Micrel MIC2842AYMT High efficiency 4 channel wled driver with damâ ¢ and single wire digital control Datasheet

MIC2842A
High Efficiency 4 Channel WLED Driver with
DAM™ and Single Wire Digital Control
General Description
Features
The MIC2842A is a high efficiency White LED (WLED)
• High Efficiency (no Voltage Boost losses)
driver designed to drive up to four LEDs and greatly
• Dynamic Average Matching™ (DAM™)
extend battery life for portable display backlighting, and
• Single wire digital control
keypad backlighting in mobile devices. The MIC2842A
• Input voltage range: 3.0V to 5.5V
architecture provides the highest possible efficiency by
• Dropout of 40mV at 20mA
eliminating switching losses present in traditional charge
pumps or inductive boost circuits. With a typical dropout of
• Matching better than ±1.5% (typical)
40mV at 20mA, the MIC2842A allows the LEDs to be
• Current accuracy better than ±1.5% (typical)
driven directly from the battery eliminating switching noise
• Maintains proper regulation regardless of how many
and losses present with the use of boost circuitry.
channels are utilized
The MIC2842A features Dynamic Average Matching™
• Available in a 10-pin 2mm x 2mm Thin MLF® package
(DAM™) which is specifically designed to provide optimum
matching across all WLEDs. The four channels are
Applications
matched better than ±1.5% typical, ensuring uniform
display illumination under all conditions. The LED
• Mobile handsets
brightness is preset by an external resistor and can be
• Handset LCD backlighting
dimmed using a single-wire digital control. The digital
• Handset keypad backlighting
interface takes commands from digital programming
pulses to change the brightness in a logarithmic scale
• Camera flash (see MIC2843A datasheet)
similar to the eye’s perception of brightness. The single• Digital cameras
wire digital brightness control is divided into two modes of
• Portable media/MP3 players
operation; full brightness mode or battery saving mode for
a total of 49 brightness steps.
• Portable navigation devices (GPS)
The MIC2842A is available in the 2mm x 2mm 10-pin Thin
• Portable application
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.
____________________________________________________________________________________________________________
Typical Application
U1 MIC2842AYMT
U1 MIC2842AYMT
VIN
VIN
C1
Low
Dropout
Linear
Driver
RSET
DC
Digital
Control
VIN
C1
Low
Dropout
Linear
Driver
RSET
DC
Control
Control
GND
LCD Display Backlight with Four WLEDs
High Current Flash Driver
DAM and Dynamic Average Matching 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
August 2009
M9999-080309-D
Micrel Inc.
MIC2842A
Ordering Information
Part Number
Mark Code(1)
Temperature Range
Package(2)
R2Y
–40°C to +125°C
10-Pin 2mm x 2mm Thin MLF®
MIC2842AYMT
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
VIN
1
10 D1
DC
2
9
D2
RSET
3
8
D3
GND
4
7
D4
N/C
5
6
N/C
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
DC
Digital control input for linear WLED driver. See Digital Dimming Interface. 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
NC
Not connected internally.
6
NC
Not connected internally.
7
D4
LED4 driver. Connect LED anode to VIN and cathode to this pin.
8
D3
LED3 driver. Connect LED anode to VIN and cathode to this pin.
9
D2
LED2 driver. Connect LED anode to VIN and cathode to this pin.
10
D1
EPAD
HS PAD
August 2009
Pin Function
LED1 driver. Connect LED anode to VIN and cathode to this pin.
Heat sink pad. Not internally connected. Connect to ground.
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Micrel Inc.
MIC2842A
Absolute Maximum Ratings(1)
Operating Ratings(2)
Main Input Voltage (VIN) .................................. –0.3V to +6V
Enable Input Voltage (VEND) ............................ –0.3V to +6V
LED Driver Voltage (VD1-D4) ............................ –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 (VDC) .................................... 0V to VIN
LED Driver Voltage (VD1-D4) ................................... 0V to VIN
Junction Temperature (TJ) ........................ –40°C to +125°C
Junction Thermal Resistance
2mm x 2mm Thin MLF® (θJA).............................90°C/W
Electrical Characteristics
WLED Linear Drivers
VIN = VDC = 3.8V, RSET = 20.5kΩ; VD1-D4 = 0.6V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted.
Parameter
Conditions
Min
(4)
Typ
Max
Units
Current Accuracy
1.5
Matching(5)
1.5
3.6
%
%
Drop-out
Where ILED = 90% of LED current seen at
VDROPNOM = 0.6V, 100% brightness level
40
80
mV
Ground/Supply Bias Current
IOUT = 20mA
1.4
1.8
mA
Shutdown Current
(current source leakage)
VDC = 0V > 1260µs
0.01
1
µA
0.2
V
1
µA
Digital Dimming
DC Input Voltage (VDC)
Logic Low
1.2
Logic High
V
Enable Input Current
VDC = 1.2V
0.01
tSHUTDOWN
Time DC pin is low to put into shutdown
1260
tMODE_UP
Time DC pin is low to change to Count Up Mode
100
160
µs
tMODE_DOWN
Time DC pin is low to change to Count Down Mode
420
500
µs
tPROG_HIGH, tPROG_LOW
Time for valid edge count; Ignored if outside limit range
2
32
µs
tDELAY
Time DC pin must remain high before a mode change
can occur
100
tPROG_SETUP
First down edge must occur in this window during
presetting brightness
tSTART_UP
Delay from DC is high to start up
5
140
µs
µs
75
µs
µs
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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Micrel Inc.
MIC2842A
Typical Characteristics
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MIC2842A
Functional Characteristics
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MIC2842A
Functional Diagram
VIN
VIN
V-to-I
D1...D4
BG
1.27V
4
DIGITAL
CONTROL
DC
POR
TSD
OSC
GND
RSET
Figure 1. MIC2842A Functional Block Diagram
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MIC2842A
RSET
The RSET pin is used by connecting a RSET resistor to
ground to set the peak current of the linear LED drivers.
The average LED current can be calculated by the
equation (1) below.
ILED (mA) = 410 * ADC / RSET (kΩ)
(1)
ADC is the average duty cycle of the LED current
controlled by the single-wire digital dimming. See Table
1 for ADC values. When the device is fully on the
average duty cycle equals 100% (ADC=1). A plot of ILED
versus RSET at 100% duty cycle is shown in Figure 2.
Functional Description
The MIC2842A is a four channel linear WLED driver.
The WLED driver is designed to maintain proper current
regulation with LED current accuracy of 1.5%, and
typical matching of 1.5% across the four channels. The
WLEDs are driven independently from the input supply
and will maintain regulation with a dropout of 40mV at
20mA. The low dropout 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
RSET resistor. If dimming is desired the MIC2842A is
controlled by a single-wire digital interface.
Block Diagram
As shown in Figure 1, the MIC2842A consists of 4
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
MIC2842A dimming is controlled by an internal Digital
Control Interface.
VIN
The input supply (VIN) provides power to the linear
drivers and the control circuitry. The VIN operating range
is 3V to 5.5V. A 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
DC
The DC pin is used to enable and control dimming of the
linear drivers on the MIC2842A. See the MIC2842A
Digital Dimming Interface in the Application Information
section for details. Pulling the DC pin low for more than
1260μs puts the MIC2842A into a low Iq sleep mode.
The DC pin cannot be left floating; a floating enable pin may
cause an indeterminate state on the outputs. A 200kΩ pull
down resistor is recommended.
August 2009
D1-D4
The D1 through D4 pins are the linear driver inputs for
WLED 1 through 4, respectively. When operating with
less than four WLEDs, leave the unused D pins
unconnected. The linear drivers are extremely versatile
in that they may be used in any combination, for
example D1 thru D4 leaving D3 unconnected or
paralleled for higher current applications.
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 for more details.
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Micrel Inc.
MIC2842A
Dynamic Average Matching (DAM™)
The Dynamic Average Matching™ architecture
multiplexes four voltage references to provide highly
accurate LED current and channel matching. The
MIC2842A achieves industry leading LED channel
matching of 1.5% across the entire dimming range.
Application Information
0
Average
Duty
Cycle (%)
100
1
80
Brightness Level
(0 - 48)
Average
ILED (mA)
IPEAK (mA)
12
9.6
2
60
7.2
3
48.33
5.8
4
36.67
4.4
5
29.17
3.5
6
21.67
2.6
7
16.67
2
8
11.67
1.4
9
9.17
1.1
10
6.67
0.8
11
5
0.6
12
3.33
0.4
13
2.5
0.3
14
1.67
0.2
15
0.83
0.1
16
0
0
17
0.83
0.1
18
0.83
0.17
19
1.25
0.25
20
1.67
0.33
21
2.08
0.42
22
2.5
0.5
23
2.92
0.58
24
3.33
0.67
25
4.17
0.83
26
5
1
27
5.83
1.17
28
6.67
1.33
29
7.92
1.58
30
9.17
1.83
31
10.42
2.08
32
11.67
2.33
33
14.17
2.83
34
16.67
3.33
35
19.17
3.83
36
21.67
4.33
37
25.42
5.08
38
29.17
5.83
39
32.92
6.58
40
36.67
7.33
41
42.5
8.5
42
48.33
9.67
43
54.17
10.83
44
60
12
45
70
14
46
80
16
47
90
18
48
100
20
High Current Parallel Operation
U1 MIC2842AYMT
60% of IPEAK
RSET = 20.5kΩ
IPEAK = 12mA
VIN
C1
DC
0
60% of IPEAK
Low
Dropout
Linear
Driver
RSET
Control
Control
Figure 3. High Current LED Driver Circuit
The linear drivers are independent of each other and can
be used individually or paralleled in any combination for
higher current applications. A single WLED can be
driven with all 4 linear drivers by connecting D1 through
D4 in parallel to the cathode of the WLED as shown in
Figure 3. This will generate a current 4 times the
individual channel current and can be used for higher
current WLEDs such as those used in flash or torch
applications.
Digital Dimming
The MIC2842A utilizes an internal dynamic pulse width
to generate an average duty cycle for each brightness
level. By varying the duty cycle the average current
achieves 49 logarithmically spaced brightness levels.
This generates a brightness scale similar to the
perception of brightness seen by the “human eye.”
Figure 4 shows the LED current at different brightness
levels. When dimming, the D1 through D4 pins are 60°
out of phase from each other to reduce electromagnetic
interference. The MIC2842A uses an internal frequency
of approximately 700Hz to dim the WLEDs. With the
period of approximately 1.43ms, the 60° phase shift
equates to a timing offset of 238μs. As shown in Figure
5, brightness level 32 was selected to show the phase
shift across the channels.
100% of IPEAK
RSET = 20.5kΩ
IPEAK = 20mA
Table 1. Digital Interface Brightness Level Table
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MIC2842A
Start Up
Assuming the MIC2842A has been off for a long time
and no presetting brightness command is issued
(presetting is discussed in a later section), the
MIC2842A will start-up in its default mode approximately
140µs (tSTART_UP) after a logic level high is applied to the
DC pin, shown in Figure 6. In the default mode the LEDs
are turned on at the maximum brightness level of 48.
Each falling edge during the tPROG_SETUP period will cause
the default brightness level to decrease by one. This is
discussed in more detail in the Presetting Brightness
section.
Figure 4. LED Current with Brightness Level Change
Figure 6. Typical Start-Up Timing
Shutdown
Whenever the DC input pin is pulled low for a period
greater than or equal to tSHUTDOWN (1260µs), the
MIC2842A will be shutdown as shown in Figure 7.
Figure 5. LED Current 60° Phase Shift
Digital Dimming Interface
The MIC2842A incorporates an easy to use single-wire,
serial programming interface that allows users to set
LED brightness up to 49 different levels, as shown in the
table1.
Brightness levels 0 through 15 are logarithmically
spaced with a peak current equal to 60% of the current
programmed by RSET. Brightness level 16 is provided for
applications that want to “fade to black” with no current
flowing through the LEDs. Brightness Level 17 has the
same duty cycle as level 18, but the peak current is only
60% of the current set by RSET; therefore, the average
current is 0.1mA. Brightness levels 18 through 48 are
also logarithmically spaced, but the peak current is equal
to 100% of the current determined by RSET. Refer to
Table 1 for the translation from brightness level to
average LED duty cycle and current. The MIC2842A is
designed to receive programming pulses to increase or
decrease brightness. Once the brightness change signal
is received, the DC pin is simply pulled high to maintain
the brightness. This “set and forget” feature relieves
processor computing power by eliminating the need to
constantly send a PWM signal to the dimming pin. With
a digital control interface, brightness levels can also be
preset so that LEDs can be turned on at any particular
brightness level.
August 2009
Figure 7. Shutdown Timing
Once the device is shutdown, the control circuit supply is
disabled and the LEDs are turned off, drawing only
0.01µA. Brightness level information stored in the
MIC2842A prior to shutdown will be erased.
Count Up Mode/Count Down Mode
The mode of MIC2842A can be in either Count Up Mode
or Count Down Mode. The Count Down/Up Modes
determine what the falling edges of the programming
pulses will do to the brightness. In Count Up Mode,
subsequent falling edges will increase brightness while
in Count Down Mode, subsequent falling edges will
decrease brightness. By default, the MIC2842A is in
Count Down Mode when first turned on. The counting
mode can be changed to Count Up Mode, by pulling the
DC pin low for a period equal to tMODE_UP (100µs to
160µs), shown in Figure 8. The device will remain in
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Micrel Inc.
MIC2842A
Count Up Mode until its mode is changed to Count Down
Mode or by disabling the MIC2842A to reset the mode
back to default.
Figure 8. Mode Change to Count Up
Figure 10. Brightness Programming Pulses
To change the mode back to Count Down Mode, pull the
DC pin low for a period equal to tMODE_DOWN (420µs to
500µs), shown in Figure 9. Now the internal circuitry will
remain in Count Down Mode until changed to Count Up
as described previously.
Multiple brightness levels can be set as shown in Figure
11. When issuing multiple brightness level adjustments
to the DC pin, ensure both tPROG_LOW and tPROG_HIGH are
within 2µs to 32µs.
To maintain operation at the current brightness level
simply maintain a logic level high at the DC pin.
Figure 9. Mode Change to Count Down
Programming the Brightness Level
MIC2842A is designed to start driving the LEDs 140µs
(tSTART_UP) after the DC pin is first pulled high at the
maximum brightness level of 48. After start up, the
internal control logic is ready to decrease the LED
brightness upon receiving programming pulses (negative
edges applied to DC pin). Since MIC2842A starts in
Count Down Mode, the brightness level can be
decreased without a mode change by applying two
programming pulses, as shown in Figure 10. Note that
the extra pulse is needed to decrease brightness
because the first edge is ignored. Anytime the first falling
edge occurs later than 32µs after a Mode Change, it will
be ignored. Ignoring the first falling edge is necessary in
order that Mode Change (tMODE_UP, tMODE_DOWN) pulses do
not result in adjustments to the brightness level. Each
programming pulse has a high (tPROG_HIGH) and a low
(tPROG_LOW) pulse width that must be between 2µs to
32µs. The MIC2842A will remember the brightness level
and mode it was changed to. For proper operation,
ensure that the DC pin remains high for at least tDELAY
(140µs) before issuing a mode change command.
August 2009
Figure 11. Decreasing Brightness Several Levels
As mentioned, MIC2842A can be programmed to set
LED drive current to produce one of 49 distinct
brightness levels. The internal logic keeps track of the
brightness level with an Up/Down counter circuit. The
following section explains how the brightness counter
functions with continued programming edges.
Counter Roll-Over
The MIC2842A internal up/down counter contains
registers from 0 to 48 (49 levels). When the brightness
level is at 0 and a programming pulse forces the
brightness to step down, then the counter will roll-over to
level 48. This is illustrated in Figure 12.
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Micrel Inc.
MIC2842A
(2µs to 32µs). Figure 15 illustrates the proper timing for
execution of a One-Step Brightness Increase.
Figure 12. Down Counter Roll-Over
Figure 15. One-Step Brightness Increase
Similarly, when the counter mode is set to Count Up and
a programming pulse forces the brightness level to step
up from level 48, then the counter will roll-over to level 0
as illustrated in Figure 13.
Presetting Brightness
Presetting the brightness will allow the MIC2842A startup at any brightness level (0 to 48). The MIC2842A does
not turn on the linear LED driver until the DC pin is kept
high for tSTART_UP (140µs). This grants the user time to
preset the brightness level by sending a series of
programming edges via the DC pin. The precise timing
for the first down edge is between 5µs to 75µs after the
DC pin is first pulled high. The 70µs timeframe between
5µs and 75µs is the tPROG_SETUP period. The first
presetting pulse edge must occur somewhere between
the timeframe of 5µs to 75µs, otherwise the MIC2842A
may continue to start up at the full (default) brightness
level.
Figure 13. Up Counter Roll-Over
One-Step Brightness Changes
The “One-Step” brightness change procedure relieves
the user from keeping track of the MIC2842A’s up/down
counter mode. It combines a Mode Change with a
programming edge; therefore, regardless of the previous
Count Mode, it will change the brightness level by one.
Figure 16. Presetting Timing
Figure 16 shows the correct presetting sequence to set
the MIC2842A brightness to level 39 prior to start up.
Notice that when using the presetting feature the first
programming pulse is not ignored. This is because the
counter’s default mode is Count Down and a Mode
Change cannot be performed in the presetting mode.
(Note that the tPROG_HIGH and tPROG_LOW pulse width must
still be between 2µs to 32µs.)
Figure 14. One-Step Brightness Decrease
The One-Step Brightness Decrease method is quite
simple. First, the DC pin is pulled low for a period equal
to the tMODE_DOWN (420µs to 500µs) and immediately
followed by a falling edge within tPROG_HIGH (2µs to 32µs)
as shown in Figure 14. This will decrease the brightness
level by 1. Similarly a One-Step Brightness Increase can
be assured by first generating a DC down pulse whose
period is equal to the tMODE_UP (100µs to 160µs) and
immediately followed by a falling edge within tPROG_HIGH
August 2009
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MIC2842A
Typical Application
U1 MIC2842AYMT
VIN
C1
1µF/6.3V
DC
R1
20.5K
1
VIN
D1
10
2
DC
D2
9
D3
8
R2
200K
3
RSET
D4
7
4
GND
NC
NC
6
5
D1
LED
VIN
D2
LED
D3
LED
D4
LED
Bill of Materials
Item
C1
D1 – D4
Part Number
Manufacturer
C1608X5R0J105K
TDK
06036D105KAT2A
AVX(2)
GRM188R60J105KE19D
Murata(3)
VJ0603G225KXYAT
Vishay
Qty.
Ceramic Capacitor, 1µF, 6.3V, X5R, Size 0603
1
WLED
4
Resistor, 20.5k, 1%, 1/16W, Size 0603
1
Resistor, 200k, 1%, 1/16W, Size 0603
1
High Efficiency 4 Channel WLED Driver with
Single Wire Digital Control
1
(4)
SWTS1007
Seoul Semiconductor(5)
99-116UNC
EverLight(6)
CRCW060320K5F5EA
Vishay(4)
R2
CRCW06032003FKEA
(4)
U1
MIC2842AYMT
R1
Description
(1)
Vishay
Micrel, Inc.(7)
Notes:
1. TDK: www.tdk.com
2. AVX: www.avx.com
3. Murata: www.murata.com
4. Vishay: www.vishay.com
5. Seoul Semiconductor: www.seoulsemicon.com
6. EverLight: www.everlight.com
7. Micrel, Inc.: www.micrel.com
August 2009
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MIC2842A
PCB Layout Recommendations
Top Layer
Bottom Layer
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MIC2842A
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
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
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.
© 2009 Micrel, Incorporated.
August 2009
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