MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 1
Monolithic Power Systems
General Description
The MP1521 is a constant-current Boost
Regulator. This IC has three individual
current-sensing feedbacks, which are ideal for
driving multiple strings of series connected
LEDs. The OLS pin is designed for detecting
loose or open LED connections.
The IC uses a peak current, constant minimum
off-time architecture. The feedback pins
measure voltage across sense resistors in
series with the LED strings. When supplying a
bias current of 20mA, the voltage drop across
the sense resistor is only 0.4V to minimize
power loss. Either a DC voltage or a PWM
signal at the BRT/PWM input can control the
LED brightness.
The MP1521 has an on board power MOSFET
switch that is protected by current limit, open
load shutdown, thermal shutdown, and under
voltage lockout.
Ordering Information
Part Number ∗ Package Temperature
MP1521EK MSOP10
-20° to +85°C
MP1521EQ QFN16 (3x3)
-20° to +85°C
EV0005 MP1521EK Evaluation Board
EV0021 MP1521EQ Evaluation Board
∗ For Tape & Reel, add suffix –Z (i.e., MP1521EK–Z)
For Lead Free, add suffix –LF (i.e., MP1521EK–LF–Z)
Features
On Board Power MOSFET
Drive 9 White LEDs from 2.7V Input
Drive 15 White LEDs from 5V Input
Up to 90% Efficiency
Over 80mA Output Current Capacity
Open Load Shutdown
Low Current Sensing Feedback Voltage
Up to 3 String Current Sensing Feedback
Analog and Digital PWM Brightness Control
UVLO, Thermal Shutdown
Soft Start
Internal Current Limit
Available in Compact MSOP10 and
Tiny 3 mm x 3 mm QFN16 Package
Evaluation Boards Available
Applications
Handheld Computers, Cell phones, PDAs,
Digital and Video Cameras, Small LCD
Displays
Li Ion and NiMH Battery Applications
Typical Application Circuit (One String of Six (6) LEDs)
8
7
IN
BRT/PWM FB1
OLS
SW 10
GND 9
CIN
COUT
EN
REF
4
3
2
1 D1
MP1521
L1
6 5 FB2
FB3
White LE D s
BRT/
PWM
EN
GND
OFF ON
VIN
Efficiency vs LED current, 1 string of 6
Using Toko D62C B 47µH Inductor
50
60
70
80
90
100
5 10 15
20
25
LED Current (mA)
Effi cien cy (%)
VIN = 5V
VIN = 4V
VIN = 3V
MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 2
Monolithic Power Systems
Absolute Maximum Ratings
Supply Voltage (VIN) 28V
Switch Voltage to GND -0.5V to 28V
VEN, VREF, VBRT, VFB1, VFB2, VFB3 –0.3V to 6V
Storage Temperature -55°C to +150°C
Recommended Operating Conditions
Supply Voltage (VIN) 2.7V to 25V
Operating Temperature -20°C to +85°C
Switch Voltage to GND -0.5V to 25V
Package Thermal Characteristics
Thermal Resistance, ΘJA (MSOP10) 150°C/W
Thermal Resistance, ΘJA (QFN16) 60°C/W
Electrical Characteristics (VIN = 5.0V, TA = 25°C unless specified otherwise)
Parameters Symbol Condition Min Typ Max Units
Supply Current (shutdown) IIN (OFF) V
EN<0.4V 1 3
µA
Supply Current (quiescent) IIN (ON) V
EN >1.5V, VBRT=0V, VFB=0V 550 700
µA
Minimum Off Time, normal
operation tOFF (NORMAL) VEN >1.5V, VBRT =0.6V
VFB =0 400 500 700 nS
Minimum Off Time, start-up
(Note 1) tOFF (START) VEN >1.5V, VBRT =0.6V,
VFB =0V 1.5 2.4
µS
UVLO
V
IN RISING 2.1 2.6 V
Under Voltage Lockout V
IN FALLING 1.9 2.4 V
Enable
Threshold 0.8 1.0 2.0 V
Hysterisis 60 mV
Leakage Current VEN=3V 1
µA
Open Load Shutdown
Threshold Measured at OLS Pin 26 29 V
VOLS=15V 1
µA
Leakage Current VOLS=25V 45 70
µA
Reference
Output Voltage IREF=0A 1.20 1.235 1.27 V
Load Regulation IREF=0 to 100µA 2.5 5 mV
Line Regulation VIN =3 to 15V, IREF=0A 2.5 5 mV
Feedback Comparator
Threshold VBRT =1.2V 380 400 420 mV
Hysterisis (Note 2) VBRT =1.2V 30 mV
FB Input Bias Current VFB=0.2V -150 -50 0 nA
PWM Mode
Output-Off Threshold 0.18 0.26 V
BRT Input Bias VBRT=0.6V -100 -30 0 nA
BRT Full Scale Threshold
(Note 3) 1.2 V
Output Switch
Switch On Resistance (Note 2) RON V
IN=5.0V 0.5 0.6
Ω
Switch Current Limit 300 400 mA
Leakage Current VSW=25V 5
µA
Thermal Shutdown (Note 2) 160 °C
Notes:
1) First 64 pulses after EN switches high.
2) Guaranteed by design.
3) The output current is off when BRT is driven below the output-off threshold and full-scale when driven above the full-scale
threshold. To PWM the output drive BRT above and below these thresholds.
