MIC2843 DATA SHEET (11/05/2015) DOWNLOAD

MIC2843
High-Efficiency 6-Channel
Linear WLED Driver with
Ultra-Fast PWM™ Control
General Description
Features
The MIC2843 is a high-efficiency linear white LED (WLED)
driver designed to drive up to six WLEDs, greatly
extending battery life for portable display backlighting,
keypad backlighting, and camera flash in mobile devices.
The MIC2843 provides the highest possible efficiency as
this architecture has no switching losses present in
traditional charge pumps or inductive boost circuits. The
MIC2843 provides six linear drivers which maintain
constant current for up to six WLEDs. It features a typical
dropout of less than 40mV at 20mA. This allows the
WLEDs to be driven directly from the battery eliminating
switching noise/losses present with the use of boost
circuitry.
The six channels are matched better than ±3% typical,
ensuring uniform display illumination under all conditions.
The brightness is controlled through an Ultra Fast PWM™
interface operating down to less than 1% duty cycle.
The MIC2843 is available in the 2mm x 2mm 10-pin Thin
®
MLF leadless package with a junction temperature range
of −40°C to +125°C.
Datasheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
•
•
•
•
•
•
•
High efficiency (no voltage boost losses)
Ultra Fast PWM™ control (200Hz to 500kHz)
Input voltage range: 3.0V to 5.5V
Dropout of less than 40mV at 20mA
Matching better than ±3% (typical)
Current accuracy better than ±1.5% (typical)
Maintains proper regulation regardless of how many
channels are utilized
• Available in a 2mm x 2mm 10-pin Thin MLF® package
Applications
• Mobile handsets
• Digital cameras
• Portable media/MP3 players
• Portable navigation devices (GPS)
• Portable applications
____________________________________________________________________________________________________________
Typical Application
LCD Display Backlight with Six WLEDs
High Current Flash Driver
Ultra Fast PWM is a trademark of Micrel, Inc.
MLF and MicroLeadFrame are registered trademark Amkor Technology Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
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MIC2843
Ordering Information
Part Number
Mark Code(1)
Temperature Range
Package(2)
MIC2843YMT
YS3
–40°C to +125°C
10-Pin 2mm x 2mm Thin MLF®
Note:
®
1.
Thin MLF ▲ = Pin 1 identifier.
2.
Thin MLF is a GREEN RoHS-compliant package. Lead finish is NiPdAu. Mold compound is halogen free.
®
Pin Configuration
10-Pin 2mm x 2mm Thin MLF® (MT)
(Top View)
Pin Description
Pin Number
Pin Name
1
VIN
Voltage Input. Connect at least 1µF ceramic capacitor between VIN and GND.
2
END
Enable LED drivers. This pin can be used as a PWM input for dimming of WLEDs. Do not leave
floating.
3
RSET
An internal 1.27V reference sets the nominal maximum WLED current. Example, apply a 20.5kΩ
resistor between RSET and GND to set LED current to 20mA at 100% duty cycle.
4
GND
Ground.
5
D6
LED6 driver input. Connect LED anode to VIN and cathode to this pin.
6
D5
LED5 driver input. Connect LED anode to VIN and cathode to this pin.
7
D4
LED4 driver input. Connect LED anode to VIN and cathode to this pin.
8
D3
LED3 driver input. Connect LED anode to VIN and cathode to this pin.
9
D2
LED2 driver input. Connect LED anode to VIN and cathode to this pin.
10
D1
LED1 driver input. Connect LED anode to VIN and cathode to this pin.
EPAD
HS PAD
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Pin Function
Heat sink pad. Not internally connected. Connect to ground.
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MIC2843
Absolute Maximum Ratings(1)
Operating Ratings(2)
Main Input Voltage (VIN) .................................. −0.3V to +6V
Enable Input Voltage (VEND) ............................ −0.3V to +6V
Current Source Voltage (VD1-D6) ..................... −0.3V to +6V
Power Dissipation .....................................Internally Limited
Lead Temperature (soldering, 10sec.)....................... 260°C
Storage Temperature (Ts) .........................−65°C to +150°C
ESD Rating(3) ................................................. ESD Sensitive
Supply Voltage (VIN)..................................... +3.0V to +5.5V
Enable Input Voltage (VEND) .................................. 0V to VIN
Current Source Voltage (VD1-D6) ............................ 0V to VIN
Junction Temperature (TJ) ........................ –40°C to +125°C
Junction Thermal Resistance
2mm x 2mm Thin MLF®-10L (θJA)......................90°C/W
Electrical Characteristics
WLED Linear Drivers
VIN = VEND = 3.8V, RSET = 20.5kΩ; VD1-D6 = 0.6V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted.
Parameter
Conditions
Current Accuracy(4)
VDROPNOM = 0.6V
Min.
Typ.
1.5
Max.
Units
(5)
Matching
VDROPNOM = 0.6V
3
5.5
%
Drop-out
Where ILED = 90% of LED current seen at
VDROPNOM = 0.6V, 100% brightness level
40
100
mV
Ground/Supply Bias Current
IOUT = 20mA
1.4
Shutdown Current
(Current Source Leakage)
VEND = 0V
0.01
%
mA
1
µA
0.2
V
PWM Dimming
Enable Input Voltage (VEND)
Logic Low
Logic High
V
1.2
Enable Input Current
VIH > 1.2V
0.01
Current Source Delay
(50% levels)
Shutdown to On
Standby to On
On to Standby
40
0.5
1
1
60
µA
µs
µs
µs
RSET = 20.5k
Current Source Transient Time
(10% − 90%)
TRISE
TFALL
Standby to Shutdown Time
VEND = 0V
1
0.3
10
20
µs
µs
40
ms
Notes:
1.
Exceeding the absolute maximum rating may damage the device.
2.
The device is not guaranteed to function outside its operating rating.
3.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
4.
As determined by average current of all channels in use and all channels loaded.
5.
The current through each LED meets the stated limits from the average current of all LEDs.
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Typical Characteristics
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Typical Characteristics (Continued)
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Functional Characteristics
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Functional Characteristics
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Functional Diagram
Figure 1. MIC2843 Functional Block Diagram
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RSET
The RSET pin is used by connecting a RSET resistor to
ground to set the peak current of the linear drivers. The
average LED current can be calculated by Equation 1
below:
Functional Description
The MIC2843 is a six-channel WLED driver. The WLED
driver is designed to maintain proper current regulation
with LED current accuracy of 1.5% while the typical
matching between the six channels to be 3% at room
temperature. The WLEDs are driven independently from
the input supply and will maintain regulation with a
dropout of 40mV at 20mA. The low dropout of the linear
drivers allows the WLEDs to be driven directly from the
battery voltage and eliminates the need for large and
inefficient charge pumps. The maximum WLED current
for each channel is set via an external resistor. If
dimming is desired the MIC2843 can dim via an Ultra
Fast PWM™ signal.
ILED (mA) = 410 × D / RSET (kΩ)
Eq. 1
D is the duty cycle of the LED current during PWM
dimming. When the device is fully on the duty cycle
equals 100% (D = 1). A plot of ILED versus RSET is shown
in Figure 2.
Block Diagram
As shown in Figure 1, the MIC2843 consists of six
current mirrors set to copy a master current determined
by RSET. The linear drivers have a designated control
block for enabling and dimming of the WLEDs. The
MIC2843 is controlled by the PWM control block that
receives PWM signals for dimming.
VIN
The input supply (VIN) provides power to the linear
drivers and the control circuitry. The VIN operating range
is 3V to 5.5V. Due to wire inductance a minimum bypass
capacitor of 1µF should be placed close to input (VIN)
pin and the ground (GND) pin. Refer to the Layout
Recommendations section for details on placing the
input capacitor (C1).
Figure 2. Peak LED Current vs. RSET
END
The END pin is equivalent to the enable pin for the linear
drivers on the MIC2843. It can also be used for dimming
using a PWM signal. See the “PWM Dimming Interface”
in the Application Information section for details.
The first pulse on the END pin must be equal or greater
to 40µs to wake the part up in a known state. This
equates to a 12.5kHz PWM signal at equal or greater
than 50% duty cycle. Higher PWM frequencies may be
used but the first pulse must be equal or greater than
40µs.
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D1-D6
The D1 through D6 pins are the linear driver inputs for
WLED 1 through 6, respectively. Connect the anodes of
the WLEDs to VIN and each cathode of the WLEDs to D1
through D6. The linear drivers are independent of each
other.
GND
The ground pin is the ground path for the linear drivers.
The current loop for the ground should be as small as
possible. The ground of the input capacitor should be
routed with low impedance traces to the GND pin and
made as short as possible. Refer to the Layout
Recommendations section for more details.
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Application Information
Ultra Fast PWM™ Dimming Interface
The MIC2843 can receive PWM signals from the END
pin for WLED dimming. Dimming is generated by pulsing
the WLEDs on and off in synchronization with the PWM
signal. The MIC2843 supports PWM frequencies from
200Hz to 500kHz. For PWM frequencies between 200Hz
– 20kHz the MIC2843 supports a duty cycle range from
1% to 100%. The MIC2843 supports Ultra Fast PWM™
frequencies from 20kHz to 500kHz with a duty cycle of
10% and greater. MIC2843 incorporates an internal
shutdown delay to ensure that the internal control
circuitry remains active during PWM dimming for
optimum Ultra Fast PWM™ performance. Due to input
PWM signal propagation delay Ultra Fast PWM™
signals have a non-linear relationship between the duty
cycle and the average LED current (Figures 3 and 4).
With the Ultra Fast PWM™ frequencies, lower duty
cycles may degrade the matching between LEDs, and
should be limited to the minimum duty cycle, as
indicated in Figure 5. Due to the shutdown-to-on delay of
60µs, at Ultra Fast PWM™ frequencies above 15kHz, a
logic high enable signal is required to first wake up prior
to PWM dimming. Figures 6 through 10 illustrate the
WLED current response when a PWM signal is applied
to the END pin.
Figure 3. Average Current per LED Dimming by Changing
PWM Duty Cycle for PWM Frequencies up to 20kHz
Figure 4. Average Current per LED Dimming by Changing
PWM Duty Cycle for PWM Frequencies from 50kHz to
500kHz
Figure 5. Minimum Duty Cycle for Varying PWM
Frequency
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Figure 6. PWM Signal at 1% Duty Cycle (Iavg = 0.2mA)
Figure 7. PWM Signal at 20% Duty Cycle (Iavg = 4mA)
Figure 8. PWM Signal at 50% Duty Cycle (Iavg = 10mA)
Figure 9. PWM Signal at 80% Duty Cycle (Iavg = 16mA)
Figure 10. PWM Signal at 100% Duty Cycle (Iavg = 20mA)
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High-Current Parallel Operation
The linear drivers are independent of each other, and
can be used individually or paralleled for larger current.
A single WLED can be driven with all six linear drivers by
connecting D1 through D6 together with the cathode of
the WLED as shown in Figure 11. This will generate a
current six times the LED current setting and can be
used for higher current WLEDs such as those used in
flash or torch applications.
Figure 12. Current Response Time to Enable Signal
Turning On (Six Paralleled Channels)
Figure 11. Six-Channel (Parallel) Application Circuit
The current is set by the RSET resistor, and can be
calculated by the following equation:
ILED (mA) = 6 * 410 * D / RSET (kΩ).
Figure 13. Current Response Time to Enable Signal
Turning Off (Six Paralleled Channels)
D is the duty cycle of the LED current during PWM
dimming. When the device is fully on the duty cycle
equals 100% (D = 1). Figure 12 shows the response
time of the six paralleled linear drivers to the enable
signal, while Figure 13 shows the turn off response. With
a RSET resistor of 1.65k, each linear driver is set to
250mA, with all 6 linear drivers connected in parallel, the
MIC2843 is capable of driving a total current of 1.5A.
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Input Capacitor
The MIC2843 is a high-performance, high-bandwidth
device. Stability can be maintained using a ceramic input
capacitor of 1µF. Low-ESR ceramic capacitors provide
optimal performance at a minimum amount of space.
Additional high-frequency capacitors, such as smallvalued NPO dielectric-type capacitors, help filter out
high-frequency noise and are good practice in any noisesensitive circuit. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V dielectrics
lose most of their capacitance over temperature and are
therefore, not recommended.
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MIC2843 Typical Application Circuit
Bill of Materials
Item
Part Number
C1
C1608X5R0J105K
R1
CRCW06032052FT1
U1
MIC2843YMT
Manufacturer
TDK(1)
(2)
Vishay
Micrel, Inc.(3)
Description
Qty.
1µF Ceramic Capacitor, 6.3V, X5R, Size 0603
1
20.5kΩ, 1%, Size 0603
1
High-Efficiency Six-Channel Linear WLED Driver with
Ultra-Fast PWM™ Control
1
Notes:
1. TDK: www.tdk.com.
2. Vishay: www.vishay.com.
3. Micrel, Inc.: www.micrel.com.
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MIC2843
PCB Layout Recommendations
Top Layer
Bottom Layer
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Package Information
10-Pin (2mm x 2mm) Thin MLF® (MT)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
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© 2008 Micrel, Incorporated.
.
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