19-0786; Rev 0; 4/07 White LED Charge Pump with 1.1W Audio Amplifier The MAX8678 integrates a charge pump for white lightemitting diodes (LEDs) with an audio loudspeaker amplifier. The high-efficiency, adaptive charge pump drives up to four LEDs with constant current for uniform brightness. The LED current is adjustable from 0.1mA/LED to 24mA/LED in 31 pseudo-logarithmic steps through a single-wire serial-pulse interface. High accuracy and LED-to-LED current matching are maintained throughout the adjustment range. Individual adaptive mode switching for each LED provides high efficiency with a wide range of LED forward voltages. The mono class AB audio amplifier directly drives an 8Ω loudspeaker with 1.1W RMS continuous power from a 5V supply with less than 1% THD+N. The gain is adjustable from -9dB to +18dB in ten 3dB steps through a singlewire serial-pulse interface. Clicks and pops are suppressed during on/off and all gain adjustments. Differential inputs improve common-mode noise rejection. The MAX8678 includes soft-start, thermal shutdown, open-circuit and short-circuit protection, and is available in the 16-pin, 3mm x 3mm Thin QFN package (0.8mm max height). Applications Features ♦ High-Efficiency White LED Charge Pump Individual Adaptive Supply for Each LED 4 Low-Dropout LED Current Regulators 24mA to 0.1mA Dimming Range Single-Wire, Serial-Pulse Dimming Interface 1% (typ) Accuracy Low 140µA Quiescent Current ♦ Mono Class AB Audio Amplifier 1.1W RMS Mono BTL Output (8Ω, VIN = 5V) Low 0.004% THD+N at 1kHz High 90dB PSRR at 1kHz Fully Differential Inputs -9dB to +18dB Gain Settings in 3dB Steps Integrated Click/Pop Suppression Low Quiescent Current ♦ Soft-Start Limits Inrush Current ♦ Thermal Shutdown, Open- and Short-Circuit Protection ♦ 16-Pin, 3mm x 3mm Thin QFN Package Ordering Information PART PIN-PACKAGE Cell Phones and Smartphones MAX8678ETE+ Camera Phones Typical Operating Circuit Pin Configuration LED2 4.7μF LED3 GND 0.1mA TO 24mA LED4 0.1μF ENLED MAX8678 BIAS LED2 LED1 BACKLIGHT OR FLASH LED3 LED1 LED4 C- IN 12 11 10 9 NEG 13 8 BIAS C- 14 7 OUT- 6 OUT+ 5 ENAMP MAX8678 C+ 15 ENAMP ENLED 16 OUTEP NEG 1 1μF 2 3 4 A- A- + LOUDSPEAKER 8Ω A+ OUT+ GND A+ IN DIFFERENTIAL AUDIO INPUT T1633-5 Note: The device is specified over the -40°C to +85°C extended temperature range. TOP VIEW AMP ON/OFF AND GAIN AFF 16 Thin QFN 3mm x 3mm 1μF C+ LED ON/OFF AND DIMMING PKG CODE +Denotes a lead-free package. PDAs, Digital Cameras, Camcorders INPUT 2.7V TO 5.5V TOP MARK THIN QFN 3mm × 3mm ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX8678 General Description MAX8678 White LED Charge Pump with 1.1W Audio Amplifier ABSOLUTE MAXIMUM RATINGS IN to GND ..............................................................-0.3V to +6.0V IN to NEG ..............................................................-0.3V to +6.0V ENLED, ENAMP, LED_, C+, A+, A-, OUT+, OUT-, BIAS to GND…….....................................-0.3V to (VIN + 0.3V) ENLED, ENAMP, LED_, C+, A+, A-, OUT+, OUT-, BIAS, C- to NEG ...................................…-0.3V to (VIN + 0.3V) GND to NEG ......................................................…-0.3V to +6.0V GND to C-..............................................................-0.3V to +6.0V OUT+, OUT- Short Circuit to GND or IN ....................Continuous Continuous Power Dissipation (TA = +70°C) 16-Pin Thin QFN 3mm x 3mm (derate 17.5mW/°C above +70°C) ............................1398mW Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS IN Operating Voltage Undervoltage-Lockout (UVLO) Threshold MIN No-Load Supply Current MAX UNITS 5.5 V 2.45 2.65 2.7 VIN rising 2.25 UVLO Hysteresis Shutdown Supply Current (All Outputs Off) TYP 100 ENLED = ENAMP = GND TA = +25°C 0.1 TA = +85°C 0.1 Charge pump inactive, LED_ = 1.6mA ENAMP = GND, TA = +25°C 140 Charge pump active, 1MHz switching, LEDs at 24mA setting, ENAMP = GND 0.45 ENAMP = IN, ENLED = GND V mV 1.5 200 µA µA mA 3 Thermal Shutdown Thermal-Shutdown Hysteresis +160 °C 20 °C SERIAL-PULSE INTERFACE (EN_) Logic Input-High Voltage VIN = 2.7V to 4.2V 1.4 VIN = 4.2V to 5.5V 1.5 V Logic Input-Low Voltage VIN = 2.7V to 5.5V 0.4 Logic Input Current VIL = 0V or VIH = 5.5V tSHDN See Figures 2 and 3 tHOLD See Figures 2 and 3 tLO See Figures 2 and 3 0.5 tHI See Figures 2 and 3 0.5 500 µs TA = +25°C 0.01 TA = +85°C 0.1 1 V µA 3.2 ms 3.2 ms 500 µs CHARGE PUMP Switching Frequency Soft-Start Time 1 MHz 0.1 ms Regulation Voltage (OVP) (VIN - VNEG) 5 V Open-Loop NEG Output Resistance ((VNEG -VIN)/INEG) 10 Guaranteed Output Current LED VF = 3.9V, VIN = 3.2V NEG Discharge Resistance in Shutdown All LEDs off, ENLED = GND 2 96 23 Ω mA 10 _______________________________________________________________________________________ kΩ White LED Charge Pump with 1.1W Audio Amplifier (VIN = 3.6V, VGND = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS 24.0 mA LED DRIVER Current-Setting Range Current Accuracy 0.1 24mA setting, TA = +25°C -2 24mA setting, TA = -40°C to +85°C -5 1.6mA setting, TA = +25°C LED_ Dropout 24mA setting (Note 2) LED_ Voltage-Mode Transition Threshold (1x to 2x) VLED_ falling +2 +5 72 120 Charge pump active 132 360 150 175 125 100 All LEDs off % ±5 Charge pump inactive LED_ Voltage-Mode Transition Hysteresis LED_ Leakage in Shutdown ±1 TA = +25°C 0.01 TA = +85°C 0.1 mV mV mV 1 µA AUDIO AMPLIFIER Common-Mode Bias Voltage Output Offset Voltage VA+ = VA- = VBIAS, gain ≤ 12dB Common-Mode Input Voltage Input Impedance (RIN) Common-Mode Rejection Ratio VIN / 2 -25 ±1 0.5 Table 2 10 67 VIN = 3.2V 50 60 f = 1kHz, VIN = 3.2V Power-Supply Rejection Ratio VA+ = VA- = VBIAS, 200mVP-P at IN Output Power THD+N = 1%, f = 1kHz (Note 3) +5% +25 mV (VIN 1.2) V 140 kΩ dB 70 f = 217Hz 93 f = 1kHz 90 RL = 8Ω, VIN = 3.2V 0.36 RL = 4Ω, VIN = 3.2V RL = 8Ω, VIN = 5V Output Current Limit Gain Accuracy -5% dB 0.5 W 0.65 0.8 1.1 0.6 1 1.6 -9dB ≤ Gain ≤ 15dB ±0.13 Gain = 18dB ±0.17 Total Harmonic Distortion + Noise RL = 8Ω, f = 1kHz, POUT = 0.25W, VIN = 3.2V Signal-to-Noise Ratio RL = 8Ω, f = 1kHz, POUT = 0.25W, VIN = 3.2V Maximum Capacitive Drive A dB 0.004 % 104 dB 500 pF Power-Up from Shutdown Time, tUP See Figure 3 10 ms Shutdown Time, tPD See Figure 3 3.5 µs Note 1: Limits are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design. Note 2: Dropout voltage is defined as the LED_ to GND (charge pump inactive) or LED_ to NEG (charge pump active) voltage at which current into LED_ drops 10% from the value at VLED_ = 0.5V. Note 3: Output power is specified by a combination of a functional output current test and characterization analysis. _______________________________________________________________________________________ 3 MAX8678 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 3.2V, RL = 8Ω, TA = +25°C, unless otherwise noted.) TOTAL HARMONIC DISTORTION + NOISE vs. OUTPUT POWER OUTPUT POWER vs. SUPPLY VOLTAGE 10 OUTPUT POWER (mW) fIN = 1kHz THD+N (%) OUTPUT POWER = 50mW 1 0.1 GAIN = 3dB 10 1000 10,000 0 100,000 0 0.2 0.4 0.6 0.8 1.0 2.5 3.5 4.5 5.5 FREQUENCY (Hz) OUTPUT POWER (W) SUPPLY VOLTAGE (V) POWER DISSIPATION vs. OUTPUT POWER OUTPUT POWER vs. LOAD RESISTANCE AMPLIFIER GAIN AND PHASE vs. FREQUENCY 1.0 OUTPUT POWER (W) 400 300 200 100 0.8 THD+N = 10% 0.6 0.4 0.2 MAX8678 toc06 25dB 20dB AMPLIFIER GAIN AND PHASE 1.2 MAX8678 toc04 500 POWER DISSIPATION POWER (mW) THD+N = 1% fIN = 100kHz GAIN = 3dB 0.001 100 THD+N = 10% 1000 0.01 OUTPUT POWER = 300mW 0.001 fIN = 10kHz MAX8678 toc05 THD+N (%) OUTPUT POWER = 150mW 0.01 2000 MAX8678 toc02 100 MAX8678 toc01 0.1 MAX8678 toc03 TOTAL HARMONIC DISTORTION + NOISE vs. FREQUENCY 15dB 10dB 5dB 0dB 0° -30° -60° -90° THD+N = 1% GAIN = 18dB 0 0 0 100 200 300 400 500 600 700 4 6 8 10 12 14 10 16 100 1k LOAD RESISTANCE (Ω) FREQUENCY (Hz) COMMON-MODE REJECTION RATIO vs. FREQUENCY POWER-SUPPLY REJECTION RATIO vs. FREQUENCY AMPLIFIER STARTUP AND SHUTDOWN MAX8678 toc07 -45dB -55dB -55dB REJECTION RATIO -35dB -45dB -65dB -75dB -85dB -95dB GAIN = 18dB VRIPPLE 18mVP-P 1V/div VOUT+ 1V/div -65dB VOUT- -75dB VOUT+ - VOUT- -85dB 100mV/div -95dB -105dB 100 1k FREQUENCY (Hz) 2V/div VENAMP -125dB 10k 100k MAX8678 toc09 MAX8678 toc08 -25dB -35dB GAIN = 18dB VRIPPLE 100mVP-P 4 10k OUTPUT POWER (mW) -25dB REJECTION RATIO MAX8678 White LED Charge Pump with 1.1W Audio Amplifier 100 1k FREQUENCY (Hz) 10k _______________________________________________________________________________________ 4ms/div White LED Charge Pump with 1.1W Audio Amplifier LED EFFICIENCY vs. SUPPLY VOLTAGE (MISMATCHED LEDs) 4 x 1.6mA 70 60 50 40 4 x 20.8mA 4 x 6.4mA 160 4 x 16mA 140 120 4 x 1.6mA 100 80 4 x 6.4mA 60 20 40 10 20 0 0 2.7 3.0 3.3 3.6 3.9 4.2 4.2 3.9 3.6 3.3 3.0 2.7 SUPPLY VOLTAGE (V) LED EFFICIENCY vs. SUPPLY VOLTAGE (MATCHED LEDs) MAX8678 EFFICIENCY vs. SUPPLY VOLTAGE (MATCHED LEDs) 100 MAX8678 toc12 90 80 90 EFFICIENCY 70 20.4mA/LED 60 50 40 30 16.4mA/LED 6.4mA/LED 1.6mA/LED 1.6mA/LED 20.4mA/LED MAX8678 toc13 SUPPLY VOLTAGE (V) 100 EFFICIENCY (%) 4 x 20.8mA 180 SUPPLY CURRENT (mA) EFFICIENCY (%) 80 30 200 MAX8678 toc11 90 MAX8678 toc10 100 SUPPLY CURRENT vs. SUPPLY VOLTAGE (MISMATCHED LEDs) 80 6.4mA/LED 70 16.4mA/LED 60 20 50 10 40 0 2.7 3.0 3.3 3.6 3.9 4.20 4.2 3.90 SUPPLY VOLTAGE (V) 3.85 3.75 3.65 3.55 3.40 3.00 3.50 3.80 3.70 3.60 SUPPLY VOLTAGE, TIME WEIGHTED (V) LED CURRENT MATCHING vs. SUPPLY VOLTAGE MAX8678 toc15 MAX8678 toc14 17.0 16.8 16.6 LED CURRENT (mA) LED STARTUP/ SHUTDOWN WAVEFORMS VENLED 2V/div VLED1 1V/div 16.4 16.2 16.0 15.8 15.6 IIN 15.4 500mA/div 15.2 4 OF 16mA/LED 15.0 2.7 3.0 3.3 3.6 3.9 4.2 1ms/div SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 5 MAX8678 Typical Operating Characteristics (continued) (VIN = 3.2V, RL = 8Ω, TA = +25°C, unless otherwise noted.) MAX8678 White LED Charge Pump with 1.1W Audio Amplifier Typical Operating Characteristics (continued) (VIN = 3.2V, RL = 8Ω, TA = +25°C, unless otherwise noted.) LINE TRANSIENT WITH MODE TRANSITION LED SINGLE-WIRE PULSE DIMMING MAX8678 toc16 VENLED MAX8678 toc17 5V/div VIN 3.8V 3.8V 1V/div 3.4V ILED 20mA/div ILED (TOTAL) 100mA/div IIN 200mA/div 4 LEDs AT 24mA EACH 200ms/div 200μs/div Pin Description PIN NAME 1 IN 2 GND 3 A+ Noninverting Differential Audio Input 4 A- Inverting Differential Audio Input 5 ENAMP 6 OUT+ Audio Amplifier Positive Output 7 OUT- Audio Amplifier Negative Output 8 BIAS DC Bias Bypass. Connect a 0.1µF ceramic capacitor from BIAS to GND as close as possible to the IC. 9–12 6 FUNCTION Analog Supply-Voltage Input. The input voltage range is 2.7V to 5.5V. Connect a 4.7µF ceramic capacitor from IN to GND as close as possible to the IC. IN is high impedance during shutdown. Ground. Connect GND to the system ground plane. Do not connect GND to the exposed paddle. Amplifier Enable and Gain Control. ENAMP is a serial-pulse interface logic input to control on/off and gain settings of the audio amplifier. LED Current Regulators. Current flowing into LED_ is regulated to the current programmed by the LED1–LED4 serial-pulse interface. Connect LED_ to the cathodes of the corresponding external LEDs. LED_ is high impedance during shutdown. If unused, connect LED_ to IN to disable the regulator. Charge-Pump Negative Output. Connect a 1µF ceramic capacitor from NEG to GND. In shutdown, an internal 10kΩ resistor pulls NEG to GND. 13 NEG 14 C- Transfer Capacitor Negative Connection. Connect a 1µF ceramic capacitor from C+ to C-. 15 C+ Transfer Capacitor Positive Connection. Connect a 1µF ceramic capacitor from C+ to C-. 16 ENLED — EP LED Enable and Dimming Control. ENLED is a serial-pulse interface logic input to control on/off and dimming of the LED regulators. Exposed Paddle. Connect the exposed paddle to NEG directly under the IC. _______________________________________________________________________________________ White LED Charge Pump with 1.1W Audio Amplifier MAX8678 C3 1μF C+ 2.7V TO 5.5V INPUT SUPPLY C- IN C1 4.7μF GND INVERTING CHARGE PUMP C2 1μF MAX8678 NEG LED1 LED2 LED ON/OFF AND DIMMING ENLED CONTROL CIRCUITRY LED CURRENT REGULATORS LED3 LED4 AMP ON/OFF AND GAIN ENAMP CONTROL CIRCUITRY A+ DIFFERENTIAL AUDIO INPUT A- HALF SUPPLY BIAS MONO CLASS AB AUDIO AMP BIAS C4 0.1μF OUT+ OUT- EARPIECE/ LOUDSPEAKER OPTIONAL FILTER CAPACITORS Figure 1. Functional Diagram Detailed Description The MAX8678 integrates a charge pump for white LEDs with an audio loudspeaker amplifier. The high-efficiency, adaptive charge pump drives up to four LEDs with constant current for uniform brightness for display backlighting or camera flash. The LED current is adjustable from 0.1mA/LED to 24mA/LED in 31 pseudo-logarithmic steps through a single-wire serial-pulse interface. High accuracy and LED-to-LED current matching are maintained throughout the adjustment range. Figure 1 is the MAX8678 functional diagram. The mono class AB audio amplifier directly drives an 8Ω loudspeaker with 1.1W RMS continuous power from a 5V supply with less than 1% THD+N. The gain is adjustable from -9dB to +18dB in ten 3dB steps through a singlewire serial-pulse interface. Clicks and pops are suppressed during on/off and all gain adjustments. Differential inputs improve common-mode noise rejection. Shutdown To reduce power consumption when not in use, the charge-pump LED driver and the audio amplifier have separate shutdown controls. To disable the LED driver, drive ENLED low for at least 3.2ms. To disable the audio amplifier, drive ENAMP low for at least 3.2ms. When both ENLED and ENAMP are held low, the IC supply current is reduced to about 0.1µA. Thermal-Overload Protection The thermal-overload protection circuitry monitors the temperature of the IC. When the die temperature reaches +160°C, the IC is shut down. The IC turns on after it has cooled by approximately 20°C. During continuous overload conditions, this results in a pulsed output. _______________________________________________________________________________________ 7 MAX8678 White LED Charge Pump with 1.1W Audio Amplifier LED Charge Pump Table 1. Internal PWM Duty Cycle vs. LED Set Current The charge pump drives up to four white LEDs with regulated constant current for displaying backlight applications. By utilizing an adaptive charge pump and extremely low-dropout current regulators, it achieves high efficiency over the full 1-cell lithium ion (Li+) battery input-voltage range. Fixed frequency of 1MHz switching allows for tiny external components. The regulation scheme is optimized to ensure low EMI and low input ripple. Adaptive Charge-Pump Modes When the supply voltage is sufficient to drive the LEDs, the charge pump is turned off to minimize the input supply current and the LED currents are linearly regulated. When the supply voltage is insufficient to drive the LEDs at the set current, the charge pump is enabled, creating a negative voltage at NEG and allowing the LED_ outputs to pull below ground to maintain the set LED current. Soft-Start and Shutdown The MAX8678 LED driver features a low-power shutdown mode for reduced current consumption. Hold ENLED low for 3.2ms to enter shutdown mode. This disables the charge pump and the LED current drivers. When initially powering the MAX8678, or when starting up from shutdown mode, a soft-start feature prevents input current overshoot. See the startup waveforms in the Typical Operating Characteristics section. 2 3 4 1 DUTY CYCLE (n/16) ILED (mA) DUTY CYCLE (n/16) 6.4 16 1.2 12 5.6 14 1.0 10 4.8 12 0.8 8 4.0 10 0.7 7 3.2 16 0.6 6 2.8 14 0.5 5 2.4 12 0.4 4 2.0 10 0.3 3 1.6 16 0.2 2 1.4 14 0.1 1 Serial-Pulse Dimming Control (ENLED) The MAX8678 includes a serial-pulse logic interface for on/off and dimming of the backlight. The dimming range is pseudo-logarithmic from 24mA to 0.1mA in 31 steps. Driving ENLED high turns on the IC and sets the internal register to 24.0mA. To dim the MAX8678, pulse ENLED low (500ns to 500µs pulse width). Each rising edge sets the LED current setting as shown in Table 2. Once the desired setting is reached, hold ENLED high for at least 3.2ms to set the internal register and the LED current changes. To set a new current level, repeat the previous sequence from the beginning. To turn off the LEDs, hold ENLED low for at least 3.2ms. Figure 2 shows a timing diagram for ENLED. If dimming control is not required, ENLED works as a simple on/off logic control. Drive ENLED high for at least 3.2ms to enable the LEDs, or drive ENLED low for at least 3.2ms for shutdown. The LED driver operates at 100% brightness under or OFF under these conditions. Low LED Current Levels The MAX8678 internally generates a PWM signal to obtain higher resolution at lower currents. As the ILED setting is below 6.4mA, the IC adjusts ILED DC current, and the duty cycle is controlled by the PWM signal. The frequency of the PWM dimming signal is set at 1kHz with a minimum duty cycle of 1/16 to avoid the LED flicking effect to human eyes. Table 1 shows the current level and the corresponding duty cycle. 1 ILED (mA) 2 3 13 14 tHI = 500ns TO 500μs tLO = 500ns TO 500μs ENLED tHI INTERNAL CURRENT SETTING OFF tLO 24.0mA 22.4mA 20.8mA tHOLD 3.2ms tHOLD 3.2ms 24.0mA 19.2mA 22.4mA 20.8mA 5.6mA tSHDN 3.2ms OFF 4.8mA 19.2mA ILED_ OFF 4.8mA Figure 2. Serial-Pulse Dimming 8 _______________________________________________________________________________________ OFF White LED Charge Pump with 1.1W Audio Amplifier ENLED RISING EDGES LED CURRENT (mA) ENLED RISING EDGES LED CURRENT (mA) 1 24.0 17 2.8 2 22.4 18 2.4 3 20.8 19 2.0 4 19.2 20 1.6 5 17.6 21 1.4 6 16.0 22 1.2 7 14.4 23 1.0 8 12.8 24 0.8 9 11.2 25 0.7 10 9.6 26 0.6 11 8.0 27 0.5 12 6.4 28 0.4 13 5.6 29 0.3 14 4.8 30 0.2 15 4.0 31 0.1 16 3.2 — — The MAX8678 contains a 1.1W RMS DirectDrive mono speaker amplifier. It features a low-power shutdown mode and click-and-pop suppression. Bias An internally generated common-mode BIAS voltage of VIN / 2 sets the DC bias level for the audio outputs. The BIAS capacitor (C4 in Figure 1) improves PSRR and THD+N by reducing power supply and other noise sources at the common-mode bias node, and also generates the clickless/popless startup DC bias waveform for the speaker amplifier. A 0.1µF BIAS capacitor is recommended for most applications. Increasing C4 to 1µF slows turn-on and turn-off times by a factor of 10 and improves PSRR by 20dB (at 1kHz). Do not connect external loads to BIAS. Shutdown Mode The MAX8678 audio amplifier features a low-power shutdown mode for reduced current consumption. Hold ENAMP low for 3.2ms to shut down the audio amplifier. Entering shutdown disables the amplifier’s bias circuitry, causes the audio outputs to go high impedance, and drives BIAS to GND. Click-and-Pop Suppression The MAX8678 features Maxim’s industry-leading clickand-pop suppression circuitry. During startup, the amplifier common-mode bias voltage ramps to the DC bias point. When entering shutdown, the amplifier outputs are high impedance to 100kΩ between the outputs. This scheme minimizes the energy present in the audio band. Open-Circuit and Short-Circuit Protection The short-circuit protection detects when an LED is shorted and disables the corresponding current regulator to avoid wasting battery power. If any LED fails as an open circuit, the charge pump is forced on and the corresponding LED_ pin is internally connected to NEG. 1 3 2 4 1 2 3 7 8 tHI = 500ns TO 500μs tLO = 500ns TO 500μs ENAMP tHI INTERNAL GAIN SETTING GAIN tLO tHOLD tHOLD tSHDN 3.2ms 3.2ms 3.2ms OFF OFF -9dB -6dB -3dB 0dB -9dB tUP 10ms typ -6dB -3dB +9dB +12dB tUP 10ms (typ) +12dB tPD 1μs (typ) 0dB OFF OFF Figure 3. Serial-Pulse Gain Adjustment _______________________________________________________________________________________ 9 MAX8678 Audio Amplifier Table 2. LED Current Levels MAX8678 White LED Charge Pump with 1.1W Audio Amplifier Serial-Pulse Gain Adjustment (ENAMP) The audio amplifier has an internal gain adjustment, controlled by a serial-pulse interface. The gain setting of the input amplifier is adjustable from -9dB to +18dB in 3dB steps. This allows the amplifier to be used for both hands-free and for receiver mode, without any external components. Driving ENAMP high turns on the amplifier and sets the internal register to -9dB. Adjust the gain by pulsing ENAMP low (500ns to 500µs pulse width). Each rising edge sets the gain as shown in Table 3. Once the desired setting is reached, hold ENAMP high for at least 3.2ms to set the internal register and change the gain. To set a new current level, repeat the previous sequence from the beginning. To shut down the amplifier, hold ENAMP low for at least 3.2ms. Figure 3 is a timing diagram for ENAMP. Table 3. Audio Amplifier-Input Impedance Applications Information Since the differential outputs are biased at midsupply, there is no net DC voltage across the load. This eliminates the need for DC-blocking capacitors required for single-ended amplifiers. These capacitors can be large, expensive, consume board space, and degrade low-frequency performance. BTL Amplifier The MAX8678 is designed to drive a load differentially, a configuration referred to as bridge-tied load (BTL). The BTL configuration offers advantages over the single-ended configuration, where one side of the load is connected to ground. Driving the load differentially doubles the output voltage, thus quadrupling output power compared to a single-ended amplifier under similar configurations. RIN A+ DIFFERENTIAL AUDIO INPUT ENAMP RISING EDGES GAIN SETTING (dB) MIN TYP MAX 1 -9 69.1 99.0 140.0 2 -6 62.4 89.2 116.0 3 -3 54.9 78.4 102.0 4 0 46.8 66.9 87.0 5 3 38.8 55.5 72.1 6 6 31.3 44.7 58.1 7 9 24.6 35.1 45.6 8 12 18.8 26.9 35.0 9 15 14.1 20.2 26.2 10 18 10.5 15.0 19.5 RIN (kΩ) MAX8678 OUT+ MONO CLASS AB AUDIO AMP A- OUT- EARPIECE / LOUDSPEAKER RIN OPTIONAL FILTER CAPACITORS Figure 4. Differential Audio Input with Optional Filter Capacitors SINGLE-ENDED AUDIO INPUT RIN A+ MAX8678 OUT+ MONO CLASS AB AUDIO AMP A- OUT- EARPIECE / LOUDSPEAKER RIN NOTE: FILTER CAPACITORS REQUIRED FOR SINGLE-ENDED AUDIO OUTPUT. Figure 5. Single-Ended Audio Input 10 ______________________________________________________________________________________ White LED Charge Pump with 1.1W Audio Amplifier f −3dB = 1 2π × RIN × CIN where RIN is the input impedance given in Table 2. Figure 5 shows a single-ended audio input. Setting f -3dB too high affects the low-frequency response of the amplifier. Use capacitors with dielectrics that have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with high voltage coefficients, such as ceramics, can increase distortion at low frequencies. PCB Layout Good PC board (PCB) layout is essential for optimizing performance. Use large traces for the power-supply inputs and amplifier outputs to minimize losses due to parasitic trace resistance and to route heat away from the device. Good grounding improves audio performance and prevents any digital switching noise from coupling into the audio signal. The exposed paddle lowers the thermal resistance of the package by providing a direct-heat conduction path from the die to the PCB. Connect the exposed paddle to NEG directly under the IC. Refer to the MAX8678 Evaluation Kit for a good PCB layout example. Chip Information PROCESS: BiCMOS ______________________________________________________________________________________ 11 MAX8678 Input Filter The fully differential amplifier inputs can be biased at voltages other than midsupply. The common-mode feedback circuit adjusts for input bias, ensuring the outputs are still biased at midsupply. Input capacitors are not required as long as the common-mode input voltage is within the specified range listed in the Electrical Characteristics. If input capacitors are used (see Figure 4), the input capacitor in conjunction with the amplifier input impedance (RIN) form a highpass filter that removes the DC bias from an incoming signal. The AC-coupling capacitor allows the amplifier to bias the signal to an optimum DC level. Assuming zero-source impedance, the -3dB point of the highpass filter is given by: Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) (NE - 1) X e E MARKING 12x16L QFN THIN.EPS MAX8678 White LED Charge Pump with 1.1W Audio Amplifier E/2 D2/2 (ND - 1) X e D/2 AAAA e CL D D2 k CL b 0.10 M C A B E2/2 L E2 0.10 C C L 0.08 C C L A A2 A1 L L e e PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm 21-0136 12 ______________________________________________________________________________________ I 1 2 White LED Charge Pump with 1.1W Audio Amplifier PKG 8L 3x3 12L 3x3 REF. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. A 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 b 0.25 0.30 0.35 0.20 0.25 0.30 0.20 0.25 0.30 D 2.90 3.00 3.10 2.90 3.00 3.10 2.90 3.00 3.10 E 2.90 3.00 3.10 2.90 3.00 3.10 2.90 3.00 3.10 e L 0.65 BSC. 0.35 0.55 16L 3x3 0.50 BSC. 0.50 BSC. 0.75 0.45 0.55 0.65 0.30 0.40 N 8 12 16 ND 2 3 4 NE 2 3 4 0 A1 A2 k 0.02 0.05 0 0.20 REF 0.25 - 0.02 0.05 0 0.20 REF - 0.25 - EXPOSED PAD VARIATIONS 0.02 0.50 0.05 0.20 REF - 0.25 - PKG. CODES E2 D2 MIN. NOM. MAX. MIN. NOM. MAX. PIN ID JEDEC TQ833-1 0.25 0.70 1.25 0.25 0.70 1.25 0.35 x 45° T1233-1 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEEC WEED-1 T1233-3 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-1 T1233-4 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-1 T1633-2 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-2 T1633F-3 0.65 0.80 0.95 0.65 0.80 0.95 0.225 x 45° WEED-2 T1633FH-3 0.65 0.80 0.95 0.65 0.80 0.95 0.225 x 45° WEED-2 T1633-4 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-2 T1633-5 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45° WEED-2 - NOTES: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. N IS THE TOTAL NUMBER OF TERMINALS. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm FROM TERMINAL TIP. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. DRAWING CONFORMS TO JEDEC MO220 REVISION C. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. WARPAGE NOT TO EXCEED 0.10mm. PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm 21-0136 I 2 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13 © 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. MAX8678 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)