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TM
MP1528
9 Lamp, 36V Precision White LED Driver
The Future of Analog IC Technology
TM
DESCRIPTION
The MP1528 is a step-up converter designed for driving up to nine (9) series White LEDs (LED) from a single cell Lithium-Ion battery. It regulates the LED current and includes an analog input for varying the LED brightness. The MP1528 uses current limited, variable frequency architecture to regulate the LED current while maintaining high efficiency. The BIAS pin measures the output voltage and turns off the converter if an over voltage condition is present to prevent damage due to an open circuit condition. The LED current is measured with an external current sense resistor. The low 0.4V full-scale regulation threshold and 0.63 power switch minimize power loss. The MP1528 is available in an 8 pin MSOP and a tiny 6 pin 3mm x 3mm QFN packages.
FEATURES
* * * * * * * * * * * Drives up to 9 Series White LEDs Integrated 0.63 Power MOSFET Low 0.4V Full-Scale Current Sense Threshold Over 20mA Output Current Capacity Analog and Digital PWM Brightness Control Open Load Shutdown Soft-Start Internal Current Limit Under Voltage Lockout Thermal Shutdown Available in 8-Pin MSOP and Tiny 3mm x 3mm 6-Pin QFN Packages Handheld Computers PDAs PDA Phones Digital and Video Cameras Small LCD Displays
APPLICATIONS
* * * * *
EVALUATION BOARD REFERENCE
Board Number EV1528DQ-00A Dimensions 2.0" x 1.5" x 0.5"
"MPS" and "The Future of Analog IC Technology" are Trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
D1 B160B VIN LED1
EFFICIENCY (%)
100 90 80 70 60 50 40 30
MP1528_TAC01
Efficiency vs LED Current
VIN = 12V
7 LEDs 6 LEDs
EN
5
EN
SW
3
C3 10nF
8 LEDs 9 LEDs
BRT
6 2
MP1528
BRT GND BIAS FB
4 1
LED9
0
5
10 15 20 25 30 LED CURRENT (mA)
35
MP1528_EC01
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
1
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
PACKAGE REFERENCE
TOP VIEW
TOP VIEW
FB 1 6 BRT
NC FB GND SW 1 2 3 4 8 7 6 5 NC BRT EN BIAS
GND
2
5
EN
SW
3
4
BIAS
MP1528_PD02-MSOP8H
EXPOSED PAD ON BACKSIDE
MP1528_PD01_QFN6
Part Number* MP1528DQ *
Package QFN6 (3mm x 3mm)
Temperature -40C to +85C
Part Number** MP1528DK
Package MSOP8
Temperature -40C to +85C
For Tape & Reel, add suffix -Z (eg. MP1528DQ-Z) For Lead Free, add suffix -LF (eg. MP1528DQ-LF-Z)
** For Tape & Reel, add suffix -Z (eg. MP1528DK-Z)
For Lead Free, add suffix -LF (eg. MP1528DK-LF-Z)
ABSOLUTE MAXIMUM RATINGS (1)
Supply Voltage VBIAS to GND ....................... 42V VSW to GND..................................-0.5V to +42V VEN, VBRT, VFB to GND ....................-0.3V to +6V Storage Temperature.............. -65C to +150C
Recommended Operating Conditions
(2)
Supply Voltage VBIAS ........................ 2.7V to 36V Operating Temperature .............-40C to +85C
Thermal Resistance
(3)
QFN6 (3mm x 3mm) ............... 50 ...... 14... C/W MSOP8 .................................. 150 ..... 65... C/W
Notes: 1) Exceeding these ratings may damage the device. 2) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately 1" square of 1 oz copper.
JA
JC
ELECTRICAL CHARACTERISTICS
VBIAS = VEN = 5.0V, VBRT = 1.2V, TA = +25C, unless otherwise noted.
Parameter Supply Current (Shutdown) Supply Current (Quiescent) Minimum Off Time (Normal Operation) Minimum Off Time (Startup) Under Voltage Lock Out BIAS Under Voltage Lock Out Enable EN High Threshold EN Hysteresis EN Input Leakage Current UVLO Symbol Condition VEN < 0.4V VEN > 2.0V, BRT = GND Min Typ 1 650 330 1.2 VBIAS Rising, 100mV Hysteresis 2.1 0.8 1.2 60 2.65 1.5 150 Max 3 800 Units A A ns s V V mV nA
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
2
TM
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
ELECTRICAL CHARACTERISTICS (continued)
VBIAS = VEN = 5.0V, VBRT = 1.2V, TA = +25C, unless otherwise noted.
Parameter Open Load Shutdown Threshold Bias Current Feedback Comparator FB Regulation Threshold FB Hysteresis FB Input Leakage Current PWM Mode Using BRT Output-Off Threshold BRT Input Leakage Current BRT Full-Scale Threshold Output Switch SW On-Resistance SW Current Limit Thermal Shutdown Symbol Condition Measured at BIAS VBIAS = 20V, VEN < 0.4V VBIAS = 40V, VEN < 0.4V VFB VBRT = 1.2V VFB = 0.2V 0.38 -150 0.18 -100 Min Typ 40 70 0.40 10 -80 5 100 0.42 Max Units V A A V mV nA V nA V mA C
0.27 1.2
VBRT = 0.6V
RON
VBIAS = 5.0V
0.63 950 160
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
3
TM
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
TYPICAL PERFORMANCE CHARACTERISTICS
Circuit on front page, VIN = 3.6V, 9 LEDs, ILED = 20mA, VBRT = 1.2V, TA = +25C, unless otherwise noted.
Feedback Voltage vs Input Voltage
430 420
FB VOLTAGE (mV) FB VOLTAGE (mV)
Feedback Voltage vs BRT Voltage
500
LED CURRENT (mA)
LED Current vs BRT Duty Cycle @ 200Hz
20 18 16 14 12 10 8 6 4 2 0
400 300 200 100 0
410 400 390 380 370 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 5.5
0
1
2 3 4 BRT VOLTAGE (V)
5
0
20 40 60 80 BRT DUTY CYCLE (%)
100
MP1528_TPC01
MP1528_TPC02
MP1528_TPC03
Steady-State Operation
VEN 5V/div.
Startup
Startup into an Open Load
VEN 5V/div. VSW 20V/div.
VSW 10V/div. VBIAS AC 0.2V/div.
VSW 10V/div.
IINDUCTOR 0.5A/div.
VBIAS 10V/div.
VBIAS 20V/div.
MP1528_TPC04
MP1528_TPC05
MP1528_TPC06
Efficiency vs LED Current
100 90
EFFICIENCY (%)
Efficiency vs LED Current
100
VIN =
12V 7.5V 5V 4.2V 3V
Efficiency vs LED Current
100
VIN =
12V 7.5V 5V 4.2V 3V
(6 LEDs)
(8 LEDs)
(9 LEDs)
VIN =
12V 7.5V 5V 4.2V 3V
90
EFFICIENCY (%)
90
EFFICIENCY (%)
80 70 60 50 40 30 0 5 10 15 20 LED CURRENT (mA)
80 70 60 50 40
80 70 60 50 40
25
30
0
5 10 15 20 LED CURRENT (mA)
25
30
0
5 10 15 20 LED CURRENT (mA)
25
MP1528_TPC07
MP1528_TPC08
MP1528_TPC09
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
4
TM
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
PIN FUNCTIONS
Pin # Name Description QFN6 MSOP8 1 2 3 2 3 4 FB GND SW Feedback Input. The MP1528 regulates the voltage across the current sense resistor between FB and GND. Connect a current sense resistor from the bottom of the LED string to GND and connect the bottom of the LED string to FB. The regulation threshold is set at 0.4V for VBRT 1.2V. Ground. Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power inductor and output rectifier to SW, which can swing between GND and 42V. Internal Power Input. BIAS powers the internal circuitry and measures the output voltage for open circuit protection. Connect BIAS to the output at the top of the LED string. If open circuit protection is not required, BIAS may be connected to the input source to reduce power consumption of the MP1528. Regulator On/Off Control Input. A high voltage applied to EN turns on the converter; a low voltage turns it off. When not used, connect EN to the input source for automatic startup. If EN is driven over 6V, place a 100k resistor in series with EN. Never leave EN floating. Analog or PWM Input for Controlling LED Brightness. When used in analog mode, apply a DC voltage of 0.27V to 1.2V. This input voltage is attenuated by 1/3 to set the voltage across the sense resistor at FB. Maximum brightness (20mA) occurs with an application of 1.2V. To control the brightness in PWM mode, apply a PWM signal with a minimum voltage less than 0.18V and a maximum voltage greater than 1.2V (when a voltage less than 0.18V is applied to this pin, the output switch is turned off). The regulator operates at maximum brightness when more than 1.2V is applied. The frequency of the PWM signal must be between 100Hz to 400Hz. No Connect
4
5
BIAS
5
6
EN
6
7
BRT
1, 8
NC
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
5
TM
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
OPERATION
BIAS EN 4 5 29V INTERNAL REGULATOR & ENABLE CIRCUIT UVLO & THERMAL SHUTDOWN 3 SW
1.23V
+ --
OPEN LOAD SHUTDOWN COMPARATOR
CONTROL LOGIC & OUTPUT DRIVER 2 GND 330ns ONE-SHOT TIMER
FEEDBACK COMPARATOR
+ -CURRENT LIMIT COMPARATOR
+ -0.6V 1 FB
MP1528_F01_BD01
+ --
BRT
6
+ -1.2V
Figure 1--Functional Block Diagram The MP1528 utilizes a constant off-time control scheme. For maximum brightness, the BRT pin is biased at or above 1.2V. Its voltage is routed through the unity gain buffer whose output is clamped at 1.2V. A resistor divider from the buffer to the inverting input of the feedback comparator divides the BRT voltage by three to set the current sense threshold. If the FB pin voltage is lower than this threshold the power MOSFET is turned on. The MOSFET and inductor currents increase until the current limit comparator trips at 950mA, turning off the MOSFET for at least 330ns. At the end of the 330ns, if the FB pin is still lower than the current sense threshold, the MOSFET is turned on again. Analog Brightness Adjust Analog brightness adjustments are accomplished by applying a voltage between 0.27V to 1.2V on the BRT pin. PWM Brightness Adjust PWM brightness adjustments are accomplished by driving the BRT pin with a digital signal whose low voltage is below 0.18V and high voltage is greater than 1.2V. A voltage below 0.18V forces the power MOSFET to turn off. A voltage greater than 1.2V will cause the FB pin to regulate at 0.4V. Open Load Shutdown Open Load Shutdown is implemented by connecting the BIAS pin to the top of the LED string. In the fault condition where the connection to the LED is open, VOUT will rise up, as the FB pin has no voltage. Once VOUT exceeds 40V, the MP1528 will cease operation until the EN pin is cycled off and on. Connecting the BIAS pin to the input will disable Open Load Shutdown.
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
6
TM
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
APPLICATION INFORMATION
Setting the LED Current The LED current is set by the voltage at BRT (VBRT) and the sense resistor (R1) at FB. The VBRT range for adjusting the LED current is 0.27V to 1.2V. Over this range, the LED current can be calculated as:
ILED = VBRT 3 x R1
Voltages greater than 1.2V can be applied to BRT. Use 1.2V in the equation if VBRT 1.2V or the BRT pin is left open. For example, the LED current is set to 20mA if VBRT 1.2V (or left open) and R1 = 20. Capacitor Selection A 4.7F to 10F ceramic input capacitor (C1) and a 0.47F to 1F ceramic output capacitor (C2) are recommended for most applications. A capacitor (C3, typically 1nF to 10nF) in parallel with the LED string improves stability, input ripple and output ripple, especially when large inductance values (10H or above) are used. For the best stability over a wide temperature range, use capacitors with a X5R or X7R dielectric. Inductor Selection The MP1528 has a 950mA inductor current limit and can drive up to 9 LEDs at 20mA. Inductance values (for L1) from 4.7H to 22H will work as well. 6.2H or 6.8H is a good choice for high efficiency and small size. To prevent saturation, use an inductor with a saturation current rating that is higher than the device current limit.
Diode Selection The MP1528's high switching frequency demands a high speed rectifier (D1) for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forward voltage drop. Ensure the diode's average and peak current ratings exceed the average output current and peak inductor current. In addition, the diode's reverse breakdown voltage must exceed the output voltage. Layout Careful PC board layout is required due to fast switching. All components must be placed as close to the IC as possible. Keep the path between the inductor L1, diode D1, and output capacitor C2 extremely short for minimal noise and ringing. The feedback components such as the sense resistor R1 must be kept close to the FB pin to prevent noise injection on the FB pin trace. The ground return of C1 and C2 should be tied close to the GND pin. See the MP1528 demo board layout for reference.
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
7
TM
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
PACKAGE INFORMATION
MSOP8
MP1528 Rev. 1.7 2/21/2006
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
8
TM
MP1528 - 9 LAMP, 36V PRECISION WHITE LED DRIVER
QFN6 (3mm x 3mm)
2.90 3.10 PIN 1 ID MARKING 0.35 0.55 1.40 1.60 PIN 1 ID SEE DETAIL A
0.35 0.45 2.90 3.10 0.95 BSC
6
1
PIN 1 ID INDEX AREA
2.20 2.40
4
3
TOP VIEW
BOTTOM VIEW
PIN 1 ID OPTION A R0.20 TYP. 0.80 1.00 0.00 0.05
PIN 1 ID OPTION B R0.20 TYP.
0.20 REF
SIDE VIEW
DETAIL A
2.90 0.80 1.50
NOTE:
1) ALL DIMENSIONS ARE IN MILLIMETERS. 2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH. 3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETER MAX. 4) JEDEC REFERENCE IS MO-229, VARIATION VEEA-2. 5) DRAWING IS NOT TO SCALE.
0.40
2.30 0.95
RECOMMENDED LAND PATTERN
NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications.
MP1528 Rev. 1.7 2/21/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2006 MPS. All Rights Reserved.
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