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TM
MP3205
1.3MHz Fixed Frequency 5 White LED Driver
The Future of Analog IC Technology
TM
DESCRIPTION
The MP3205 is a step-up converter designed for driving up to 5 series white LEDs from a single cell Lithium Ion battery. The MP3205 uses current mode, fixed frequency architecture to regulate the LED current, which is measured through an external current sense resistor. Its low 104mV feedback voltage reduces power loss and improves efficiency. The MP3205 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. The MP3205 is available in a small 5-pin TSOT23 package.
FEATURES
* * * * * * * * * * * * * On Board Power MOSFET Drives up to 5 Series White LEDs Up to 87% Efficiency Over 1MHz Fixed Switching Frequency Low 104mV Feedback Voltage Soft-Start/PWM Dimming UVLO, Thermal Shutdown Internal Current Limit Available in a TSOT23-5 Package Cell Phones Handheld Computers and PDAs Digital Still Cameras Small LCD Displays Application
APPLICATIONS
EVALUATION BOARD REFERENCE
Board Number EV3205DJ-00A Dimensions 1.9"X x 1.8"Y x 0.4"Z
"MPS" and "The Future of Analog IC Technology" are Trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
CMDSH-3 VIN 5V LED1 LED2 LED3
5 1 SW IN EN
Efficiency vs LED Current
88 87 86 85 84 83 82 81 80 79 78 77 4 LEDs
LED4 LED5
3
EFFICIENCY (%)
EN
4 2
5 LEDs
MP3205
FB
GND
3 LEDs VIN=3.6V 5 10 15 LED CURRENT (mA) 20
MP3205-TAC-S01
MP3205-EC01
MP3205 Rev. 1.3 7/13/2005
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved.
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TM
MP3205 - 1.3 MHz FIXED FREQUENCY 5 WHITE LED DRIVER
PACKAGE REFERENCE
TOP VIEW SW GND FB 1 2 3 4 EN 5 IN
ABSOLUTE MAXIMUM RATINGS (1)
SW ............................................... -0.5V to +28V All Other Pins.............................. -0.3V to +6.5V Storage Temperature ..............-55C to +150C
Recommended Operating Conditions
(2)
IN Supply Voltage.............................. 2.5V to 6V Output Voltage....................................VIN to 21V Operating Temperature .............-40C to +85C
MP3205-PD01_TSOT23
Thermal Resistance
(3)
TSOT23-5.............................. 220 .... 110.. 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
Part Number* MP3205DJ *
Package TSOT23-5
Temperature -40C to +85C
For Tape & Reel, add suffix -Z (eg. MP3205DJ-Z) For Lead Free, add suffix -LF (eg. MP3205DJ -LF-Z)
ELECTRICAL CHARACTERISTICS
VIN = VEN = 5V, TA = +25C, unless otherwise noted.
Parameter Symbol Using Parameter Set Heading Operating Input Voltage VIN Supply Current (Shutdown) Supply Current (Quiescent) Switching Frequency fSW Maximum Duty Cycle Undervoltage Lockout IN Under Voltage Lockout UVLO Under Voltage Lockout Hysteresis Enable EN Threshold EN Threshold EN Hysteresis EN Input Bias Current Feedback FB Voltage FB Input Bias Current Output Switch SW On-Resistance (4) RON SW Current Limit Thermal Shutdown (4)
Note: 4) Guaranteed by design.
Condition
Min 2.5
Typ
Max 6 1 750 1.5
Units V A A MHz % V mV
VEN = 0V VFB = 0.15V VFB = 0V VIN Rising 1.0 85
0.1 690 1.3 92 2.25 92
2.45
VEN Rising VEN Rising, VIN = 2.5V VEN = 0V, 5V
1.0 0.8
1.35 90
1.6
1 94 -600 104 -300 0.5 350 160 114
V V mV A mV nA mA C
VFB = 0.1V
Duty Cycle = 60%
MP3205 Rev. 1.3 7/13/2005
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved.
2
TM
MP3205 - 1.3 MHz FIXED FREQUENCY 5 WHITE LED DRIVER
PIN FUNCTIONS
Pin # 1 2 3 Name Description SW GND FB Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power inductor and output rectifier to SW. SW can swing between GND and 25V. Ground. Feedback Input. The MP3205 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. Connect the bottom of the LED string to FB. The regulation voltage is 104mV. Regulator On/Off Control Input. A high input at EN turns on the converter, and a low input turns it off. When not used, connect EN to the input source for automatic startup. The EN pin cannot be left floating. Input Supply Pin. Must be locally bypassed.
4 5
EN IN
OPERATION
The MP3205 uses a constant frequency, peak current mode boost regulator architecture to regulate the series string of white LEDs. The operation of the MP3205 can be understood by referring to the block diagram of Figure 1. At the start of each oscillator cycle the FET is turned on through the control circuitry. To prevent subharmonic oscillations at duty cycles greater than 50 percent, a stabilizing ramp is added to the output of the current sense amplifier and the result is fed into the positive input of the PWM comparator. When this voltage equals the output voltage of the error amplifier the power FET is turned off. The voltage at the output of the error amplifier is an amplified version of the difference between the 104mV reference voltage and the feedback voltage. In this way the peak current level keeps the output in regulation. If the feedback voltage starts to drop, the output of the error amplifier increases. This results in more current to flow through the power FET, thus increasing the power delivered to the output.
FB
+ + AMPLIFIER CONTROL LOGIC M1 SW
104mV
PWM COMPARATOR
+ + CURRENT SENSE AMPLIFIER 1.3MHz OSC
MP3205-F03-BD01
GND
Figure 1--Functional Block Diagram
3
MP3205 Rev. 1.3 7/13/2005
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved.
TM
MP3205 - 1.3 MHz FIXED FREQUENCY 5 WHITE LED DRIVER
APPLICATION INFORMATION
VIN 2.5V to 6V
5 IN 4 2 1 SW
CMDSH-3 LED1 LED2 LED3
FB 3
OFF ON
EN GND
MP3205
MP3205_F02_AP_S01
Figure 2--Driving 3 White LEDs
COMPONENT SELECTION
A typical application circuit can be seen in Figure 2. The 3 white LEDs can be driven from a voltage supply range of 2.5V to 6V at an output current of 20mA. A 0.22F output capacitor is sufficient for most applications but an output capacitor up to 1F may be used. A 22H inductor with low DCR (Inductor resistance) is recommended to improve efficiency. A 1F ceramic capacitor is recommended for the input capacitance in the real system. Schottky diodes have fast recovery and a low forward voltage and are recommended. Schottky diodes rated with 100mA to 200mA are sufficient for the MP3205. The switching characteristics during normal operation can be seen in Figure 3. The MP3205 has internal soft-start to limit the amount of current through VIN at startup and to also limit the amount of overshoot on the output. The current limit is increased by a fourth every 40s giving a total soft-start time of 120s.
Figure 4 shows the startup behavior of the MP3205. The ramped voltage that is added to the current sense amplifier reduces the current output as the duty cycle increases. As more LEDs are added, the output voltage rises but the current that can be delivered to the load is reduced as well.
VEN 5V/div.
VOUT 5V/div. IIN 100mA/div.
MP3205_F04_WF02
Figure 4--Startup Waveforms VIN=3.6V, 3 LEDs, 20mA Figure 5 shows the dependence on current limit versus duty cycle.
500
CURRENT LIMIT (mA)
VSW 5V/div. VOUT RIPPLE (AC COUPLED) 50mV/div. IL 100mA/div.
400 300 200 100 0
MP3205_F03_WF01
0
20
Figure 3--Steady-State Operation VIN=3.6V, 3 LEDs, 20mA
MP3205 Rev. 1.3 7/13/2005
40 60 80 DUTY CYCLE (%)
100
MP3205_F05
Figure 5--Current Limit vs. Duty Cycle
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TM
MP3205 - 1.3 MHz FIXED FREQUENCY 5 WHITE LED DRIVER
Setting the LED Current The LED current is controlled by the feedback resistor, R1, in Figure 2. The current through the LEDs is given by the equation 104mV/R1. Table 1 shows the selection of resistors for a given LED current. Table 1--ILED vs. R1
ILED (mA) 1 5 10 15 20 R1 () 104 20.8 10.4 6.93 5.2
signal used in Figure 7 should be 1KHz or below due to the soft start function.
LED1 LED2 LED3 PWM
4
MP3205
EN FB
3
MP3205_F07_S01
Analog and Digital Dimming There are three different ways to control dimming for the MP3205 during normal operation. The first way uses a DC voltage to control the feedback voltage. This can be seen in Figure 6. As the DC voltage increases, current starts flowing down R1, R2 and R3. The loop will continue to regulate the feedback voltage to 104mV. Thus the current has to decrease through the LEDs by the same amount of current as is being injected from the DC voltage source. With a VDC from 0V to 2V, the resistor values shown for R2 and R3 can control the LED current from 0mA to 20mA.
VDC
Figure 7--PWM Dimming Control Using a Logic Signal If the PWM signal is above 1KHz, dimming can be achieved by using the circuit shown in Figure 8.
LED1
MP3205
FB 3
LED2 LED3
PWM
LED1
MP3205_F08_S01
LED2 LED3
Figure 8--Dimming Control Using a Filtered PWM Signal Layout Considerations Careful attention must be paid to the PCB board layout and component placement. Proper layout of the high frequency switching path is critical to prevent noise and electromagnetic interference problems. Due to the high frequency switching the length and area of all the traces connected to the switch node should be minimized. Refer to the evaluation board EV3205DJ-00A for a sample layout of theBMP3205.
MP3205
FB
3
MP3205_F06_S01
Figure 6--Dimming Control Using a DC Voltage Other applications need to use a logic signal to do the dimming. This can be seen in Figure 7. The PWM signal is applied to the EN pin of the MP3205. The LEDs will switch between full load to completely shut off. The average current through the LEDs will increase proportionally to the duty cycle of the PWM signal. The PWM
MP3205 Rev. 1.3 7/13/2005
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved.
5
TM
MP3205 - 1.3 MHz FIXED FREQUENCY 5 WHITE LED DRIVER
VIN 2.5V to 6V
5 IN 4 2
CMDSH-3
1 SW
LED1 LED2 LED3
OFF ON
EN GND
MP3205
FB 3
MP3205_F09
Figure 9--LED Driver with Overload Protection
PACKAGE INFORMATION
TSOT23-5
2 .9 0 B S C 0 .9 5 0 TYP. 0 .9 5 0 TYP. 1 0 T Y P . (2 p l cs) 3
3
C L
1.60BSC
2.80BSC
0
0.25 BSC .
+ 4 - 0 0.10
0 .4 0 0
0 .3 0 0 (M i n ) 0 .5 0 0 (M a x) (5 P L C S )
Ga u g e P l a n e
C L
1.00Max.
0.870.03
S E A T IN G P L A N E 0 .1 2 7 T Y P . 10T Y P . (2 p l c s )
0.00- 0.10
D ime n sio n s a re in millime te rs
Note: 1.Dimens ions and toleranc es are as per A NSI Y 14.5M, 1994. 2. Die is f ac ing up f or mold. Die is f ac ing dow n f or trim/f orm, ie. Rev ers e trim/f orm 3 Dimens ions are ex c lus iv e of mold f las h and gate burr. 3. 4.The f ootlength meas uring is bas ed on the gauge plane method. 5. A ll s pec if ic ation c omply to Jedec Spec MO193 Is s ue C.
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.
MP3205 Rev. 1.3 7/13/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved.
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