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19-3097; Rev 1; 4/04
KIT ATION EVALU ABLE AVAIL
White LED 1x/1.5x Charge Pump for Main and Sub-Displays
General Description Features
Powers Main and Sub-Display LEDs 85% Average Efficiency (PLED / PBATT) Over Li+ Battery Discharge 2% LED Current Matching Up to 30mA/LED Drive Capability Adaptive 1x/1.5x Mode Switchover Low Input Ripple and EMI Individual 5% to 100% Dimming Through Single-Wire Serial Pulse Interface Low 0.1A Shutdown Current 2.7V to 5.5V Supply Voltage Range Soft-Start Limits Inrush Current Output-Overvoltage Protection Thermal-Shutdown Protection 16-Pin Thin QFN 4mm x 4mm Package
MAX1575
The MAX1575 charge pump drives up to four white LEDs in the main display and up to two white LEDs in the sub-display with regulated constant current for uniform intensity. By utilizing adaptive 1x/1.5x chargepump modes and very-low-dropout current regulators, it achieves high efficiency over the full 1-cell lithiumbattery input voltage range. A 1MHz fixed-frequency switching allows for tiny external components, and the regulation scheme is optimized to ensure low EMI and low input ripple. The MAX1575 uses an external resistor to set the fullscale 100% LED current. Two enable inputs, ENM and ENS, are used for simple on/off controls for the main and sub-displays, respectively. By repeatedly pulsing either enable input, the LEDs can be dimmed in multiple steps down to 5%. Once the desired brightness is set, the MAX1575 maintains that brightness setting as long as the enable input is kept high. If an enable input is kept low for more than 2ms, the LED current for the respective display is set to zero. If both enable inputs are kept low for more than 2ms, the MAX1575 enters shutdown. The MAX1575 is available in a 16-pin 4mm x 4mm thin QFN package (0.8mm max height).
Ordering Information
PART TEMP RANGE -40C to +85C PIN-PACKAGE 16 Thin QFN 4mm x 4mm MAX1575ETE
Applications
Cell Phones with Main and Sub-Displays PDAs/Smart Phones with Up to Six White LEDs
Typical Operating Circuit
1F
Pin Configuration
C1P LED1 LED2 LED3 GND TOP VIEW 2.7V TO 5.5V 1F IN C1N OUT 1F
12 C1N 13 IN 14 C2N 15 C1P 16 1 C2P
11
10
9 8 7 LED4 LED5 LED6 ENM
MAX1575
GND LED1 ENABLE MAIN ON/OFF AND DIMMING ENABLE SUB ON/OFF AND DIMMING LED2 ENM LED3 ENS SET LED6 RSET C2P C2N LED4 LED5 SUB MAIN
MAX1575
6 5
2 OUT
3 SET
4 ENS
THIN QFN 4mm x 4mm
1F
________________________________________________________________ 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 for Main and Sub-Displays MAX1575
ABSOLUTE MAXIMUM RATINGS
IN, OUT, ENM, ENS to GND..................................-0.3V to +6.0V SET, LED_, C1N, C2N to GND.....................-0.3V to (VIN + 0.3V) C1P, C2P to GND.............................................................-0.3V to the greater of (VOUT + 1V) or (VIN + 1V) OUT Short Circuit to GND ..........................................Continuous Continuous Power Dissipation (TA = +70C) 16-Pin Thin QFN 4mm x 4mm (derate 16.9 mW/C above +70C) ............................1349mW Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = 3.6V, VGND = 0V, ENM = ENS = IN, RSET = 6.81k, CIN = C1 = C2 = COUT = 1F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER IN Operating Voltage Undervoltage-Lockout Threshold Undervoltage-Lockout Hysteresis OUT Overvoltage-Protection Threshold No-Load Supply Current Shutdown Supply Current Soft-Start Time SET Bias Voltage SET Leakage in Shutdown SET Current Range SET-to-LED_ Current Ratio (ILED_ / ISET) LED Current Accuracy LED-to-LED Current Matching (Note 2) Maximum LED_ Sink Current LED_ Dropout Voltage LED_ 1x-to-1.5x Transition Threshold LED Leakage in Shutdown Maximum OUT Current Open-Loop OUT Resistance Switching Frequency OUT Pulldown Resistance ENM, ENS High Voltage ENM, ENS Low Voltage ENM, ENS Input Current Shutdown Delay ENM = ENS = GND VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V VEN_ = 0V or 5.5V From falling edge of ENM and ENS 1.0 0.01 2 1.6 0.4 1 3.3 ENM = ENS = GND TA = 0C to +85C TA = -40C to +85C 100% setting TA = +25C to +85C TA = -40C to +85C TA = +25C to +85C TA = -40C to +85C RSET = 4.53k (Note 3) VLED falling ENM = ENS = GND, VLED_ = 5.5V VIN 3.4V, VOUT = 3.9V, 100% setting 1x mode (VIN - VOUT) / IOUT 1.5x mode (1.5 x VIN - VOUT) / IOUT 120 1 4.2 1 5 2.5 10 90 -8 -9.5 -5 -6.5 27.4 30.0 60 100 0.01 100 110 1 1.5 10 30 234 2 +8 +9.5 +5 +6.5 VOUT rising 1MHz switching in 1.5x mode No switching in 1x mode,10% setting ENM = ENS = OUT = GND VIN falling CONDITIONS MIN 2.7 2.25 2.45 35 5 2 0.5 0.1 2 0.6 0.01 1 130 130 2 TYP MAX 5.5 2.60 UNITS V V mV V mA A ms V A A A/A % % mA mV mV A mA MHz k V V A ms
2
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White LED 1x/1.5x Charge Pump for Main and Sub-Displays
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.6V, VGND = 0V, ENM = ENS = IN, RSET = 6.81k, CIN = C1 = C2 = COUT = 1F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER tLO (ENM, ENS) (Figure 1) tHI (ENM, ENS) (Figure 1) Initial tHI (ENM, ENS) (Figure 1) Thermal-Shutdown Threshold Thermal-Shutdown Hysteresis Only required for first EN_ pulse CONDITIONS MIN 0.5 0.5 50 +160 20 TYP MAX 500 UNITS s s s C C
MAX1575
Note 1: Specifications to -40C 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 current into the LED drops 10% from the LED current at VLED_ = 0.2V.
Typical Operating Characteristics
(VIN = 3.6V, ENM = ENS = IN, circuit of Figure 2, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE DRIVING SIX WHITE LEDs
MAX1575 toc01
INPUT CURRENT vs. SUPPLY VOLTAGE DRIVING SIX WHITE LEDs
MAX1575 toc02
INPUT CURRENT vs. SUPPLY VOLTAGE DRIVING FOUR WHITE LEDs
180 160 INPUT CURRENT (mA) 140 120 100 80 60 40 8mA/LED 2mA/LED 2.7 3.0 3.3 3.6 3.9 4.2 20mA/LED SUPPLY VOLTAGE FALLING
MAX1575 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 SUPPLY VOLTAGE FALLING 20 2.7 3.0 3.3 3.6 3.9 2mA/LED 8mA/LED 20mA/LED
200 180 160 INPUT CURRENT (mA) 140 120 100 80 60 40 20 0 2mA/LED SUPPLY VOLTAGE FALLING 8mA/LED 20mA/LED
200
20 0 3.3 3.6 3.9 4.2
4.2
2.7
3.0
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
INPUT CURRENT vs. SUPPLY VOLTAGE DRIVING TWO WHITE LEDs
MAX1575 toc04
INPUT RIPPLE vs. SUPPLY VOLTAGE DRIVING SIX WHITE LEDs
MAX1575 toc05
LED CURRENT MATCHING vs. SUPPLY VOLTAGE
MAX1575 toc06
200 180 160 INPUT CURRENT (mA) 140 120 100 80 60 40 20 0 2.7 3.0 3.3 3.6 3.9 8mA/LED 2mA/LED 20mA/LED SUPPLY VOLTAGE FALLING
70 60 INPUT RIPPLE (mVP-P) 50 40 30 20 10 0 8mA/LED 2mA/LED 20mA/LED
22
21 LED CURRENT (mA)
20
19
18
17 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V)
4.2
SUPPLY VOLTAGE (V)
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3
White LED 1x/1.5x Charge Pump for Main and Sub-Displays MAX1575
Typical Operating Characteristics (continued)
(VIN = 3.6V, ENM = ENS = IN, circuit of Figure 2, TA = +25C, unless otherwise noted.)
OUTPUT CURRENT vs. SUPPLY VOLTAGE DRIVING SIX LEDs AT 20mA EACH
MAX1575 toc07
LED CURRENT vs. RSET
MAX1575 toc08
OPERATING WAVEFORMS (1x)
MAX1575 toc09
123 122 OUTPUT CURRENT (mA) 121 120 119 118
100
VOUT
200mV/div AC-COUPLED 50mV/div AC-COUPLED
LED CURRENT (mA)
VIN 10 IIN
50mA/div
100% BRIGHTNESS SETTING 117 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 SUPPLY VOLTAGE (V) 1 1 10 RSET (k) 100 400ns/div 0mA
OPERATING WAVEFORMS (1.5x)
MAX1575 toc10
STARTUP WAVEFORMS
MAX1575 toc11
MAIN STARTUP WITH SUB-DISPLAY ON
MAX1575 toc12
VOUT
VENM 200mV/div AC-COUPLED AND VENS 50mV/div AC-COUPLED IIN 50mA/div
5V/div
VENM
5V/div
VIN
100mA/div 0
IIN
100mA/div 0
IIN VOUT 2V/div 0 0 400ns/div 1ms/div 1ms/div VOUT 500mV/div
DIMMING RESPONSE
MAX1575 toc13
LINE TRANSIENT 3.8V TO 3.3V TO 3.8V
MAX1575 toc14
VENM AND VENS
2V/div
VIN
1V/div
50mA/div IOUT 0
VOUT
1V/div AC-COUPLED
50mA/div IOUT VOUT 10ms/div 2V/div 0mA 40s/div
4
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White LED 1x/1.5x Charge Pump for Main and Sub-Displays MAX1575
Pin Description
PIN 1 2 3 NAME C2P OUT SET FUNCTION Transfer-Capacitor 2 Positive Connection. Connect a 1F ceramic capacitor from C2P to C2N. Output. Connect a 1F ceramic capacitor from OUT to GND. Connect OUT to the anodes of all the LEDs. OUT is internally pulled down with 5k during shutdown. Current-Set Input. Connect a resistor (RSET) from SET to GND to set the maximum LED current. ILED(MAX) = 234 x 0.6V / RSET. SET is internally biased to 0.6V. SET is high impedance during shutdown. Enable and Dimming Control for LED5 and LED6 (Sub-Display). The first time ENS goes high (50s min), LED5 and LED6 turn on at 100% brightness. Pulsing ENS low dims the LEDs in multiple steps. If ENS is held low for more than 2ms (typ), LED5 and LED6 turn off. When ENM and ENS are both held low for more than 2ms (typ), the IC goes into shutdown mode. See Figure 1. Enable and Dimming Control for LED1-LED4 (Main Display). The first time ENM goes high (50s min), LED1-LED4 turn on at 100% brightness. Pulsing ENM low dims the LEDs in multiple steps. If ENM is held low for more than 2ms (typ), LED1-LED4 turn off. When ENM and ENS are both held low for more than 2ms (typ), the IC goes into shutdown mode. See Figure 1. Sub-Display LEDs Cathode Connection. Current flowing into LED_ is described in the ENS and SET descriptions above. The charge pump regulates the lowest-enabled LED_ voltage to 180mV. Connect LED_ to IN if the LED is not populated. LED_ is high impedance during shutdown. Main-Display LEDs Cathode Connection. Current flowing into LED_ is described in the ENM and SET descriptions above. The charge pump regulates the lowest-enabled LED_ voltage to 180mV. Connect LED_ to IN if the LED is not populated. LED_ is high impedance during shutdown. Ground. Connect GND as close as possible to system ground and to the ground of the input bypass capacitor. Transfer-Capacitor 1 Negative Connection. Connect a 1F ceramic capacitor from C1P to C1N. Supply Voltage Input. Connect a 1F ceramic capacitor from IN to GND. The input voltage range is 2.7V to 5.5V. IN is high impedance during shutdown. Transfer-Capacitor 2 Negative Connection. Connect a 1F ceramic capacitor from C2P to C2N. Transfer-Capacitor 1 Positive Connection. Connect a 1F ceramic capacitor from C1P to C1N. Exposed Paddle. Connect the exposed paddle to GND.
4
ENS
5
ENM
6 7 8 9 10 11 12 13 14 15 16 --
LED6 LED5 LED4 LED3 LED2 LED1 GND C1N IN C2N C1P EP
Detailed Description
The MAX1575 charge pump drives up to four white LEDs in the main display and up to two white LEDs in the sub-display with regulated constant current for uniform intensity. By utilizing adaptive 1x/1.5x chargepump modes and very-low-dropout current regulators, it achieves high efficiency over the 1-cell lithium-battery input voltage range. 1MHz fixed-frequency switching allows for tiny external components and low input ripple.
When the input voltage rises above VOUT by about 50mV, the MAX1575 switches back to 1x mode.
Soft-Start
The MAX1575 includes soft-start circuitry to limit inrush current at turn-on. When starting up, the output capacitor is charged directly from the input with a ramped current source (with no charge-pump action) until the output voltage approaches 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. During the soft-start time, the output current is set to 5% of the maximum set by RSET. In the case of 1.5x mode, soft-start operates until the lowest of LED1-LED6 reaches regulation. If an overload condition occurs, soft-start repeats every 2ms. If the output is shorted to ground (or <1.25V), the part reverts to softstart and the ramped current source.
5
1x to 1.5x Switchover
When VIN is higher than VOUT, the MAX1575 operates in 1x mode and VOUT is pulled up to VIN. The internal current regulators regulate the LED current. As VIN drops, VLED_ eventually falls below the switchover threshold of 100mV and the MAX1575 starts switching in 1.5x mode.
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump for Main and Sub-Displays MAX1575
Setting the Output Current
The LED current at full (100%) brightness is set (up to 30mA) by a resistor, RSET, as follows: RSET = 0.6V x 234 ILED _
Shutdown Mode
When both ENM and ENS are held low for 2ms or longer, the MAX1575 is shut down and put in a low-current mode. OUT is internally pulled to GND with 5k during shutdown.
Overvoltage Protection
If any LED fails as an open circuit, the output voltage is limited to approximately 5V by gating on/off the charge pump. In case any LED_ is floating or grounded, the MAX1575 operates in the same overvoltage-protection mode. To avoid overvoltage-protection mode when using fewer than six LEDs, connect any unused LED_ to IN.
ENM and ENS Dimming Controls
When the LEDs are enabled by driving ENM or ENS high, the LED current initially goes to ILED_. Dimming for the main display is done by pulsing ENM low (500ns to 500s pulse width). Dimming for the subdisplay is done by pulsing ENS low (500ns to 500s pulse width). Each pulse reduces the LED current by 10%, so after one pulse the LED current is 0.9 x ILED. The 10th pulse reduces the current by 5% so the LED current reduces from 0.1 x ILED_ to 0.05 x ILED. The 11th pulse sets the LED current back to ILED_. Figure 1 shows a timing diagram for EN_. Because soft-start is longer than intitial tHI, apply dimming pulses quickly upon startup (after initial tHI) to avoid LED_ current transitioning through full brightness. If dimming control is not required, EN_ work as simple on/off controls. Drive ENM high to enable the main LEDs, or drive ENM low to turn off the main LEDs. Drive ENS high to enable the sub-LEDs, or drive ENS low to turn off the sub-LEDs. Drive both ENM and ENS low to put the IC in low-power shutdown mode.
Thermal Shutdown
The MAX1575 includes a thermal-limit circuit that shuts down the IC at approximately +160C. The part turns on after the IC cools by approximately 20C.
Applications Information
Driving Fewer than Six LEDs
When driving fewer than six LEDs, connect any unused LED_ directly to IN (Figure 3). When connected in this manner, the corresponding LED driver is disabled.
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. Alternately, increasing CIN to 2.2F cuts input ripple in half with only a small increase in footprint. The 1x mode always has very low input ripple.
INITIAL tHI 50s 0 ENM OR ENS 1 2 3 4 5 6 7 8 9 10 11
tSOFT-START 100% 90% 80% 70% tLO 500ns TO 500s 60% 50% tHI 500ns 40% 30% 20% 10% 5% 100% 90% tSHDN 2ms (typ)
ILED_
SHDN
SHDN
Figure 1. EN_ Timing Diagram
6
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump for Main and Sub-Displays MAX1575
C1 1F C2 1F
C1P 2.7V TO 5.5V CIN 1F GND CONTROL AND REFERENCE MAIN ENABLE AND DIMMING SUB ENABLE AND DIMMING ENM 0.18V ENS SUB CONTROL MAIN CONTROL 0.6V CONTROLLED CURRENT MIRROR IN
C1N
C2P
C2N OUT COUT 1F
1x/1.5x REGULATING CHARGE PUMP
ERROR AMP1
OVD 1.25V
SELMIN
LED1
D1
LED2
D2
LED3 ERROR AMP2 SET RSET LED5
D3
LED4
D4
D5
LED6
D6
Figure 2. Functional Diagram and Typical Application Circuit
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7
White LED 1x/1.5x Charge Pump for Main and Sub-Displays MAX1575
Component Selection
1F
Use only ceramic capacitors with an X5R, X7R, or better dielectric. See Table 1 for a list of recommended parts.
PC Board Layout and Routing
C1P 2.7V TO 5.5V 1F IN C1N OUT 1F
MAX1575
GND LED1 ENABLE MAIN ON/OFF AND DIMMING ENABLE SUB ON/OFF AND DIMMING LED2 ENM LED3 ENS SET LED6 RSET C2P C2N LED4 LED5 SUB MAIN
The MAX1575 is a high-frequency switched-capacitor voltage regulator. For best circuit performance, use a solid ground plane and place CIN, COUT, C1, and C2 as close to the MAX1575 as possible. Connect GND to the exposed paddle directly under the IC. Refer to the MAX1575 evaluation kit for an example.
Chip Information
TRANSISTOR COUNT: 5738 PROCESS: BiCMOS
1F
Figure 3. Driving Fewer than Six White LEDs
Table 1. Recommended Components
DESIGNATION VALUE MANUFACTURER Murata CIN, COUT, C1, C2 1F Taiyo Yuden TDK D1-D6 RSET -- As required Nichia Kamaya Panasonic PART GRM155R60J105K JMK107BJ105KA C1005X5R0J105M NSCW215T -- DESCRIPTION 1F 10%, 6.3V X5R ceramic capacitors (0402) 1F 10%, 6.3V X5R ceramic capacitors (0603) 1F 20%, 6.3V X5R ceramic capacitors (0402) White LEDs 1% resistor
8
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White LED 1x/1.5x Charge Pump for Main and Sub-Displays
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
MAX1575
PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm
21-0139
C
1 2
PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm
21-0139
C
2 2
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 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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