Micrel MIC2845A-SCYMT High efficiency 6 channel linear wled driver with damâ ¢, ultra fast pwmâ ¢ control and dual low iq ldo Datasheet

MIC2845A
High Efficiency 6 Channel Linear WLED
Driver with DAM™, Ultra Fast PWM™
Control and Dual Low IQ LDOs
General Description
Features
The MIC2845A is a high efficiency White LED (WLED)
driver designed to drive up to six LEDs, greatly extending
battery life for portable display backlighting, keypad
backlighting, and camera flash in mobile devices. The
MIC2845A provides the highest possible efficiency as this
architecture has no switching losses present in traditional
charge pumps or inductive boost circuits. The MIC2845A
provides six linear drivers channels which maintain
constant current for up to six LEDs. It features a typical
dropout of 40mV at 20mA. This allows the LEDs to be
driven directly from the battery eliminating switching
noise/losses present with the use of boost circuitry.
The MIC2845A features Dynamic Average Matching™
(DAM™) which is specifically designed to provide optimum
matching across all WLEDs. The six channels are
matched better than ±1.5% typical, ensuring 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 MIC2845A also features two independently enabled
low quiescent current LDOs. Each LDO offers ±3%
accuracy from the nominal voltage over temperature, low
dropout voltage (150mV @ 150mA), and low ground
current under all load conditions (typically 35µA). Both
LDOs can be disabled to draw virtually no current.
The MIC2845A is available in the 14-pin 2.5mm x 2.5mm
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.
WLED Driver
•
•
•
•
•
•
•
•
High Efficiency (no Voltage Boost losses)
Dynamic Average Matching™ (DAM™)
Ultra Fast PWM™ control (200Hz to 500kHz)
Input voltage range: 3.0V to 5.5V
Dropout of 40mV at 20mA
Matching better than ±1.5% (typical)
Current accuracy better than ±1.5% (typical)
Maintains proper regulation regardless of how many
channels are utilized
LDOs
•
•
•
•
•
Very low ground current – Typical 35µA
Stable with 1µF ceramic output capacitor
Dropout of 150mV at 150mA
Thermal shutdown and current limit protection
Available in a 14-pin 2.5mm x 2.5mm Thin MLF®
package
Applications
• Mobile handsets
• LCD Handset backlighting
• Handset keypad backlighting
• Digital cameras
• Portable media/MP3 players
• Portable navigation devices (GPS)
• Portable applications
DAM, Dynamic Average Matching and Ultra Fast PWM are trademarks 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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M9999-041210-C
Micrel Inc.
MIC2845A
Typical Application
LCD Display Backlight with 6 WLEDs and Camera Module
High Current Flash Driver
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MIC2845A
Ordering Information
Mark Code(1)
LDO1
VOUT
LDO2
VOUT
Temperature Range
Package(2)
MIC2845A-MFYMT
YNMF
2.8V
1.5V
–40°C to +125°C
14-Pin 2.5mm x 2.5mm Thin MLF®
MIC2845A-MGYMT
YNMG
2.8V
1.8V
–40°C to +125°C
14-Pin 2.5mm x 2.5mm Thin MLF®
MIC2845A-PGYMT
YNPG
3.0V
1.8V
–40°C to +125°C
14-Pin 2.5mm x 2.5mm Thin MLF®
MIC2845A-PPYMT
YNPP
3.0V
3.0V
–40°C to +125°C
14-Pin 2.5mm x 2.5mm Thin MLF®
MIC2845A-SCYMT
YNSC
3.3V
1.0V
–40°C to +125°C
14-Pin 2.5mm x 2.5mm Thin MLF®
Part Number
Notes:
®
1. Thin MLF ▲ = Pin 1 identifier.
®
2. Thin MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is halogen free.
3. Contact Micrel for other voltage options.
D5
D6
EN1
LDO1
Pin Configuration
VIN
D4
LDO2
GND
EPAD
EN2
D2
D1
RSET
END
D3
14-Pin 2.5mm x 2.5mm Thin MLF® (MT)
(Top View)
Pin Description
Pin Number
Pin Name
1
VIN
2
LDO2
3
EN2
4
END
Enable for LED driver. Can be used as a PWM input for dimming of LEDs. Do not leave floating.
5
RSET
An internal 1.27V reference sets the nominal maximum LED current. Example, apply a 20.5kΩ
resistor between RSET and GND to set LED current to 20mA at 100% duty cycle.
6
D1
LED1 driver. Connect LED anode to VIN and cathode to this pin.
7
D2
LED2 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
GND
10
D4
LED4 driver. Connect LED anode to VIN and cathode to this pin.
11
D5
LED5 driver. Connect LED anode to VIN and cathode to this pin.
12
D6
LED6 driver. Connect LED anode to VIN and cathode to this pin.
13
EN1
14
LDO1
EPAD
HS PAD
April 2010
Pin Function
Voltage Input. Connect at least 1µF ceramic capacitor between VIN and GND.
Output of LDO2. Connect at least 1µF ceramic output capacitor.
Enable Input for LDO2. Active High Input. Logic High = On; Logic Low = Off; Do not leave floating.
Ground.
Enable Input for LDO1. Active High Input. Logic High = On; Logic Low = Off; Do not leave floating.
Output of LDO1. Connect at least 1µF ceramic output capacitor.
Heat sink pad. Not internally connected. Connect to ground.
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MIC2845A
Absolute Maximum Ratings(1)
Operating Ratings(2)
Main Input Voltage (VIN) .................................. –0.3V to +6V
Enable Input Voltage (VEND, VEN1, VEN2) .......... –0.3V to +6V
LED Driver Voltage (VD1-D6) ............................ –0.3V to +6V
Power Dissipation .................................. Internally Limited(3)
Lead Temperature (soldering, 10sec.)....................... 260°C
Storage Temperature (Ts) .........................–65°C to +150°C
ESD Rating(4) ................................................. ESD Sensitive
Supply Voltage (VIN)..................................... +3.0V to +5.5V
Enable Input Voltage (VEND, VEN1, VEN2) ................ 0V to VIN
LED Driver Voltage (VD1-D6) ................................... 0V to VIN
Junction Temperature (TJ) ........................ –40°C to +125°C
Junction Thermal Resistance
2.5mm x 2.5mm Thin MLF-14L (θJA) .................89°C/W
Electrical Characteristics
WLED Linear Drivers
VIN = VEND = 3.8V, VEN1 = VEN2 = 0V, RSET = 20.5kΩ; VD1-D6 = 0.6V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ 125°C;
unless noted.
Parameter
Conditions
Min
Typ
Max
Units
Current Accuracy(5)
1.5
(6)
1.5
3.6
%
Matching
%
Drop-out
Where ILED = 90% of LED current seen at
VDROPNOM = 0.6V, 100% brightness level
40
80
mV
Supply Bias Current
ILED = 20mA
1.4
1.8
mA
Shutdown Current
(current source leakage)
VEND = 0V
0.01
1
µA
0.2
V
0.01
1
µA
80
µs
PWM Dimming
Enable Input Voltage (VEND)
Logic Low
Logic High
V
1.2
Enable Input Current
VIH = 1.2V
Current Source Delay
(50% levels)
Shutdown to On
40
Standby to On
2
µs
On to Standby
0.3
µs
TRISE
1.3
µs
TFALL
0.3
µs
Current Source Transient Time
(10%-90%)
Stand-by to Shutdown Time
April 2010
VEND = 0V
10
4
24
40
ms
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Micrel Inc.
MIC2845A
LDOs
VIN = VEN1 = VEN2 = 3.8V, VEND = 0V, COUT1 = COUT2 = 1µF, IOUT1 = IOUT2 = 100µA; TJ = 25°C, bold values indicate –40°C ≤
TJ ≤ 125°C; unless noted.
Parameter
Conditions
Output Voltage Accuracy
Variation from nominal VOUT
Min
Max
Units
–2
+2
%
–3
+3
%
0.3
%/V
150
330
mV
35
70
µA
0.05
1
µA
500
mA
VIN Line Regulation
0.02
Load Regulation
IOUT = 100µA to 150mA
Dropout Voltage(7)
VOUT ≥ 3.0V, IOUT = 150mA
7
Ground Pin Current
Ground Pin Current in Shutdown
Typ
VEN = 0V
Ripple Rejection
f = 1kHz; COUT = 2.2µF
Current Limit
VOUT =0V
Output Voltage Noise
Frequency 10Hz to 100kHz
mV
65
175
300
dB
200
µVRMS
Enable Inputs (EN1, EN2)
Enable Input Voltage
Logic Low
0.2
Logic High
Enable Input Current
VEN1 = VEN2 = 1.2V
Turn-on Time
COUT = 1µF; 90% of VOUT
V
V
1.2
0.01
1
µA
50
100
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. The maximum allowable power dissipation of any TA (ambient temperature) is PD(max) = (TJ(max) – TA) / θJA. Exceeding the maximum allowable power
dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown (150°C).
4. Devices are ESD sensitive. Handling precautions recommended. Human Body Model (HBM), 1.5kΩ in series with 100pF.
5. As determined by average current of all channels in use and all channels loaded.
6. The current through each channel meets the stated limits from the average current of all channels.
7. Dropout voltage is defined as the input-output differential at which the output voltage drops 2% below its nominal value measured at VIN = VOUT+ 1V.
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MIC2845A
Typical Characteristics
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MIC2845A
Typical Characteristics (LDO)
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MIC2845A
Functional Characteristics (WLED Driver)
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MIC2845A
Functional Characteristics (LDO)
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MIC2845A
Functional Diagram
EN2 EN1
VIN
VIN
EN
V-to-I
OUT
TSD
LDO1
D1...D6
BG
1.27V
VREF
GND
6
VIN
EN
TSD
PWM
CONTROL
END
OUT
LDO2
POR
VREF
TSD
GND
OSC
RSET
GND
Figure 1. MIC2845A Functional Block Diagram
which reduces the operating current to less than 1µA in
shutdown. Both linear regulators are stable with just 1µF
of output capacitance.
Functional Description
The MIC2845A is a six channel linear LED driver with
dual 150mA LDOs. The LED driver is designed to
maintain proper current regulation with LED current
accuracy of 1.5% while the typical matching between the
six channels is 1.5% at room temperature. The LED
currents are independently driven from the input supply
and will maintain regulation with a dropout of 40mV at
20mA. 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 END pin. The
MIC2845A accommodates a wide PWM frequency range
as outlined in the application information section.
The MIC2845A has two LDOs with a dropout voltage of
150mV at 150mA and consume 35µA of current in
operation. Each LDO has an independent enable pin,
April 2010
Block Diagram
As shown in Figure 1, the MIC2845A consists of two
LDOs with six 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 MIC2845A dimming is controlled by the
Ultra Fast PWMTM control block that receives PWM
signals for dimming. The LDOs each have their own
control and are independent of the linear LED drivers.
Each LDO consists of internal feedback resistors, an
error amplifier, a PFET transistor and a control circuit for
enabling.
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MIC2845A
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).
LDO1/LDO2
The output pins for LDO one and LDO two are labeled
LDO1 and LDO2, respectively. A minimum of 1µF
bypass capacitor should be placed as close as possible
to the output pin of each LDO. Refer to the layout
recommendations section for details on placing the
output capacitor (C2, C3) of the LDOs.
Figure 2. Peak LED Current vs. RSET
EN1/EN2
A logic high signal on the enable pin activates the LDO
output voltage of the device. A logic low signal on the
enable pin deactivates the output and reduces supply
current to less than 1µA. EN1 controls LDO1 and EN2
controls LDO2. Do not leave these control pins floating.
D1-D6
The D1 through D6 pins are the linear driver for LED 1
through 6, respectively. Connect the anodes of the LEDs
to VIN and each cathode of the LEDs to D1 through D6.
When operating with less than six LEDs, leave the
unused D pins unconnected. The six LED channels are
independent of one another and may be combined or
used separately.
END
The END pin is equivalent to the enable pin for the linear
drivers on the MIC2845A. 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 END low for more than 24ms puts the
MIC2845A into a low Iq sleep mode. The END pin cannot
be left floating; a floating enable pin may cause an
indeterminate state on the outputs. A 200kΩ pull down
resistor is recommended.
GND
The ground pin is the ground path for the linear drivers
and LDOs. 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.
RSET
The RSET pin is used to set the peak current of the linear
driver by connecting a RSET resistor to ground. The
average LED current can be calculated by equation (1):
(1)
ILED (mA) = 410 * D / RSET (kΩ)
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.
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MIC2845A
Application Information
Dynamic Average Matching (DAM™)
The Dynamic Average Matching architecture multiplexes
four current references to provide highly accurate LED
current and channel matching. The MIC2845A achieves
industry leading LED channel matching of 1.5% across
the entire dimming range.
Ultra Fast PWM™ Dimming Interface
The MIC2845A 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.
Figure 4. Channel Current Response to PWM Control
Signal Frequencies from 50kHz to 500kHz
WLED dimming is achieved by applying a pulse width
modulated (PWM) signal to the END pin. For PWM
frequencies between 200Hz – 20kHz the MIC2845A
supports a duty cycle range from 1% to 100%, as shown
in Figure 3. The MIC2845A 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
MIC2845A 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 Figure 5. Figures
6 through 10 show the WLED current response when a
PWM signal is applied to the END pin (1).
Figure 5. Minimum Duty Cycle
for Varying PWM Frequency
(1)
From the low Iq sleep mode PWM frequencies above
15kHz require a logic high enable signal for 80μs to first
enable the MIC2845A prior to PWM dimming.
Figure 6. PWM Signal at 1% Duty Cycle (Iavg = 0.2mA)
Figure 3. Average Current per LED Dimming
by Changing PWM Duty Cycle for PWM Frequencies
up to 20kHz
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MIC2845A
Figure 10. PWM Signal at 100% Duty Cycle (Iavg = 20mA)
Figure 7. PWM Signal at 20% Duty Cycle (Iavg = 4mA)
High Current Parallel Operation
Figure 8. PWM Signal at 50% Duty Cycle (Iavg = 10mA)
Figure 11. Six Channel (Parallel) Application Circuit
The linear drivers are independent of each other and can
be used individually or paralleled to provide larger
current. A single LED can be driven with all 6 linear
drivers by connecting D1 through D6 together with the
cathode of the LED as shown in Figure 11. This will
generate a current 6 times the LED current setting and
can be used for higher current LEDs such as those used
in flash or torch applications. The current is set by the
RSET resistor, and can be calculated by the following
equation.
ILED (mA) = 6 * 410 * D / RSET (kΩ).
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.
Figure 9. PWM Signal at 80% Duty Cycle (Iavg = 16mA)
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MIC2845A
Output Capacitor
The MIC2845A LDOs require an output capacitor of at
least 1µF or greater to maintain stability, however, the
output capacitor can be increased to 2.2µF to reduce
output noise without increasing package size. The
design is optimized for use with low-ESR ceramic chip
capacitors. High ESR capacitors are not recommended
because they may cause high frequency oscillation.
X7R/X5R dielectric-type ceramic capacitors are
recommended due to their improved temperature
performance compared to Z5U and Y5V capacitors.
X7R-type capacitors change capacitance by 15% over
their operating temperature range and are the most
stable type of ceramic capacitors. Z5U and Y5V
dielectric capacitors change value by as much as 50%
and 60%, respectively, over their operating temperature
ranges. While using Z5U and Y5V ceramic capacitors,
ensure that the loss in capacitance does not drop below
the minimum requirement of the device.
Figure 12. Current Response Time to Enable Signal
Turning On (Six Paralleled Channels)
No-Load Stability
Unlike many other voltage regulators, the MIC2845A
LDOs will remain stable and in regulation with no load.
Thermal Considerations
The MIC2845A LDOs are each designed to provide
150mA of continuous current. Maximum ambient
operating temperature can be calculated based on the
output current and the voltage drop across the part. For
example if the input voltage is 3.6V, the output voltage is
2.8V, and the output current = 150mA. The actual power
dissipation of the regulator circuit can be determined
using the equation:
Figure 13. Current Response Time to Enable Signal
Turning Off (Six Paralleled Channels)
PLDO1 = (VIN – VOUT1) I OUT + VIN IGND
Because this device is CMOS and the ground current
(IGND) is typically <100µA over the load range, the power
dissipation contributed by the ground current is < 1%
and can be ignored for this calculation.
PLDO1 = (3.6V – 2.8V) x 150mA
LDO
MIC2845A LDOs are low noise 150mA LDOs. The
MIC2845A LDO regulators are fully protected from
damage due to fault conditions, offering linear current
limiting and thermal shutdown.
PLDO1 = 0.120W
Since there are two LDOs in the same package, the
power dissipation must be calculated individually and
then summed together to arrive at the total power
dissipation.
PTOTAL = PLDO1 + PLDO2
Input Capacitor
The MIC2845A LDOs are high-performance, high
bandwidth devices. 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 small-valued NPO dielectric-type capacitors,
help filter out high-frequency noise and are good
practice in any noise sensitive 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.
April 2010
To determine the maximum ambient operating
temperature of the package, use the junction-to-ambient
thermal resistance (θJA = 60°C/W) of the device and the
following basic equation:
⎛ TJ(max) − TA
PTOTAL(max) = ⎜⎜
θ JA
⎝
14
⎞
⎟
⎟
⎠
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MIC2845A
PLDO2 = (3.6V – 1.5V) x 150mA = 0.315W
PTOTAL=0.120W+ 0.315W = 0.435W
= (125°C – TA)/(60°C/W)
TA = 125°C – 0.435W x 60°C/W
TA = 98.9°C
Therefore, under the above conditions, the maximum
ambient operating temperature of 98.9°C is allowed.
TJ(max) = 125°C, is the maximum junction temperature of
the die and θJA, is the thermal resistance = 60°C/W.
Substituting PTOTAL for PTOTAL(max) and solving for the
ambient operating temperature will give the maximum
operating conditions for the regulator circuit.
For example, when operating the MIC2845A LDOs
(LDO1 = 2.8V and LDO2 = 1.5V) at an input voltage of
3.6V with 150mA load on each, the maximum ambient
operating temperature TA can be determined as follows:
PLDO1 = (3.6V – 2.8V) x 150mA = 0.120W
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MIC2845A
MIC2845A Typical Application Circuit
Bill of Materials
Item
C1, C2,
C3
Part Number
Manufacturer
C1608X5R0J105K
TDK
06036D105KAT2A
AVX(2)
GRM188R60J105KE19D
Murata(3)
VJ0603G225KXYAT
Vishay(4)
SWTS1007
Seoul Semiconductor(5)
D1 – D6
99-116UNC
EverLight
(6)
CRCW060320K5F5EA
Vishay(4)
R2
CRCW06032003FKEA
(4)
U1
MIC2845A-xxYMT
R1
Description
Qty.
(1)
Vishay
Micrel, Inc.(7)
Ceramic Capacitor, 1µF, 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
6 Channel Ultra Fast PWM™ Linear WLED Driver
with DAM™ and Dual Low IQ LDOs
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
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MIC2845A
PCB Layout Recommendations
Top Layer
Bottom Layer
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MIC2845A
Package Information
14-Pin (2.5mm x 2.5mm) 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.
April 2010
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