AAT2833/34 240mA Total Display Solution for Portable Devices General Description Features 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 AS2Cwire™ (Advanced Simple Serial Control™) 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. • • • • • Applications • • • • • ChargePump™ 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 < 1µA 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 Digital Still Cameras LCD Display Modules MP3 Players White LED Drivers Wireless Handsets Typical Application RGB LED COUT 2.2μF OUT BL1 IN VBATTERY Single-cell Li+ EN/SET CIN 2.2μF AS2Cwire Serial Control 2833.2007.09.1.0 BL2 BL3 BL4 BL5 BL 6 R G B BSET AAT2833/34 C1+ C1- C2+ C2- C1 1μF PGND AGND RBSET 280kΩ C2 1μF 1 AAT2833/34 240mA Total Display Solution for Portable Devices Pin Description Pin # Symbol Function 1 2 3 4 5, 17, 18, 19, 20 6 7 8 9 10 11 12 13 14 15 16 21 BL3 BL2 BL1 AGND N/C EN/SET R G B C2+ C2OUT IN C1+ C1PGND BSET 22 23 24 EP BL6 BL5 BL4 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 19 20 21 22 23 24 BL3 BL2 BL1 AGND N/C EN/SET 1 18 2 17 3 16 4 15 5 14 6 13 N/C N/C PGND C1C1+ IN 12 11 9 10 8 7 OUT C2C2+ B G R 2 2833.2007.09.1.0 AAT2833/34 240mA Total Display Solution for Portable Devices Absolute Maximum Ratings1 TA = 25°C, 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 Units -0.3 to 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -40 to +150 300 V V V °C °C Value Units 50 2.0 °C/W W Value Units -40 to +85 °C Thermal Characteristics2 Symbol θJA PD Description Maximum Thermal Resistance Maximum Power Dissipation Recommended Operating Conditions Symbol T Description Ambient Temperature Range 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 3 AAT2833/34 240mA Total Display Solution for Portable Devices Electrical Characteristics1 VIN = 3.6V; CIN = 4.7µF; C1 = C2 = 1µF; COUT = 2.2µF; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol Description Conditions Charge Pump Section VIN IN Operating Supply Voltage Range IIN IN Operating Supply Current ISHDN IOUT 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) BL1-BL6 Maximum Current ΔIBL BL1-BL6 Current Matching2 Min Typ Max Units 2.7 Address = 0, Data = 1, VIN - VF = 1.5V Address = 0, Data = 1, VIN - VF = 1.5V 4 mA 5 0.3 1 27 BL1-BL6 Charge Pump Mode Transition Threshold RGB LED Outputs R-G-B Maximum Current VRGB_(TH) RGB Charge Pump Mode Transition Threshold 240 µA mA 500 mV 0.7 2 200 140 15 V MHz µs °C °C 30 33 mA 1 % 100 Address = 12, Data = 7, VIN - VF = 1.5V V 0.6 VBL_(TH) IRGB_(MAX) 5.5 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 = 25°C 51 60 100 mV 69 mA mV 1. The AAT2833/34 is guaranteed to meet performance specifications over the -40°C to +85°C 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. 4 2833.2007.09.1.0 AAT2833/34 240mA Total Display Solution for Portable Devices Electrical Characteristics1 VIN = 3.6V; CIN = 4.7µF; C1 = C2 = 1µF; COUT = 2.2µF; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C. Symbol EN/SET Logic VENS(L) VENS(H) IEN/SET TEN/SET_LO TEN/SET_HI_MIN TEN/SET_HI_MAX TOFF TLAT 2833.2007.09.1.0 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 1 75 50 75 500 500 V V µA µs ns µs µs µs 5 AAT2833/34 240mA Total Display Solution for Portable Devices Typical Characteristics AAT2833 Backlight Section Efficiency Backlight Current Matching vs. Temperature 32 100 30mA/Channel 19mA/Channel 80 70 60 50 2.1mA/Channel 40 LED Current (mA) Efficiency (%) 90 31.5 31 30.5 Channel 5 Channel 6 30 29.5 29 Channel 3 28.5 30 2.7 3.1 3.5 3.9 4.3 4.7 5.1 Channel 4 28 -40 5.5 Channel 1 -15 10 Input Voltage (V) 85 140 450 120 400 Threshold (mV) Hysteresis (mV) 60 BL1-BL6 Mode Transition Threshold vs. Current Setting 500 350 300 250 200 150 100 100 80 60 40 20 50 0 2 0 2 4 6 8 10 12 14 16 25°C -40°C 1.1 1.0 0.9 0.8 0.7 85°C 0.6 0.5 0.4 0.3 0.2 2.7 3.1 3.5 3.9 4.3 Input Voltage (V) 4.7 5.1 6 8 10 12 14 16 EN/SET Low Threshold Voltage vs. Input Voltage EN/SET Low Threshold (V) EN/SET High Threshold Voltage vs. Input Voltage 1.2 4 Current Setting (Address 0, Data #) Current Setting (Address 0, Data #) EN/SET High Threshold (V) 35 Temperature (°C) 1X Mode Hysteresis vs. Current Settings 6 Channel 2 5.5 1.2 25°C -40°C 1.1 1.0 0.9 0.8 0.7 85°C 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 Input Voltage (V) 2833.2007.09.1.0 AAT2833/34 240mA Total Display Solution for Portable Devices Typical Characteristics EN/SET Latch Timeout vs. Input Voltage 500 600 450 550 500 400 25°C TOFF (µs) TLAT (µs) EN/SET Off Timeout vs. Input Voltage 85°C 350 300 -40°C 250 25°C 450 -40°C 85°C 400 350 300 250 200 150 2.7 200 3.1 3.5 3.9 4.3 4.7 5.1 5.5 150 2.7 3.1 Input Voltage (V) 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) Turn On to 1X Mode Backlight Turn On to 1.5X Mode Backlight (30mA/channel; Address 0, Data 16; VIN = 4.4V) (30mA/channel; Address 0, Data 16; VIN = 3.5V) VEN/SET (2V/div) VEN/SET (2V/div) VOUT (2V/div) VOUT (2V/div) VBLX (0.5V/div) VBLX (0.5V/div) IIN (0.1A/div) IIN (0.2A/div) Time (200µs/div) Time (200µs/div) Turn On to 2X Mode Backlight Turn Off from 1.5X Mode Backlight (30mA/channel; Address 0, Data 16; VIN = 2.7V) (30mA/channel; Address 0, Data 16) VEN/SET (2V/div) VEN/SET (2V/div) VOUT (2V/div) VDIODE (2V/div) VBLX (0.5V/div) ILED (0.02A/div) IIN (0.2A/div) Time (200µs/div) 2833.2007.09.1.0 Time (100µs/div) 7 AAT2833/34 240mA Total Display Solution for Portable Devices Typical Characteristics Operating Characteristics Operating Characteristics (VIN = 3.4V; 1.5X Mode; 30mA/channel; AC Coupled) (VIN = 2.7V; 2X Mode; 30mA/channel; AC Coupled) VIN (100mV/div) VIN (100mV/div) VOUT (100mV/div) VOUT (100mV/div) IIN (20mA/div) IIN (20mA/div) Time (500ns/div) 8 Time (500µs/div) 2833.2007.09.1.0 AAT2833/34 240mA Total Display Solution for Portable Devices Functional Block Diagram C1+ C1– IN C2+ C2– OUT 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. 2833.2007.09.1.0 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 (500µs). 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 AAT2833/34 240mA Total Display Solution for Portable Devices in data values. When EN/SET is held low longer than TOFF (500µs), the AAT2833/34 enters shutdown mode operation and draws less than 1µA 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 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 19 20 24 25 26 27 28 29 32 Table 1a: AS2Cwire Serial Interface Addressing with Independent Channel Control Disabled. 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 Address Function 0 1 2 3 7 8 9 10 11 12 15 17 18 19 20 24 25 26 27 28 29 32 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 BL % of BSET 9 10 11 12 13 14 15 16 44 51 56 63 71 79 89 100 Table 2a: Addresses 0-2 with Independent Channel Control Disabled, Backlight Current Level. Data BL % of BSET EN/SET Rising Edges Data 1 2 3 4 5 6 7 8 0 21 22 25 29 32 35 40 Data BL % of BSET 9 10 11 12 13 14 15 16 44 51 56 63 71 79 89 100 Table 2b: Address 1 with Independent Channel Control Enabled, Backlight Current Level. Table 1b: AS2Cwire Serial Interface Addressing with Independent Channel Control Enabled. 10 2833.2007.09.1.0 AAT2833/34 240mA Total Display Solution for Portable Devices Backlight Independent Channel Control (Address 15) IBLED (% of BSET) 120 100 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Data Code Figure 1: Addresses 0-2 Backlight Current Level. 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 Individual BL Control 8 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. Data BL1-BL4 Current On BL5-BL6 Current On BL % of BSET 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 No No No No No No No No Yes Yes Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes No No No No Yes Yes Yes Yes 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 4: Address 15, Backlight Independent Channel Control Data BL6 BL5 BL4 BL3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Off Off Off Off Off Off Off Off On On On On On On On On Off Off Off Off On On On On Off Off Off Off On On On On Off Off On On Off Off On On Off Off On On Off Off On On Off On Off On Off On Off On Off On Off On Off On Off On 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 = 280kΩ). 2833.2007.09.1.0 11 AAT2833/34 240mA Total Display Solution for Portable Devices Data BL2 BL1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Off Off Off Off Off Off Off Off On On On On On On On On Off Off Off Off On On On On Off Off Off Off On On On On 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 >500µs). The functionality of Addresses 7-12 are unmodified by the enabling of independent channel control. Table 6: Address 3 with Independent Channel Control Enabled, BL1-BL2 On/Off Control. Data Address THI TLO TLAT EN/SET 1 Address 2 17 18 1 0 2... n ≤ 16 1 DATA1 1 DATA0 1 n Figure 2: AS2Cwire Serial Interface Timing Details. 12 2833.2007.09.1.0 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 128µs. The settings can be calculated as follows: R = (DATA7 - 1) · 128μs G = (DATA8 - 1) · 128μs B = (DATA9 - 1) · 128μs 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. 2833.2007.09.1.0 The RGB period can be calculated using the following equation: T = [(DATA10 - 1) · 3 + 15] · 128μs 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. 13 AAT2833/34 240mA Total Display Solution for Portable Devices Data RGB Current as % of BSET 1 2 3 4 5 6 7 0 33 66 100 133 167 200 IR = ISINK · R T G T B IB = ISINK · T IG = ISINK · 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: 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 (500µs) will activate the AAT2833/34's shutdown mode. Data and Address registers are cleared (reset to 0) during shutdown. R Red ISINK ISINK T G Green ISINK B Blue ISINK Figure 3: RGB Diode Current Timing. 14 2833.2007.09.1.0 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 = 280kΩ 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 > 550kΩ. PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4 = PIN VIN · IIN η= 4 · VLEDX · ILEDX ; x = 1, 2, 3 or 4 and IIN = 4 · ILEDX VIN · IIN VLEDX η= 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. 45 40 35 IBLED (mA) η= 30 25 20 15 10 5 0 100 200 300 400 500 600 700 800 900 1000 RBSET (kΩ Ω) Figure 4: Maximum Backlight LED Current vs RBSET. 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. η= PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4 = PIN VIN · IIN 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: 2833.2007.09.1.0 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: η= η= 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 VLEDX η = 1.5V IN 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: η= PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4 = PIN VIN · IIN η= 4 · VLEDX · ILEDX ; x = 1, 2, 3 or 4 and IIN = 2(4 · ILEDX) VIN · IIN VLEDX η = 2V IN 15 AAT2833/34 240mA Total Display Solution for Portable Devices LED Selection PCB Layout 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. 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. 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. 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 100mΩ. 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 2.2µF or greater value is recommended, and a 1µF 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 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 (θJA) 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. 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. 2833.2007.09.1.0 Figure 7: AAT2833/34 Evaluation Board Solder Side Layout. 17 AAT2833/34 240mA Total Display Solution for Portable Devices Evaluation Board Schematic VOUT D1 D2 D3 D4 D5 D6 DC+ VIN R9 = 280K for 30mA/chnl backlight. J1 R9 280K C7 5 6 N/C N/C BL6 BSET N/C BL2 N/C BL1 PGND AGND C1- N/C C1+ EN/SET VIN 8 9 10 C2 1.0μF 4 3 7 Optional footprints for R auxiliary lighting LEDs . U1 AA T2833 BL3 R EN 19 11 18 17 16 15 C1 14 1.0μF 13 OUT 4 20 C2- 3 21 C2+ 2 G 1 22 BL5 23 BL4 24 B Optional 100μF lab supply bypass C4 4.7μF 12 C3 2.2μF RGB G B Figure 8: AAT2833/34 Evaluation Board Schematic. R7 EN 220 J2 R8 100K VIN VIN R1 R2 R3 R4 R5 1K 1K 1K 1K 1K U2 SW1 SW2 1 2 3 4 VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 8 7 6 5 C6 1μF R6 330 PIC12F675 LED7 RED SW3 SW4 SW5 Figure 9: AAT2833/34 Microcontroller Section Schematic. 18 2833.2007.09.1.0 AAT2833/34 240mA Total Display Solution for Portable Devices Options Option Flash Backlight RGB Package AAT2833 AAT28343 N N Y Y Y Y TQFN44-24 TQFN44-24 Function Backlight Plus 4096-Combination RGB Backlight Plus 64-Combination RGB Ordering Information Package Marking1 Part Number (Tape and Reel)2 TQFN44-24 TQFN44-24 SVXYY 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 Pin 1 Identification Chamfer 0.300 ×45° 0.255 ± 0.025 1 2.700 ± 0.050 4.000 ± 0.050 2.700 ± 0.050 Top View 0.000 −0.050 Bottom View 0.214 ± 0.036 0.750 ± 0.050 4.000 ± 0.050 Pin 1 Dot By Marking 0.500 BSC 0.400 ± 0.050 TQFN44-24 Side View All dimensions in millimeters. © 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