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AAT2833/34
240mA Total Display Solution for Portable Devices General Description
The AAT2833/34 is a total solution IC for portable display applications. Based on a tri-mode charge pump power engine, it is capable of delivering 240mA of output current for white LED (WLED) backlight and RGB applications. The high conversion efficiency and high level of integration make the AAT2833/34 an optimal solution for battery life and size-critical applications. AnalogicTech's AS2CwireTM (Advanced Simple Serial ControlTM) serial digital interface is used to enable, disable, and set current levels for all of the light emitting diodes (LEDs). Each backlight channel can be programmed to 16 levels of current, from a recommended maximum of 30mA programmed by the RBSET resistor. The RGB module can be adjusted to 8 levels of current, up to a recommended maximum of 60mA. The RGB module is programmable with up to 4096 (AAT2833) or 64 (AAT2834) color/intensity (brightness) combinations. The AAT2833/34 is offered in a Pb-free, thermally enhanced 24-pin 4x4x0.75mm TQFN package.
Features
* *
ChargePumpTM
*
*
Applications
* * * * * Digital Still Cameras LCD Display Modules MP3 Players White LED Drivers Wireless Handsets
* * * * *
Input Supply Voltage Range: 2.7V to 5.5V Tri-Mode (1X/1.5X/2X) Charge Pump: -- Delivers up to 240mA of Output Current -- Switching Frequency: Up to 2MHz Total Display Solution for RGB and Backlight Applications -- 6-Channel Backlight WLED Backlight * User-Programmable Full-Scale Current, up to 30mA -- 3-Channel RGB * User-Programmable Full-Scale Output Current/Duty Cycle * AAT2833: 4096 Color/Intensity Combinations * AAT2834: 64 Color/Intensity Combinations Single-Wire AS2Cwire Serial Interface for Configuration/Control -- Eleven Addressable Registers -- Fast, 1MHz Serial Interface True Load Disconnect in Shutdown, IIN < 1A Built-in Thermal Protection Built-in Auto-Disable for Open LED Condition Automatic Soft-Start Minimizes Inrush Current Available in 4x4x0.75mm TQFN44-24 Package
Typical Application
COUT 2.2F
RGB LED
OUT BL1 IN EN/SET
BL2 BL3 BL4 BL5 BL 6
RGB BSET PGND AGND
AAT2833/34
C1+ C1- C2+ C2-
VBATTERY Single-cell Li+
CIN 2.2F AS2Cwire Serial Control
RBSET 280k
C1 1F
C2 1F
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AAT2833/34
240mA Total Display Solution for Portable Devices Pin Description
Pin #
1 2 3 4 5, 17, 18, 19, 20 6 7 8 9 10 11 12 13 14 15 16 21 22 23 24 EP
Symbol
BL3 BL2 BL1 AGND N/C EN/SET R G B C2+ C2OUT IN C1+ C1PGND BSET BL6 BL5 BL4
Function
Power return (cathode) for backlight channel 3. If not used, connect to the OUT pin. Power return (cathode) for backlight channel 2. If not used, connect to the OUT pin. Power return (cathode) for backlight channel 1. If not used, connect to the OUT pin. Signal ground. Not connected. Enable and AS2Cwire serial interface control input. Power return (cathode) for Red LED of the RGB module. Power return (cathode) for Green LED of the RGB module. Power return (cathode) for Blue LED of the RGB module. Positive node of flying capacitor 2. Negative node of flying capacitor 2. Output voltage pin. Connect to anode of all LEDs. Input voltage pin. Positive node of flying capacitor 1. Negative node of flying capacitor 1. Power ground. Maximum backlight current programming resistor input. Ground this pin to use default values. Power return (cathode) for backlight channel 6. If not used, connect to the OUT pin. Power return (cathode) for backlight channel 5. If not used, connect to the OUT pin. Power return (cathode) for backlight channel 4. If not used, connect to the OUT pin. Exposed pad (bottom); connect to GND directly beneath the package.
Pin Configuration
TQFN44-24 (Top View) N/C N/C BSET BL6 BL5 BL4
24 23 22 21 20 19
BL3 BL2 BL1 AGND N/C EN/SET
1 2 3 4 5 6 10 11 12 7 8 9
18 17 16 15 14 13
N/C N/C PGND C1C1+ IN
OUT C2C2+ B G R
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AAT2833/34
240mA Total Display Solution for Portable Devices Absolute Maximum Ratings1
TA = 25C, unless otherwise noted. Symbol
VN VN VN TJ TLEAD
Description
[OUT, IN, BL1, BL2, BL3, BL4, BL5, BL6, R, G, B] to GND [C1+, C2+] to GND [EN/SET, BSET, C1-, C2-] to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -40 to +150 300
Units
V V V C C
Thermal Characteristics2
Symbol
JA PD
Description
Maximum Thermal Resistance Maximum Power Dissipation
Value
50 2.0
Units
C/W W
Recommended Operating Conditions
Symbol
T
Description
Ambient Temperature Range
Value
-40 to +85
Units
C
1. Stresses above those listed in Absolute Maximum Ratings may cause damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Mounted on a demo board (FR4, in still air). 2833.2007.09.1.0
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AAT2833/34
240mA Total Display Solution for Portable Devices Electrical Characteristics1
VIN = 3.6V; CIN = 4.7F; C1 = C2 = 1F; COUT = 2.2F; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol Description Conditions Min Typ Max Units
2.7 1X Mode, Address = 0, Data = 1, VEN/SET = VIN 1.5X Mode, Address = 0, Data = 1, VEN/SET = VIN 2X Mode, Address = 0, Data = 1, VEN/SET = VIN 1X LL Mode, Address = 3, Data = 1, VEN/SET = VIN VEN/SET = 0V, TA = 25C 240 500 0.7 2 200 140 15 Address = 0, Data = 1, VIN - VF = 1.5V Address = 0, Data = 1, VIN - VF = 1.5V 5.5 0.6 4 mA 5 0.3 1 A mA mV V MHz s C C V
Charge Pump Section VIN IN Operating Supply Voltage Range
IIN
IN Operating Supply Current
IN Shutdown Current OUT Maximum Output Current BL1-BL6, RGB Charge Pump VTH(HYS) Mode Transition Hysteresis VBSET BSET Pin Voltage fOSC Charge Pump Oscillator Frequency tSS Charge Pump Soft-Start Delay TSD Over-Temperature Shutdown Threshold TSD(HYS) Over-Temperature Shutdown Hysteresis BL1-BL6 Backlight LED Outputs IBL_(MAX) IBL VBL_(TH) BL1-BL6 Maximum Current BL1-BL6 Current Matching2
ISHDN IOUT
27
30
33 1
mA % mV
BL1-BL6 Charge Pump Mode Transition Threshold RGB LED Outputs IRGB_(MAX) VRGB_(TH) R-G-B Maximum Current RGB Charge Pump Mode Transition Threshold Address = 12, Data = 7, VIN - VF = 1.5V 51
100
60 100
69
mA mV
1. The AAT2833/34 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Current matching is defined as the deviation of any sink current from the average of all active channels.
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AAT2833/34
240mA Total Display Solution for Portable Devices Electrical Characteristics1
VIN = 3.6V; CIN = 4.7F; C1 = C2 = 1F; COUT = 2.2F; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C. Symbol
EN/SET Logic VENS(L) VENS(H) IEN/SET TEN/SET_LO TEN/SET_HI_MIN TEN/SET_HI_MAX TOFF TLAT
Description
Control EN/SET Input Low Threshold Voltage EN/SET Input High Threshold Voltage EN/SET Input Leakage Current EN/SET Low Time Minimum EN/SET High Time Maximum EN/SET High Time EN/SET Off Timeout EN/SET Latch Timeout
Conditions
Min Typ Max Units
0.4 1.4 -1 0.3 50 75 500 500 1 75 V V A s ns s s s
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AAT2833/34
240mA Total Display Solution for Portable Devices Typical Characteristics
AAT2833 Backlight Section Efficiency
100
Backlight Current Matching vs. Temperature
32
Efficiency (%)
80 70 60 50 40 30 2.7
19mA/Channel
LED Current (mA)
90
30mA/Channel
31.5 31 30.5 30 29.5 29 28.5
Channel 5 Channel 6
2.1mA/Channel
Channel 3 Channel 4
-15
Channel 2
Channel 1
10 35 60 85
3.1
3.5
3.9
4.3
4.7
5.1
5.5
28 -40
Input Voltage (V)
Temperature (C)
1X Mode Hysteresis vs. Current Settings
500 450 400 350 300 250 200 150 100 50 0 2 4 6 8 10 12 14 16 140 120
BL1-BL6 Mode Transition Threshold vs. Current Setting
Hysteresis (mV)
Threshold (mV)
100 80 60 40 20 0 2
4
6
8
10
12
14
16
Current Setting (Address 0, Data #)
Current Setting (Address 0, Data #)
EN/SET High Threshold Voltage vs. Input Voltage
EN/SET High Threshold (V)
1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
EN/SET Low Threshold Voltage vs. Input Voltage
EN/SET Low Threshold (V)
1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
1.2
-40C
25C
-40C
25C
85C
85C
Input Voltage (V)
Input Voltage (V)
6
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AAT2833/34
240mA Total Display Solution for Portable Devices Typical Characteristics
EN/SET Latch Timeout vs. Input Voltage
500 450 400 600 550 500
EN/SET Off Timeout vs. Input Voltage
TOFF (s)
TLAT (s)
25C 85C -40C
25C -40C 85C
450 400 350 300 250
350 300 250 200 150 2.7
200 3.1 3.5 3.9 4.3 4.7 5.1 5.5 150 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
Input Voltage (V)
Turn On to 1X Mode Backlight
(30mA/channel; Address 0, Data 16; VIN = 4.4V)
Turn On to 1.5X Mode Backlight
(30mA/channel; Address 0, Data 16; VIN = 3.5V)
VEN/SET (2V/div) VOUT (2V/div) VBLX (0.5V/div) IIN (0.1A/div) Time (200s/div)
VEN/SET (2V/div) VOUT (2V/div) VBLX (0.5V/div) IIN (0.2A/div) Time (200s/div)
Turn On to 2X Mode Backlight
(30mA/channel; Address 0, Data 16; VIN = 2.7V)
Turn Off from 1.5X Mode Backlight
(30mA/channel; Address 0, Data 16)
VEN/SET (2V/div) VOUT (2V/div) VBLX (0.5V/div) IIN (0.2A/div) Time (200s/div)
VEN/SET (2V/div)
VDIODE (2V/div) ILED (0.02A/div)
Time (100s/div)
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AAT2833/34
240mA Total Display Solution for Portable Devices Typical Characteristics
Operating Characteristics
(VIN = 3.4V; 1.5X Mode; 30mA/channel; AC Coupled) VIN (100mV/div) VOUT (100mV/div) VIN (100mV/div)
Operating Characteristics
(VIN = 2.7V; 2X Mode; 30mA/channel; AC Coupled)
VOUT (100mV/div) IIN (20mA/div)
IIN (20mA/div)
Time (500ns/div)
Time (500s/div)
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AAT2833/34
240mA Total Display Solution for Portable Devices Functional Block Diagram
C1+ C1- C2+ C2- OUT
IN
Tri-Mode Charge Pump Control
VF Monitoring
3
6
PGND
BL1 EN/SET
AS2Cwire Control
Main Ref
BL2 BL3 BL4
Sub Ref
BL5 BL6
BSET
DAC
R
RGB Ref
G B
AGND
Functional Description
The AAT2833/34 is a multi-functional power solution for display systems in portable devices. It includes six individual channels for backlight white LEDs, and three individual channels for RGB LEDs. All of these functionalities are powered by a highly efficient tri-mode charge pump power engine that is capable of delivering 240mA of output current. The six backlight channels can be turned on or off all together, in two groups, or individually. The twogroup operation allows LEDs to be turned on and off in for dual display applications: the main display (BL1-BL4) and sub-display (B5-B6). The individual on/off feature supports applications other than main/sub-display backlighting, such as keypad lighting. The maximum backlight current is programmable with an external resistor, RBSET. The RGB channels can be programmed with up to 4096 or 64 different combinations of colors and lighting intensities (brightness). R, G, and B channels are individually controlled and can be used for alternative functions, such as keyboard lighting, "fun" lighting, etc.
AS2Cwire Serial Interface
Each current channel input on the AAT2833/34 is controlled by AnalogicTech's AS2Cwire serial digital interface. The AS2Cwire interface uses the number of rising edges on the EN/SET pin to address and load the LED configuration registers. AS2Cwire latches data or addresses after the EN/SET pin has been held logic high for longer than TLAT (500s). Addresses and data are differentiated by the number of EN/SET rising edges. Since the data registers are 4 bits each, the differentiating number of pulses is 24 or 16, so that Address 0 is signified by 17 rising edges, Address 1 by 18 rising edges, Address 2 by 19 rising edges, and so on. Data is set to any number of rising edges between 1 and including 16. A typical write protocol consist of the following: first a burst of EN/SET rising edges that identify/target a particular address followed by EN/SET being held logic high for the TLAT timeout period to latch the address value in the registers, then another burst of rising edges that signify data with the accompanying TLAT timeout period to latch the data value in the registers. Once an address is set, then multiple writes to the corresponding data register are allowed without having to write to the address for every change 9
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AAT2833/34
240mA Total Display Solution for Portable Devices
in data values. When EN/SET is held low longer than TOFF (500s), the AAT2833/34 enters shutdown mode operation and draws less than 1A from the input supply voltage. Data and address registers are cleared (reset to 0) in shutdown mode operation. Table 1a contains the AS2Cwire serial interface address functionality when independent channel control is disabled (independent channel control is disabled by default) and conversely Table 1b contains the AS2Cwire serial interface address functionality when independent channel control is enabled. EN/SET Rising Address Edges
0 1 2 3 7 8 9 10 11 12 15 17 18 19 20 24 25 26 27 28 29 32
Backlight Current Control (Addresses 0-2)
The six channel backlight inputs, BL1-BL6, can drive six individual LEDs to a maximum current of 30mA per channel. The EN/SET AS2Cwire serial interface enables all channels and sets the current magnitude as a percentage of the maximum current, programmed by an external resistor at BSET (see Figure 4). To set the backlight current (minimum to maximum current) of the main display LEDs (BL1-BL4), the user would write data to Address 1. To set the backlight current for the sub display LEDs (BL5-BL6), the user would write data to Address 2. To write to both main display and sub display LEDs (BL1-BL6) at the same time, the user would write to Address 0. Data BL % of BSET
1 2 3 4 5 6 7 8 0 21 22 25 29 32 35 40
Function
Backlight Current BL1-BL6 Main Backlight Current BL1-BL4 Sub Backlight Current BL5-BL6 Low Backlight Current Red Color Green Color Blue Color RGB Intensity RGB Mode RGB Current Backlight Independent Channel Control
Data
9 10 11 12 13 14 15 16
BL % of BSET
44 51 56 63 71 79 89 100
Table 1a: AS2Cwire Serial Interface Addressing with Independent Channel Control Disabled. EN/SET Rising Edges
17 18 19 20 24 25 26 27 28 29 32
Table 2a: Addresses 0-2 with Independent Channel Control Disabled, Backlight Current Level. Data BL % of BSET Data
9 10 11 12 13 14 15 16
BL % of BSET
44 51 56 63 71 79 89 100
Address
0 1 2 3 7 8 9 10 11 12 15
Function
Not Applicable Backlight Current BL1-BL6 BL1-BL4 On/Off Control BL5-BL6 On/Off Control Red Color Green Color Blue Color RGB Intensity RGB Mode RGB Current Not Applicable
1 2 3 4 5 6 7 8
0 21 22 25 29 32 35 40
Table 2b: Address 1 with Independent Channel Control Enabled, Backlight Current Level.
Table 1b: AS2Cwire Serial Interface Addressing with Independent Channel Control Enabled. 10
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240mA Total Display Solution for Portable Devices
120 100 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
IBLED (% of BSET)
Backlight Independent Channel Control (Address 15)
The AAT2833/34 can also individually control each backlight channel. This mode allows the user to turn on some or all of the channels in any desired combination. This control is achieved by changing the functionality of the AS2Cwire registers. To enable individual LED control mode, a user would write Data 8 to Address 15. All channels that are enabled must carry the same current, which is set using the new functionality of Address 1 (see Table 2b). Data
8
Data Code
Figure 1: Addresses 0-2 Backlight Current Level.
Individual BL Control
On
Low Backlight Current (Address 3)
In addition to the current levels set by Addresses 0, 1, and 2 (shown in Table 2a and Figure 1), there is also a low backlight current level that can be set. To set the low backlight current level, the user would write data to Address 3, as shown in Table 3. For example, to toggle between 1.7% and 25% of the maximum backlight current on all LEDs, write Data = 14 to Address 3 and Data 4 to Address 0. To set BL1BL4 to 25% and BL5-BL6 to 0.2%, write Data = 5 to Address 3, and Data = 4 to Address 2. BL1-BL4 Current On
No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes
Table 4: Address 15, Backlight Independent Channel Control Data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
BL6
Off Off Off Off Off Off Off Off On On On On On On On On
BL5
Off Off Off Off On On On On Off Off Off Off On On On On
BL4
Off Off On On Off Off On On Off Off On On Off Off On On
BL3
Off On Off On Off On Off On Off On Off On Off On Off On
Data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
BL5-BL6 Current On
No No No No Yes Yes Yes Yes No No No No Yes Yes Yes Yes
BL % of BSET
0 0 0 0 0.2 1.7 3.5 7.0 0.2 1.7 3.5 7.0 0.2 1.7 3.5 7.0
Table 5: Address 2 with Independent Channel Control Enabled, BL3-BL6 On/Off Control.
Table 3: Address 3 with Independent Channel Control Disabled, Low-Backlight Current Levels (RBSET = 280k).
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AAT2833/34
240mA Total Display Solution for Portable Devices
With independent channel control enabled, the functionality of Addresses 1, 2, and 3 will conform to what is described in Tables 2b, 5, and 6. Also, Addresses 0 and 15 are no longer applicable after independent channel control has been enabled. As indicated by the possible settings listed in the tables, any combination of backlight channels can be enabled and disabled. The original functionalities (Sub Backlight Current BL5-BL6 and Low Backlight Current) of Addresses 2 and 3 are no longer available unless the internal state machine has been reset to default mode operation (when EN/SET is logic low for >500s). The functionality of Addresses 7-12 are unmodified by the enabling of independent channel control.
Data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
BL2
Off Off Off Off Off Off Off Off On On On On On On On On
BL1
Off Off Off Off On On On On Off Off Off Off On On On On
Table 6: Address 3 with Independent Channel Control Enabled, BL1-BL2 On/Off Control.
Address
THI TLO TLAT
Data
EN/SET
1 2 17 18 1 2... n 16
Address
0
1
DATA1
1
n
DATA0
1
Figure 2: AS2Cwire Serial Interface Timing Details.
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AAT2833/34
240mA Total Display Solution for Portable Devices
RGB Control
The Red, Green, and Blue LED PWM timing, along with the overall period, is controlled by five registers. The current level for the RGB LEDs is controlled by another register (Address 12) which makes it possible to change the peak currents from 33% up to 200% of the backlight maximum current set by RBSET. A mode register (Address 11) sets the method of update for the color and intensity registers. All registers are updated simultaneously or individually, depending on how the mode register is set. If updated simultaneously, the color registers are updated when the period register is updated. Up to 4096 different color/brightness combinations are programmable in the AAT2833 and 64 color/brightness combinations are programmable in the AAT2834. Address 7, 8, 9: RGB Color Registers The AAT2833's RGB color registers store up to 16 levels of lighting intensity for a given color channel. The first level (DATA = 1) is reserved for the off-state. Every setting thereafter increases the on-time of the respective LED by 128s. The settings can be calculated as follows: R = (DATA7 - 1) * 128s G = (DATA8 - 1) * 128s B = (DATA9 - 1) * 128s Where R, G, and B are the on-times of the respective LEDs and DATA7, DATA8, and DATA9 are the data inputs into Registers 7, 8, and 9, respectively. DATAN can be set to a value from 1 to 16 with the default DATAN value equal to 1. Since the AAT2834 supports 64 color/brightness combinations, DATAN can be set from 1 to 4. Address 10: RGB Timebase Register - T The overall period is set by the AAT2833/34's T register. Adjusting this register allows a user to adjust how often the RGB LED sequence is repeated. The longer the period, the smaller the effective duty cycle, and thus RGB light intensity (brightness) is reduced. The RGB period can be calculated using the following equation: T = [(DATA10 - 1) * 3 + 15] * 128s Where T is the period of repetition and DATA10 is the data input into Register 10. In the AAT2833, DATA10 can be set to a value from 1 to 16, with the default DATA10 value equal to 1. In the AAT2834, DATA10 can be set from 1 to 4, with the default DATA10 value equal to 1. Please note that if the user sets the period to be smaller than the combined on-times (R+G+B), then the RGB sequence will automatically begin again once time T has been reached, whether or not all on-times have been completed. Address 11: RGB Mode Register The AAT2833/34's RGB mode register can have one of two DATA11 values. If DATA11 is set to 1 (the default), then each RGB LED on-time will be updated immediately after their respective register is set. If DATA11 is set to 2, then as the user sets the Red, Green, and Blue on-time registers, none of the LEDs will be updated until the timebase register is set. For example, if the user wants to set a certain Red-Green-Blue combinations, the Red on-time can be programmed first, followed by the Green ontime, followed by the Blue on-time, and then the RGB period T last. If DATA11 is set to 1, then after the Red on-time is programmed the user will see the Red LED turn on immediately. After the Green on-time is programmed, the Red-Green color combinations will appear, etc. If DATA11 is set to 2, then none of those intermediate colors will appear until the RGB period register T has been set and loaded. Address 12: RGB Current Level Register, ISINK The ISINK current level in the RGB LED can be adjusted by writing data to Register 12. The maximum current is two times (200%) the maximum backlight current set by RBSET (see Table 7). By increasing or decreasing the current, the brightness level can easily be changed for any particular color combination.
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AAT2833/34
240mA Total Display Solution for Portable Devices
R T
Data
1 2 3 4 5 6 7
RGB Current as % of BSET
0 33 66 100 133 167 200
IR = ISINK * IG = ISINK *
G T B IB = ISINK * T
Shutdown
Since the channel backlight power returns are the only power returns for all the LEDs, there is no leakage current if all channels are disabled. Applying a HIGH-to-LOW transition on the EN/SET pin and holding LOW for at least TOFF (500s) will activate the AAT2833/34's shutdown mode. Data and Address registers are cleared (reset to 0) during shutdown.
Table 7: Address 12, RGB Current Level Register (ISINK). RGB LED Current Calculation The average current in a particular color channel is a function of the values in the R, G, B, T, and ISINK registers, as follows:
R ISINK T G
Red
ISINK
Green
ISINK
B
Blue
ISINK
Figure 3: RGB Diode Current Timing.
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AAT2833/34
240mA Total Display Solution for Portable Devices Applications Information
Adjusting the Maximum Backlight LED Current Level
The value of RBSET determines the maximum LED current level for the backlight section. In the typical application, selecting RBSET = 280k results in a maximum 30mA/channel LED current level. The relationship between RBSET and the maximum backlight current is illustrated graphically in Figure 4. The AAT2833/34's LED current control circuits have been optimized for full-scale current settings higher than 15mA, RBSET > 550k.
45 40 35
=
=
PLEDs VLED1 * ILED1 + ... + VLED4 * ILED4 = PIN VIN * IIN
4 * VLEDX * ILEDX ; x = 1, 2, 3 or 4 and IIN = 4 * ILEDX VIN * IIN
VLEDX = V IN
Due to the very low 1X mode quiescent current, the input current nearly equals the total output current delivered to the LEDs. Further, the low resistance bypass switch introduces a negligible voltage drop from input to output. The AAT2833/34 further maintains optimized performance and efficiency by detecting when the input voltage is not sufficient to sustain the LED bias current. The device automatically switches to 1.5X mode when the input voltage drops too low in relation to the LED forward voltages. In 1.5X mode, the output voltage can be boosted to 1.5X the input voltage. The 1.5X conversion ratio introduces a corresponding 0.5X increase in input current. For ideal conversion, the 1.5X mode efficiency is given by: =
=
IBLED (mA)
30 25 20 15 10 5 0 100 200 300 400 500 600 700 800 900 1000
RBSET (k)
Figure 4: Maximum Backlight LED Current vs RBSET.
PLEDs VLED1 * ILED1 + ... + VLED4 * ILED4 = PIN VIN * IIN
4 * VLEDX * ILEDX ; x = 1, 2, 3 or 4 and IIN = 1.5(4 * ILEDX) VIN * IIN
IN
Device Power Efficiency
The AAT2833/34's power conversion efficiency depends on the charge pump mode of operation. By definition, device efficiency is expressed as the output power delivered to the LEDs divided by the total input power consumed. = PLEDs VLED1 * ILED1 + ... + VLED4 * ILED4 = PIN VIN * IIN
VLEDX = 1.5V
When the input voltage is sufficiently greater than the LED forward voltages, the device optimizes efficiency by operating in 1X mode. In 1X mode, the device is working as a bypass switch and passing the input supply directly to the output. By simplifying the conditions such that the LEDs have uniform VF, the power conversion efficiency can be approximated by:
Similarly, when the input falls further, such that 1.5X mode can no longer sustain the LED bias currents, the AAT2833/34 will automatically switch to 2X mode. In 2X mode, the output voltage can be boosted to 2X the input voltage. The 2X conversion ratio introduces a corresponding 1X increase in input current. For ideal conversion, the 2X mode efficiency is given by: =
=
PLEDs VLED1 * ILED1 + ... + VLED4 * ILED4 = PIN VIN * IIN
4 * VLEDX * ILEDX ; x = 1, 2, 3 or 4 and IIN = 2(4 * ILEDX) VIN * IIN
VLEDX = 2V IN
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AAT2833/34
240mA Total Display Solution for Portable Devices
LED Selection
The AAT2833/34 is designed to drive high-intensity white LEDs. It is particularly suitable for LEDs with an operating forward voltage in the range of 4.2V to 1.5V. The AAT2833/34 can also drive other loads that have similar characteristics to white LEDs. For various load types, the AAT2833/34 provides a high current, programmable, ideal constant current channel/sink.
PCB Layout
To achieve adequate electrical and thermal performance, careful attention must be given to the printed circuit board (PCB) layout. In the worst-case operating condition, the chip must dissipate considerable power at full load. Adequate heat-sinking must be achieved to ensure intended operation. Figures 6 and 7 illustrate an example PCB layout. The bottom of the package features an exposed metal pad. The exposed pad acts, thermally, to transfer heat from the chip and, electrically, as a ground connection. The junction-to-ambient thermal resistance (JA) for the AAT2833/34 package can be significantly reduced by following a couple of important PCB design guidelines. The PCB area directly underneath the package should be plated so that the exposed pad can be mated to the top layer PCB copper during the reflow process. Multiple copper plated thru-holes should be used to electrically and thermally connect the AAT2833/34's exposed pad area to additional ground plane(s). The chip ground is internally connected to both the paddle and to the AGND and PGND pins. It is good practice to connect the GND pins to the exposed pad area with traces as shown in Figure 5. The flying capacitors (C1 and C2), input capacitor (C4), and output capacitor (C3) should be connected as close as possible to the IC. In addition to the external passive components being placed as close as possible to the IC, all traces connecting the AAT2833/34 should be as short and wide as possible to minimize path resistance and potential coupling.
Capacitor Selection
Careful selection of the four external capacitors CIN, C1, C2, and COUT are important because they will affect turn-on time, output ripple, and transient performance. Optimum performance will be obtained when low equivalent series resistance (ESR) ceramic capacitors are used. In general, low ESR is defined as a resistance that is less than 100m. X7R and X5R ceramic capacitors are highly recommended over all other types of capacitors for use with the AAT2833/34. For the input (CIN) and output (COUT) capacitors, a 2.2F or greater value is recommended, and a 1F or greater value is recommended for the flying (C1/C2) capacitors. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lowest cost, has a smaller PCB footprint, and is non-polarized. Low ESR ceramic capacitors help maximize charge pump transient response.
16
2833.2007.09.1.0
AAT2833/34
240mA Total Display Solution for Portable Devices
Pin #1
Figure 5: AAT2833/34 Package PCB Layout.
Evaluation Board Layout
Figure 6: AAT2833/34 Evaluation Board Component Side Layout.
Figure 7: AAT2833/34 Evaluation Board Solder Side Layout.
2833.2007.09.1.0
17
AAT2833/34
240mA Total Display Solution for Portable Devices Evaluation Board Schematic
VOUT
D1 DC+ VIN J1
D2
D3
D4
D5
D6
R9 = 280K for 30mA/chnl backlight. R9 280K
Optional 100F lab supply bypass
C7
24 23 22 21 20 19
BSET
N/C
BL4
BL5
1 2 3 4 5
BL6
N/C
U1 AA T2833 N/C N/C PGND C1C1+ VIN
18 17 16 15
BL3 BL2 BL1 AGND N/C EN/SET OUT C2+ C2G R B
C1
14 13
EN
6
1.0F C4 4.7F
7
8
9
10
11
12
C2 1.0F
C3 2.2F
3 Optional footprints for R auxiliary lighting LEDs . RGB G B
Figure 8: AAT2833/34 Evaluation Board Schematic.
R7 220 J2 R8 100K VIN VIN R1 R2 R3 R4 R5 1K 1K 1K 1K 1K U2 1 2 3 4 VDD GP5 GP4 GP3 PIC12F675 VSS GP0 GP1 GP2 8 7 6 5 C6 1F R6 330 LED7 RED EN
SW1 SW2 SW3 SW4 SW5
Figure 9: AAT2833/34 Microcontroller Section Schematic.
4
18
2833.2007.09.1.0
AAT2833/34
240mA Total Display Solution for Portable Devices Options
Option
AAT2833 AAT28343
Flash
N N
Backlight
Y Y
RGB
Y Y
Package
TQFN44-24 TQFN44-24
Function
Backlight Plus 4096-Combination RGB Backlight Plus 64-Combination RGB
Ordering Information
Package
TQFN44-24 TQFN44-24
Marking1
SVXYY
Part Number (Tape and Reel)2
AAT2833IBK-T1 AAT2834IBK-T13
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. Contact factory for AAT2834 availability. 2833.2007.09.1.0
19
AAT2833/34
240mA Total Display Solution for Portable Devices Package Information
TQFN44-24
Pin 1 Dot By Marking
0.400 0.050
0.255 0.025
Pin 1 Identification Chamfer 0.300 x45
1
4.000 0.050
0.500 BSC
4.000 0.050
2.700 0.050
Top View
Bottom View
2.700 0.050 0.214 0.036
0.000 -0.050
Side View
All dimensions in millimeters.
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737- 4600 Fax (408) 737- 4611 20
2833.2007.09.1.0
0.750 0.050

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