DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs General Description Features The AAT2845A is a highly integrated power solution for single-cell lithium-ion-based LCD display applications. It includes a four-channel LED backlight driver and two integrated 200mA LDOs as additional power supplies for display and camera-related chipsets. • Input Voltage Range: 2.7V to 5.5V • Four-Channel LED Driver: ▪ Tri-Mode Charge Pump ▪ Up to 20mA/Channel ▪ Easy Control with Single Wire Interface ▪ 16 Current Levels ▪ Four Low Current Settings Down to 50μA ▪ Low IQ (50μA) for Low Current Mode ▪ >90% Peak Efficiency • Dual 200mA LDOs • Automatic Soft-Start • Over-Temperature Protection • Available in 3x4mm TQFN34-20 Package • -40°C to +85°C Temperature Range The backlight driver is a low noise, constant frequency charge pump DC/DC converter that uses a tri-mode load switch (1X), fractional (1.5X), and doubling (2X) conversion to maximize efficiency. Each of the four channels is capable of driving up to 20mA per channel. Skywroks' S2Cwire™ (Simple Serial Control™) serial digital input is used to enable, disable, and set current for each LED with 16 available settings down to 50μA. The low current mode supply current can be as low as 50μA to save power and maintain high efficiency. Applications Each LED output is equipped with built-in protection for short-circuit and auto-disable functions. Built-in softstart circuitry prevents excessive inrush current during start-up. A low current shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1μA. • • • • Camera Function Power Supplies Camera Phone Displays LCD Modules White LED Backlighting The AAT2845A is available in a Pb-free, thermallyenhanced 20-pin 3x4mm TQFN package. Typical Application C1 1μF C1- C2 1μF C1+ C2- IN C2+ OUT AAT2845A VBAT 3.6V CIN 2.2μF COUT 1μF D1 D2 D3 D4 IN LDOA 200mA Co1 FBA S2Cwire Backlight Control EN/SET LDO Enable ENLDO LDOB 200mA Co2 CBYP 0.1μF CBP GND FBB Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 1 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Pin Descriptions Pin # Symbol 1 2 3 D2 D1 LDOB 4 IN 5 6 7 8 9 10 PGND IN FBA LDOA C2C2+ 11 OUT 12 13 14 15 16 17 18 19 20 EP C1C1+ EN/SET ENLDO D4 D3 GND CBP FBB Function Current sink input #2. Current sink input #1. Output of LDO B. Connect a 2.2μF or larger ceramic capacitor to ground. Input power supply for charge pump. Requires a 1μF or larger ceramic capacitor connected between this pin and ground. Power ground. Input power pin for both LDOs. Connect a 1μF or larger ceramic capacitor from this pin to PGND. Feedback pin of LDO A. Regulated at 1.2V. Output of LDO A. Connect a 2.2μF or larger ceramic capacitor to ground. Flying capacitor 2 negative terminal. Flying capacitor 2 positive terminal. Connect a 1μF ceramic capacitor between C2+ and C2-. Charge pump output to drive load circuit. Connect a 1μF or larger ceramic capacitor between this pin and PGND. Flying capacitor 1 negative terminal. Flying capacitor 1 positive terminal. Connect a 1μF ceramic capacitor between C1+ and C1-. S2Cwire control pin for backlighting. Enable pin for LDO A and B. Current sink input #4. Current sink input #3. Ground. Bypass pin for the internal reference. Connect a 0.1μF ceramic capacitor from this pin to GND. Feedback pin of LDO B. Regulated at 1.2V. Exposed paddle (bottom); connect to PGND as closely as possible to the device. Pin Configuration TQFN34-20 (Top View) D3 GND CBP FBB 17 18 19 20 D2 D1 LDOB IN PGND IN 1 16 2 15 3 14 4 13 5 12 6 11 D4 ENLDO EN/SET C1+ C1OUT 9 10 8 7 C2+ C2LDOA FBA 2 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Absolute Maximum Ratings1 TA = 25°C, unless otherwise noted. Symbol TJ TLEAD Description IN, OUT, D1,D2, D3, D4 Voltage to GND C1+, C1-, C2+, C2- Voltage to GND LDOA, LDOB, FBA, FBB, EN/SET, ENLDO, CBP Voltage to GND PGND Voltage to GND Operating 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 -0.3 to +0.3 -40 to 150 300 V V V V °C °C Value Units 50 2 °C/W W Thermal Information2, 3, 4 Symbol JA PD Description Thermal Resistance Maximum Power Dissipation 1. Stresses above those listed in Absolute Maximum Ratings may cause permanent 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. Based on long-term current density limitation. 3. Derate 20mW/°C above 40°C ambient temperature. 4. Mounted on an FR4 circuit board. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 3 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Electrical Characteristics1 CIN = CO1 = CO2 = 2.2μF, C1 = C2 = 1.0μF, CBP = 0.1μF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C and VIN = 3.6V. Symbol Description Conditions Power Supply VIN Supply Voltage ISHDN Total Shutdown Current at VIN and LDOIN Charge Pump ICC IDX I(D-Match) Operating Current Average Current Accuracy Current Matching 1X to 1.5X or 1.5X to 2X Transition VTH Threshold at Any DX Pin TSS Soft-Start Time FCLK Clock Frequency TSD Over-Temperature Shutdown Threshold THYS Over-Temperature Shutdown Hysteresis EN/SET Logic Control TEN/SET LO EN/SET Low Time TEN/SET HI MIN Minimum EN/SET High Time TEN/SET HI MAX Maximum EN/SET High Time TOFF EN/SET Off Timeout TLAT EN/SET Latch Timeout IEN/SET EN/SET Input Leakage LDOs IIN IN Operating Current VFB Feedback Voltage VDO Dropout Voltage VOUT/ Line Regulation VOUT*VIN PSRR Power Supply Rejection Ratio LDO Logic Control VIL EN/SET, ENLDO Pins Logic Low Threshold VIH EN/SET, ENLDO Pins Logic High Threshold 2 Min Typ Max Units 5.5 1.0 V μA 2.7 EN/SET = ENLDO = GND 1X Mode, 3.0 VIN 5.5, Active, No Load Current 1.5X Mode, 3.0 VIN 5.5, Active, No Load Current 2X Mode, 3.0 VIN 5.5, Active, No Load Current 50μA Setting, 1X Mode 20mA Setting, TA = 25°C 1mA Setting, TA = 25°C VIN - VF = 1.5V 1.0 3.0 5.0 18 0.9 20mA Setting, TA = 25°C 50 20 1.0 0.5 μA 22 1.1 1.0 100 1 140 15 μs MHz °C °C 75 -1 1.17 VIN = (VOUT + 1V) to 5.0V IOUT =10mA, 1kHz % mV 75 500 500 1 μs ns μs μs μs μA 150 1.23 300 μA V mV 50 ENLDO = IN, EN/SET = AGND, No Load IOUT = 1mA to 200mA IOUT = 150mA mA 150 0.3 VEN/SET = VIN = 5V mA 80 1.2 150 0.09 %/V 50 dB 0.4 1.4 V V 1. The AAT2845A 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 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Typical Characteristics CIN = CO1 = CO2 = 2.2μF, C1 = C2 = 1.0μF, CBP = 0.1μF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C and VIN = 3.6V. Backlight Efficiency vs. Supply Voltage Turn-On to 1X Mode (VIN = 4.2V; 20mA/ch Load) 100 Efficiency (%) 90 20mA/ch 80 EN/SET (2V/div) VOUT (2V/div) 70 60 1mA/ch 50 15.2mA/ch 40 30 VSINK (1V/div) IIN (100mA/div) 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 Supply Voltage (V) Time (100µs/div) Turn-On to 1.5X Mode Turn-On to 2X Mode (VIN = 3.5V; 20mA/ch Load) EN/SET (2V/div) (VIN = 2.8V; 20mA/ch Load) EN/SET (2V/div) VOUT (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (200mA/div) VSINK (500mV/div) IIN (500mA/div) Time (100µs/div) Time (100µs/div) Turn-Off from 1.5X Mode Backlight EN/SET (2V/div) VF (2V/div) IIN (200mA/div) Time (100µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 5 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Typical Characteristics CIN = CO1 = CO2 = 2.2μF, C1 = C2 = 1.0μF, CBP = 0.1μF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C and VIN = 3.6V. Backlight Operating Characteristic Backlight Operating Characteristic (VIN = 2.9V; 2X Mode; 20mA/ch Load) (VIN = 2.9V; 2X Mode; 13.5mA/ch Load) VIN (20mV/div) VIN (20mV/div) VOUT (40mV/div) VOUT (40mV/div) VSINK (40mV/div) VSINK (40mV/div) Time (500ns/div) Time (500ns/div) Backlight Operating Characteristic Backlight Operating Characteristic (VIN = 2.9V; 2X Mode; 13.5mA/ch Load) (VIN = 3.7V; 1.5X Mode; 20mA/ch Load) VIN (20mV/div) VIN (20mV/div) VOUT (40mV/div) VOUT (40mV/div) VSINK (20mV/div) VSINK (40mV/div) Time (500ns/div) Time (500ns/div) 500 400 350 300 -40°C 250 200 150 100 25°C 85°C 50 0 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 Supply Voltage (V) 6 EN/SET Off Timeout vs. Supply Voltage EN/SET Off Timeout (µs) EN/SET Latch Timeout (µs) EN/SET Latch Timeout vs. Supply Voltage 450 400 350 -40°C 300 250 200 150 100 25°C 85°C 50 0 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 Supply Voltage (V) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Typical Characteristics EN/SET Low Threshold Voltage vs. Supply Voltage 1 0.9 -40°C 0.8 0.7 0.6 25°C 0.5 85°C 0.4 0.3 0.2 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 EN/SET High Threshold Voltage (V) EN/SET Low Threshold Voltage (V) CIN = CO1 = CO2 = 2.2μF, C1 = C2 = 1.0μF, CBP = 0.1μF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C and VIN = 3.6V. EN/SET High Threshold Voltage vs. Supply Voltage 1 -40°C 0.9 0.8 0.7 0.6 25°C 0.5 85°C 0.4 0.3 0.2 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 Supply Voltage (V) Supply Voltage (V) LDOs A and B Turn-On Characteristic LDOs A and B Line Regulation (10mA Load) 0.4 0.3 ENLDO (2V/div) Error (%) 0.2 VOUT (500mV/div) 0.1 OUTA 0.0 -0.1 OUTB -0.2 -0.3 -0.4 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 Time (50µs/div) Supply Voltage (V) LDOs A and B Load Regulation LDOs A and B Line Transient Response (VOUT = 1.2V) (VOUT = 2.5V; 10mA Load) 1.0 0.8 VIN (400mV/div) Error (%) 0.6 0.4 VIN = 4.2V 0.2 OUTA 0.0 VIN = 3.7V -0.2 -0.4 VOUT (10mV/div) OUTB -0.6 -0.8 -1.0 0.1 1 10 Load Current (mA) 100 1000 Time (40µs/div) Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 7 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Typical Characteristics CIN = CO1 = CO2 = 2.2μF, C1 = C2 = 1.0μF, CBP = 0.1μF; TA = 25°C, unless otherwise noted. Typical values are at TA = 25°C and VIN = 3.6V. LDOs A and B Load Transient Response (VOUT = 2.5V) IOUT (100mA/div) VOUT (100mV/div) Time (20µs/div) 8 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Functional Block Diagram C1+ C1- C2+ C2- Tri-Mode (1X, 1.5X and 2X) Charge Pump IN OUT Soft-Start Control 1MHz Oscillator Voltage Reference EN/SET S2Cwire Interface 6x16 Bit ROM IN LDO A ENLDO CBP D/A D1 D/A D2 D/A D3 D/A D4 LDOA FBA 1.2V Reference LDO B LDOB FBB GND Functional Description The AAT2845A is an integrated solution for LCD display applications with a built-in driver for white LED backlight and two LDO voltage regulators for logic power supplies. The backlight driver is a tri-mode load switch (1X) and high-efficiency (1.5X or 2X) charge pump device. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required on each constant current sink input and sets the load switch and charge pump modes based on the input battery voltage and the current sink input voltage. As the battery discharges over time, the charge pump is enabled when any of the four current sink inputs nears dropout. The charge pump initially starts in 1.5X mode. If the charge pump output droops enough for any current source output to become close to dropout, the charge pump will automatically transition to 2X mode. The charge pump requires only four external components: two 1μF ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1μF ceramic input capacitor (CIN), and one 0.33μF to 1μF ceramic charge pump output capacitor (COUT). The four constant current sink inputs (D1 to D4) can drive four individual LEDs with a maximum current of 20mA each. The unused sink inputs must be connected to the OUT pin; otherwise the part will operate only in 2X charge pump mode. The S2Cwire serial interface enables the charge pump and sets the current sink magnitudes. Constant Current Output Level Settings The constant current sink levels for D1 to D4 are set via the S2Cwire serial interface according to a logarithmic scale for the first 12 codes, and a separate low-current scale for the last four codes. Because the inputs D1 to D4 are true independent constant current sinks, the voltage observed on any single given input will be determined by the difference between VOUT and the actual forward voltage (VF) of the LED being driven. Since the current level is programmable, no PWM (pulse width modulation) or additional control circuitry is needed to control LED brightness. This feature greatly reduces the burden on a microcontroller or system IC to manage LED or display brightness, allowing the user to “set it and forget it.” With its high-speed serial interface Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 9 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs (>1MHz data rate), the LED current drive can be changed successively to brighten or dim LEDs in smooth transitions (e.g., to fade out) or in abrupt steps, giving the user complete programmability and real-time control of LED brightness. to the desired code must be applied on the EN/SET pin. When the EN/SET pin is held low for an amount of time longer than TOFF (500μs), the AAT2845A enters shutdown mode and draws less than 1μA from the input. An internal data register is reset to zero during shutdown. The last four codes of the current level scale engage a reduced quiescent current mode that enhances the lowcurrent setting efficiency. This mode is especially useful for low-current applications where a continuous, lowcurrent state is maintained for a substantial length of time. Auto-Disable Feature The charge pump in the AAT2845A is equipped with an auto-disable feature for each LED channel. After the IC is enabled and started up, a test current of 100μA (typical) is forced through each sink channel. The channel will be disabled if the voltage of that particular DX pin does not drop to a certain threshold. This feature is convenient for disabling an unused channel or during an LED fail-short event. S2Cwire Serial Interface The current sink magnitude is controlled by Skyworks' S2Cwire serial digital input. The interface records rising edges of the EN/SET pin and decodes them into 16 different states. The 16 current level settings available are indicated in Table 1. Data Output (mA/Ch) Data Output (mA/Ch) 1 2 3 4 5 6 7 8 20 18.4 16.8 15.2 13.5 11.9 10 8.4 9 10 11 12 13 14 15 16 6.8 5.2 3.5 2.0 1.0 0.5 0.10 0.05 Low Dropout Regulators The AAT2845A includes two LDO linear regulators. The regulators run from the same 2.7V to 5.5V input voltage as the charge pump. The regulators use a single on/off control input, ENLDO. The LDO output voltages are set through a resistive voltage divider from the output (OUTA or OUTB) to the feedback input (FBA or FBB). The ratio of resistor values determines the LDO output voltage. The low 200mV dropout voltage at 200mA load current allows the regulator to maintain output voltage regulation. Each LDO regulator can supply a continuous load current up to 200mA. Both LDOs include current limiting and thermal overload protection to prevent damage to the load or to the LDOs. Table 1: Current Level Settings. The S2Cwire serial interface has flexible timing. Data can be clocked-in at speeds higher than 1MHz, or much slower, such as 15kHz. After data is applied, EN/SET is held high to latch the data. Once EN/SET has been held in the logic high state for time TLAT (500μs), the programmed current becomes active and the internal data register is reset to zero. For subsequent current level programming, the number of rising edges corresponding Thermal Protection The charge pump has a built-in thermal protection circuit that will shut down the charge pump and the LDOs if the die temperature rises above the thermal limit, as is the case during a short-circuit of the OUT pin. T HI T LO TOFF TLAT EN/SET 1 Data Reg 2 n-1 0 n ≤ 16 n 0 Figure 1: S2Cwire Serial Interface Timing. 10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Applications Information LED Selection The AAT2845A is specifically intended for driving white LEDs. However, the device design will allow the AAT2845A to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.7V. LED applications may include mixed arrangements for display backlighting, color (RGB) LEDs, infrared (IR) diodes, and any other load needing a constant current source generated from a varying input voltage. Since the D1 to D4 constant current sinks are matched with negligible voltage dependence, the constant current channels will be matched regardless of the specific LED forward voltage (VF) levels. The low dropout current sinks in the AAT2845A maximize performance and make it capable of driving LEDs with high forward voltages. Multiple channels can be combined to obtain a higher LED drive current without complication. Device Switching Noise Performance The AAT2845A operates at a fixed frequency of approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of cellular telephone handsets or other communication devices. Back-injected noise appearing on the input pin of the charge pump is 20mV peak-to-peak, typically ten times less than inductor-based DC/DC boost converter white LED backlight solutions. The AAT2845A soft-start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit. Shutdown Since the sink switches are the only power returns for all loads, there is no leakage current when all of the sink switches are disabled. To activate the shutdown mode, hold the EN/SET input low for longer than TOFF (500μs). In this state, the AAT2845A typically draws less than 1μA from the input. Data and address registers are reset to 0 in shutdown. LDO Output Voltage Programming The output voltages for LDOA and LDOB are programmed by an external resistor divider network. As shown below, the selection of R8 and R9 is a straightforward matter. R9 is chosen by considering the tradeoff between the feedback network bias current and resistor value. Higher resistor values allow stray capacitance to become a larger factor in circuit performance, whereas lower resistor values increase bias current and decrease efficiency. OUTA (OUTB) VOUT R8 (R10) FBA (FBB) VREF = 1.2V R9 (R11) Figure 2: Selection of External Resistors. To select appropriate resistor values, first choose R9 such that the feedback network bias current is reasonable. Then, according to the desired VOUT, calculate R8 according to the equation below. An example calculation follows. R9 is chosen to be 120K, resulting in a small feedback network bias current of 1.2V/120K = 10μA. The desired output voltage is 1.8V. From this information, R8 is calculated from the equation below. R8 = R9(VOUT - 1.2V) 1.2V The result is R8 = 60K. Since 60K is not a standard 1% value, 60.4K is selected. From this example calculation, for VOUT = 1.8V, use R9 = 120K and R8 = 60.4K. A table of example output voltages and corresponding resistor values is provided below. Standard 1% Values (R9, R11 = 120K) VOUT (V) R8, R10 () 2.8 2.5 2.0 1.8 1.5 160K 130K 79.6K 60.4K 30.1K Table 2: Example Output Voltages and Corresponding Resistor Values Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 11 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Power Efficiency and Device Evaluation The charge pump efficiency discussion in the following sections accounts only for efficiency of the charge pump section itself. Due to the unique circuit architecture and design of the AAT2845A, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT2845A outputs are pure constant current sinks and typically drive individual loads, it is difficult to measure the output voltage for a given output (D1 to D4) to derive an overall output power measurement. For any given application, white LED forward voltage levels can differ, yet the output drive current will be maintained as a constant. This makes quantifying output power a difficult task when taken in the context of comparing to other white LED driver circuit topologies. A better way to quantify total device efficiency is to observe the total input power to the device for a given LED current drive level. The best white LED driver for a given application should be based on trade-offs of size, external component count, reliability, operating range, and total energy usage...not just % efficiency. The AAT2845A efficiency may be quantified under very specific conditions and is dependent upon the input voltage versus the output voltage seen across the loads applied to outputs D1 through D4 for a given constant current setting. Depending on the combination of VIN and voltages sensed at the current sinks, the device will operate in load switch mode. When any one of the voltages sensed at the current sinks nears dropout, the device will operate in 1.5X or 2X charge pump mode. Each of these modes will yield different efficiency values. Refer to the following two sections for explanations for each operational mode. The expression to define the ideal efficiency () can be rewritten as: η= POUT VOUT · IOUT VOUT = = PIN VIN · IOUT VIN -or- η(%) = 100 1.5X and 2X Charge Pump Mode Efficiency The AAT2845A contains a fractional charge pump which will boost the input supply voltage in the event where VIN is less than the voltage required to supply the output. The efficiency () can be simply defined as a linear voltage regulator with an effective output voltage that is equal to one and one half or two times the input voltage. Efficiency () for an ideal 1.5X charge pump can typically be expressed as the output power divided by the input power. η= POUT PIN In addition, with an ideal 1.5X charge pump, the output current may be expressed as 2/3 of the input current. The expression to define the ideal efficiency () can be rewritten as: η= POUT VOUT · IOUT VOUT = = PIN VIN · 1.5IOUT 1.5VIN -or- 1X Mode Efficiency The AAT2845A 1X mode is operational at all times and functions alone to enhance device power conversion efficiency when VIN is higher than the voltage across the load. When in 1X mode, voltage conversion efficiency is defined as output power divided by input power: η= 12 POUT PIN ⎛ VOUT ⎞ ⎝ VIN ⎠ η(%) = 100 ⎛ VOUT ⎞ ⎝ 1.5VIN⎠ For a charge pump with an output of 5V and a nominal input of 3.5V, the theoretical efficiency is 95%. Due to internal switching losses and IC quiescent current consumption, the actual efficiency can be measured at 93%. These figures are in close agreement for output load conditions from 1mA to 100mA. Efficiency will decrease substantially as load current drops below 1mA or when the level of VIN approaches VOUT. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs The same calculations apply for 2X mode, where the output current then becomes 1/2 of the input current. Capacitor Selection Careful selection of the four external capacitors CIN, C1, C2, and COUT is 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 may be defined as less than 100m. A value of 1μF for all four capacitors is a good starting point when choosing capacitors. If the constant current sinks are only programmed for light current levels, then the capacitor size may be decreased. Capacitor Characteristics Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2845A. 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 nonpolarized. Low ESR ceramic capacitors help maximize charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Equivalent Series Resistance ESR is an important characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capacitor that is caused by the leads, internal connections, size or area, material composition, and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. Ceramic Capacitor Materials Ceramic capacitors less than 0.1μF are typically made from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials. Large ceramic capacitors (i.e., larger than 2.2μF) are often available in low-cost Y5V and Z5U dielectrics, but capacitors larger than 1μF are not typically required for AAT2845A applications. Capacitor area is another contributor to ESR. Capacitors that are physically large will have a lower ESR when compared to an equivalent material smaller capacitor. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size. Evaluation Board User Interface The user interface for the AAT2845A evaluation board is provided by three buttons and two connection terminals. The board is operated by supplying external power and pressing individual buttons or button combinations. The table below indicates the function of each button or button combination. To power-on the evaluation board, connect a power supply or battery to the DC- and DC+ terminals. Close the board’s supply connection by positioning the J1 jumper to the ON position. A red LED indicates that power is applied. The evaluation board is made flexible so that the user can disconnect the enable lines from the microcontroller and apply external enable signals. By removing the jumpers from J2, and/or J3, external enable signals can be applied to the board. External enable signals must be applied to the ON pin of each J2, or J3 terminal. When applying external enable signals, consideration must be given to the voltage levels. The externally applied voltages should not exceed the supply voltage that is applied to the IN pins of the device (DC+). The LDO loads can be connected directly to the evaluation board. For adequate performance, be sure to connect the load between OUTA/OUTB and DC- as opposed to some other GND in the system. Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 13 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Button(s) Pushed1 DATA LIGHT LIGHT+DATA ENLDO DATA+LIGHT+ENLDO Description Increment the backlight data setting. Hold down the button to auto-cycle through the brightness levels. Toggle ON/OFF the backlighting section. Set the brightness level using the DATA button. Decrement the backlight data setting. Hold down to auto-cycle. Toggle ON/OFF the LDOs. Reset. Clear data and bring all enable lines low. Table 3: Evaluation Board User Interface. DC+ 1 2 VOUT 3 C9 100μF J1 D1 D2 D3 D4 Optional 100μF capacitor to bypass lab supply C7 0.1μF D3 D2 D4 16 D1 ENLDO 15 ENL 3 LDOB EN/SET 14 EN/SET 4 IN C1+ 13 5 PGND C1- 12 6 IN OUTCP 11 7 8 9 C1 1.0μF C3 1.0μF C2+ C4 2.2μF U1 AAT2845A 2 C2- R11 120K C6 2.2μF GND FBB R10 160K 17 1 LDOA Programmed for 2.8V output 18 FBA OUTB 19 CBYP 20 10 C2 1.0μF OUTA R8 60.4K C5 2.2μF Programmed for 1.8V output R9 120K Figure 5: AAT2845A Section Schematic. 1. The “+” indicates that these buttons are pressed and released together. 14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs J2 R6 220 EN/SET 3 2 1 R7 100K VIN VIN R1 R2 R3 1K 1K 1K U2 1 2 3 4 DATA SW1 VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 C8 1μF 8 7 6 5 R5 330 LED7 RED PIC12F675 LIGHT SW2 ENLDO J3 SW3 ENL 3 2 1 R4 100K DC- Figure 6: MCU Section Schematic. Evaluation Board Component Listing Component Part# Description Manufacturer U1 U2 D1 - D4 C1 - C3 C4 - C6 C7 C8 C9 R1 - R3 R4, R7 R5 R6 R8 R9, R11 R10 J1 - J3 LED7 SW1 - SW3 AAT2845AIML-EE-T1 PIC12F675 LW M673 GRM18x GRM18x GRM18x GRM31x TAJBx Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PRPN401PAEN CMD15-21SRC/TR8 PTS645TL50 Four-Channel Backlight Driver with Dual LDOs 8-bit CMOS, FLASH MCU; 8-pin PDIP Mini TOPLED White LED; SMT 1.0μF, 10V, X5R, 0603, ceramic 2.2μF, 10V, X5R, 0603, ceramic 0.1μF, 16V, X7R, 0603, ceramic 1μF, 10V, X5R, 1206, ceramic 100μF, 10V, 10μA, tantalum 1K, 5%, 1/4W; 1206 100K, 5%, 1/4W; 1206 330, 5%, 1/4W; 1206 220, 5%, 1/4W; 1206 60.4K, 1%, 1/10W; 0603 120K, 1%, 1/10W; 0603 160K, 1%, 1/10W; 0603 Conn. Header, 2mm zip Red LED; 1206 Switch Tact, SPST, 5mm Skyworks Microchip OSRAM Murata Murata Murata Murata AVX Vishay Vishay Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp ITT Industries Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012 15 DATA SHEET AAT2845A Four-Channel Backlight Driver with Dual LDOs Ordering Information Package Marking1 Part Number (Tape and Reel)2 TQFN34-20 YEXYY AAT2845AIML-EE-T1 Skyworks Green™ products are compliant with all applicable legislation and are halogen-free. For additional information, refer to Skyworks Definition of Green™, document number SQ04-0074. Package Information3 TQFN34-20 3.00 ± 0.05 0.40 ± 0.100 1.55 ± 0.05 2.55 ± 0.05 0.50 BSC 0.24 ± 0.060 4.00 ± 0.05 Detail "A" Top View Bottom View 0.75 ± 0.05 Detail "A" 0.025 ± 0.025 Side View 0.214 ± 0.036 All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved. Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. 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Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference. 16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com 202067A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012