Datasheet LM4780, LM4780TABD (Texas Instruments) - 9

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LM4780 , LM4780TABD www.ti.com
SNAS193B – JULY 2003 – REVISED APRIL 2013
External Components Description
(Figure 1 to Figure 6)
Components Functional Description
Prevents current from entering the amplifier's non-inverting input. This current may pass through to the load during 1 RB system power down, because of the amplifier's low input impedance when the undervoltage circuitry is off. This phenomenon occurs when the V+ and V-supply voltages are below 1.5V. 2 Ri Inverting input resistance. Along with Rf, sets AC gain. 3 Rf Feedback resistance. Along with Ri, sets AC gain. Feedback resistance. Works with Cf and Rf creating a lowpass filter that lowers AC gain at high frequencies. The - 4 R (1) f2 3dB point of the pole occurs when: (Rf - Ri)/2 = Rf // [1/(2πfcCf) + Rf2] for the Non-Inverting configuration shown in Figure 6. 5 C (1) f Compensation capacitor. Works with Rf and Rf2 to reduce AC gain at higher frequencies. (1) Compensation capacitor. Reduces the gain at higher frequencies to avoid quasi-saturation oscillations of the output 6 CC transistor. Also suppresses external electromagnetic switching noise created from fluorescent lamps. 7 C (1) i Feedback capacitor which ensures unity gain at DC. Along with Ri also creates a highpass filter at fc = 1/(2πRiCi). Provides power supply filtering and bypassing. Refer to the SUPPLY BYPASSING application section for proper 8 CS placement and selection of bypass capacitors. 9 R (1) V Acts as a volume control by setting the input voltage level. Sets the amplifier's input terminals DC bias point when CIN is present in the circuit. Also works with CIN to create a 10 R (1) IN highpass filter at fC = 1/(2πRINCIN). If the value of RIN is too large, oscillations may be observed on the outputs when the inputs are floating. Recommended values are 10kΩ to 47kΩ. Refer to Figure 6. 11 C (1) IN Input capacitor. Prevents the input signal's DC offsets from being passed onto the amplifier's inputs. 12 R (1) SN Works with CSN to stabilize the output stage by creating a pole that reduces high frequency instabilities. (1) Works with RSN to stabilize the output stage by creating a pole that reduces high frequency instabilities. The pole is 13 CSN set at fC = 1/(2πRSNCSN). Refer to Figure 6. 14 L(1) Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the Q of the series resonant circuit. Also provides a low impedance at low frequencies to short out R and pass audio signals 15 R(1) to the load. Refer to Figure 6. 16 RA Provides DC voltage biasing for the transistor Q1 in single supply operation. 17 CA Provides bias filtering for single supply operation. (1) Limits the voltage difference between the amplifier's inputs for single supply operation. Refer to the CLICKS AND 18 RINP POPS application section for a more detailed explanation of the function of RINP. Provides input bias current for single supply operation. Refer to the CLICKS AND POPS application section for a 19 RBI more detailed explanation of the function of RBI. Establishes a fixed DC current for the transistor Q1 in single supply operation. This resistor stabilizes the half- 20 RE supply point along with CA. Mute resistance set up to allow 0.5mA to be drawn from each MUTE pin to turn the muting function off. 21 RM → RM is calculated using: RM ≤ (|VEE| − 2.6V)/l where l ≥ 0.5mA. Refer to the Figure 21 curves in the Typical Performance Characteristics section. 22 CM Mute capacitance set up to create a large time constant for turn-on and turn-off muting. 23 S1 Mute switch. When open or switched to GND, the amplifier will be in mute mode. 24 ROUT Reduces current flow between outputs that are caused by Gain or DC offset differences between the amplifiers. (1) Optional components dependent upon specific design requirements.
Optional External Component Interaction
The optional external components have specific desired functions. Their values are chosen to reduce the bandwidth and eliminate unwanted high frequency oscillation. They may, however, cause certain undesirable effects when they interact. Interaction may occur when the components produce reactions that are nearly equal to one another. One example is the coupling capacitor, CC, and the compensation capacitor, Cf. These two components are low impedances at certain frequencies. They may couple signals from the input to the output. Please take careful note of basic amplifier component functionality when selecting the value of these components and their placement on a printed circuit board (PCB). The optional external components shown in Figure 5 and Figure 6, and described above, are applicable in both single and split supply voltage configurations. Copyright © 2003–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM4780 LM4780TABD Document Outline Features Applications Key Specifications Description Typical Application Connection Diagram Absolute Maximum Ratings Operating Ratings Electrical Characteristics Bridged Amplifier Application Circuit Parallel Amplifier Application Circuit Single Supply Application Circuit Auxiliary Amplifier Application Circuit External Components Description Optional External Component Interaction Typical Performance Characteristics Application Information MUTE MODE UNDER-VOLTAGE PROTECTION OVER-VOLTAGE PROTECTION SPiKe PROTECTION THERMAL PROTECTION DETERMlNlNG MAXIMUM POWER DISSIPATION DETERMINING THE CORRECT HEAT SINK SUPPLY BYPASSING BRIDGED AMPLIFIER APPLICATION PARALLEL AMPLIFIER APPLICATION SINGLE-SUPPLY AMPLIFIER APPLICATION CLICKS AND POPS PROPER SELECTION OF EXTERNAL COMPONENTS HIGH PERFORMANCE CONSIDERATIONS SIGNAL-TO-NOISE RATIO LEAD INDUCTANCE PHYSICAL IC MOUNTING CONSIDERATIONS LAYOUT, GROUND LOOPS AND STABILITY REACTIVE LOADING INVERTING AMPLIFIER APPLICATION LM4780 REFERENCE BOARD ARTWORK Bill Of Materials For Reference Pcb Revision History Page 1