MP1518
Fixed Frequency
White LED Driver
The Future of Analog IC Technology
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TM
TM
DESCRIPTION
The MP1518 is a step-up converter designed for driving up to 6 ries white LEDs from a single cell Lithium Ion battery. The MP1518 us current mode, fixed frequency architecture to regulate the LED current, which is measured through an external current n resistor. Its low 104mV feedback voltage reduces power loss and improves efficiency. The OV pin monitors the output voltage and turns off the converter if an over-voltage condition is prent due to an open circuit condition.
The MP1518 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload.
The MP1518 is available in small 6-pin TSOT23 or 8-pin QFN (2mm x 2mm) packages.
Also available is the MP1518DJE, which has slightly slower switching slew rate, thus is ideal for applications where low EMI is critical.
EVALUATION BOARD REFERENCES
Board Number Dimensions EV0056 1.9”X x 1.8”Y x 0.4”Z EV1518DG-00A
2.0”X x 1.8”Y x 0.4”Z
FEATURES
• On Board Power MOSFET
• Drives up to 6 Series White LEDs • Up to 87% Efficiency
• Over 1MHz Fixed Switching Frequency • Open Load Shutdown
• Low 104mV Feedback Voltage • Soft-Start/PWM Dimming • UVLO, Thermal Shutdown • Internal Current Limit
• Available in TSOT23-6 and QFN8 Packages
APPLICATIONS
• Cell Phones
• Handheld Computers and PDAs • Digital Still Cameras • Small LCD Displays
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, plea visit MPS website under Quality Assurance. “MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
V
88
868482807876E F F I C I E N C Y (%)
5
101520
LED CURRENT (mA)
Efficiency vs LED Current
ORDERING INFORMATION
Part Number
Package
Top Marking
MP1518DJ* A8
MP1518DJE TSOT23-6
F6
MP1518DG** QFN8 (2x2mm) A8 * For Tape & Reel, add suffix –Z (e.g. MP1518DJ–Z);
For RoHS, compliant packaging, add suffix –LF (e.g. MP1518DJ–LF–Z).
* For Tape & Reel, add suffix –Z (e.g. MP1518DG–Z);
For RoHS, compliant packaging, add suffix –LF (e.g. MP1518DG–LF–Z).
PACKAGE REFERENCE
ABSOLUTE MAXIMUM RATINGS (1)
SW , –0.5V to +28V All .–0.3V to +6.5V
Continuous Power Dissipation (T A = +25°C) (2)
TSOT23-6…………………………………....0.57W QFN8 (2x2mm)……………………………....1.6W –55°C to +150°C
Recommended Operating Conditions (3)
IN .2.5V to 6V V IN to 25V Operating Junction Temp. (T J ).-40°C to +125°C
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Thermal Resistance (4)
θJA θJC
<.110..°C/W QFN8 (2mm x 2mm)...............80......16...°C/W
Notes:
1) Exceeding the ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature T J (MAX), the junction-to-ambient thermal resistance θJA , and the
打卤面ambient temperature T A . The maximum allowable continuous power dissipation at any ambient temperature is calculated by P D (MAX) = (T J (MAX)-T A )/θJA . Exceeding the maximum allowable power dissipation will cau excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage.
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3) The device is not guaranteed to function outside of its
西线风景operating conditions.
4) Measured on JESD51-7, 4-layer PCB.
ELECTRICAL CHARACTERISTICS
V IN = V EN = 5V, T A = +25°C, unless otherwi noted.
Typ
Max Units
Condition Min Parameters Symbol
Operating Input Voltage V IN 2.5 6 V
Supply Current (Shutdown) V EN = 0V 0.1 1 µA
Supply Current (Quiescent) V FB = 0.15V 690 750µA
威客兼职Switching Frequency f SW 1.0 1.3 1.5
MHz
Maximum Duty Cycle V FB = 0V 85 92 %
Under Voltage Lockout
IN Under Voltage Lockout UVLO V IN Rising 2.25 2.45V
Under Voltage Lockout
92 mV Hysteresis
Open Lamp Shutdown
V OV V OV Rising 28 V Threshold
Enable
EN Threshold V EN Rising 1.0 1.35 1.6 V
EN Threshold V EN Rising, V IN = 2.5V 0.8 V
EN Hysteresis 90 mV
EN Input Bias Current V EN = 0V, 5V 1 µA
Feedback
FB Voltage 94 104 114mV
FB Input Bias Current V FB = 0.1V -600 -300 nA
Output Switch
SW On-Resistance (5)R ON 0.5 Ω
SW Current Limit (5)Duty Cycle = 60% 350 mA
Thermal Shutdown (5)160
°C
Notes:
5) Guaranteed by design.
PIN FUNCTIONS
TSOT23-6 Pin #
QFN8 Pin #
Name Pin Function
1 8 SW 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.
2 1, 5 GND Ground.
3 6 FB
Feedback Input. The MP1518 regulates the voltage across the current n resistor between FB and GND. Connect a current n resistor from the bottom
of the LED string to GND. Connect the bottom of the LED string to FB. The regulation voltage is 104mV.
4 4 EN Regulator On/Off Control Input. A high input at EN turns on the converter, and a
绝不饶恕low input turns it off. When not ud, connect EN to the input source for
automatic startup. The EN pin cannot be left floating.
5 3 OV
Over Voltage Input. OV measures the output voltage for open circuit protection.
Connect OV to the output at the top of the LED string.
6 2 IN Input Supply Pin. Must be locally bypasd.
OPERATION
The MP1518 us a constant frequency, peak current mode boost regulator architecture to regulate the ries string of white LEDs. The operation of the MP1518 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 sub-harmonic oscillations at duty cycles greater than 50 percent, a stabilizing ramp is added to the output of the current n 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 increas. This results in more current flowing through the power FET, thus increasing the power delivered to the output.
SW
GND FB
Figure 1—Functional Block Diagram
APPLICATION INFORMATION
Figure 2—Circuit for Driving 3 WLEDs
A typical application circuit can be en in Figure 2. The 3 white LEDs can be driven from a voltage s
upply range of 2.5V to 6V at an output current of 20mA. A 0.22µF output capacitor is sufficient for most applications but an output capacitor up to 1µF may be ud. A 22µH inductor with low DCR (Inductor resistance) is recommended to improve efficiency. A 1µF 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 MP1518. The switching characteristics during normal operation can be en in Figure 3. The MP1518 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 incread by a fourth every 40µs giving a total soft-start time of 120µs.
V SW 5V/div.V OUT AC 50mV/div.
I L
100mA/div.
200ns/div.
Steady State Operation
V IN = 3.6V, 3 LEDS, 20mA
Figure 3—Steady State Operation Figure 4 shows the startup behavior of the MP1518. The ramped voltage that is added to the current n amplifier reduces the current output as the duty cycle increas. As more LEDs are added, the output voltage ris but the current that can be delivered to the load is reduced as well.
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