MAX1573
19-2847; Rev 2; 8/05
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
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 fixedfrequency switching allows for tiny external components 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.
Features
♦ Proprietary Adaptive 1x/1.5x Modes
♦ High Efficiency (PLEDs/PBATT), 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
Applications
♦ Tiny UCSP (2.1mm x 2.1mm x 0.6mm) and Thin
QFN (4mm x 4mm) Packages
Ordering Information
Cell Phones, Smart Phones
PDAs, Digital Cameras, Camcorders
MP3 Players
Other Handhelds with Color Displays
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.
VIN
2.7V TO 5.5V
C1N
C1P C2N
C2P
OUT
IN
VOUT
UP TO 4 LEDS
1μF
1μF
ON/OFF
AND
DIMMING
CONTROL
EN1
MAX1573
13
IN
14
LED3
LED4
12
11
10
9
8
LED1
7
LED2
MAX1573
LED1
LED2
EN2
CIN
GND
TOP VIEW
1μF
1μF
Pin Configurations
N.C.
Typical Operating Circuit
C2N
15
6
SET
C1P
16
5
EN2
2
3
4
N.C.
RSET
1
EN1
GND
C2P
LED4
SET
OUT
LED3
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
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.
1
MAX1573
General Description
MAX1573
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
ABSOLUTE MAXIMUM RATINGS
IN, OUT, EN1, EN2 to GND ...................................-0.3V to +6.0V
SET, LED1, LED2, LED3, LED4 to GND ......-0.3V to (VIN + 0.3V)
C1N, C2N to GND ..........................................-0.3V to (VIN + 1V)
C1P, C2P to GND ............................................-0.3V to greater of
.............................................................(VOUT + 1V) or (VIN + 1V)
OUT Short Circuit to GND ..........................................Continuous
Continuous Power Dissipation (TA = +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
(VIN = VEN1 = VEN2 = 3.6V, CIN = C1 = C2 = COUT = 1µF, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise
noted.) (Note 1)
PARAMETER
CONDITIONS
IN Operating Voltage
MIN
Undervoltage Lockout Threshold
VIN rising or falling, 35mV hysteresis
Supply Current
Switching, no load, ISET = 130µA
Shutdown Supply Current
EN1 = EN2 = OUT = GND, TA = +25°C
2.25
Soft-Start Completion Time
MAX
UNITS
5.5
V
2.45
2.60
V
2
4
mA
0.1
10
µA
2.1
SET Bias Voltage
SET Leakage in Shutdown
TYP
2.7
0.570
EN1 = EN2 = GND, TA = +25°C
SET Current Range
ms
0.6
0.630
V
0.01
1
µA
130
µA
40
EN1 = EN2 = IN
190
219
245
EN1 = IN, EN2 = GND
58
66
74
EN1 = GND, EN2 = IN
19.5
22
25.0
SET to LED_ Current Ratio (ILED/ISET)
ISET = 60µA
LED_ Current Accuracy
EN1 = EN2 = IN, RSET = 4.64kΩ, TA = 0°C to +85°C
±0.6
%
LED_ Current Matching
ISET = 130µA, TA = 0°C to +85°C (Note 2)
±0.2
%
Maximum LED_ Sink Current
ISET = 130µA, EN1 = EN2 = IN
LED_ Dropout Voltage
ISET = 87µA (Note 3)
LED_ Minimum Regulation Voltage (1.5x Mode)
EN1 = EN2 = IN, ISET = 87µA
LED Leakage in Shutdown
EN1 = EN2 = GND, VLED = 5.5V, TA = +25°C
Maximum OUT Current
VIN ≥ 3.4V, VOUT ≥ 3.9V, EN1 = EN2 = IN
Open-Loop OUT Resistance
25.9
100
mA
40
80
mV
150
200
mV
0.01
1
120
1.5
1.5x mode (1.5 x VIN - VOUT) / IOUT
10
1
VIN = 2.7V to 5.5V
µA
mA
1x mode (1 x VIN - VOUT) / IOUT
Switching Frequency
EN1, EN2 Logic High Voltage
28
A/A
Ω
MHz
1.6
V
EN1, EN2 Logic Low Voltage
VIN = 2.7V to 5.5V
EN1, EN2 Input Current
VEN_ = GND or 5.5V, TA = +25°C
0.01
Thermal-Shutdown Threshold
20°C hysteresis
160
0.4
V
1
µA
°C
Note 1: Specifications to -40°C are guaranteed by design and not production tested.
Note 2: LED_ current matching is defined as: (ILED - IAVG) / IAVG.
Note 3: Dropout voltage is defined as the LED_ to GND voltage at which the LED_ current drops 10% from the value at VLED = 200mV.
2
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
EFFICIENCY (PLEDs/PBATT)
vs. Li+ BATTERY DISCHARGE
EFFICIENCY (PLEDs/PBATT)
vs. SUPPLY VOLTAGE
1/10
70
80
70
60
60
50
50
3.8
3.7
3.6
3.2
Li+ BATTERY VOLTAGE, TIME-WEIGHTED (V)
6
5
4
3
3/10
2
3.6
3.8
4.0
4.2
LED4
19
LED2
17
LED3
15
LED1
14
13
4.2
17.0
16.9
16.8
16.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
LED CURRENT vs. RSET
TYPICAL OPERATING WAVEFORMS
IN 1x MODE
25
5.5
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80
TEMPERATURE (°C)
TYPICAL OPERATING WAVEFORMS
IN 1.5x MODE
MAX1573 toc08
MAX1573 toc07
30
MAX1573 toc03
17.1
16.6
4.0
4.2
17.2
10
3.8
4.0
17.3
0
3.6
3.8
17.4
16.7
3.4
3.6
17.5
11
3.2
3.4
LED CURRENT vs. TEMPERATURE
18
16
3.2
SUPPLY VOLTAGE (V)
1
3.0
1/10
3.0
12
1/10
LED CURRENT (mA)
3/10
LED CURRENT vs. SUPPLY VOLTAGE
LED CURRENT (mA)
INPUT RIPPLE (mVRMS)
7
3.4
20
MAX1573 toc04
FULL
8
40
SUPPLY VOLTAGE (V)
INPUT RIPPLE vs. SUPPLY VOLTAGE
9
60
0
3.0
3.5 3.4 3.0
FULL
20
LED CURRENT (mA)
4.2 3.9
80
MAX1573 toc06
EFFICIENCY (%)
3/10
100
BATTERY CURRENT (mA)
90
FULL
80
FULL
3/10
120
MAX1573 toc02
1/10
MAX1573 toc05
90
EFFICIENCY (%)
100
MAX1573 toc01
100
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
3.6V Li+ BATTERY INPUT
MAX1573 toc09
3.4V Li+ BATTERY INPUT
VIN
20mV/
div
VIN
20mV/
div
IIN
10mA/
div
IIN
10mA/
div
20
FULL
15
3/10
10
1/10
5
20mV/
VOUT
div
VOUT
20mV/
div
0
5
6
7
8
9
10 11 12 13 14 15
500ns/div
500ns/div
RSET (kΩ)
_______________________________________________________________________________________
3
MAX1573
Typical Operating Characteristics
(VIN = 3.6V, EN1 = EN2 = IN, CIN = C1 = C2 = COUT = 1µF, RSET = 7.50kΩ, TA = +25°C, unless otherwise noted.)
MAX1573
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
Typical Operating Characteristics (continued)
(VIN = 3.6V, EN1 = EN2 = IN, CIN = C1 = C2 = COUT = 1µF, RSET = 7.50kΩ, TA = +25°C, unless otherwise noted.)
STARTUP AND SHUTDOWN RESPONSE
DIMMING RESPONSE
MAX1573 toc10
MAX1573 toc11
5V/
div
VEN_
2V/
div
VENI1
50mA/
div
IIN
VOUT
LED_ = 4 ✕ 17mA
EN1 = EN2
2V/
div
IOUT
50mA/
div
EN2 = IN
500μs/div
5μs/div
Pin Description
PIN
NAME
FUNCTION
TQFN
UCSP
1
B2
C2P
Transfer Capacitor 2 Positive Connection. See the Component Selection section for capacitor value.
2
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.
3
A3
EN1
Enable, Dimming Control Input 1. EN1 and EN2 control shutdown and the LED current. See Table 1.
4
—
N.C.
No Connection
5
A4
EN2
Enable, Dimming Control Input 2. EN1 and EN2 control shutdown and the LED current. See Table 1.
6
B4
SET
Bias-Current Set Input. Connect a resistor from SET to GND to set the LED bias current (ISET). ISET =
600mV/RSET.
7
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.
8
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.
9
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.
10
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.
11
D2
GND
Ground
12
—
N.C.
No Connection
4
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
PIN
NAME
FUNCTION
TQFN
UCSP
13
D1
C1N
Transfer Capacitor 1 Negative Connection. See the Component Selection section for capacitor value.
14
C1
IN
Supply Voltage Input. IN supplies power for the IC. Bypass IN to GND with a 1µF ceramic capacitor.
15
B1
C2N
Transfer Capacitor 2 Negative Connection. See the Component Selection section for capacitor value.
16
A1
C1P
Transfer Capacitor 1 Positive Connection. See the Component Selection section for capacitor value.
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 (RSET) programs the full-scale LED
current, while two digital inputs control on/off and provide brightness control.
Output Regulation
EN1
0.15V
1.25V
BRIGHTNESS
CONTROL
0.6V
EN2
MINIMUM
SELECT
P
P
LDO CURRENT
REGULATOR
LED1
LDO CURRENT
REGULATOR
LED2
LDO CURRENT
REGULATOR
LED3
LDO CURRENT
REGULATOR
LED4
N
SET
The MAX1573 operates in 1x mode until just above
dropout. Then the MAX1573 switches to 1.5x chargepump 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 regulates 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
MAX1573
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 DACramped 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 condition 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
MAX1573
Pin Description (continued)
MAX1573
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
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 voltage and shorts the transfer capacitor nodes to either IN
or OUT as necessary. The output is high impedance in
either case.
Applications Information
Dimming Using EN1 and EN2
Use EN1 and EN2 inputs as a digital 2-bit number to
control on/off, 1/10, 3/10, and full current (see Table 1).
RSET programs the full current level (see the Setting the
Output Current section).
Thermal Shutdown
Dimming Using PWM into EN1
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.
Use EN2 for shutdown and drive EN1 with a PWM signal. Current can be varied from 1/10 to full. The waveforms in the Typical Operating Characteristics show the
response time of dimming. EN2 keeps the part on, eliminating any soft-start delay that would impede PWM control, allowing a PWM frequency up to 50kHz (Figure 1).
Setting the Output Current
SET controls the LED bias current. Current flowing into
LED1, LED2, LED3, and LED4 is a multiple of the current
flowing out of SET. Set the output current as follows:
⎛ 0.6V ⎞
ILED _ = K x ⎜
⎟
⎝ RSET ⎠
where K = 22, 66, or 219 (depending upon EN1 and
EN2, see Table 1), and RSET is the resistor connected
between SET and GND (see the Typical Operating
Circuit).
Table 1. EN1/EN2 States
EN1/EN2 STATES
BRIGHTNESS
LED CURRENT
EN1 = low, EN2 = low
Shutdown
ILED = 0
EN1 = low, EN2 = high
1/10 Brightness
ILED = 22 x ISET
EN1 = high, EN2 = low
3/10 Brightness
ILED = 66 x ISET
EN1 = high, EN2 = high
Full Brightness
ILED = 219 x ISET
Dimming Using a Filtered PWM Signal
Use a high-frequency PWM signal to drive an R-C-R filter on the SET pin (Figure 2). A 0% PWM duty cycle
corresponds to 18.7mA/LED, while a 100% PWM duty
cycle corresponds to 0mA/LED. At PWM frequencies
above 5kHz, C3 may be reduced.
Input Ripple
For LED drivers, input ripple is more important than output ripple. Input ripple depends on the source supply’s
impedance. Adding a lowpass filter to the input further
reduces input ripple. Figure 3 shows a C-R-C filter used
to reduce input ripple to less than 2mVP-P when driving
a 75mA load. Alternately, increasing CIN to 2.2µF or
4.7µF yields input ripple of 17mVP-P or 9mVP-P, respectively, with only a small increase in footprint. The 1x
mode always has very low input ripple.
True Shutdown is a trademark of Maxim Integrated Products, Inc.
1μF
1μF
1μF
1μF
C1P C1N
C2P C2N
C1P C1N
C2P C2N
OUT
IN
VIN
1μF
1μF
1μF
MAX1573
EN2
LED1
EN1
LED2
SET
LED3
LED4
RSET
GND
Figure 1. Dimming Using PWM Signal into EN1
6
PWM
INPUT
0 TO
2.5V
R1
14.3kΩ
C3
1μF
R2
14.3kΩ
0 TO 18.7mA/LED
1μF
MAX1573
PWM INPUT
OUT
IN
VIN
EN1
LED1
EN2
LED2
SET
LED3
LED4
RSET
9.09kΩ
GND
Figure 2. Dimming Using Filtered PWM Signal
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
Component Selection
Use ceramic capacitors with an X5R dielectric or better
temperature coefficient. The transfer capacitors may be
reduced in value if the input voltage does not fall below
3.4V, if only two or three LEDs are used, or if four LEDs
are used at 10mA or less. Some typical external component values are shown in Table 2.
Under normal operating conditions, power dissipation
is low. Maximum power dissipation occurs at an input
voltage of 4.2V and all four LEDs (with VF = 4V) are driven with 30mA per LED. The power is calculated as:
PD = [(1.5 x VIN) - VF] x 120mA = 276mW
At higher input voltages, the MAX1573 switches to 1x
mode and power dissipation decreases.
Pin Configurations (continued)
VIN
1Ω
1μF
1μF
C1P C1N
C2P C2N
TOP VIEW
OUT
IN
1
2
3
4
C1P
OUT
EN1
EN2
C2N
C2P
A
1μF
2.2μF
2.2μF
MAX1573
EN1
EN2
LED1
IN
LED2
SET
SET
B
LED4
LED2
LED3
LED1
C
LED3
LED4
C1N
RSET
GND
D
GND
UCSP 4 ✕ 4
Figure 3. C-R-C Filter Reduces Input Ripple
Table 2. Typical Component Values
COMPONENT
Input/Output
Capacitors
Transfer
Capacitors
VALUE (µF)
MANUFACTURER
PART
DESCRIPTION
1
Taiyo Yuden
JMK107BJ105KA
1µF ±10%, 6.3V X5R ceramic capacitor (0603)
1
Taiyo Yuden
JMK107BJ105KA
1µF ±10%, 6.3V X5R ceramic capacitor (0603)
0.47
Taiyo Yuden
LMK107BJ474KA
0.47µF ±10%, 10V X5R ceramic capacitor (0603)
0.22
Taiyo Yuden
LMK107BJ224KA
0.22µF ±10%, 10V X7R ceramic capacitor (0603)
LED
—
Nichia
NSCW215T
RSET
As required
Panasonic
—
White LEDs
±1% resistor (0603)
Chip Information
TRANSISTOR COUNT: 3655
PROCESS: BiCMOS
_______________________________________________________________________________________
7
MAX1573
PC Board Layout and Routing
The MAX1573 is a high-frequency switched-capacitor
voltage regulator. For best circuit performance, use a
solid ground plane and place CIN and COUT as close
to the MAX1573 as possible. Also, place their ground
pads close together and as close as possible to GND.
See the MAX1573 EV kit for an example.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.
24L QFN THIN.EPS
MAX1573
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
E
1
2
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
8
E
2
2
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
16L,UCSP.EPS
PACKAGE OUTLINE, 4x4 UCSP
21-0101
H
1
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
MAX1573
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.
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