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.
MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 3
Monolithic Power Systems
Pin Description
MSOP10 QFN16
Part Marking: MP1521EK Part Marking: A1xx
Table 1: MP1521 MSOP10 and QFN16 Pin Assignments
MSOP
Pin # QFN
Pin# Pin
Name Pin Function
1 16 IN
Input supply pin. It can be connected to the regulator’s input supply, or to the
output for boot-strapped operation (boot-strapped operation is required for VIN of
less than 3V).
2 2 EN
Regulator On/Off control input. Logic high (VEN>1V) turns on IC, logic low puts it
into low current shutdown mode. Place a 100KΩ resistor in series with EN if it is
connected to a voltage greater than 10V.
3 4 REF
1.23V reference used for setting the analog control voltage at BRT input. This
reference can supply up to 200µA to an external load. Do not connect any
bypass capacitors to this pin. It is internally compensated.
4 5 BRT
Analog or PWM input for controlling LED brightness. When used in analog
mode, apply a DC voltage of 0.3 to 1.2V. This input voltage is attenuated by 1/3
to set the voltage across sense resistors at FB1, FB2, and FB3. Maximum
brightness (20mA) occurs with 1.2V applied. To control brightness in PWM
mode, apply a PWM square wave with a minimum voltage less the 0.18V and a
maximum 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 100 to 400 Hz.
5
6
7
7
8
9
FB3
FB2
FB1
Feedback input for measuring voltage across current-sense resistor that is in
series with LED string. Unused feedback pins must be connected to any used
feedback pin.
8 10 OLS
Open Load Shutdown pin senses regulator output voltage to protect IC during
open load operation. When this pin’s voltage exceeds 28V, the output switch is
shut off. The output switch remains off until the IC is reset by cycling the enable
pin (EN) or input supply (IN) pin.
9 11, 12 GND Signal and power ground. Connect directly to ground plane.
10 14 SW Output switch pin, power DMOS low-side switch.
- 1, 3, 6,
13, 15
N/C No Connect
SW
GND
OLS
FB1
FB2
IN
EN
REF
BRT
FB3
1
2
3
4
5
10
9
8
7
6
NC
EN
NC
REF
Top
View
GND
GND
OLS
FB1
BRT
NC
FB3
FB2
IN
NC
SW
NC
1
2
3
4
5
6
7
8
12
11
10
9
16
15
14
13
MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 4
Monolithic Power Systems
Figure 2: MP1521 Functional Block Diagram
Internal
Regulator
& Enable
Circuit
UVLO &
The r ma l
Shutdown
Control
Logic &
Output
Driver
+
-
GND
+
-
500nS
One-Shot
Time r
+
-
SW
EN
IN
Open Load
Shutdown
Comparator
1.23V
160K
17V
20K
0.25V
Current Limit
Comparator
0.5 W
Power
FET
+
-
FB1
Feedback
Comparator
+
-
10K20K
1.2V
+
-
FB2
+
-
FB3
OLS
REF Bandgap
Reference
1.23V
BRT
MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 5
Monolithic Power Systems
Functional Description
Operation
The MP1521 utilizes a constant off-time
control scheme (Refer to the Block
Diagram). For maximum brightness, the
BRT pin is biased at or above 1.2V. Its
voltage is routed through the unity gain
buffer whose the output of is clamped at
1.2V. A 20K/10K divider from the Buffer to
the non-inverting input of the Feedback
comparator divides the BRT voltage by
three to set the current sense threshold. If
any of the feedback pins FB1, FB2, or FB3
is lower than this threshold the Power FET
is turned on. The Power MOSFET and
inductor current increases until the current
limit comparator trips at 0.5A turning off the
MOSFET for 500ns. At the end of 500ns if
any of the Feedback pins are still lower
than the current sense threshold. The
Power FET is again turned on. This cycle
repeats itself until all three of the feedback
pins exceed the threshold.
Analog Brightness Adjust
Analog Brightness Adjust is accomplished
by applying a voltage between 0.26V to
1.2V on the BRT pin. The 1.23V REF
output can be used to bias a potentiometer
whose wiper drives the BRT pin.
PWM/ Brightness Adjust
PWM Brightness Adjust is accomplished
by driving the BRT pin with a square wave
whose low voltage is below 0.2V and
whose high voltage is greater than 1.2V. A
voltage below 0.2V forces the Power
MOSFET off. A voltage greater than 1.2V
will cause all three feedback pins to
regulate at or above 0.4V
Open Load Shut-Off
Open Load Shut-Off is implemented by
connecting the OLS pin to VOUT. In the
fault condition where the connection to the
LED’s is open, VOUT will rise up, as all the
feedback pins are absent of voltage. Once
VOUT exceeds 28V, the part will cease
operation until the EN pin is cycled off and
on. To disable the open load shut-off
feature, connect the OLS pin to GND.
MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 6
Monolithic Power Systems
8
7
IN
BRT FB1
OLS
SW 10
GND 9
CIN
4.7µF
VIN
COU
T
1µF
EN
REF
4
3
2
1 D1, B130
20
MP1521
L1
6
5 FB2
FB3
White LEDs
EN
GND
OFF ON
BRT
Application Circuits
Figure 3: One String of Four (4) LEDs
Figure 4: One String of Six (6) LEDs (Low inductor height for portables)
8
7
IN
BRT FB1
OLS
SW 10
GND 9
CIN
4.7µF
VIN
COUT
1
µ
F
EN
REF
4
3
2
1 D1, B130
20
MP1521
L
47µH
6 5 FB2
FB3
Whi t e LEDs
BRT
EN
GND
OFF ON
Line regulation using 1. 2mm Hi gh
Sumida CMD4D11 Inductor
15.0
17.0
19.0
21.0
23.0
2.5 33.5 4 4.5
VIN (V)
6.8µH
10µH
15µH
Efficiency vs VIN using 1.2mm High
Sumida CMD4D11 Inductor
70
75
80
85
2.5 33.5 4 4.5
VIN (V)
6.8µH
10µH
15µH
Efficiency (%)
LED Current (m A)
15
16
17
18
19
20
21
22
2.4 3.0 3.6 4.2
VIN (V)
LED Current (m A)
Efficiency vs LED current using
47µH Toko D62CB Inductor
75
80
85
90
VIN = 4V
VIN = 3V
Efficiency (%)
Line regulation using
47µH Toko D62CB Inductor
LED Current mA
5 10 15 20
MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 10/06/04 www.monolithicpower.com 7
Monolithic Power Systems
8
7
IN
BRT FB1
OLS
SW 10
GND 9
CIN
4.7µF
COU
T
1µF
EN
REF
4
3
2
1 D1, B130
2020
MP1521
L1
47µH
6
5 FB2 FB3
Whi t e LED s
BRT
EN
GND
O
FF
ON
20
VIN
Efficiency vs LED current using
47
µ
H Toko D62CB Inductor
50
60
70
80
90
100
020 40 60 80
LED current (mA)
Efficiency (%)
VIN = 5V
VIN = 4V
VIN = 3V
Application Circuits Continued
Figure 5: Two Strings of Four (4) LEDs or Eight (8) LEDs Total
Figure 6: Three Strings of Three (3) LEDs or Nine (9) LEDs Total
Efficiency vs LED current using
47µH Toko D62CB Inductor
50
60
70
80
90
515 25 35 45
Total LED Current (mA)
Efficiency (%)
VIN = 5V
VIN = 4V
VIN = 3V
Line Regulation using
47µH Toko D62CB
Inductor
10
15
20
25
2.5 3 3.5
4
4.5
VIN (V)
LED current (mA)
8
7
IN
BRT FB1
OLS
SW 10
GND 9
CIN
4.7µF
VIN
COUT
1uF
EN
REF
4
3
2
1 D1, B130
20
MP1521
L1
47µH
6 5 FB2 FB3
White LEDs
BRT
EN
GND
OFF
ON
20
Line regulation using
47µH Toko D62CB Inductor
16
20
22
2.
6
3.0 3.6
4.2
VIN (V)
LED Current (m A)
18
2.01.4
MP1521
High Efficiency
White LED Driver
MP1521 Rev 2.7 Monolithic Power Systems, Inc. 8
10/06/04 983 University Ave, Building A, Los Gatos, CA 95032 USA
© 2004 MPS, Inc. Tel: 408-357-6600
♦
Fax: 408-357-6601
♦
www.monolithicpower.com
Monolithic Power Systems
Package Information
MSOP10
NOTE:
1) Control dimension is in inches. Dimension in bracket is millimeters.
SEE DETAIL "A"
0.004(0.100)
0.008(0.200)
GATE PLANE 0.010(0.250)
0.017(0.400)
0.025(0.600)
0o-6oDETAIL "A"
0.014(0.350)TYP
0.014(0.350)TYP
0.114(2.900)
0.122(3.100)
0.032(0.800)
0.044(1.100)
0.008(0.200)REF
0.030(0.750)
0.038(0.950)
0.002(0.050)
0.006(0.150)
0.0197(0.500)TYP
PIN 1
IDENT
.0.114(2.900)
0.122(3.100) 0.184(4.700)
0.200(5.100)
QFN16 (3 x 3)
3.00
(0.118)
BSC
0.18 ( 0 .007)
0.28 ( 0 .011)
0.550 (0.0217)
0.450 (0.0177)
1.400 (0.055)
1.700 (0.067)
ex p. pa d
NOTE:
1) Control dimension is in millimeters. Dimension in bracket is inch.
3.00 (0.118)
BSC
Pin 1
Identification
0.178 (0.007)
0.228 (0.009)
0.90 (0.035)
1.00 (0.039)
0.00 (0.000)
0.05 (0.002)
Pin 1
Identification
1.500
(0.059)
Ref.
16
1 4
5
8
912
13
Bottom
View
0.450 (0.0177)
0.350 (0.0138)
NOTICE: MPS believes the information in this document to be accurate and reliable. However, it is subject to change
without notice. Please contact the factory for current specifications. No responsibility is assumed by MPS for its use or fit to
any application, nor for infringement of patent or other rights of third parties.
