PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM General Description Features The AAT3192 is a charge-pump based, current-sink white LED driver capable of driving one or two LEDs up to 30mA, each. It automatically switches between 1x mode and 2x mode to maintain the highest efficiency and optimal LED current accuracy and matching. • • • • The AAT3192 charge pump’s 1x mode (bypass mode) has very low resistance allowing LED current regulation to be maintained with input supply voltage approaching the LED forward voltage. • • • • • • The AAT3192 is available in the 2x2mm, 10-lead SC70JW10 package. Drives up to 2 LEDs at up to 30mA, each Automatic Switching Between 1x and 2x Modes 0.9MHz Switching Frequency Linear LED Output Current Control ▪ Single-wire, S2Cwire Interface • AAT3192-1: 16-step • AAT3192-2: 8-step • AAT3192-3: 4-step ▪ ON/OFF or PWM Interface • AAT3192-4 ±10% LED Output Current Accuracy ±3% LED Output Current Matching Low-Current Shutdown Mode Built-in Thermal Protection Automatic Soft-Start Available in 2x2mm SC70JW-10 Package Applications • • • • Entry Entry Entry Entry Level Level Level Level Cordless Phone Handsets Digital Cameras Mobile Phone Handsets MP3 and PMP Players Typical Application Input Voltage 2.7V to 5.5V IN OUT C+ C IN 1μF CP 1μF AAT3192-1 C- EN/SET S2Cwire Interface EN/SET RSET C OUT 1μF WLEDs OSRAM LW M 678 or equivalent D1 D2 GND R SET 14.3kΩ 3192.2008.07.1.3 www.analogictech.com 1 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Pin Descriptions Pin Symbol 1 N/C 2 OUT 3 4 CC+ 5 IN EN/SET (AAT3192-1/-2/-3) 6 EN/PWM (AAT3192-4) 7 RSET 8 GND 9 D2 10 D1 Description No connection. Charge pump output. OUT is the output of the charge pump. Bypass OUT to GND with a 1μF or larger ceramic capacitor. Charge pump capacitor negative node. Charge pump capacitor positive node. Connect a 1μF ceramic capacitor between C+ and C-. Power source input. Connect IN to the power source, typically the battery. Bypass IN to GND with a 1μF or larger ceramic capacitor. LED enable and serial control input. EN/SET is the ON/OFF control for the LED and the S2Cwire digital input for the AAT3192-1/-2/-3 to control serially the LED brightness according to the maximum current set by RSET. LED ON/OFF and PWM control input. This logic input controls the LED outputs for the AAT3192-4. Alternatively, a PWM signal from a GPIO or an equivalent signal from a separate controller can be used to control LED output current linearly. A PWM signal, ranging from 10% to 100% duty cycle, controls the LED current linearly between ZS and FS. A 1% tolerance resistor from this pin to GND sets the maximum LED current level. For optimal LED output current accuracy and matching in the AAT3192-1/-2/-4, a 14.3kΩ resistor sets each full-scale output current to 20mA, maximum. For the AAT3192-3, a 11.5kΩ resistor is recommended. Ground. Connect this pin to the system’s ground plane. LED2 Current Sink Input. D2 is the input of LED2 current sink. Connect LED2’s anode to OUT and its cathode to D2. LED1 Current Sink Input. D1 is the input of LED1 current sink. Connect LED1’s anode to OUT and its cathode to D1. Pin Configuration SC70JW-10 (Top View) N/C OUT CC+ IN 2 1 10 2 9 3 8 4 7 5 6 D1 D2 GND RSET EN/SET www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Part Number Descriptions Part Number Interface Current Control, Inverting AAT3192IJQ-1 AAT3192IJQ-2 AAT3192IJQ-3 AAT3192IJQ-4 S2Cwire S2Cwire S2Cwire PWM 16-step 8-step 4-step Linear Absolute Maximum Ratings1 Symbol Description IN, C+, C-, OUT, D1, D2, and RSET Pin Voltages to GND EN/SET or EN/PWM Pin Voltage to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec) Value Units -0.3 to 6.0 -0.3 to VIN + 0.3 -40 to 150 300 V V °C °C Value Units 625 160 mW °C/W Thermal Information Symbol PD θJA Description Maximum Power Dissipation2, 3 Maximum Thermal Resistance2 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. Mounted on an FR4 circuit board. 3. Derate 6.25mW/°C above 40°C ambient temperature. 3192.2008.07.1.3 www.analogictech.com 3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Electrical Characteristics1 IN = EN = 3.6V; CIN = 1μF; COUT = 1μF; CCP = 1μF; RSET = 14.3kΩ; TA =-40°C to 85°C unless otherwise noted. Typical values are at TA = 25°C. Symbol Description Conditions AAT3192-1/2/3/4 Input Power Supply IN Input Voltage Range IIN Input Operating Current IIN(SHDN) Input Shutdown Current Charge Pump Section OUT Maximum Output Current IOUT fOSC Charge Pump Oscillator Frequency VIN_(TH) Charge Pump Mode Hysteresis tOUT Output Start-Up Time AAT3192-1/-2/-4: LED Current Sink Outputs ID_(MAX) D1 - D2 Current Accuracy ΔID_(MAX) D1 - D2 Current Matching D1 - D2 Current Accuracy ID_(DATA15) (AAT3192-1 only) D1 - D2 Current Accuracy ID_(DATA8) (AAT3192-2 only) D1 - D2 Current Accuracy ID_(10%) (AAT3192-4 only) D1 - D2 Charge Pump Mode VD_(TH) Transition Threshold Min Typ 2.7 EN/SET or EN/PWM = IN; VD1 = VD2 = IN, excluding ID1-ID2 EN/SET or EN/PWM = IN; ID1 = ID2 = FS, excluding ID1-ID2; VIN – VF = 1.5V Operating, ID1 = ID2 = FS; D1 and D2 = OPEN IN = 5.5V; EN/SET or EN/PWM = GND Max Units 5.5 V 2.5 2.5 0.65 ID1 = ID2 = 20mA; Excluding AAT3192-4, PWM Option EN/SET or EN/PWM = IN mA 7.0 1 μA 100 0.9 1.15 mA MHz 115 250 mV 150 μs DATA = 1; VIN - VF = 1.5V DATA = 1; VIN - VF = 1.5V 18 20 ±3 22 mA % DATA = 15; VIN - VF = 1.5V 1.0 1.3 1.56 mA DATA = 8; VIN - VF = 1.5V 1.0 1.3 1.56 mA DC = 10%; fPWM = 10kHz; VIN - VF = 1.5V 2.4 mA ID1 = ID2 = 20mA 125 mV 1. The AAT3192 is guaranteed to meet performance specification over the -40°C to 85°C operating temperature range and is assured by design, characterization and correlation with statistical process controls. 4 www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Electrical Characteristics1 IN = EN = 3.6V; CIN = 1μF; COUT = 1μF; CCP = 1μF; RSET = 14.3kΩ; TA =-40°C to 85°C unless otherwise noted. Typical values are at TA = 25°C. Symbol Description Conditions AAT3192-3: LED Current Sink Outputs ID_(MAX) D1 - D2 Current Accuracy ΔID_(MAX) D1 - D2 Current Matching ID_(DATA4) D1 - D2 Current Accuracy D1 - D2 Charge Pump Mode Transition VD_(TH) Threshold AAT3192-1/-2/-3: EN/SET and S2Cwire Control EN Input High Threshold Voltage VENH VENL EN Input Low Threshold Voltage IEN(LKG) EN Input Leakage Current tEN/SET(OFF) EN/SET Input OFF Timeout tEN/SET(LAT) EN/SET Input Latch Timeout tEN/SET(LOW) EN/SET Input LOW Time tENSET(H-MIN) EN/SET Minimum High Time tENSET(H-MAX) EN/SET Maximum High Time AAT3192-4: EN/PWM Current Control VENH EN/PWM Input High Threshold Voltage EN/PWM Input Low Threshold Voltage VENL IEN(LKG) EN/PWM Input Leakage Current tPWM(ON) PWM Control Turn-on Delay tEN/PWM EN/PWM Input OFF Timeout fPWM PWM Control Frequency RSET = 11.5kΩ; DATA = 1; VIN - VF = 1.5V RSET = 11.5kΩ; DATA = 1; VIN - VF = 1.5V RSET = 11.5kΩ; DATA = 4; VIN - VF = 1.5V Min Typ Max Units 18 20 ±3 0.9 22 mA % mA 0.72 RSET = 11.5kΩ; ID1 = ID2 = 20mA 1.1 125 mV 1.4 EN/SET = IN = 5V 0.4 1 500 500 75 -1 0.3 50 75 1.4 EN/PWM = IN = 5V 0.4 1 -1 2 0.15 Duty Cycle = 80% 1 50 V V μA μs μs μs ns μs V V μA μs ms kHz 1. The AAT3192 is guaranteed to meet performance specification over the -40°C to 85°C operating temperature range and is assured by design, characterization and correlation with statistical process controls. 3192.2008.07.1.3 www.analogictech.com 5 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Typical Characteristics Shutdown Current vs. Temperature Operating Current (No Load) vs. Input Voltage 0.010 3.50 0.008 IQ (mA) 3.40 IIN(SHDN) (µA) 3.60 85°C 3.30 25°C 3.20 3.10 3.00 2.7 3.1 3.5 3.9 4.3 4.7 5.5V 0.004 0.002 0°C -45°C 0.006 5.1 2.7V 0.000 -40 5.5 -15 Efficiency vs. Input Voltage 60 85 Current Matching vs. Temperature 21.0 100% 90% 20.5 Current (mA) 80% Efficiency (%) 35 Temperature (°°C) VIN (V) 70% 60% 30mA VF = 3.8V 50% 40% 30% 10mA VF = 3.2V 20% 10% 0% 2.7 10 3.1 3.5 3.9 20mA VF = 3.5V 4.3 D1 20.0 19.5 19.0 D2 18.5 4.7 5.1 5.5 18.0 -40 Input Voltage (V) -15 10 35 60 85 Temperature (°C) Turn On to 2X Mode Turn Off from 2X Mode (VIN = 3.6V; 19.6mA/ch) (2X Mode; 19.6mA/ch) EN/SET (2V/div) EN/SET (2V/div) VF (2V/div) VF (1V/div) VSINK (2V/div) IIN (200mA/div) IIN (200mA/div) Time (200µs/div) 6 Time (200µs/div) www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Typical Characteristics Turn On to 1X Mode Maximum LED Current vs RSET (VIN = 4.2V; 19.6mA/ch) 32 EN/SET (2V/div) 28 VF (2V/div) 20 ILED (mA) 24 VSINK (2V/div) 16 12 8 IIN (200mA/div) 4 0 8 13 18 1.2 1.2 1.0 1.0 0.8 0.8 85°C 0.4 0.2 2.7 -40°C 0.6 3.5 3.9 -40°C 0.4 0.2 3.1 4.3 4.7 5.1 5.5 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) EN/SET Input Latch Timeout vs. Input Voltage EN/SET Input OFF Timeout vs. Input Voltage 350 350 85°C 85°C 300 TEN/SET(OFF) (µs) 300 TEN/SET(LAT) (µs) 25°C 85°C Input Voltage (V) 250 25°C 200 -40°C 150 100 2.7 33 EN Input Low Threshold Voltage vs. Input Voltage VENL (V) VENH (V) EN Input High Threshold Voltage vs. Input Voltage 25°C 28 RSET (kΩ Ω) Time (200µs/div) 0.6 23 3.1 3.5 3.9 4.3 4.7 5.1 5.5 250 -40°C 150 100 2.7 Input Voltage (V) 3192.2008.07.1.3 25°C 200 3.1 3.5 3.9 4.3 4.7 5.1 5.5 Input Voltage (V) www.analogictech.com 7 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Typical Characteristics Transition of LED Current Transition of LED Current (19.6mA to 1.3mA) (1.3mA to 19.6mA) EN (2V/div) EN (2V/div) VOUT (1V/div) VSINK (1V/div) VOUT (1V/div) 4.0V VSINK (1V/div) 0.5V IIN (50mA/div) 4.2V 1.5V IIN (50mA/div) Time (100µs/div) Time (100µs/div) Output Ripple Waveform Input Current vs. Input Voltage (2X Mode; 20mA Load) (Excluding AAT3192-4, PWM Option) 200 VIN (AC Coupled) (20mV/div) Input Current (mA) 180 VOUT (AC Coupled) (20mV/div) VSINK (AC Coupled) (50mV/div) 160 VIN Rising 140 120 100 ILED = 20mA 80 60 40 ILED = 10mA 20 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 Input Voltage (V) Time (1µs/div) 8 VIN Falling ILED = 30mA www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Functional Block Diagram C+ C- OUT Two-Mode CP Control IN D1 VF Monitoring 2 D2 GND IREF EN/SET (EN/PWM) S2Cwire Control (PWM Control) Functional Description The AAT3192 is a low-cost charge-pump solution designed to drive up to two white LEDs. The charge pump operates from a 2.7V to 5.5V power source and converts it to voltage levels necessary to drive the LEDs. LED current is individually controlled through integrated current sinks powered from the output of the charge pump. Low 1x charge-pump output resistance and low-drop voltage current sinks allow the charge pump to stay in 1x mode with an input voltage as low as 3.75V and LED forward voltages as high as 3.5V. Once in 2x mode, the charge pump monitors the input supply voltage and automatically switches back to 1x mode when there is sufficient input voltage. The AAT3192 requires only four external components: one 1μF ceramic capacitor for the charge pump flying capacitors (CP), one 1μF ceramic input capacitor (CIN), one 1μF ceramic output capacitor (COUT) and a resistor 3192.2008.07.1.3 DAC RSET (RSET) to set the maximum LED current. The AAT3192 can drive two constant output sinks (D1 and D2) with up to 30mA maximum current each. AnalogicTech’s S2Cwire serial interface enables the AAT3192-1/-2/-3 and changes the current sink magnitudes through the EN/SET pin. The AAT3192-4 uses an external PWM signal to enable the IC and control the brightness of the LEDs. Constant Current Control using RSET The maximum current is programmed by an external resistor at the RSET pin. Using a 14.3kΩ external resistor at the RSET pin, the AAT3192-1/-2/-4 includes an integrated serial LED current control that sets the fullscale LED current between 20mA and 0.63mA. For the AAT3192-3, a 11.5kΩ external resistor at the RSET pin sets the full-scale LED current between 20mA and 1.3mA. The full-scale LED current can set higher or lower than 20mA; see Table 5. For maximum accuracy, a 1% tolerance resistor is recommended. www.analogictech.com 9 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM S2Cwire Serial Interface (AAT3192-1/-2/-3 only) by a pause with EN/SET held high for at least tLAT (500μs). The programmed current is then seen at the current sink outputs. When EN/SET is held low for an amount of time longer than tOFF (500μs), the AAT3192 enters into shutdown mode and draws less than 1μA from the input and the internal data register is reset to zero. The LED output current of the AAT3192 is controlled by AnalogicTech’s S2Cwire serial interface. Since the LED current is programmable, no PWM 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 (1MHz data rate), the LED current can be changed quickly and easily. Also the non-pulsating LED current reduces system noise and improves LED reliability. The S2Cwire interface relies on the number of rising edges to the EN/SET pin to set the register. A typical write protocol is a burst of EN/SET rising edges, followed The AAT3192-1/2/3’s serial interface reduces the LED current on each rising pulse of the enable input. If the AAT3192 is in shutdown, the first rising edge of the EN/ SET input turns on the LED driver to the maximum current. Successive rising edges decrease the LED current as shown in Table 1 and Figure 2 for the AAT3192-1. For the AAT3192-2, Table 2 and Figure 3 illustrate an 8-step LED current control profile. For the AAT3192-3, Table 3 and Figure 4 illustrate a 4-step LED current control profile. THI TLO TOFF TLAT EN/SET 1 2 n-1 Data Reg n ≤ 16 0 n-1 0 Figure 1: S2C Serial Interface Timing. EN Rising Edges D1-D2 Current (mA) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 20 18.7 17.3 16 14.7 13.3 12 10.7 9.3 8 6.7 5.3 4 2.7 1.3 0.63 20.00 Dx Output Current (mA) Data 15.00 10.00 5.00 0.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 S2Cwire Interface Data Code Figure 2: AAT3192-1 Current Control Profile. Table 1: AAT3192-1 LED Current Settings. 10 www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Data EN Rising Edges D1-D2 Current (mA) 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 20 17.3 14.7 12 9.3 6.7 4 1.3 PWM (Pulse Width Modulation) is an industry standard technique of controlling LED brightness by modulating the conduction duty cycle of the LED current. LED brightness is determined by the average value of the PWM signal multiplied by the LED’s intensity where intensity is proportional to the LED drive current. A PWM control signal can be applied into the EN/PWM pin of the AAT3192-4. By changing the duty cycle of the PWM signal from 100% (logic high) to 10%, LEDs sink current can be programmed from 20mA to 2.4mA. To save power when not used, AAT3192-4 can be shutdown by holding the EN/PWM pin low for 1ms. Table 2: AAT3192-2 LED Current Settings. Dx Output Current (mA) 20.00 Lastly, Table 4 and Figure 5 illustrate the AAT3192-4’s LED current control profile as a function of a PWM control signal. 15.00 10.00 5.00 0.00 PWM Control (AAT3192-4 only) 1 2 3 4 5 6 7 EN/PWM Duty Cycle D1-D2 Current (mA) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 20 17.9 15.9 14 12.1 10.1 8.2 6.3 4.3 2.4 8 S2Cwire Interface Data Code Figure 3: AAT3192-2 Current Control Profile. Data EN Rising Edges D1-D2 Current (mA) 1 2 3 4 1 2 3 4 20 13.3 6.7 0.87 Table 4: AAT3192-4 LED Current Settings (RSET = 14.3kΩ, fPWM = 50kHz). 20.00 Dx Output Current (mA) Table 3: AAT3192-3 LED Current Settings. Dx Output Current (mA) 20.00 15.00 10.00 10.00 5.00 0.00 5.00 0.00 15.00 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% EN/PWM Input Pin Duty Cycle (%) 1 2 3 4 Figure 5: AAT3192-4 Current Control Profile (RSET = 14.3kΩ, fPWM = 50kHz). 2 S Cwire Interface Data Code Figure 4: AAT3192-3 Current Control Profile. 3192.2008.07.1.3 www.analogictech.com 11 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Applications Information Device Switching Noise Performance LED Selection The AAT3192 is specifically intended for driving white LEDs. However, the device design will allow the AAT3192 to drive most types of LEDs with forward voltage specifications ranging from 2.2V to 4.7V. LED applications may include mixed arrangements for display backlighting, keypad display, and any other application needing a constant current sink generated from a varying input voltage. Since the D1 to D2 constant current sinks are matched with negligible supply 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 AAT3192 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. Constant Current Setting The LED current is controlled by the RSET resistor. For maximum accuracy, a 1% tolerance resistor is recommended. Table 5 shows RSET resistor values for AAT3192-1/2/4 and Table 6 shows RSET resistor values for AAT3192-3 for various LED full-scale current levels. ILED (mA) RSET (KΩ) 30 25 20 18 15 10 9.53 11.5 14.3 15.8 19.1 28.7 Table 5: Maximum LED Current and RSET Resistor Values (1% Resistor Tolerance) for the AAT3192-1/2/4. ILED (mA) RSET (KΩ) 30 20 15 10 7.68 11.5 15.4 23.2 Table 6: Maximum LED Current and RSET Resistor Values (1% Resistor Tolerance) for the AAT3192-3. 12 The AAT3192 operates at a fixed frequency of approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of mobile 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 AAT3192 soft-start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit. Shutdown Since the current switches are the only power returns for all loads, there is no leakage current when all sink switches are disabled. To activate the shutdown operation, the EN/SET input for the AAT3192-1/2/3 should be strobed low for longer than tOFF (500μs). For the 3192-4 PWM options, shutdown operation is enabled when the EN/PWM input is strobed low longer than 1ms. In this state, the AAT3192 typically draws less than 1μA from the input. Registers are reset to 0 in shutdown. 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 AAT3192, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT3192 outputs are pure constant current sinks and typically drive individual loads, it is difficult to measure the output voltage for a given output 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. www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM The AAT3192 efficiency may be quantified under very specific conditions and is dependent upon the input voltage versus the output voltage across the loads applied to outputs D1 through D2 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 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. In addition, with an ideal 2x charge pump, the output current may be expressed as 1/3 of the input current. The expression to define the ideal efficiency (η) can be rewritten as: η= -or- ⎛ VF ⎞ η (%) = 100 · 2V ⎝ IN⎠ 1x Mode Efficiency The AAT3192 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. An expression for the ideal efficiency (η) in 1x chargepump mode can be expressed as: POUT V ·I VF = F LED = PIN VIN · 2IOUT 2VIN For a charge pump with an output of 5V and a nominal input of 3.5V, the theoretical efficiency is 71%. Due to internal switching losses and IC quiescent current consumption, the actual efficiency can be measured at 51%. Efficiency will decrease substantially as load current drops below 1mA or when the voltage level at VIN approaches the voltage level at VOUT. Additional Applications P V ·I VF η = OUT = F LED ≅ PIN VIN · IOUT VIN The current sinks of the AAT3192 can be combined to drive higher current levels through a single LED. As an example, a single LED can be driven at 60mA total by combining together the D1-D2 outputs. -or- ⎛ VF ⎞ η (%) = 100 · V ⎝ IN⎠ C2 1μF 2x Charge Pump Mode Efficiency The AAT3192 contains a 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 (η) can be simply defined as a linear voltage regulator with an effective output voltage that is equal to one and two times the input voltage. Efficiency (η) for an ideal 2x charge pump can typically be expressed as the output power divided by the input power. η= 3192.2008.07.1.3 PF PIN 1 2 3 4 5 C1 1μF VIN C3 1μF D1 N/C D1 OUT D2 CGND C+ RSET IN EN/SET AAT3192 10 9 8 7 6 R1 9.53k EN/SET Figure 6: Higher Current, Single LED Application. For lower-cost applications, the flying capacitor can be removed. This will force the AAT3192 to operate in 1x mode. To maintain regulated LED current, the input supply voltage has to be higher than the charge-pump’s dropout voltage in 1x mode. www.analogictech.com 13 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM C2 1μF D1 lowest cost, has a smaller PCB footprint, and is non-polarized. Low ESR ceramic capacitors help maximizing charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. D2 U1 1 2 3 4 5 VIN C3 1μF N/C D1 D2 OUT GND CC+ RSET IN EN/SET AAT3192 10 9 8 7 6 Equivalent Series Resistance R1 9.53k EN/SET Figure 7: Lower Cost 1x Mode Application. Capacitor Selection Careful selection of the three external capacitors CIN, CP, 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 100mΩ. 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 AAT3192. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is 14 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 AAT3192 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. www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Evaluation Board Schematic 3 2 DC+ 1 DC- C2 1μF VIN J1 D1 D2 JPx GND JP5 C1 1μF 1 2 3 4 5 C3 1μF N/C D1 OUT D2 CGND C+ RSET IN EN/SET U1 10 9 8 7 6 R1 9.53k AA T3192 GND GND R7 220 J2 R6 100K VIN GND R3 R2 R1 1K 1K 1K CYCLE 0 2 4 SW3 1 3 5 UP 0 2 4 DOWN 0 2 4 SW2 1 3 5 U2 1 2 3 4 VDD GP5 GP4 GP3 VSS GP0 GP1 GP2 PIC12F675 VR4 POT10K 8 7 6 5 C5 1μF R5 330 LED7 RED R4 330 GND GND SW1 1 3 5 LED0 GRN GND GND 3192.2008.07.1.3 www.analogictech.com 15 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Evaluation Board Layout1 Figure 8: AAT3192 Evaluation Board Component Side Layout. Figure 9: AAT3192 Evaluation Board Solder Side Layout. 1. The AAT3193 Evaluation Board is also used for the AAT3192; for the AAT3192, LED diodes D2 = D1, D3 = D2, and D1 is not connected. 16 www.analogictech.com 3192.2008.07.1.3 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Ordering Information Package Interface Current Control, Inverting Marking Part Number (Tape and Reel) SC70JW-10 SC70JW-10 SC70JW-10 SC70JW-10 S2Cwire S2Cwire S2Cwire PWM 16-step 8-step 4-step Linear ZYXYY AAT3192IJQ-1-T1 AAT3192IJQ-2-T1 AAT3192IJQ-3-T1 AAT3192IJQ-4-T1 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/about/quality.aspx. Package Information SC70JW-10 2.20 ± 0.20 1.75 ± 0.10 0.40 BSC 0.225 ± 0.075 Top View 0.100 7° ± 3° 0.45 ± 0.10 4° ± 4° 0.05 ± 0.05 0.15 ± 0.05 1.10 MAX 0.85 ± 0.15 2.00 ± 0.20 2.10 ± 0.30 Side View End View All dimensions in millimeters. 1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3192.2008.07.1.3 www.analogictech.com 17 PRODUCT DATASHEET AAT3192 ChargePump 2-Channel Charge-Pump LED Driver TM Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611 © 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. 18 www.analogictech.com 3192.2008.07.1.3