Micrel MIC2844A High efficiency 6 channel wled driver with damâ ¢ and single wire digital control Datasheet

MIC2844A
High Efficiency 6 Channel WLED Driver
with DAM™ and Single Wire Digital Control
General Description
Features
The MIC2844A is a high efficiency linear White LED (WLED)
• High Efficiency (no Voltage Boost losses)
driver designed to drive up to six WLEDs, greatly extending
• Dynamic Average Matching™ (DAM™)
battery life for portable display backlighting keypad
• Single wire digital control
backlighting, and camera flash in mobile devices. The
• Input voltage range: 3.0V to 5.5V
MIC2844A provides the highest possible efficiency as this
• Dropout of 40mV at 20mA
architecture has no switching losses present in traditional
charge pumps or inductive boost circuits. The MIC2844A
• Matching better than ±1.5% (typical)
provides six linear drivers which maintain constant current for
• Current accuracy better than ±1.5% (typical)
up to six WLEDs. It features a typical dropout of 40mV at
• Maintains proper regulation regardless of how many
20mA. This allows the WLEDs to be driven directly from the
channels are utilized
battery eliminating switching noise/losses present with the
• Available in a 10-pin 2mm x 2mm Thin MLF® package
use of boost circuitry.
The MIC2844A features Dynamic Average Matching™
Applications
(DAM™) which is specifically designed to provide optimum
matching across all WLEDs. The six channels are matched
• Mobile handsets
better than ±1.5% typical, ensuring uniform display
• Handset LCD backlighting
illumination under all conditions. The LED brightness is preset
• Handset keypad backlighting
by an external resistor and can be dimmed using a singlewire digital control. The digital interface takes commands
• Camera flash (see MIC2843A datasheet)
from digital programming pulses to change the brightness in
• Digital cameras
a logarithmic scale similar to the eye’s perception of
• Portable media/MP3 players
brightness. The single-wire digital brightness control is
divided into two modes of operation; full brightness mode, or
• Portable navigation devices (GPS)
battery saving mode for a total of 49 brightness steps.
• Portable applications
The MIC2844A is available in the 10-pin 2mm x 2mm 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.
____________________________________________________________________________________________________________
Typical Application
U1 MIC2844AYMT
U1 MIC2844AYMT
VIN
VIN
C1
Low
Dropout
Linear
Driver
RSET
DC
Digital
Control
C1
VIN
LCD Display Backlight with Six WLEDs
Low
Dropout
Linear
Driver
RSET
DC
Digital
Control
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.
MIC2844A
Ordering Information
Part Number
Mark Code(1)
Temperature Range
Package(2)
T4Y
–40°C to +125°C
10-Pin 2mm x 2mm Thin MLF®
MIC2844AYMT
Note:
®
1.
Thin MLF S = 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
D6
5
6
D5
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
D6
LED6 driver. Connect LED anode to VIN and cathode to this pin.
6
D5
LED5 driver. Connect LED anode to VIN and cathode to this pin.
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.
MIC2844A
Absolute Maximum Ratings(1)
Operating Ratings(2)
Main Input Voltage (VIN) .................................. –0.3V to +6V
Enable Input Voltage (VDC).............................. –0.3V to +6V
LED Driver 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 (VDC) .................................... 0V to VIN
LED Driver Voltage (VD1-D6) ................................... 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
VIN = VDC = 3.8V, RSET = 20.5kΩ; VD1-D6 = 0.6V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C; unless noted.
Parameter
Conditions
Min
(4)
Current Accuracy
Max
1.5
(5)
Matching
Drop-out
Typ
Where ILED = 90% of LED current seen at
VDROPNOM = 0.6V, 100% brightness level
Units
%
1.5
3.6
%
40
80
mV
Ground/Supply Bias Current
ILED = 20mA
1.4
1.8
mA
Shutdown Current
(current source leakage)
VDC = 0V > 1260µs
0.01
1
µA
0.2
V
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
32
tPROG_HIGH, tPROG_LOW
Time for valid edge count; Ignored if outside limit range
2
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
1
µA
µs
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.
August 2009
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Micrel Inc.
MIC2844A
Typical Characteristics
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Micrel Inc.
MIC2844A
Functional Characteristics
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MIC2844A
Functional Diagram
VIN
VIN
V-to-I
D1...D6
BG
1.27V
6
DIGITAL
CONTROL
DC
POR
TSD
OSC
GND
RSET
Figure 1. MIC2844A Functional Block Diagram
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MIC2844A
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 MIC2844A is a six 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 six 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 MIC2844A is
controlled by a single-wire digital interface.
Block Diagram
As shown in Figure 1, the MIC2844A consists of six
current mirrors set to copy a master current determined
by the RSET resistor. The linear drivers have a
designated control block for enabling and dimming of the
WLEDs.
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
D1-D6
The D1 through D6 pins are the linear driver for WLED 1
through 6, respectively. When operating with less than
six 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 D6 leaving
D5 unconnected or paralleled for higher current
applications.
DC
The DC pin is used to enable and control dimming of the
linear drivers on the MIC2844A. See the MIC2844A
Digital Dimming Interface in the Application Information
section for details. Pulling the DC pin low for more than
1260μs puts the MIC2844A 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
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.
MIC2844A
Dynamic Average Matching™ (DAM™)
The Dynamic Average Matching™ architecture
multiplexes four voltage references to provide highly
accurate LED current and channel matching. The
MIC2844A 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 MIC2844AYMT
60% of IPEAK
RSET = 20.5kΩ
IPEAK = 12mA
VIN
C1
DC
0
60% of IPEAK
Low
Dropout
Linear
Driver
RSET
VIN
Digital
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 6 linear drivers by connecting D1 through
D6 in parallel to the cathode of the WLED as shown in
Figure 3. This will generate a current 6 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 MIC2844A 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 for a single channel at
different brightness levels. When dimming, the D1
through D6 pins are 60° out of phase from each other to
reduce electromagnetic interference. The MIC2844A
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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MIC2844A
Start Up
Assuming the MIC2844A has been off for a long time
and no presetting brightness command is issued
(presetting is discussed in a later section), the
MIC2844A 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
MIC2844A will be shutdown as shown in Figure 7.
Figure 5. LED Current 60° Phase Shift
Digital Dimming Interface
The MIC2844A 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 MIC2844A 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
MIC2844A prior to shutdown will be erased.
Count Up Mode/Count Down Mode
The mode of MIC2844A 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 MIC2844A 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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M9999-080309-D
Micrel Inc.
MIC2844A
Count Up Mode until its mode is changed to Count Down
Mode or by disabling the MIC2844A 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
MIC2844A 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 MIC2844A 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 MIC2844A 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, MIC2844A 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 MIC2844A 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.
MIC2844A
(2µs to 32µs). Figure 15 illustrates the proper timing for
execution of a One-Step Brightness Increase.
Figure 12. Down Counter Roll-Over
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.
Figure 15. One-Step Brightness Increase
Presetting Brightness
Presetting the brightness will allow the MIC2844A startup at any brightness level (0 to 48). The MIC2844A 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 MIC2844A
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 MIC2844A’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 MIC2844A 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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Micrel Inc.
MIC2844A
Typical Application
U1 MIC2844AYMT
VIN
C1
2.2µF/6.3V
DC
VIN
D1
10
2
DC
D2
9
D2
LED
D3
8
D4
7
D5
6
D3
LED
D4
LED
D5
LED
D6
LED
R2
200K
3
R1
20.5K
D1
LED
1
RSET
GND
D6
4
5
VIN
Bill of Materials
Item
C1
D1 – D6
R1
R2
U1
Part Number
Manufacturer
C1608X5R0J225K
TDK
06036D225KAT2A
AVX(2)
GRM188R60J225KE19D
Murata(3)
VJ0603G225KXYAT
Vishay(4)
SWTS1007
Seoul Semiconductor(5)
99-116UNC
EverLight(6)
CRCW060320K5F5EA
Vishay(4)
CRCW06032003FKEA
(4)
MIC2844AYMT
Description
Qty.
(1)
Vishay
Micrel, Inc.(7)
Ceramic Capacitor, 2.2µF, 6.3V, X5R, Size 0603
1
WLED
6
Resistor, 20.5k, 1%, 1/16W, Size 0603
1
Resistor, 200k, 1%, 1/16W, Size 0603
1
High Efficiency 6 Channel WLED Driver with
Single Wire Digital Control
1
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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MIC2844A
PCB Layout Recommendations
Top Layer
Bottom Layer
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MIC2844A
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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