3718 LOW-VOLTAGE AUDIO POWER AMPLIFIER Data Sheet 27117.25 3718 LOW-VOLTAGE AUDIO POWER AMPLIFIER Providing a low-cost, compact alternative to discrete transistor amplifiers, the ULN3718M integrated circuit is ideal for application as a headphone driver in portable radios, tape players, and other battery-operated equipment. The low-power audio amplifier’s wide frequency response and low noise ensure premium performance. T C U Y D L O N R O P E D C E N U E N ER I T N EF O R C R S I O D F — The amplifier will operate (at reduced volume) with supply voltages as low as 1.8 V without a significant increase in distortion. This feature allows operation with a 3 V battery supply and minimizes concern about weak batteries. The class-AB audio amplifier has low quiescent current drain for maximum battery life. This device is rated for operation with supply voltages up to 9 V. The ULN3718M audio amplifier is supplied in an 8-pin mini-DIP plastic package. A copper alloy lead frame gives the amplifier enhanced power dissipation ratings. FEATURES ■ ■ ■ ■ ■ ■ ■ Wide Operating Voltage Range 1.8 - 9.0 V Low Quiescent Current AC Short-Circuit Protection Low External Parts Count Low Distortion 40 dB Voltage Gain Low Noise ABSOLUTE MAXIMUM RATINGS Supply Voltage, VCC . . . . . . . . . . . . . . 10 V Package Power Dissipation, PD . . . . . . . . . . . . . . . . . . . . See Graph Operating Temperature Range, TA . . . . . . . . . . . . . . . . -20°C to +85°C Storage Temperature Range, TS . . . . . . . . . . . . . . . -65°C to +150°C Always order by complete part number: ULN3718M . 3718 LOW-VOLTAGE AUDIO POWER AMPLIFIER ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = 3 V, RL = 32Ω, fin = 400 Hz (unless otherwise noted). Characteristic Symbol Supply Voltage Range VCC Quiescent Supply Current ICC Voltage Gain Test Conditions Min. POUT Distortion THD Units 1.8 3.0 9.0 V VCC = 3.0 V — 6.0 10 mA VCC = 6.0 V — 9.0 15 mA VCC = 9.0 V — 12 20 mA 36 40 44 dB RL = 8Ω, VCC = 3.0 V, THD = 10% — 80 — mW RL = 8Ω, VCC = 6.0 V, THD = 10% 250 430 — mW RL = 32Ω, VCC = 3.0 V, THD = 10% 15 25 — mW RL = 32Ω, VCC = 6.0 V, THD = 10% — 125 — mW POUT = 10 mW — 0.3 1.0 % POUT = 1.0 mW, VCC = 1.8 V — 1.5 3.0 % AV Audio Power Output Limits Typ. Max. Output Noise Vout Input Shorted, BW = 80 kHz — 200 500 µV Input Resistance RIN Pin 8 — 250 — kΩ CD (Pin 1) = 500 µF, f = 120 Hz — 28 — dB ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS Power Supply Rejection PSRR TEST CIRCUIT AND TYPICAL APPLICATION 2.0 RθJC = 55°C/W 1.5 1.0 0.5 0 25 FREE AIR, R θJA = 80°C/W 50 75 100 TEMPERATURE IN °C 125 150 Dwg. GP-009-1B 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 W Copyright © 1985, 1995, Allegro MicroSystems, Inc. 3718 LOW-VOLTAGE AUDIO POWER AMPLIFIER TYPICAL CHARACTERISTICS QUIESCENT SUPPLY CURRENT AS A FUNCTION OF SUPPLY VOLTAGE OUTPUT POWER AS A FUNCTION OF SUPPLY VOLTAGE 1000 5 8Ω L = L = 16 Ω 600 R 10 THD = 10% f in = 400 Hz 800 R OUTPUT POWER, POUT IN mW 15 400 2Ω =3 RL 200 0 0 0 2 4 6 8 SUPPLY VOLTAGE, VCC IN VOLTS 0 10 2 4 6 8 SUPPLY VOLTAGE, VCC IN VOLTS Dwg. GS-011 10 Dwg. GS-010 POWER SUPPLY REJECTION RATIO AS A FUNCTION OF FREQUENCY 0 POWER SUPPLY REJECTION RATIO IN dB QUIESCENT SUPPLY CURRENT, I CC IN mA 20 10 C D = 20 10 0 µF C D = 50 0 µF 30 40 10 30 100 300 FREQUENCY IN HERTZ 1k Dwg. GS-012 3718 LOW-VOLTAGE AUDIO POWER AMPLIFIER APPLICATIONS INFORMATION Selection of power-supply voltage and speaker impedance allows a designer to choose audio power levels within the allowable package power dissipation rating for any maximum operating temperature. No unique precautions are necessary when designing with this device. It is stable and ac short-circuit immune. External component selection for this low-power amplifier involves only two capacitors — one for output coupling and one for feedback and ripple decoupling. The coupling capacitor value should be selected to provide the desired low-frequency cutoff with the chosen load impedance. The decoupling capacitor should be chosen for both low-frequency audio rolloff and supply-ripple rejection. Ripple rejection is not practical to calculate due to the large number of mechanisms involved. A 500 µF capacitor achieves typically 25 dB rejection at 120 Hz. The high gain and the high input impedance of the power amplifier recommend use of this device in many diverse applications. However, the input stage does have other characteristics that should be taken into account for best results. The input is referenced to ground for internal biasing and must be provided with a dc path to ground. A current of typically 1 µA flows from the input through the volume control. This produces an IR drop that is multiplied by the closed loop dc gain of the amplifier and appears as an error in output centering. This recommends a value of 200 kΩ or less for the volume control; values of less than 100 kΩ are preferred. The selection of amplifier load impedance involves more than just consideration of the desired power output. A low load impedance will produce the highest power output for any given supply voltage. Higher impedances will furnish significant reduction in harmonic distortion and improvement in overall repeatability in power output capacity. Special steps toward minimizing tendencies towards instabilities of all types were taken in the design of this device. However, as with all high-gain circuits, care should be given to printed wiring board layout to avoid undesirable effects. Inputs and outputs should be well separated and should avoid common-mode impedances wherever possible. For best performance, connect low-level input-signal ground terminals and the decoupling capacitor ground terminal together at pin 3 (signal ground); connect the high-level speaker ground terminal and the power supply ground terminal together at pin 2 (power ground). The signal ground and the power ground should be interconnected at only one point. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 3718 LOW-VOLTAGE AUDIO POWER AMPLIFIER Dimensions in Inches 0.014 0.008 8 5 0.430 MAX 0.280 0.240 0.300 BSC 1 0.070 0.045 4 0.005 MIN 0.400 0.355 0.210 MAX 0.015 0.150 0.115 MIN 0.022 0.014 0.100 Dwg. MA-001-8A in BSC Dimensions in Millimeters (Based on 1” = 25.4 mm) 0.355 0.204 5 8 10.92 MAX 7.11 6.10 7.62 BSC 4 1 1.77 1.15 0.13 MIN 10.16 9.02 5.33 MAX 0.39 3.81 2.93 MIN 0.558 0.356 2.54 BSC NOTES: 1. Lead thickness is measured at seating plane or below. 2. Lead spacing tolerance is non-cumulative. 3. Exact body and lead configuration at vendor’s option within limits shown. Dwg. MA-001-8A mm 3718 LOW-VOLTAGE AUDIO POWER AMPLIFIER Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the design of its products. Components made under military approvals will be in accordance with the approval requirements. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000