MP46885
80V Input, 500mA High
Power LED Driver
The Future of Analog IC Technology
DESCRIPTION
FEATURES
The MP46885 is a high voltage input step-down
switching regulator to deliver a constant current of
up to 0.5A to high power LEDs. It integrates a
high-side high voltage power MOSFET with a
current limit of 1.0A (typical value). The wide 4.5V
to 80V input range accommodates a variety of
step-down applications, making it ideal for
automotive, industry and general lighting
applications. Hysteresis current mode control is
applied for very fast response, which makes the
20kHz dimming frequency possible. MPS’s
proprietary feedback control scheme minimizes
the number of external components while
delivering a LED current with typical ±5%
accuracy.
The switching frequency is up to 2MHz, thus
allowing for small component size. The thermal
shut down, short circuit protection, and optional
output voltage limitation provide reliable, fault
tolerant operations. A 170µA quiescent current
allows its use in battery-powered applications.
Wide 4.5V to 80V Operating Input Range
No Output Capacitor Required
±5% LED Current Accuracy
Hysteretic Control: No Compensation
Up to 2MHz Switching Frequency
Up to 20kHz Dimming Frequency
Dedicated PWM Dimming Control Input
Short circuit protection with integrated high
side MOSFET
Optional Output Voltage Limitation
Thermal shut down
200mV reference voltage for high efficiency
Up to 95% Efficiency
170μA Quiescent Current
Available in SOIC8 with Exposed Pad
Packages
APPLICATIONS
The MP46885 is available in SOIC8 with exposed
pad packages.
High Power LED Driver
Automotive, Industry and General Lighting
Constant Current Source
“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of
Monolithic Power Systems, Inc.
TYPICAL APPLICATION
DIM
PWM
BST
EN
Enable
VIN
VIN
CBST
SW
D1
FB
RFB
MP46885 Rev. 1.0
7/7/2011
CIN
LO
4.5V to 80V
VOUT
GND
ILED
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© 2011 MPS. All Rights Reserved.
1
MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
ORDERING INFORMATION
Part Number*
Package
Top Marking
Free Air Temperature (TA)
MP46885DN
SOIC8E
MP46885
-40C to +85C
* For Tape & Reel, add suffix –Z (e.g. MP46885DN–Z);
For RoHS compliant packaging, add suffix –LF (e.g. MP46885DN–LF–Z)
PACKAGE REFERENCE
(4)
ABSOLUTE MAXIMUM RATINGS (1)
Thermal Resistance
Supply Voltage (VIN)......................-0.3V to +80V
Switch Voltage (VSW)............. -0.5V to VIN + 0.5V
BST to SW ......................................-0.3V to +6V
All Other Pins ..................................-0.3V to +6V
Junction Temperature ...............................150C
Continuous Power Dissipation (TA = +25°C) (2)
............................................................. 2.5W
Lead Temperature ....................................260C
Storage Temperature ............... -65°C to +150C
SOIC8E (Exposed Pad) .......... 50 ...... 10 ... C/W
Recommended Operating Conditions
(3)
Supply Voltage VIN ........................... 4.5V to 75V
EN and DIM Voltages ........................... 0V to 5V
Switching Frequency ................................ 2MHz
Operating Junct. Temp. ........... -40C to +125C
MP46885 Rev. 1.0
7/7/2011
θJA
θJC
Notes:
1) Exceeding these ratings may damage the device.
2) The maximum allowable power dissipation is a function of the
maximum junction temperature TJ(MAX), the junction-toambient thermal resistance θJA, and the ambient temperature
TA. The maximum allowable continuous power dissipation at
any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/θJA. Exceeding the maximum allowable power dissipation
will cause excessive die temperature, and the regulator will go
into thermal shutdown. Internal thermal shutdown circuitry
protects the device from permanent damage.
3) The device is not guaranteed to function outside of its
operating conditions.
4) Measured on JESD51-7 4-layer board.
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2
MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
ELECTRICAL CHARACTERISTICS
VIN = 60V, TA= +25C, unless otherwise noted.
Specifications over temperature are guaranteed by design and characterization.
Parameter
Symbol Condition
VIN UVLO Threshold
VIN UVLO Hysteresis
Shutdown Supply Current
Quiescent Supply Current
Upper Switch On Resistance (5)
Upper Switch Leakage Current
Current Limit
EN Up Threshold
EN Threshold Hysteresis
EN Input Current
EN Sinking Current
DIM Up Threshold
DIM Threshold Hysteresis
DIM Input Current
RDS(ON)
ISWLK
IPK
VENH
VENHY
IENI
IENS
VDIMH
VDIMHY
IDIM
DIM On Propagation Delay
TDIMDH
DIM Off Propagation Delay
TDIMDL
Feedback Voltage Threshold High (5)
VFBH
Feedback Voltage Threshold Low (5)
VFBL
FB Pin Input Current
FB Propagation Delay to Output
High
TFBDH
FB Propagation Delay to Output
High
TFBDL
Thermal Shutdown
IFB
VEN = 0V
No load, VFB = 250mV
VBST – VSW = 5V
VEN = 0V, VSW = 0V
VFB = 0.15V
Min
Typ
Max
Units
3.6
4.0
0.4
2
170
360
0.01
1.0
1.55
320
0.01
2
1.15
300
4.4
V
V
µA
µA
mΩ
µA
A
V
mV
µA
µA
V
mV
µA
0.75
1.4
VEN =5V
VEN =2V
0.8
VDIM =5V or 0V
VFB=0V, VDIM Rising edge to
VSW Rising Edge
VFB=0V, VDIM Falling edge to
VSW Falling Edge
4.5V < VIN < 75V, VFB rising
from 0V until VSW < 30V
4.5V < VIN < 75V, VFB falling
from 0.25V until VSW > 30V
VFB=5V or 0V
Falling edge of VFB from 0.25V
to 0V to VSW rising edge
-1
5
220
1
1.7
1
3
1.5
1
50
ns
50
ns
210
215
220
mV
180
185
190
mV
300
nA
-300
100
ns
Rising edge of VFB from 0V to
0.25V to VSW falling edge
100
ns
Hysteresis = 20C
150
C
Note:
5) Guaranteed by design.
MP46885 Rev. 1.0
7/7/2011
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© 2011 MPS. All Rights Reserved.
3
MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
PIN FUNCTIONS
SOIC8E
Pin #
1
2
3
4
5
6
7
8
Name
Description
Feedback. This is the input to hysteretic comparators. An external current sensing resistor is
connected in series with the LEDs to GND. The feedback voltage is connected to this pin
and is regulated at +200mV with 15% current ripple.
N/C
Not connected
Input Supply. This supplies power to all the internal control circuitry, both BS regulators and
VIN
the high-side switch. A decoupling capacitor to ground must e placed close to this pin to
minimize switching spikes.
Bootstrap. This is the positive power supply for the internal floating high-side MOSFET
BST
driver. Connect a bypass capacitor between this pin and SW pin.
Switch Node. This is the output from the high-side switch. A low VF Schottky rectifier to
SW
ground is required. The rectifier must be close to the SW pins to reduce switching spikes.
PWM Dimming Input. Pulling this pin below the specified threshold for dimming off. Pulling it
DIM
up above the specified threshold for dimming on. If there is no need for dimming function,
connect DIM and EN pins together.
Enable Input. Pulling this pin below the specified threshold shuts the chip down. Pulling it up
EN
above the specified threshold or leaving it floating enables the chip.
GND, Ground. It should be connected as close as possible to the output capacitor avoiding the
Exposed high current switch paths. Connect exposed pad to GND plane for optimal thermal
pad
performance.
FB
MP46885 Rev. 1.0
7/7/2011
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MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
BLOCK DIAGRAM
Figure 1—Function Block Diagram
MP46885 Rev. 1.0
7/7/2011
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© 2011 MPS. All Rights Reserved.
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MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
TYPICAL PERFORMANCE CHARACTERISTICS
L=47μH, 1 LED Load, TA=25 oC, unless otherwise noted.
100
200.50
98
200.40
90
85
80
75
200.30
96
V FB ( mV )
EFFICIENCY (%)
EFFICIENCY (%)
95
94
200.20
200.10
200.00
199.90
92
199.80
1
2
3
4
NUM BER OF LEDS
MP46885 Rev. 1.0
7/7/2011
5
90
9
11
13
15
NUM BER OF LEDS
17
199.70
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
V IN ( V )
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© 2011 MPS. All Rights Reserved.
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MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
OPERATION
Hysteresis Current Control with Adaptive
Threshold Adjustment
MP46885 operates in a hysteresis current
control mode to regulate the LED current
accurately. FB pin is the sensed voltage of LED
current across the sensing resistor. The power
MOSFET is turned on and remains on until FB
pin rises to 215mV. The power MOSFET is
turned off and remains off until FB pin falls to
185mV. The two thresholds of 215mV and
185mV are adaptive adjusted to compensate all
the circuit delays so that the LED current is
regulated very accurately with 200mV average
value at FB pin.
Enable Control
The MP46885 has a dedicated enable control
pin (EN) with the positive logic. Its falling
threshold is a precision 1.2V, and its rising
threshold is 1.5V (300mV higher).
When floating, EN is pulled up to about 3.0V by
an internal 1µA current source so it is enabled.
To pull it down, over 1µA current capability is
needed.
Floating Driver and Bootstrap Charging
The floating power MOSFET driver is powered
by an external bootstrap capacitor. This floating
driver has its own UVLO protection. This
UVLO’s rising threshold is 2.2V with a threshold
of 150mV.
Thermal Shutdown
Thermal shutdown is implemented to prevent
the chip from operating at exceedingly high
temperatures. When the silicon die temperature
is higher than its upper threshold, it shuts down
the whole chip. When the temperature is lower
than its lower threshold, the chip is enabled
again.
LED Short Protection
The LED current is well regulated with FB pin
voltage at 200mV. As long as the LED sensing
resistor is not failed, the output current is within
limitation. If the LED sensing resistor is failed or
the output is shorted to GND directly, the FB pin
voltage is low even the power MOSFET is
turned on. The power MOSFET will be shut off
if such failure time is longer than 10us.
MP46885 will retry the operation after about
300us delay.
The power MOSFET current is also accurately
sensed via a current sense MOSFET. If the
current is over current limit, the IC is shut down.
This offers extra protection under output short
conditions.
The bootstrap capacitor is charged and
regulated to about 5V by the dedicated internal
bootstrap regulator.
In case the internal circuit does not have
sufficient voltage and the bootstrap capacitor is
not well charged, extra external circuitry can be
used to ensure the bootstrap voltage is in the
normal operational region. Refer to External
Bootstrap Diode in Application section.
Under-Voltage Lockout (UVLO)
Under-voltage lockout (UVLO) is implemented
to protect the chip from operating at insufficient
supply voltage. The UVLO rising threshold is
about 4.0V while its falling threshold is a
consistent 3.65V.
MP46885 Rev. 1.0
7/7/2011
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© 2011 MPS. All Rights Reserved.
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MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
APPLICATION INFORMATION
COMPONENT SELECTION
Input Capacitor CIN
Setting the LED Current
The input current to the step-down converter is
discontinuous, therefore a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance especially under high switching
frequency applications.
The LED current ILED is set using a sensing
resistor RFB, which is in series with the LEDs
and connected to GND. The voltage on the
sensing resistor RFB is connected to FB pin.
ILED
VFB
RFB
For example, for a 700mA LED current, RFB is
287mΩ.
The RMS current through the input capacitor is
about:
Inductor Selection and Frequency Setting
The inductor LO is required to supply a constant
current to the LED. The inductor value is related
to the switching frequency fs setting:
(V VOUT ) VOUT
fs IN
VIN LO ILED 15%
Where, VIN is the input voltage, VOUT is the
output voltage to drive the LEDs. A larger value
inductor will result in smaller switching
frequency.
The peak inductor current is about:
ILP ILED 1.15
Choose an inductor that will not saturate under
the maximum inductor peak current.
Output Rectifier Diode
The output rectifier diode supplies the current to
the inductor when the high-side switch is off. To
reduce losses due to the diode forward voltage
and recovery times, use a Schottky diode.
The RMS current through the diode is about:
ID ILED 1
VOUT
VIN
Choose a diode whose maximum reverse
voltage rating is greater than the maximum
input voltage, and whose current rating is
greater than the maximum diode current.
MP46885 Rev. 1.0
7/7/2011
VOUT
’
VIN
ID ILED
With low ESR capacitors, the input voltage
ripple can be estimated by:
VIN
V
V
ILED
OUT 1 OUT
fs CIN VIN
VIN
Choose the input capacitor with enough RMS
current rating and enough capacitance for small
input voltage ripple.
When electrolytic or tantalum capacitors are
applied, a small, high quality ceramic capacitor,
i.e. 0.1μF, should be placed as close to the IC
as possible.
Output Capacitor COUT
The output capacitor (COUT) is not necessary for
MP46885. The LED current ripple (peak-topeak value) is about 15% of the LED DC
current. Output capacitor can be used to further
reduce the LED current ripple. Low ESR
capacitors are preferred to keep the output
voltage ripple low so that the AC ripple current
through the LEDs is small. The output voltage
ripple can be estimated by:
VOUT
VOUT
V
1 OUT
fS L O
VIN
1
RESR
8 fS COUT
where RESR is the equivalent series resistance
(ESR) value of the output capacitor.
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MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
External Bootstrap Diode
Layout Consideration
An external bootstrap diode may enhance the
efficiency of the LED driver. In below cases, an
external BST diode is recommended from the
5V to BST pin:
It is essential to place the input decoupling
capacitor, catch diode and the MP46885 (VIN
pin, SW pin and PGND) as close as possible,
with traces that are very short and fairly wide.
This can help to greatly reduce the voltage
spike on SW node, and lower the EMI noise
level as well.
There is a 5V rail available in the system;
VIN is no greater than 5V;
VOUT is between 3.3V and 5V;
This diode is also recommended for high duty
cycle operation (when VOUT/VIN>65%) and very
high frequency (over 1.5MHz) applications.
The bootstrap diode can be a low cost one
such as IN4148 or BAT54.
5V
BS
MP46885
SW
Figure 2—External Bootstrap Diode
MP46885 Rev. 1.0
7/7/2011
Try to run the feedback trace as far from the
inductor and noisy power traces as possible. It
is often a good idea to run the feedback trace
on the side of the PCB opposite of the inductor
with a ground plane separating the two.
To help to improve the thermal conduction, a
grid of thermal vias can be created right under
the exposed pad. It is recommended that they
be small (15mil barrel diameter) so that the hole
is essentially filled up during the plating
process, thus aiding conduction to the other
side. Too large a hole can cause ‘solder
wicking’ problems during the reflow soldering
process. The pitch (distance between the
centers) of several such thermal vias in an area
is typically 40mil.
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9
MP46885 – 80V INPUT, 500mA HIGH POWER LED DRIVER
PACKAGE INFORMATION
SOIC8E (EXPOSED PAD)
0.189(4.80)
0.197(5.00)
0.124(3.15)
0.136(3.45)
8
5
0.150(3.80)
0.157(4.00)
PIN 1 ID
1
0.228(5.80)
0.244(6.20)
0.089(2.26)
0.101(2.56)
4
TOP VIEW
BOTTOM VIEW
SEE DETAIL "A"
0.051(1.30)
0.067(1.70)
SEATING PLANE
0.000(0.00)
0.006(0.15)
0.013(0.33)
0.020(0.51)
0.0075(0.19)
0.0098(0.25)
SIDE VIEW
0.050(1.27)
BSC
FRONT VIEW
0.010(0.25)
x 45o
0.020(0.50)
GAUGE PLANE
0.010(0.25) BSC
0.050(1.27)
0.024(0.61)
0o-8o
0.016(0.41)
0.050(1.27)
0.063(1.60)
DETAIL "A"
0.103(2.62)
0.138(3.51)
RECOMMENDED LAND PATTERN
0.213(5.40)
NOTE:
1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN
BRACKET IS IN MILLIMETERS.
2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS OR GATE BURRS.
3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH
OR PROTRUSIONS.
4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING)
SHALL BE 0.004" INCHES MAX.
5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA.
6) DRAWING IS NOT TO SCALE.
NOTICE: The information in this document is subject to change without notice. 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.
MP46885 Rev. 1.0
7/7/2011
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
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