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MP1521
High Efficiency White LED Driver
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.
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
Ordering Information
Part Number
MP1521EK MP1521EQ EV0005 EV0021
Package
MSOP10 QFN16 (3x3)
Temperature
-20 to +85C -20 to +85C
MP1521EK Evaluation Board MP1521EQ Evaluation Board
For Tape & Reel, add suffix -Z (i.e., MP1521EK-Z) For Lead Free, add suffix -LF (i.e., MP1521EK-LF-Z)
Typical Application Circuit (One String of Six (6) LEDs)
L1 D1
1
VIN
CIN
Efficiency vs LED current, 1 string of 6 Using Toko D62CB 47H Inductor 100 Efficiency (%) 90 80 70 60 50 5 10 15 20 25 LED Current (mA) VIN = 5V VIN = 4V VIN = 3V
IN
SW
10
ON OFF
MP1521 EN
2
COUT GND
9
GND
EN
3
REF
OLS
8
BRT/ PWM
4
BRT/PWM
FB1
7
White LEDs
5
FB3
FB2
6
MP1521 Rev 2.7 10/06/04
www.monolithicpower.com
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MP1521
High Efficiency White LED Driver
Monolithic Power Systems
Absolute Maximum Ratings
Supply Voltage (VIN) Switch Voltage to GND VEN, VREF, VBRT, VFB1, VFB2, VFB3 Storage Temperature 28V -0.5V to 28V -0.3V to 6V -55C to +150C
Recommended Operating Conditions
Supply Voltage (VIN) Operating Temperature Switch Voltage to GND 2.7V to 25V -20C to +85C -0.5V to 25V 150C/W 60C/W
Package Thermal Characteristics
Thermal Resistance, JA (MSOP10) Thermal Resistance, JA (QFN16)
Electrical Characteristics (VIN = 5.0V, TA = 25C unless specified otherwise)
Parameters Supply Current (shutdown) Supply Current (quiescent) Minimum Off Time, normal operation Minimum Off Time, start-up (Note 1) UVLO Under Voltage Lockout Enable Threshold Hysterisis Leakage Current Open Load Shutdown Threshold Leakage Current Reference Output Voltage Load Regulation Line Regulation Feedback Comparator Threshold Hysterisis (Note 2) FB Input Bias Current PWM Mode Output-Off Threshold BRT Input Bias BRT Full Scale Threshold (Note 3) Output Switch Switch On Resistance (Note 2) RON Switch Current Limit Leakage Current Thermal Shutdown (Note 2) Symbol IIN (OFF) IIN (ON) tOFF (NORMAL) tOFF (START) Condition Min VEN<0.4V VEN >1.5V, VBRT=0V, VFB=0V VEN >1.5V, VBRT =0.6V 400 VFB =0 VEN >1.5V, VBRT =0.6V, 1.5 VFB =0V VIN RISING VIN FALLING 2.1 1.9 0.8 VEN=3V Measured at OLS Pin VOLS=15V VOLS=25V IREF=0A IREF=0 to 100A VIN =3 to 15V, IREF=0A VBRT =1.2V VBRT =1.2V VFB=0.2V VBRT=0.6V 26 45 1.20 1.235 2.5 2.5 400 30 -50 -30 1.0 60 Typ 1 550 500 Max 3 700 700 2.4 2.6 2.4 2.0 1 29 1 70 1.27 5 5 420 0 0.26 0 1.2 VIN=5.0V 300 VSW=25V 160 0.5 400 0.6 5 Units A A nS S V V V mV A V A A V mV mV mV mV nA V nA V mA A C
380 -150 0.18 -100
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 Rev 2.7 10/06/04 www.monolithicpower.com 2
MP1521
High Efficiency White LED Driver
Monolithic Power Systems
Pin Description
MSOP10 QFN16
SW
14
NC
16
15
IN EN REF BRT FB3
1 2 3 4 5
10 9 8 7 6
SW GND OLS FB1 FB2 NC EN NC REF
1 2 3
13 12
NC GND GND OLS FB1
11 10 8 9
IN
5 4
Top View
6 7
FB3
BRT
Part Marking: MP1521EK
Part Marking: A1xx
Table 1: MP1521 MSOP10 and QFN16 Pin Assignments
MSOP Pin # 1 QFN Pin# 16 Pin Name IN Pin Function 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). Regulator On/Off control input. Logic high (VEN>1V) turns on IC, logic low puts it into low current shutdown mode. Place a 100K resistor in series with EN if it is connected to a voltage greater than 10V. 1.23V reference used for setting the analog control voltage at BRT input. This reference can supply up to 200A to an external load. Do not connect any bypass capacitors to this pin. It is internally compensated. 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. 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. 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. Signal and power ground. Connect directly to ground plane. Output switch pin, power DMOS low-side switch. No Connect
2
2
EN
3
4
REF
4
5
BRT
5 6 7 8
7 8 9 10
FB3 FB2 FB1 OLS
9 10 -
11, 12 14 1, 3, 6, 13, 15
GND SW N/C
MP1521 Rev 2.7 10/06/04
www.monolithicpower.com
FB2
NC
3
MP1521
High Efficiency White LED Driver
Monolithic Power Systems
Figure 2: MP1521 Functional Block Diagram
IN
EN
Internal Regulator & Enable Circuit
UVLO & Thermal Shutdown SW
OLS
17V 160K 1.23V 20K + 500nS One-Shot Timer + Control Logic & Output Driv er
0.5 W Power FET
Open Load Shutdown Comparator
Current Limit Comparator + 20K 1.2V + + + 10K + -
GND
0.25V
REF
Bandgap Reference 1.23V
Feedback Comparator FB1
FB2
FB3
BRT
MP1521 Rev 2.7 10/06/04
www.monolithicpower.com
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MP1521
High Efficiency White LED Driver
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 Rev 2.7 10/06/04
www.monolithicpower.com
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MP1521
High Efficiency White LED Driver
Monolithic Power Systems
Application Circuits
Figure 3: One String of Four (4) LEDs
Efficiency vs LED current using 47H Toko D62CB Inductor Efficiency (%)
90 85
VIN
D1, B130
1
L 47H
CIN 4.7F
IN
SW
10
VIN = 4V VIN = 3V
5 10 15 20
ON
MP1521
EN
2
COUT 1F
GND
80 75
OFF
EN
GND
9
White LEDs
3
REF
OLS
8
LED Current mA Line regulation using 47H Toko D62CB Inductor
BRT
4
BRT
FB1
7
LED Current (mA)
22 21 20 19 18 17 16 15 2.4
5
FB3
FB2
6
20
3.0 VIN (V)
3.6
4.2
Figure 4: One String of Six (6) LEDs (Low inductor height for portables)
L1 D1, B130
1
VIN
CIN 4.7F
85
Efficiency (%)
Efficiency vs VIN using 1.2mm High Sumida CMD4D11 Inductor
IN
SW
10
ON OFF
MP1521 EN
2
COUT 1F GND
9
GND
80 75
6.8H 10H 15H
EN
3
REF
OLS
8
70
BRT
4
BRT
FB1
7
White LEDs
2.5
3
3.5
4
4.5
VIN (V)
5
FB3
FB2
6
LED Current (mA)
Line regulation using 1.2mm High Sumida CMD4D11 Inductor
23.0 21.0 19.0 17.0 15.0
20
6.8H 10H 15H 2.5 3 3.5 4 4.5
VIN (V)
MP1521 Rev 2.7 10/06/04
www.monolithicpower.com
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MP1521
High Efficiency White LED Driver
Monolithic Power Systems
Application Circuits Continued
Figure 5: Two Strings of Four (4) LEDs or Eight (8) LEDs Total
L1 47H
VIN
IN CIN 4.7F
Efficiency vs LED current using 47H Toko D62CB Inductor Efficiency (%) 90 80 VIN = 5V 70 60 50 VIN = 4V VIN = 3V
D1, B130
1
SW
10
ON OFF
MP1521 EN
2
COUT 1uF GND 9 White LEDs
GND
EN
3
REF
OLS 8
BRT
4
BRT
FB1
5
7
15
25
35
45
Total LED Current (mA)
5
FB3
FB2
6
LED current (mA)
20
25 20 15 10 2.5
Line Regulation using 47H Toko D62CB Inductor
20
3
3.5 VIN (V)
4
4.5
Figure 6: Three Strings of Three (3) LEDs or Nine (9) LEDs Total
L1 47H
VIN
D1, B130
1
Efficiency vs LED current using 47H Toko D62CB Inductor 100 Efficiency (%) 90 80 70 60 50 VIN = 5V VIN = 4V VIN = 3V
IN
SW
10
CIN 4.7F
ON
MP1521 EN
2
COUT 1F GND
9
GND
OFF
EN
White LEDs
3
REF
OLS
8
BRT
4
BRT
FB1
7
0
20
40
60
80
LED current (mA)
5
FB3
FB2
6
LED Current (mA)
22 20 18 16 1.4
Line regulation using 47H Toko D62CB Inductor
20
20
20
2.0
2. 6
3.0 VIN (V)
3.6
4.2
MP1521 Rev 2.7 10/06/04
www.monolithicpower.com
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MP1521
High Efficiency White LED Driver
Monolithic Power Systems
Package Information
MSOP10
0.0197(0.500)TYP
0.004(0.100) 0.008(0.200) PIN 1 IDENT . 0.114(2.900) 0.122(3.100) 0.184(4.700) 0.200(5.100)
SEE DETAIL "A"
0.014(0.350)TYP GATE PLANE 0.010(0.250) 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)
0o-6o 0.017(0.400) 0.025(0.600)
DETAIL "A"
NOTE: 1) Control dimension is in inches. Dimension in bracket is millimeters.
QFN16 (3 x 3)
3.00 (0.118) BSC Pin 1 Identification Pin 1 Identification 1 4 0.450 (0.0177) 0.350 (0.0138)
0.18 (0.007) 0.28 (0.011)
16
5
3.00 (0.118) BSC 0.550 (0.0217) 0.450 (0.0177)
Bottom View
13 8
1.400 (0.055) 1.700 (0.067) exp. pad
12 0.90 (0.035) 1.00 (0.039) 1.500 (0.059) Ref.
9
0.178 (0.007) 0.228 (0.009)
0.00 (0.000) 0.05 (0.002)
NOTE: 1) Control dimension is in millimeters. Dimension in bracket is inch.
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.
MP1521 Rev 2.7 10/06/04 (c) 2004 MPS, Inc.
Monolithic Power Systems, Inc. 983 University Ave, Building A, Los Gatos, CA 95032 USA Tel: 408-357-6600 Fax: 408-357-6601 www.monolithicpower.com
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