Micrel MIC4802YME High efficiency 800ma single channel linear wled driver with ultra fast pwmâ ¢ control Datasheet

MIC4802
High Efficiency 800mA Single Channel
Linear WLED Driver with
Ultra Fast PWM™ Control
General Description
Features
The MIC4802 is a high efficiency White LED (WLED)
driver designed to drive a single LED up to 800mA. The
MIC4802 constant current driver is designed to drive high
power LED’s in various lighting applications. The MIC4802
provides the highest possible efficiency as this architecture
has no switching losses present in traditional charge
pumps or inductive boost circuits. It features a typical
dropout of 280mV at 800mA. This allows the LEDs to be
driven directly from the voltage source eliminating
switching noise/losses present with the use of boost
circuitry. The high accuracy (±1% Typical) current
regulated WLED channel ensures uniform display
illumination under all conditions. The brightness is
controlled through an Ultra Fast PWM™ Control interface
operating down to less than 1% duty cycle.
The MIC4802 is available in the 8-pin SOIC Epad 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 280mV at 800mA
Programmable LED current with external resistor
Current accuracy of ±1% typical
Applications
• Bill board displays
• Marquee displays
• Instrument displays
• Architectural lighting
____________________________________________________________________________________________________________
Typical Application
High Current Lighting Schematic
Ultra Fast PWM is a trademark of Micrel, 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
January 2011
M9999-013111-B
Micrel Inc.
MIC4802
Ordering Information
Part Number
Temperature Range
Package
MIC4802YME
–40°C to +125°C
8-Pin EPAD SOIC
Pin Configuration
8-Pin Epad SOIC (ME)
(Top View)
Pin Description
Pin Number
Pin Name
1
VIN
Voltage Input. Connect at least 2.2µF ceramic capacitor between VIN and GND.
2
EN
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 6.19kΩ
resistor between RSET and GND to set LED current to 830mA at 100% duty cycle.
4
GND
Ground.
5
D1
LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be
connected to the LED.
6
D1
LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be
connected to the LED.
7
D1
LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be
connected to the LED.
8
D1
LED1 driver input. Connect LED anode to VIN and cathode to this pin. All D1 pins must be
connected to the LED.
EPAD
HS PAD
January 2011
Pin Function
Heat sink pad. Not internally connected. Connect to ground.
2
M9999-013111-B
Micrel Inc.
MIC4802
Absolute Maximum Ratings(1)
Operating Ratings(2)
Main Input Voltage (VIN) .................................. –0.3V to +6V
Enable Input Voltage (VEN).............................. –0.3V to +6V
LED Driver Voltage (VD1) ................................ –0.3V to +6V
Power Dissipation .....................................Internally Limited
Lead Temperature (soldering, 10sec.)....................... 260°C
Storage Temperature (Ts) .........................–65°C to +150°C
Supply Voltage (VIN)..................................... +3.0V to +5.5V
Enable Input Voltage (VEN) .................................... 0V to VIN
LED Driver Voltage (VD1) ....................................... 0V to VIN
Junction Temperature (TJ) ........................ –40°C to +125°C
Junction Thermal Resistance
EPAD SOIC-8L (θJA)..........................................41°C/W
Electrical Characteristics
VIN = VEN = 5V, RSET = 6.19kΩ; VD1 = 1.2V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted.
Parameter
Conditions
(3)
Current Accuracy
Min
Typ
Max
Units
747
830
913
mA
Drop-out
Where ILED = 90% of LED current seen at
VDROPNOM = 1.2V, 100% brightness level
280
500
mV
Ground/Supply Bias Current
IOUT = 830mA
4.1
5.7
mA
Shutdown Current
VEN = 0V
0.01
1
µA
0.2
V
PWM Dimming
Enable Input Voltage (VEN)
Logic Low
1.2
Logic High
V
Enable Input Current
VIH > 1.2V
0.01
1
µA
Current Source Delay
(50% levels)
Shutdown to on
Standby to on
On to Standby
40
2
0.3
60
µs
µs
µs
Current Source Transient Time
(10%-90%)
TRISE
TFALL
1
0.3
Stand-by to Shutdown Time
VEN = 0V
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. As determined by average current based on RSET resistance.
January 2011
3
M9999-013111-B
Micrel Inc.
MIC4802
Typical Characteristics
1.4
1.2
VIN = 3.5V
1
0.8
VIN = 3.0V
0.6
0.4
500
VIN = 5.5V
0.8
LED CURRENT (A)
LED CURRENT (A)
1
0.9
VIN = 5.5V
Dropout Voltage
vs. LED Current
LED Current
vs. LED Anode Voltage
450
VIN = 3.5V
0.7
0.6
VIN = 3.0V
0.5
0.4
0.3
0.2
0.2
0.1
5.5
5
4.5
4
3.5
3
5.5
2.5
4.5
4
3.5
3
LED ANODE VOLTAGE (V)
Supply Bias Current
vs. LED Anode Voltage
Peak LED Current
vs. RSET
10000
VIN = 3.5V
VIN = 2.5V
4
3.5
3
2.5
1
10
500
fPWM = 200kHz
300
200
0
60
DUTY CYCLE (%)
January 2011
600
fPWM = 5kHz
500
400
300
fPWM = 10kHz
200
0
80
20
100
40
60
80
100
DUTY CYCLE (%)
Typical ILED vs. VLED
2
1.8
VIN = 5.0V
1.6
1.36
1.34
1.32
1.3
1.28
1.4
1.2
1
0.8
0.6
0.4
1.26
fPWM = 500kHz
40
fPWM = 1kHz
700
10000
LED CURRENT (A)
RSET VOLTAGE (V)
fPWM = 100kHz
20
1000
1.38
700
0
100
1.4
fPWM = 20kHz
100
600 800 1000 1200 1400
VIN = 5V
RSET Voltage
vs. LED Current
900
400
400
RSET (kΩ)
LED Current
vs. PWM Duty Cycle
600
200
0
1
LED BATTERY VOLTAGE (V)
800
VIN = 5V
100
RSET = 4.64kΩ
0
4.5
100
900
10
5
150
LED Current
vs. PWM Duty Cycle
100
2
5.5
200
0
LED CURRENT (mA)
5
1
250
LED CURRENT (mA)
1000
3
300
800
6
4
350
0
2.5
VIN = 5.5V
7
ILED (mA)
Supply Bias Current (mA)
5
LED BATTERY VOLTAGE (V)
8
400
50
0
0
LED CURRENT (mA)
DROPOUT VOLTAGE (mV)
LED Battery Voltage
vs. LED Current
VIN = 5V
1.24
0
200
400 600 800 1000 1200 1400
LED CURRENT (mA)
4
0.2
0
2.4
2.6
2.8
3
3.2
3.4
3.6
LED FORWARD VOLTAGE (V)
M9999-013111-B
Micrel Inc.
MIC4802
Functional Characteristics
January 2011
5
M9999-013111-B
Micrel Inc.
MIC4802
Functional Diagram
Figure 1. MIC4802 Functional Block Diagram
Block Diagram
As shown in Figure 1, the MIC4802 consists of current
mirrors set to copy a master current determined by RSET.
The linear LED drivers have a designated control block
for enabling and dimming of the LEDs. The MIC4802
dimming is controlled by the Ultra Fast PWMTM control
block that receives PWM signals for dimming.
Functional Description
The MIC4802 is a single channel linear LED driver with a
maximum 800mA current capability. The LED driver is
designed to maintain proper current regulation with LED
current accuracy of ±10%. The dropout is 280mV at
800mA. The low dropout of the linear drivers allows the
LEDs to be driven directly from the battery voltage and
eliminates the need for boost or large and inefficient
charge pumps. The maximum LED current for each
channel is set via an external resistor. Dimming is
controlled by applying a PWM signal to the EN pin. The
MIC4802 accommodates a wide PWM frequency range
as outlined in the application information section.
January 2011
6
M9999-013111-B
Micrel Inc.
MIC4802
VIN
The input supply (VIN) provides power to the linear LED
drivers and the control circuitry. The VIN operating range
is 3V to 5.5V. A minimum bypass capacitor of 1µF
should be placed close to the input (VIN) pin and the
ground (GND) pin. Refer to the layout recommendations
section for details on placing the input capacitor (C1).
Peak LED Current
vs. RSET
ILED (mA)
1000
EN
The EN pin is equivalent to the enable pin for the linear
drivers on the MIC4802. It can also be used for dimming
applying a PWM signal. See the PWM Dimming
Interface in the Application Information section for
details. Pulling the EN low for more than 40ms puts the
MIC4802 into a low IQ sleep mode. The EN pin cannot be
left floating; a floating enable pin may cause an
indeterminate state on the outputs. The first pulse on the EN
pin must be equal or greater than 60µs to wake the part up
in a known state. This equates to an 8.3kHz 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 60µs.
100
10
1
1
10
100
1000
10000
RSET (kΩ)
Figure 2. Peak LED Current vs. RSET
D1
The D1 pins are the linear driver inputs for the LED.
Connect the anode of the LED to VIN and the cathode to
the D1 pins. All the D1 pins must be connected together.
The D1 voltage at dropout is the minimum voltage
required by the linear driver in order for the LED to be
fully biased.
RSET
The RSET pin is used to set the peak current of the linear
driver by connecting a RSET resistor to ground. The
theoretical average LED current can be estimated by
equation (1):
ILED (mA) = 4920 * D / RSET (kΩ)
(1)
RSET (kΩ) = 4920 * D / ILED (mA)
(2)
GND
The ground pin is the ground path for the linear driver.
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 for
more details.
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.
Due to DC losses across current paths internal and
external to the package, the calculated RSET resistance
equation is modified by a factor K, where K is calculated
to be 0.280kΩ.
RSET (kΩ) = 4920 * D / ILED (mA) + 0.280 (kΩ)
(3)
ILED (mA) = 4920 * D / ((RSET (kΩ) – 0.280 (kΩ))
(4)
The modified LED current equation is more accurate in
determining the actual LED current based on the RSET
resistor value.
January 2011
7
M9999-013111-B
Micrel Inc.
MIC4802
Application Information
LED Current
vs. PWM Duty Cycle
Ultra Fast PWM™ Dimming Interface
The MIC4802 supports a wide range of PWM control
signal frequencies from 200Hz to 500kHz. This
extremely wide range of control provides ultimate
flexibility for handheld applications using high frequency
PWM control signals.
WLED dimming is achieved by applying a pulse width
modulated (PWM) signal to the END pin. For PWM
frequencies between 200Hz – 10kHz the MIC4802
supports a duty cycle range from 1% to 100%, as shown
in Figure 3. The MIC4802 incorporates an internal
shutdown delay to ensure that the internal control
circuitry remains active during PWM dimming. This
feature prevents the possibility of backlight flickering
when using low frequency PWM control signals. The
MIC4802 also supports Ultra Fast PWM™ frequencies
from 20kHz to 500kHz. Due to input signal propagation
delay, PWM frequencies above 20kHz have a non-linear
relationship between the duty cycle and the average
LED current, as shown in Figure 4 and 5. Figures 6
through 9 show the WLED current response when a
PWM signal is applied to the END pin (1).
900
LED CURRENT (mA)
800
fPWM = 200kHz
400
300
200
fPWM = 500kHz
0
20
40
60
80
100
DUTY CYCLE (%)
Figure 4. Channel Current Response to PWM Control
Signal Frequencies from 50kHz to 500kHz
Minimum Duty Cycle
vs. Frequency
35
30
MINIMUM DUTY (%)
LED Current
vs. PWM Duty Cycle
25
20
15
10
5
0
100
900
LED CURRENT (mA)
500
0
From the low IQ sleep mode higher PWM frequencies above 15kHz
require a logic high enable signal for 60μs to first enable the MIC4802
prior to PWM dimming.
VIN = 5V
fPWM = 1kHz
1000
10000
100000
1000000
FREQUENCY (Hz)
700
600
Figure 5. Minimum Duty Cycle
for Varying PWM Frequency
fPWM = 5kHz
500
fPWM = 100kHz
600
100
(1)
800
fPWM = 20kHz
700
400
300
fPWM = 10kHz
200
100
0
0
20
40
60
80
100
DUTY CYCLE (%)
Figure 3. Average Current per LED Dimming
by Changing PWM Duty Cycle for PWM Frequencies
up to 20kHz
Figure 6. PWM Signal at 1% Duty Cycle (Iavg = 8mA)
January 2011
8
M9999-013111-B
Micrel Inc.
MIC4802
Thermal Consideration
The MIC4802 thermal considerations involve calculating
the junction temperature based on the voltage drop
across the package and the LED current. The voltage
drop across the package is equal to the voltage at D1
with respect to ground times the LED current.
PLOSS = ILED * VD1
The temperature rise (ΔT) is calculated:
ΔT = PLOSS * θJA
Assuming the ILED is 800mA and VD1 is 500mV at 20°C
room temperature, we can calculate the junction
temperature:
TJ = TA + ΔT
TJ = 20°C + 0.4W * 41°C/W
TJ = 20°C + 16.4°C = 36.4°C
The junction temperature will be 36.4°C.
Figure 7. PWM Signal at 20% Duty Cycle (Iavg = 160mA)
Figure 8. PWM Signal at 50% Duty Cycle (Iavg = 400mA)
Figure 9. PWM Signal at 80% Duty Cycle (Iavg = 640mA)
January 2011
9
M9999-013111-B
Micrel Inc.
MIC4802
MIC4802 Typical Application Circuit
Bill of Materials
Item
C1
Part Number
Manufacturer
C1608X5R0J225K
TDK(1)
06036D225KAT2A
AVX(2)
GRM188R60J225KE19D
Murata(3)
VJ0603G225KXYAT
Vishay(4)
R42180
Seoul Semiconductor(5)
LED
RSET
CRCW06036K19FKEA
U1
MIC4802YME
(4)
Vishay
Micrel, Inc.(6)
Description
Qty.
Ceramic Capacitor, 2.2µF, 6.3V, X5R, Size 0603
1
3.8W High Power WLED
1
Resistor, 6.19kΩ, 1%, 1/16W, Size 0603
1
800mA Single Channel Ultra Fast PWM™
Linear WLED Driver
1
Notes:
1. TDK: www.tdk.com
2. AVX: www.avx.com
3. Murata: www.murata.com
4. Vishay: www.vishay.com
5. Seoul Semi: http://www.acriche.com/en
6. Micrel, Inc.: www.micrel.com
January 2011
10
M9999-013111-B
Micrel Inc.
MIC4802
Layout Recommendations
Top Layer
Bottom Layer
January 2011
11
M9999-013111-B
Micrel Inc.
MIC4802
Package Information
8-Pin SOIC (ME)
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
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2010 Micrel, Incorporated.
January 2011
12
M9999-013111-B
Similar pages