Application Note Mobile Backligh Selection Guide

Application Note
DN[Document ID]
Mobile Backlight
Selection Guide
For ams Lightning Management Units
and Backlight Drivers
ams Application Note
[v1-02] 2014-Jul-18
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Mobile Backlight Selection Guide
Content Guide
1
General Description ............................................................................................................. 4
2
Driving LEDs for Mobile Backlight Applications ................................................................... 4
3
LED Configuration Nomenclature ........................................................................................ 5
4
Product Overview ................................................................................................................. 6
5
Choosing the LED Congiguration ........................................................................................ 8
6
LED Configurations for Chargepump ................................................................................... 8
7
LED Configurations for DCDC ........................................................................................... 10
7.1
DCDC Regulation............................................................................................................... 12
7.1.1
AS3687xm/75/76 DCDC .................................................................................................... 12
7.1.2
AS3677 DCDC ................................................................................................................... 13
7.1.3
AS3490/AS3492 DCDC ..................................................................................................... 14
7.1.4
High Voltage Current Sink Overview ................................................................................. 15
7.2
General DCDC Application Component Selection ............................................................. 15
7.3
Single String Solutions ....................................................................................................... 16
7.3.1
Single String Solutions with higher Forward Voltages ....................................................... 18
7.4
Multiple String Solutions .................................................................................................... 20
7.4.1
Multiple Strings for Tablets ................................................................................................ 21
7.4.2
What is the best Configuration? ......................................................................................... 22
7.4.3
Increasing Efficiency in light load conditions ..................................................................... 24
7.5
Driving the DCDC with Serial Batteries.............................................................................. 25
7.6
Dimension of the external Components ............................................................................. 25
8
Conclusion ......................................................................................................................... 27
9
Design Examples ............................................................................................................... 28
9.1
Smartphone with 4.3" Display ............................................................................................ 28
9.2
Smartphone with 4.5" Display ............................................................................................ 30
9.3
Mid-range Smartphone, Backlight, Keypad, Torch and ALS ............................................. 31
9.4
10.1" Table with 7Sx6 Configuration (42 LEDs) + ALS ..................................................... 32
9.5
Smartphone backlight: 4.3~5" with higher Currents .......................................................... 32
9.6
Smartphone backlight: 4.3~5" + Button Backlight & ALS .................................................. 33
9.7
7" Tablet Backlight ............................................................................................................. 34
9.8
Headlamp for ebooks or e-ink devices............................................................................... 35
9.9
Feature phone - low size Backlight + 2x RGB LEDs ......................................................... 36
9.10
Feature phone - high efficiency backlight + 2x RGB LEDs................................................ 36
10
Contact Information ............................................................................................................ 37
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Copyrights & Disclaimer ..................................................................................................... 38
12
Revision Information .......................................................................................................... 39
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1
General Description
This guide enables the determination which LED driver product, LED configuration, and external
component selection will give the best output in terms of efficiency and solution size for mobile
lightning applications.
2
Driving LEDs for Mobile Backlight Applications
Depending on the application or display size, the amount of LEDs is different. For smartphone and
feature phones the LED requirements are quite similar. LEDs are used in the current range of
2~30mA. The bigger the display gets the more LEDs are needed, also the more pixels the display
contains for higher resolution the more LEDs are required to brighten up the display. Typically all
LEDs inside the display are driven with the same amount of current.
Figure 1: Market Research of several on the market available phones: display size vs. LED
count
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Figure 2: Example of a 4.3” smartphone display with 10 LEDs
3
LED Configuration Nomenclature
The ams display nomenclature can be used for any kind of display or non-display LED
configurations. The nomenclature explains the relation of serial LEDs in a string to the amount of
parallel strings.
First number is the amount of LEDs in series.
Second number is the amount of LED strings in parallel
For example:
6Sx2 = 6 LEDs in one string with 2 parallel strings
Figure 3: ams Display Nomenclature Examples
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4
Product Overview
Figure 4: Product Overview
Part Number
Keypad
AS3490
AS3492
AS3675
AS3676
AS3677
AS3687
XM
AS3688
AS3689
400mA
400mA
50mA
150mA
400mA
400mA
13
13
6
6
12
15
Lighting
Inductive DCDC
Chargepump
Display
# Current Sinks
3
5
ALS
DLS
Camera
(2x)
Flash
Flash Current
150mA
150mA
900mA
150mA
1
1
2
1
Flash Timeout
Indicator LED
Supply LDOs
Features
LED Test
LED Dimming
RGB Pattern
Audio Sync
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Package
Type
WLP12
WLP12
WLP30
WLP30
WLP25
WLP20
QFN32
WLP36
Size in mm
1.8x1.4
1.8x1.4
3x2.5
3x2.5
2.2x2.2
2x2.5
5x5
3x3
Pitch in mm
0.4
0.4
0.5
0.5
0.4
0.5
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0.5
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5
Choosing the LED Configuration
The LED configuration should be considered after the number of LEDs given by the application,
i.e. by the display and notification lights. As an adder to this, it is necessary to take external
factors into account. A few of these are highlighted below:
•
LED forward voltage
•
LED max. forward voltage
•
DCDC maximum ratings and limitations
•
External component limits
•
Required display runtime / efficiency
NOTE: The LED configuration could also be already fixed by the display module suppliers, which
then makes the LED configuration easy. It is recommended for display applications to use the
inductive DCDC boost converter due to a broader efficiency range.
Although for small size applications or applications which have parallel LED configurations it is
also possible to use the capacitive boost converter.
LED configurations which need individual control like RGB LEDs or indicator LEDs should be
connected to the capacitive charge-pump converter. It is not recommended to combine a larger
number of serial connected LEDs with an shorter LED string in terms of forward voltage, due to
the energy waste.
6
LED Configurations for Chargepump
Figure 5: LED Configurations for Chargepump
Configuration
Product
1Sx4
AS3687XM, AS3676, AS3668
1Sx5
AS3676
1Sx6
AS3676
1Sx7 or higher
AS3676
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Figure 6: Example for small solution size with the AS3687xm chargepump for display
backlight and a RGB notification LED
Figure 7: PCB placement example using the AS3687xm with its chargepump for 4 LED
backlight in 1Sx4 configuration with a RGB notification LED
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Figure 8: Example for the AS3668 as backlight driver for 4 LEDs backlight in a 1Sx4
configuration
7
LED Configurations for DCDC
Figure 9: LED Configurations for DCDC
LED
Configuration
Product
Recommended
(*2)
4Sx1
AS3687xm/AS3677/AS3676
AS3677
2Sx2
AS3490/ AS3687xm
AS3490
5Sx1
AS3677/AS3676
AS3677
3Sx2
AS3687xm, AS3676,
AS3677
AS3687xm(*1), AS3676,
AS3677
AS3490, AS3687xm,
AS3676,AS3677
AS3677
AS3676
AS3676
4 LEDs
5 LEDs
6 LEDs
6Sx1
2Sx3
AS3677
AS3490
7 LEDs
7Sx1
8 LEDs
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8Sx1
AS3676(*1)
AS3676
4Sx2
AS3676, AS3677, AS3687
AS3677
2Sx4
AS3492
AS3492
9Sx1
AS3676(*1)
AS3676
3Sx3
AS3676, AS3677
AS3677
10Sx1
AS3676(*1)
AS3676
5Sx2
AS3676, AS3677
AS3677
2Sx5
AS3492
AS3492
12Sx1
AS3676(*1)
AS3676
6Sx2
AS3676, AS3677
AS3676
4Sx3
AS3676, AS3677
AS3677
5Sx3
AS3676, AS3677(*5)
AS3676
3Sx5
AS3676(*3), AS3677(*6)
AS3676
6Sx3
AS3676, AS3677(*5)
AS3676
3Sx6
AS3676(*3)
AS3676
4Sx5
AS3676(*3)
AS3676
Up to 7Sx6
AS3676(*4)
AS3676
9 LEDs
10 LEDs
12 LEDs
15 LEDs
18 LEDs
20 LEDs
More LEDs
Notes:
*1 = external cascode transistor may be needed / depending on Vf of the LED string
*2 = recommendation criteria: optimized for size and efficiency.
*3 = possible if the display module has connected top anodes and bottom cathodes together
*4 = maximum current = 114mA
*5 = depending on Vf and VBatmin
Green Box
= best efficiency
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7.1
DCDC Regulation
7.1.1 AS3687xm/75/76 DCDC
Figure 10: AS3687xm/75/76 DCDC
Battery
C8
1µF
L1
10µH
D1
Q1
DCDC_GATE
C9
10µF
Vout
DCDC_SNS
Step Up DC/DC
Converter
R1
100mΩ
R2
1MΩ
DCDC_FB
DCDC_GATE
VLED
HV Current Sinks
each 0.15–38.25mA
Curr1
CURR2
CURR6
VCURR
This DCDC boost has basically no limitation in output voltage. The maximum output voltage is
defined by the limits of the external NMOS, the maximum output voltage of the output capacitor and
the diode. The high voltage current-sinks of the AS3687xm/75 are capable of allowing up to 15V.
The high voltage current sinks of the AS3676 are able to allow up to 25V. If the voltage limits of the
high voltage current-sinks are exceeded, an external cascode transistor has to be used. Otherwise
an irreversible damage could happen to the IC. Please refer to selection for “Single string solution’s
with higher forward voltages” for detailed explanation.
The driving current of this DCDC is limited by the saturation current of the inductor, resistance of
inductor / transistors, current limit of the sense resistor and the current driving ability of the high
voltage current-sinks. High-voltage DCDC regulated strings need to be connected to the HV current
sinks CURR1,CURR2, and CURR6.
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7.1.2 AS3677 DCDC
Figure 11: AS3677 DCDC
The AS3677 has an integrated NMOS, with internal programmable overvoltage protection and
additionally internal overcurrent limitation. The voltage limit can be set to max. 25V. The maximum
NMOS current is 1200mA ( typ ), for worst case calculation the minimum value has to be chosen.
The maximum output current for 25V close applications is 50mA. High-voltage DCDC regulated
strings need to be connected to the HV current sinks CURR1, CURR 2, and CURR 6.
The AS3687xm/75/76/77 DCDC Regulates with the principle of :
Vout = VLED + Vcurr
for AS3687xm/75/76/77 Vcurr is regulated to 500mV
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7.1.3 AS3490/AS3492 DCDC
Figure 12: AS3490/AS3492 DCDC
The AS3490/AS3492 has an Integrated NMOS and PMOS, also unlike the other backlight drivers
this device has high side current sources. High sided current sources offer the advantage that the
return line of LED current can be used as GND line. This offers additional PCB routing benefits. The
voltage limit of the DCDC is 9.3V ( typ ). This allows the use of 2 LEDs in series configurations, from
2Sx2 to 2Sx5.
The output voltage of the AS3490/ AS3492 is regulated under the condition:
VOUT = VLED + VCURR
for the AS3490/ AS3492 VCURR can be assumed with 100mV
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7.1.4 High Voltage Current Sink Overview
Figure 13: High Voltage Current Sink Overview
High Voltage
current sinks
Max. voltage
for HV-current
sinks
Current of HV
current sinks
Compliance
voltage
AS3687xm
3x
15V
38.25mA
500mV
AS3675
3x
15V
38.25mA
500mV
AS3676
3x
25V
38.25mA
500mV
AS3677
3x
25V
25.5mA
500mV
AS3490
3x
10V
25.5mA
100mV
AS3492
5x
10V
25.5mA
100mV
7.2
General DCDC Application Component Selection
The performance of the application depends on:
•
Inductor
o
too small inductors or wrong selected inductors do not improve the efficiency
o
for most applications Wire-wound inductors show better performance than multi layer
inductors
multilayer type inductors have the disadvantage that with higher output
voltage the parasitic capacitance and core losses are more dominant
compared to wire-wound inductors
•
o
higher Inductances help to increase for light load conditions ( 12~15~18uH )
o
much too big inductors in terms of size do not improve the efficiency
LED Configuration
o
•
•
Switching Transistor
o
low gate charge helps to increase the efficiency in light load conditions
o
integrated diode in the transistor module is beneficial for size & efficiency
Driver IC
o
•
multiple strings reduce the parasitic capacitance at the switching node and core
losses
low quicence current at DCDC & currentsink increase the application efficiency
Schottky Diode
o
too small discrete diodes are decreasing efficiency
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o
7.3
too big diode capacity also decreases the DCDC efficiency
Single String Solutions
Single string configurations are the most used solution for displays. Single String solutions are
possible with the AS3687xm/75/76/77.
Figure 14: Design Example with the AS3677 for a 6Sx1 LED configuration
Figure 15: AS3677 6Sx1 Application Efficiency
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If the DCDC voltage is higher than the maximum voltage of the current-sinks it is mandatory to use
a cascode transistor. Please refer to the chapter “Single string solutions with higher forward
voltages” for detailed explanation.
Figure 16: AS3676 DCDC Efficiency vs VOUT
Figure 17: AS3676 DCDC Efficiency vs VOUT Measurement Setup
IC
AS3676
Load
0.5W constant power load / VOUT Sweep
Transistor
FDFMA3N109
Diode
FDFMA3N109
Inductor
different
Shunt
0R1
Frequency
1MHz
Used LED
Resistors used
Due to the parasitic capacitance at the switching node and core losses the efficiency of the
DCDC converter reduces the higher the output voltage becomes. This graph has been measured
with the AS3676 and a constant power of 0.5W to the LEDs, which comes close to the power
requirements of a 4” Display.
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Figure 18: AS3676 LED Configuration Comparison
This graph shows the AS3676 with different single string LED configurations: 5Sx1, 6Sx1,
7Sx1,8Sx1, 9Sx1, 10Sx1.
Figure 19: AS3676 LED Configuration Comparison Measurement Setup
IC
AS3676
Voltage
Sweep
Load
20mA
Transistor
FDFME3N311ZT
Fairchild
Diode
FDFME3N311ZT
Fairchild
Inductor
LPS3010-123
Coilcraft
Frequency
1MHz
Shunt
0R1
Config
different
Used LED
CL-120A
per LED
Citizen
7.3.1 Single String Solutions with higher Forward Voltages
For driving a Display with single string solutions with higher forward voltage, it needs to be
considered that the current-sinks can only drive a certain amount of voltage. For the AS3687 the
maximum voltage for the high voltage current-sinks is limited to 15V. The AS3676 maximum voltage
limit for the high voltage current-sinks is 25V. If voltages are required which go above the maximum
voltage limits of the high voltage current-sinks a cascode transistor can be used to protect the
current-sink.
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Figure 20: AS3687 with external cascode transistor, 12 LEDs in series, DCDC output Voltage
= 39,6V, LED Current = 100mA
The external cascode transistor has to have a maximum drain source voltage which is higher
than the application voltage.
Efficiency improvement possiblities for higher String voltages:
•
increasing the inductance
•
reduction of switching frequency
•
inductors with lower parasitic capacitance
•
transistors with lower capacity between drain-source and drain-gate
•
schottky diodes with less forward voltage
•
schottky diodes with less capacity
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7.4
Multiple String Solutions
Multiple string solutions can be used to reduce the maximum output voltage of the DCDC. This
helps to reduce the component sizes of capacitors and inductors. For example the output capacitors
get bigger the more voltage they need to sustain.
Figure 21: AS3677 design example for a 4Sx2 configuration - 4” Smartphone
This example shows the AS3677 with it’s integrated NMOS and an external schottky diode for a
4Sx2 configuration. Additionally the chargepump is driving a 50mA torch LED.
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Figure 22: AS3676 design example for a 6Sx3 configuration – 7” tablet
This example shows the AS3676 with an external NMOS with integrated schottky diode for a 6Sx3
configuration which can drive up to 2 Watts of LED power. Additionally there are 2 RGB LEDs and 4
indicator LEDs for the status indication of capacitive buttons.
7.4.1 Multiple Strings for Tablets
Figure 23: Design example for the AS3676 as 10.1” tablet backlight driver for a 6Sx6 LED
configuration
Balance Resistors R3,R4,R5,R6,R7 and R8 are Optional
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Design example for the AS3676 as 10.1” tablet backlight driver for a 6Sx6 LED configuration.
Additionally there are 2x RGB indication LEDs and 4 indication LEDs. The AS3676 is connected
with the TSL253CL for ambient light control. The RGB LEDs, indication LEDs and display backlight
can be controled with independent ambient light calculation tables.
Light Value [Lux]
Figure 24: Light Value vs Current
Current[mA]
Red = indication LED control curve
Blue = rgb LEDs control curve
Green = display backlight control curve
7.4.2 What is the best Configuration?
The best configuration for LEDs depends on the amount of LEDs needed for the application, and
the typical use-case of current, DCDC efficiency and the compliance voltage of the current sinks.
Figure 26: AS3676 LED Configuration Comparison Measurement Setup
IC
AS3676
Voltage
3.7V
Load
20mA
Transistor
FDFME3N311ZT
Fairchild
Diode
FDFME3N311ZT
Fairchild
Inductor
LPS3010-123
Shunt
0R1
Frequency
1MHz
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per LED
-
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Config
different
Used LED
CL-120A
Citizen
Figure 27: AS3674/AS3492 LED Configuration Comparison Measurement Setup
IC
AS3674(AS3492)
Voltage
3.7V
Load
20mA
Transistor
Internal NMOS
Diode
Internal PMOS
Inductor
CIG21K4R7SCD
Frequency
2MHz
Config
2Sx3/4/5
Used LED
Firefly
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-
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7.4.3 Increasing efficiency in light load conditions
As light sensors are common in mobile handheld devices the dynamic range of the backlight can
vary depending on the light condition. To increase the application efficiency in light load conditions it
can be useful to increase the inductance. This can have, depending on the resistance of the
inductor wire and the core losses, negative effects on the efficiency under high load conditions.
Figure 28: AS3677 4Sx3 Applicatin Efficiency
Figure 29: AS3677 4Sx3 Applicatin Efficiency Measurement Setup
Pout @ 60mA
0.75W
Pout @ 20mA
0.25W
Used LED Config
4Sx3
10uH Inductor
LQH3NPN100MJ0
15uH Inductor
LQH3NPN150NJ0
Used Diode
CMDSH05-4
Inductor Size
3x3x1mm
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7.5
Driving the DCDC with Serial Batteries
Figure 30: Driving the DCDC with Serial Batteries
It is possible to connect the AS3687xm/75/76/77 to supply systems which have 2 batteries in series.
The way how to do this is supplying IC VBAT pin with a general purpose system supply and
connecting the Battery directly to the DCDC for the backlight application. This connection will have
a beneficial effect to the system application efficiency. This example shows how the AS3676 is
connected in a system with two serial batteries. The 7” tablet display module is configured in a 4Sx5
configuration where the LEDs are connected together at the bottom cathodes and the top anodes.
The high voltage currentsinks of the AS3676 can drive, connected together, up to 114mA of current.
Additionally this example is using the ams-TAOS TSL253CL as ambient light sensor for backlight
control, and the 400mA chargepump as flash LED driver.
7.6
Dimension of external Components
Output Capacitor:
It is mandatory that the capacity of the output capacitor for AS3687xm/75/76/77 has under all
conditions more than 0.7uF. For this please check the DC bias characteristics of the capacitor
with the maximum voltage which would happen in the application with max. LED forward voltage
and include the tolerances of the capacitor.
For AS3492 or AS3490 the minimum capacity is 4.8uF.
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Figure 1: Example for the DC Bias characteristics of a 10uF capacitor
Inductor:
The inductor is an important component to select for the DCDC. Too small inductors will result in
bad efficiency. Also too big inductors will also result in bad efficiency values. Also it can be that
10uH is not always the best suitable inductor as shown below. It is necessary to check if the
inductor for AS3687xm/75/76/77 has all conditions more than 7uH. For AS3490 and AS3492 the
minimum inductance under all conditions is 2,45uH.
Figure 32: AS3677 40mA Application Efficiency
This measurement graph shows that the 12uH - 3x3x1 Inductor was best in class. Also that the
2,6x2x1mm Inductor has a low application efficiency of 79%.
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Figure 33: AS3677 40mA Application Efficiency Measurement Setup
Output Current
20mA
Frequency
1MHz
Inductor
Sweep
Load
4Sx2
IC
AS3677
8
per LED
Conclusion
Figure 34: Recommended Configurations
LED Amount
Recommended
Configuration
IC
Display
4
2Sx2
AS3490
Up to 3.2”
5
5Sx1
AS3677
Up to 3.5”
6
2Sx3
AS3490
Up to 3.7”
7
7Sx1
AS3676
Up to 4.0”
8
2Sx4
AS3492
Up to 4.3”
9
3Sx3
AS3677
4.0~4.5”
10
2Sx5
AS3492
4.0~4.7”
12
4Sx3
AS3677
4.5”~5.0”
15
5Sx3
AS3676
5.0”~
18
6Sx3
AS3676
7.0”~
20
4Sx5
AS3676
7.0”~
36
6Sx6
AS3676
10.1”~
42
7Sx6
AS3676
10.1”
Conclusion of single string solutions:
Pro:
•
less connections to the display
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Con:
•
efficiency suffering due to parasitic capacitance on the switching node and core losses (
higher ripple current )
•
bigger inductor and lower frequency needed to improve efficiency
•
output capacitors get bigger due to high voltage
Conclusion of multiple string solutions
Pro:
•
higher efficiency due to lower parasitic capacitance and core losses at the DCDC
•
smaller external components like inductor and capacitors possible
Con:
•
9
9.1
more connections needed
Design Examples
Smartphone with 4.3” Display
Figure 2: AS3492 backlight driver for smartphones
This example shows the AS3492 as backlight driver for smartphones with display sizes up to
4.3” or depending on specifications even bigger. The components are tiny, as the DCDC has a
switching with a frequency of 2MHz. The CIG21E4R7MNE Inductor from SEMCO, or the
LQM2HPN4R7_G Inductor from Murata have a size of 2x1,2x1mm, the input capacitor is a 2.2uF
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0402 capacitor, while the output capacitor is a 10uF, 25V 0603 capacitor. The solution enables
the AS3492 to reduce it’s solution size down to 15mm² ( with ams design rules ).
Figure 3: PCB 3D Drawing of the AS3492
Figure 4: PCB Drawing of the AS3492
Additionally keeping the GND away from the Inductor helps to reduce eddy current losses. This
efficiency improving PCB design technique is ams internally known as “hovering Inductor
layout”, it is an additional efficiency improvement technique. The GND plane can be placed
already on MID Layer #1 or Layer#2.
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9.2
Smartphone with 4.5” Display
Figure 38: AS3676 smartphone LED driver
The example shows the AS3676 as smartphone LED driver. It has an 8Sx1 LED configuration for
the display backlight which is powered by the inductive DCDC. The display can have a size from 4”
to 4.5”. Also there are LEDs which are powered by the capacitive charge pump for the keypad
backlight, camera indication and the RGB notification LED.
Figure 39: Application efficiency of the 8Sx1 configuration for display backlight
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9.3
Mid – range Smartphone, Backlight, Keypad, Torch and ALS
Figure 40: AS3677 display backlight driver
AS3677 as display backlight driver with a 6Sx1 configuration. Additionally the DCDC also drives a
keypad backlight with low current. The chargepump is used for a 50mA torch LED. Generally it is
recommended to have balanced LED strings – if this is not possible the efficiency will be reduced,
but as the energy in the keypad LED string is usually much smaller compared to the backlight LED
string it will only slightly affect efficiency.
Additionally it should be checked if the power dissipation inside the driver due to unbalanced LED
strings does not exceed the datasheet specifications (see absolute max. ratings)
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9.4
10.1” Tablet with 7Sx6 configuration (42 LEDs) + ALS
Figure 5: AS3676 as display backlight driver for 42 LEDs in a 7Sx6 configuration
9.5
Smartphone backlight: 4.3 ~ 5” with higher currents
Figure 6: AS3687xm as 5” tablet backlight driver; max. current = 38mA per LED
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Figure 7: Application efficiency of the AS3687xm as 5” tablet backlight driver
9.6
Smartphone backlight: 4.3 ~ 5” + Button Backlight & ALS
Figure 8: AS3677 as 5” tablet backlight driver with ambient light sensing and keypad LED
control. This solution is optimized for best efficiency and lowest size, max. current per LED =
25mA.
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Figure 9: Application efficiency of the AS3677 setup above. Inductor: Murata
LQH3NPN100MJ0, Diode CMDSH05-4
9.7
7” Tablet Backlight
Figure 10: This design example shows the AS3676 as 7” Tablet backlight driver with a 4Sx5
configuration, a 70mA torch LED, ambient light control, and an RGB notification LED.
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9.8
Headlamp for ebooks or e-ink devices
Figure 11: AS3677 headlamp for ebooks and E-Ink devices
This design example shows how the AS3677 is implemented as headlamp for ebooks or E-Ink
devices. As these devices do not have any backlight it is not possible to read in the dark. It is
possible to read by turning on side LEDs as headlamp. To optimize power consumption a light
sensor can be used. As ebook or e-ink devices tend to turn off their main processor during the
reading activity of the user, the automatic ambient light control will determine if actual light
amount requires the need of the headlamp or not. This solution is optimized for higher efficiency
for lower load currents as the application requires typically low light output.
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9.9
Feature phone – low size Backlight + 2x RGB LEDs
Figure 12: AS3687xm with 4 LEDs as display backlight and 2 RGB LEDs as low size solution
for feature phones. Balance resistors are required depending on the current accuarcy for the
RGB LEDs.
9.10
Feature phone – high efficiency Backlight + 2x RGB LEDs
Figure 13: AS3687xm with 4 LEDs as display backlight with high efficiency and 2 RGB LEDs
which can be controlled independently. Typical application: feature phones.
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10 Contact Information
Buy our products or get free samples online at:
www.ams.com/ICdirect
Technical Support is available at:
www.ams.com/Technical-Support
Provide feedback about this document at:
www.ams.com/Document-Feedback
For further information and requests, e-mail us at:
[email protected]
For sales offices, distributors and representatives, please visit:
www.ams.com/contact
Headquarters
ams AG
Tobelbaderstrasse 30
8141 Unterpremstaetten
Austria, Europe
Tel: +43 (0) 3136 500 0
Website: www.ams.com
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11 Copyrights & Disclaimer
Copyright ams AG, Tobelbader Strasse 30, 8141 Unterpremstaetten, Austria-Europe. Trademarks
Registered. All rights reserved. The material herein may not be reproduced, adapted, merged,
translated, stored, or used without the prior written consent of the copyright owner.
Information in this document is believed to be accurate and reliable. However, ams AG does not
give any representations or warranties, expressed or implied, as to the accuracy or completeness of
such information and shall have no liability for the consequences of use of such information.
Applications that are described herein are for illustrative purposes only. ams AG makes no
representation or warranty that such applications will be appropriate for the specified use without
further testing or modification. ams AG takes no responsibility for the design, operation and testing
of the applications and end-products as well as assistance with the applications or end-product
designs when using ams AG products. ams AG is not liable for the suitability and fit of ams AG
products in applications and end-products planned.
ams AG shall not be liable to recipient or any third party for any damages, including but not limited
to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect,
special, incidental or consequential damages, of any kind, in connection with or arising out of the
furnishing, performance or use of the technical data or applications described herein. No obligation
or liability to recipient or any third party shall arise or flow out of ams AG rendering of technical or
other services.
ams AG reserves the right to change information in this document at any time and without notice.
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12 Revision Information
Changes from 1-01 (2012-Aug-25) to current revision 1-02 (2014-Jul-18)
Update to corporate format
Page
1-45
Note: Page numbers for the previous version may differ from page numbers in the current revision.
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