MPS MP3204 1.3mhz fixed frequency 5 white led driver with open led protection Datasheet

TM
MP3204
1.3MHz Fixed Frequency
5 White LED Driver with Open LED Protection
The Future of Analog IC Technology
TM
DESCRIPTION
FEATURES
The MP3204 is a step-up converter designed
for driving up to 5 series white LEDs from a
single cell Lithium Ion battery. The MP3204
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 OV pin
monitors the output voltage and turns off the
converter if an over-voltage condition is present
due to an open circuit condition.
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The MP3204 includes under-voltage lockout,
current limiting and thermal overload protection
preventing damage in the event of an output
overload. The MP3204 is available in a small
6-pin TSOT23 package.
APPLICATIONS
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•
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EVALUATION BOARD REFERENCE
Board Number
Dimensions
EV3204DJ-00A
1.9”X x 1.8”Y x 0.4”Z
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
Open Load Shutdown
Available in a TSOT23-6 Package
Cell Phones
Handheld Computers and PDAs
Digital Still Cameras
Small LCD Displays
“MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic
Power Systems, Inc.
TYPICAL APPLICATION
VIN
5V
Efficiency vs
LED Current
LED1
LED2
EN
4
2
IN
EN
1
SW
5
OV
MP3204
GND
FB
EFFICIENCY (%)
LED3
6
LED4
LED5
3
MP3204-TAC-S01
88
87
86
85
84
83
82
81
80
79
78
77
4 LEDs
5 LEDs
3 LEDs
VIN=3.6V
5
10
15
LED CURRENT (mA)
20
MP3204-EC01
MP3204 Rev. 1.3
9/23/2005
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TM
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
ABSOLUTE MAXIMUM RATINGS (1)
PACKAGE REFERENCE
SW Voltage.................................. –0.5V to +28V
All Other Pins.............................. –0.3V to +6.5V
Storage Temperature .............. –55°C to +150°C
TOP VIEW
SW
1
6
IN
Recommended Operating Conditions
GND
2
5
OV
FB
3
4
EN
IN Supply Voltage.............................. 2.5V to 6V
Output Voltage....................................VIN to 21V
Operating Temperature ............. –40°C to +85°C
Thermal Resistance
TSOT23
(3)
θJA
θJC
TSOT23-6.............................. 220 .... 110.. °C/W
MP3204-PD01_TSOT23
Part Number*
Package
Temperature
MP3204DJ
TSOT23-6
–40°C to +85°C
*
(2)
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.
For Tape & Reel, add suffix –Z (eg. MP3204DJ–Z)
For Lead Free, add suffix –LF (eg. MP3204DJ–LF–Z)
ELECTRICAL CHARACTERISTICS
VIN = VEN = 5V, TA = +25°C, unless otherwise noted.
Parameters
Symbol
Operating Input Voltage
Supply Current (Shutdown)
Supply Current (Quiescent)
Switching Frequency
Maximum Duty Cycle
Under Voltage Lockout
IN Under Voltage Lockout
Under Voltage Lockout
Hysteresis
Open Lamp Shutdown
Threshold
MP3204 Rev. 1.3
9/23/2005
Condition
VIN
Min
2.5
VEN = 0V
VFB = 0.15V
fSW
VFB = 0V
UVLO
VOV
Typ
1.0
85
VIN Rising
VOV Rising
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0.1
690
1.3
92
2.25
Max
Units
6
1
750
1.5
V
µA
µA
MHz
%
2.45
V
92
mV
28
V
2
TM
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
ELECTRICAL CHARACTERISTICS (continued)
VIN = VEN = 5V, TA = +25°C, unless otherwise noted.
Parameters
Enable
EN Threshold
EN Threshold
EN Hysteresis
Symbol
Condition
Min
Typ
Max
Units
VEN Rising
VEN Rising, VIN = 2.5V
1.0
0.8
1.35
1.6
V
V
mV
1
µA
114
mV
nA
90
EN Input Bias Current
VEN = 0V, 5V
Feedback
FB Voltage
FB Input Bias Current
Output Switch
SW On-Resistance (4)
SW Current Limit
VFB = 0.1V
94
-600
RON
Duty Cycle = 60%
Thermal Shutdown (4)
104
-300
0.5
350
Ω
mA
160
°C
Notes:
4) Guaranteed by design, not tested.
PIN FUNCTIONS
Pin #
Name
1
SW
2
GND
3
FB
4
EN
5
OV
6
IN
MP3204 Rev. 1.3
9/23/2005
Description
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 MP3204 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.
Over Voltage Input. OV measures the output voltage for open circuit protection. Connect
OV to the output at the top of the LED string.
Input Supply. This pin must be locally bypassed.
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TM
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
OPERATION
The MP3204 uses constant frequency, peak
current mode boost regulator architecture to
regulate a series of white LEDs. The operation
of the MP3204 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%, 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
FB
3
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. This is the
manner in which the peak current level keeps
the output in regulation. If the feedback voltage
begins to drop, the output of the error amplifier
increases. This results in more current flowing
through the power FET, thus increasing the
power delivered to the output.
+
+
AMPLIFIER
CONTROL
LOGIC
M1
1 SW
PWM
COMPARATOR
104mV
+
+
2 GND
CURRENT
SENSE
AMPLIFIER
1.3MHz
OSC
MP3204_F01_BD01
Figure 1—Functional Block Diagram
MP3204 Rev. 1.3
9/23/2005
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TM
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
APPLICATION INFORMATION
VIN
2.5V to 6V
CMDSH-3
LED1
LED2
OFF ON
4
2
6
IN
EN
1
SW
MP3204
GND
OV
FB
5
LED3
3
MP3204_F02
Figure 2—Driving 3 White LEDs
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 0.22µF output
capacitor is sufficient for most applications but
an output capacitor of up to 1µF may be used.
A 22µH inductor with low DCR (inductor
resistance) is recommended for improved
efficiency. A 1µF ceramic capacitor is
recommended for the input capacitance in the
real system. Schottky diodes have fast recovery
times and a low forward voltage and are also
recommended. Schottky diodes with ratings of
100mA to 200mA are sufficient for use with the
MP3204. The switching characteristics during
normal operation can be seen in Figure 3. The
MP3204 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 40µs, giving a total soft start time of
120µs.
MP3204 Rev. 1.3
9/23/2005
VSW
5V/div.
VOUT RIPPLE
(AC COUPLED)
50mV/div.
IL
100mA/div.
MP3204_F03
Figure 3—Steady-State Operation
(VIN=3.6V, 3 LEDs, 20mA)
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TM
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
Figure 4 shows the startup behavior of the
MP3204. 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.
MP3204_F04
Figure 4—Startup Waveforms
(VIN=3.6V, 3 LEDs, 20mA)
Figure 5 shows the dependence on current limit
versus duty cycle.
Table 1—ILED vs. R1
ILED (mA)
1
5
10
15
20
R1 (Ω)
104
20.8
10.4
6.93
5.2
Analog and Digital Dimming
There are three different ways to control
dimming for the MP3204 during normal
operation. The first way uses a DC voltage to
control the feedback voltage, which 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
500
CURRENT LIMIT (mA)
LED1
400
LED2
300
LED3
200
MP3204
FB
3
100
0
0
20
40
60
80
DUTY CYCLE (%)
100
MP3204_F06
MP3204_F05
Figure 5—Current Limit vs. Duty Cycle
Figure 6—Dimming Control Using a DC
Voltage
Setting the LED Current
The LED current is controlled by the feedback
resistor, R1, as shown in Figure 2. The current
through the LEDs is equal to 104mV/R1. Table
1 shows the selection of resistors for a given
LED current.
MP3204 Rev. 1.3
9/23/2005
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TM
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
Other applications require the use of a logic
signal to execute the dimming. This can be
seen in Figure 7. The PWM signal is applied to
the EN pin of the MP3204. The LEDs will switch
between full load to complete shutoff. The
average current through the LEDs will increase
proportionally to the duty cycle of the PWM
signal. The signal used in Figure 7 should be
1KHz or below due to the soft-start function.
LED1
LED2
LED3
PWM
4
MP3204
EN
FB
Open Load Protection
Open Load protection will shutoff the MP3204 if
the output voltage goes too high when the OV
pin is tied to the output. In some cases an LED
may fail, which will result in the feedback
voltage always being zero. The part will run at
the maximum duty cycle, boosting the output
voltage higher and higher. By tying the OV pin
to the top of the LED string the MP3204 checks
the said condition and if the output ever
exceeds 28V the MP3204 will shutdown. The
part will not switch on again until the power is
recycled. Figure 9 shows the behavior of the
MP3204 into an open load.
VEN
5V/div.
3
VOV
10V/div.
MP3204_F07
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
MP3204
LED2
FB
3
LED3
PWM
MP3204_F08
Figure 8—Dimming Control Using a Filtered
PWM Signal
MP3204 Rev. 1.3
9/23/2005
VSW
10V/div.
MP3204_F09
Figure 9—Startup Waveforms into an Open
Load (VIN=3.6V)
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
EV3204DJ-00A for a sample layout of
theBMP3204.
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TM
MP3204 – 6V, 1.3MHz WHITE LED DRIVER
PACKAGE INFORMATION
TSOT23-6
2.90 BSC
10°TYP.
(2 plcs)
0.950
TYP.
1.60 BSC
2.80 BSC
3
0.950
TYP.
3
C
L
+ 4°
- 0°
0°
0.25 BSC.
0.400
±0.10
Gauge Plane
0.300(Min)
0.500(Max)
C
L
1.00 Max.
0.87±0.03
(6 PLCS)
0.127 TYP.
10° TYP.
(2 plcs)
SEATING PLANE
0.00-0.10
NOTE:
1. Dimensions and tolerances are as per ANSI
Y14.5M, 1994.
2. Die is facing up for mold. Die is facing
down for trim/form, ie. reverse trim/form.
3. Dimensions are exclusive of mold flash and gate burr.
4. The footlength measuring is based on the
gauge plane method.
5. All specification comply to Jedec Spec MO193 Issue 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.
MP3204 Rev. 1.3
9/23/2005
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2005 MPS. All Rights Reserved.
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