
2
4
mA
Shutdown Supply Current
EN1 = EN2 = OUT = GND, T
A
= +25°C
0.1
10
µA
Soft-Start Completion Time
2.1
ms
SET Bias Voltage
0.570
0.6
0.630
V
SET Leakage in Shutdown
EN1 = EN2 = GND, T
A
= +25°C
0.01
1
µA
SET Current Range
40
130
µA
EN1 = EN2 = IN
190
215
245
EN1 = IN, EN2 = GND
58
65
74
SET to LED_ Current Ratio (I
LED
/I
SET
)
I
SET
= 60µA
EN1 = GND, EN2 = IN
19.5
22
25.0
A/A
LED_ Current Accuracy
E N 1 = E N 2 = IN , R
S E T
= 10k
, T
A
= 0°C to + 85°C ±2.0
%
LED_ Current Matching
I
SET
= 60µA, T
A
= 0°C to +85°C (Note 2)
±2.0
%
Maximum LED_ Sink Current
I
SET
= 130µA, EN1 = EN2 = IN
25.9
28
mA
LED_ Dropout Voltage
I
SET
= 87µA (Note 3)
40
80
mV
LED_ Minimum Regulation Voltage (1.5x Mode)
EN1 = EN2 = IN, I
SET
= 87µA
100
150
200
mV
LED Leakage in Shutdown
EN1 = EN2 = GND, V
LED
= 5.5V, T
A
= +25°C
0.01
1
µA
Maximum OUT Current
V
IN
3.4V, V
OUT
3.9V, EN1 = EN2 = IN
120
mA
1x mode (1 x V
IN
- V
OUT
) / I
OUT
1.5
Open-Loop OUT Resistance
1.5x mode (1.5 x V
IN
- V
OUT
) / I
OUT
10
Switching Frequency
1
MHz
EN1, EN2 Logic High Voltage
V
IN
= 2.7V to 5.5V
1.6
V
EN1, EN2 Logic Low Voltage
V
IN
= 2.7V to 5.5V
0.4
V
EN1, EN2 Input Current
V
EN
_ = GND or 5.5V, T
A
= +25°C
0.01
1
µA
Thermal-Shutdown Threshold
20°C hysteresis
160
°C
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.
MAX1573
White LED 1x/1.5x Charge Pump in UCSP
_______________________________________________________________________________________
3
50
60
70
80
90
100
4.2
3.8
3.7
3.9
3.6
3.5 3.4 3.0
EFFICIENCY (P
LEDs
/P
BATT
)
vs. Li+ BATTERY DISCHARGE
MAX1573 toc01
Li+ BATTERY VOLTAGE, TIME-WEIGHTED (V)
EFFICIENCY (%)
FULL
3/10
1/10
50
60
80
70
90
100
3.0
3.4
3.2
3.6
3.8
4.0
4.2
EFFICIENCY (P
LEDs
/P
BATT
)
vs. SUPPLY VOLTAGE
MAX1573 toc02
SUPPLY VOLTAGE (V)
1/10
3/10
FULL
EFFICIENCY (%)
0
40
20
80
60
100
120
3.0
3.4
3.6
3.2
3.8
4.0
4.2
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1573 toc03
SUPPLY VOLTAGE (V)
BATTERY CURRENT (mA)
FULL
1/10
3/10
0
2
1
5
4
3
8
7
6
9
3.0
3.4
3.2
3.6
3.8
4.0
4.2
INPUT RIPPLE vs. SUPPLY VOLTAGE
MAX1573 toc04
SUPPLY VOLTAGE (V)
INPUT RIPPLE (mV
RMS
)
FULL
3/10
1/10
10
13
12
11
15
14
19
18
17
16
20
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
LED CURRENT vs. SUPPLY VOLTAGE
MAX1573 toc05
SUPPLY VOLTAGE (V)
LED CURRENT (mA)
LED4
LED2
LED1
LED3
17.5
17.4
17.3
17.2
17.1
17.0
16.9
16.8
16.7
16.6
16.5
-40
-20 -10
-30
0 10 20 30 40 50 60 70 80
LED CURRENT vs. TEMPERATURE
MAX1573 toc06
TEMPERATURE (
°C)
LED CURRENT (mA)
0
15
10
5
20
25
30
5
9
8
6
7
10 11 12 13 14 15
LED CURRENT vs. R
SET
MAX1573 toc07
R
SET
(k
)
LED CURRENT (mA)
FULL
1/10
3/10
Typical Operating Characteristics
(V
IN
= 3.6V, EN1 = EN2 = IN, C
IN
= C1 = C2 = C
OUT
= 1µF, R
SET
= 7.50k
, T
A
= +25°C, unless otherwise noted.)
500ns/div
20mV/
div
10mA/
div
20mV/
div
V
IN
I
IN
V
OUT
TYPICAL OPERATING WAVEFORMS
IN 1x MODE
MAX1573 toc08
3.6V Li+ BATTERY INPUT
500ns/div
20mV/
div
10mA/
div
20mV/
div
V
IN
I
IN
V
OUT
TYPICAL OPERATING WAVEFORMS
IN 1.5x MODE
MAX1573 toc09
3.4V Li+ BATTERY INPUT
MAX1573
White LED 1x/1.5x Charge Pump in UCSP
4
_______________________________________________________________________________________
Typical Operating Characteristics (continued)
(V
IN
= 3.6V, EN1 = EN2 = IN, C
IN
= C1 = C2 = C
OUT
= 1µF, R
SET
= 7.50k
, T
A
= +25°C, unless otherwise noted.)
STARTUP AND SHUTDOWN RESPONSE
MAX1573 toc10
500
µs/div
5V/
div
2V/
div
50mA/
div
V
EN_
V
OUT
I
IN
LED_ = 4
17mA
EN1 = EN2
DIMMING RESPONSE
MAX1573 toc11
5
µs/div
2V/
div
50mA/
div
V
ENI1
I
OUT
EN2 = IN
Pin Description
PIN
NAME
FUNCTION
A1
C1P
Transfer Capacitor 1 Positive Connection. See the Component Selection section for capacitor value.
A2
OUT
Output. Bypass to GND with a 1µF ceramic capacitor. Connect to the anodes of all the LEDs. OUT is high
impedance during shutdown.
A3
EN1
Enable, Dimming Control Input 1. EN1 and EN2 control shutdown and the LED current. See Table 1.
A4
EN2
Enable, Dimming Control Input 2. EN1 and EN2 control shutdown and the LED current. See Table 1.
B1
C2N
Transfer Capacitor 2 Negative Connection. See the Component Selection section for capacitor value.
B2
C2P
Transfer Capacitor 2 Positive Connection. See the Component Selection section for capacitor value.
B4
SET
Bias-Current Set Input. Connect a resistor from SET to GND to set the LED bias current (I
SET
). I
SET
= 600mV/R
SET
.
C1
IN
Supply Voltage Input. IN supplies power for the IC. Bypass IN to GND with a 1µF ceramic capacitor.
C3
LED4
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.
C4
LED2
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.
D1
C1N
Transfer Capacitor 1 Negative Connection. See the Component Selection section for capacitor value.
D2
GND
Ground
D3
LED3
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.
D4
LED1
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.
Detailed Description
The MAX1573 is a complete charge-pump buck-boost
converter requiring only four small ceramic capacitors.
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
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 LED1LED4 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
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
LED1LED4 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.
True Shutdown Mode
When EN1 and EN2 are grounded, the MAX1573 is in
shutdown, and the charge pump examines whether the
input voltage is greater than or less than the output volt-
age and shorts the transfer capacitor nodes to either IN
or OUT as necessary. The output is high impedance in
either case.
Thermal Shutdown
The MAX1573 includes a thermal-limit circuit that shuts
down the IC at about +160°C. Turn-on occurs after the
IC cools by approximately 20°C.
MAX1573
White LED 1x/1.5x Charge Pump in UCSP
_______________________________________________________________________________________
5
P
P
N
MAX1573
0.6V
SET
EN2
EN1
C1P
IN
0.15V
BRIGHTNESS
CONTROL
MINIMUM
SELECT
1x/1.5x REGULATED CHARGE PUMP
C1N
C2P C2N
1.25V
OUT
LED1
LED2
LED3
LED4
GND
LDO CURRENT
REGULATOR
LDO CURRENT
REGULATOR
LDO CURRENT
REGULATOR
LDO CURRENT
REGULATOR
Block Diagram
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