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Texas Instruments LM1972M/NOPB
- Part No.:
- LM1972M/NOPB
- Manufacturer:
- Texas Instruments
- Category:
- Audio Special Purpose
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
LM1972M/NOPB.pdf
- Description:
- LM1972 MICRO-POT 2-CHANNEL 78 DB
- Quantity:
- Payment:
- Shipping:
Inventory:144
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Product details
Overview
LM1972M/NOPB from Texas Instruments is a dual-channel, digitally controlled CMOS audio attenuator with 78 dB total attenuation range (0–78 dB), 104 dB mute capability, and pop-free logarithmic step control. It features a 3-wire TTL/CMOS-compatible serial interface, daisy-chain capability, and operates from ±4.5 V to ±12 V supplies. Used in studio mixing consoles and PC audio systems for precise channel-level control.
For engineers reviewing the LM1972M/NOPB datasheet, LM1972M/NOPB pinout, LM1972M/NOPB application, or LM1972M/NOPB equivalent, key selection criteria include its 0.5 dB/1.0 dB programmable step resolution, 110 dB SNR (A-weighted), 100 dB channel separation, and SOIC-20 package compatibility with automated audio signal routing designs.
Technical Context
The LM1972M/NOPB implements two independent resistor ladder networks - one per channel - each with digitally addressable tap switches controlled via an 8-bit channel address + 8-bit attenuation data register. Its logarithmic attenuation curve is software-customizable across 159 discrete steps (0–78 dB in 0.5 dB increments up to 47.5 dB, then 1.0 dB steps).
Operation relies on a synchronous 3-wire digital interface (CLOCK, LOAD/SHIFT, DATA-IN) with DATA-OUT supporting multi-device daisy-chaining. Mute is achieved by physically disconnecting input from output and grounding the output through ~2 kΩ, delivering ≥104 dB isolation without requiring external switching circuitry.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Attenuation Range | 78 dB (0 dB to −78 dB); enables full-scale analog volume control without clipping in line-level audio paths. |
| Mute Attenuation | ≥104 dB; provides true signal isolation by internal switch disconnection and output grounding - eliminates need for external mute relays. |
| Signal-to-Noise Ratio | ≥110 dB (A-weighted, ref. 4 Vrms); ensures ultralow noise floor critical for high-fidelity music reproduction systems. |
| Channel Separation | ≥100 dB; prevents crosstalk between left/right channels in stereo panning or dual-mono applications. |
| THD+N | ≤0.003 % (max at 1 kHz, 0 dB attenuation); preserves audio fidelity across entire dynamic range without harmonic distortion artifacts. |
| Frequency Response | ≥100 kHz (−3 dB); supports extended bandwidth for high-resolution audio and ultrasonic test signal handling. |
| Supply Voltage Range | ±4.5 V to ±12 V (dual supply) or +4.5 V to +12 V (single supply with VSS tied to GND); accommodates legacy ±5 V and modern +5 V/+12 V audio rails. |
Pinout & Package
LM1972M/NOPB is housed in a 20-pin SOIC (DW) package with 1.27 mm pitch, 12.6–13.0 mm body length, and 7.4–7.6 mm width. Pin 1 is marked with a beveled corner or dot; device is RoHS-compliant and moisture-sensitive level 3 (260 °C peak reflow).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 3, 5, 6, 14, 16, 19 | AC Ground / Signal Ground | Unused die pads requiring external AC grounding to prevent coupling; pins 1, 5, 6, 14, 16 must be connected to ground via 1 µF capacitors for optimal noise immunity. |
| 2, 17 | Signal Output | Independent buffered outputs OUT1 and OUT2; require JFET-input op-amp buffering to maintain linearity and avoid clicks/pops during attenuation changes. |
| 4, 20 | Signal Input | Independent inputs IN1 and IN2; nominal 40 kΩ constant input impedance regardless of attenuation setting. |
| 7, 18 | Negative Supply | VSS1 and VSS2; tied to ground in single-supply operation; support dual-rail ±6 V configuration for symmetrical audio swing. |
| 8 | Digital Ground | Logic ground for CLOCK, LOAD/SHIFT, DATA-IN, DATA-OUT; must be isolated from analog grounds to prevent digital noise injection. |
| 9 | Clock Input | TTL/CMOS-compatible clock (≤2 MHz); rising edge loads serial data into internal shift register. |
| 10 | Load/Shift | Active-low enable; held low during 16-bit serial transfer (8-bit address + 8-bit data), then pulsed high to latch new settings. |
| 11 | Data-In | Serial data input; accepts MSB-first 16-bit frame where bits [15:8] = channel address (00000000 = CH1), bits [7:0] = attenuation code. |
| 12 | Data-Out | Daisy-chain output; shifts out prior data when new bits are clocked in; must be terminated with 2 kΩ to ground if unused to suppress noise coupling. |
| 13, 15 | Positive Supply | VDD1 and VDD2; independent positive rails allowing separate power domains for each channel's analog section. |
Key Features
| Feature | Design Value |
|---|---|
| Pop-and-click free attenuation | Eliminates audible transients during volume changes by ensuring monotonic step transitions and requiring external JFET buffer (e.g., LF412ACN) to isolate output impedance variation. |
| Software-customizable attenuation curve | Permits re-mapping of 159-step ladder (e.g., constant 1 dB or 2 dB steps) via microcontroller firmware - enabling panning, balance, or gain-control functions beyond standard volume. |
| Daisy-chain serial interface | Reduces system wiring by allowing multiple LM1972M/NOPB devices to share CLOCK, LOAD/SHIFT, and DATA-IN lines while using cascaded DATA-OUT for synchronized updates. |
| 104 dB hardware mute | Internally disconnects input from output and grounds output pin, achieving deeper silence than relay-based solutions and eliminating PCB space for external mute switches. |
| High channel separation (100 dB) | Enables true stereo imaging in sound reinforcement systems by minimizing inter-channel leakage even at maximum attenuation settings. |
Applications
| Studio Mixing Console Control | PC Audio Volume Management |
|---|---|
Use Scenario: Automated fader control in broadcast-grade analog mixing desks with remote MCU supervision. IC Role / Device Role / Timing Role: Dual-channel logarithmic attenuator providing precise, synchronized channel gain adjustment under serial command. Use Value: 0.5 dB step resolution and 100 dB channel separation preserve stereo image integrity during real-time mix automation. | Use Scenario: Front-panel volume knob replacement in desktop PCs and all-in-one systems with Windows audio stack integration. IC Role / Device Role / Timing Role: Digitally addressed audio attenuator interfacing directly with USB HID or SPI-connected microcontrollers. Use Value: Pop-free transitions and 110 dB SNR ensure clean user-initiated volume changes without audible artifacts or background hiss. |
| Music Reproduction System | Sound Reinforcement Processor |
Use Scenario: High-end DAC output stage conditioning in audiophile CD players and streamers before power amplification. IC Role / Device Role / Timing Role: Precision analog gain control element placed between DAC and line driver, calibrated for logarithmic loudness perception. Use Value: Customizable 1 dB step curve matches Fletcher-Munson curves, delivering perceptually linear volume response across 78 dB range. | Use Scenario: Input gain staging in portable PA mixers with multiple mic/line inputs routed to DSP engine. IC Role / Device Role / Timing Role: Channel-specific pre-attenuator before ADC sampling, enabling headroom management without clipping. Use Value: 100 kHz bandwidth and ≤0.003 % THD+N preserve transient detail and harmonic richness in live vocal and instrument signals. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar audio attenuator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| PGA2310U | Single-channel, I²C interface, 90 dB dynamic range, integrated op-amp buffers, no mute function. | Requires external mute circuitry; suited for fixed-gain amplifier stages rather than pure attenuation paths. | Select PGA2310U when integrated buffering and I²C simplicity outweigh dual-channel requirement and mute necessity. |
| DS1669S+ | Single-channel, 3-wire interface, 64-step (1 dB) resolution, 90 dB attenuation, no daisy-chain support. | Limited to basic volume control; lacks software-programmable step schemes and channel separation specs. | Choose DS1669S+ only for cost-sensitive, non-critical mono audio paths where 78 dB range and 100 dB separation are not required. |
Compared with PGA2310U and DS1669S+, the LM1972M/NOPB uniquely delivers dual-channel operation with 104 dB mute, daisy-chain scalability, and customizable logarithmic step mapping - making it the only option qualified for professional stereo mixing and high-SNR studio signal routing.
Availability
LM1972M/NOPB is available at Aetrix Electronics and suitable for studio mixing consoles, PC audio subsystems, and high-fidelity music reproduction systems requiring stable component supply and long-term industrial availability.
Supply support for LM1972M/NOPB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity technologies with over 50 years of innovation in precision signal chain components.
The LM1972M/NOPB belongs to TI's μPot™ family of digitally controlled analog attenuators, engineered specifically for high-fidelity audio systems demanding low THD+N, wide dynamic range, and glitch-free digital control.
FAQ
What is the maximum clock frequency supported by the LM1972M/NOPB serial interface?
The LM1972M/NOPB supports a maximum clock frequency of 2 MHz, as specified in its Electrical Characteristics table. This allows rapid updates of both channels within 8 µs per 16-bit frame. Exceeding this limit risks incomplete data latching or metastability in the internal shift register. The LM1972M/NOPB clock input is TTL/CMOS compatible and requires clean edges with <150 ns setup time relative to LOAD/SHIFT assertion.
Does the LM1972M/NOPB require external buffering at its output, and why?
Yes, the LM1972M/NOPB requires an external JFET-input op-amp (e.g., LF412ACN) at each output to prevent audible clicks/pops and maintain linearity. Its output impedance varies nonlinearly (25–35 kΩ) with attenuation step changes, and bipolar op-amps draw bias current that causes DC voltage transients. The LM1972M/NOPB's architecture mandates high-impedance loading to avoid measurement errors and distortion - a condition met only by JFET buffers.
How does the mute function operate in the LM1972M/NOPB, and what attenuation does it achieve?
The LM1972M/NOPB achieves mute by internally disconnecting the analog signal path and grounding the output pin through ~2 kΩ, delivering ≥104 dB attenuation. This occurs when any data word ≥01111111 (127 decimal) is sent to the attenuation register. Unlike soft-mute techniques, this is a hard hardware disconnect - verified in the Electrical Characteristics table under "AM Mute Attenuation" with a minimum of 96 dB and typical 104 dB.
Can the LM1972M/NOPB be used with a single supply, and what modifications are needed?
Yes, the LM1972M/NOPB supports single-supply operation: tie VSS1 and VSS2 (pins 7 and 18) to ground, and apply +4.5 V to +12 V to VDD1 and VDD2 (pins 13 and 15). Input signals must be DC-biased to mid-supply (e.g., VDD/2) using coupling capacitors and bias resistors. The LM1972M/NOPB's absolute maximum ratings confirm VSS = 0 V is valid, and all electrical specs (THD+N, SNR) are tested under dual-supply conditions but remain functional in single-supply mode.
What is the purpose of the AC Ground pins (1, 3, 5, 6, 14, 16, 19) on the LM1972M/NOPB?
These seven pins are unconnected die pads requiring external AC grounding to suppress electromagnetic coupling between adjacent signal traces. They must be tied to ground via 1 µF capacitors (not direct shorts) to provide low-impedance return paths for high-frequency noise. Pin 14 is recommended to connect to VDD pins (13, 15) for improved isolation. Leaving them floating degrades crosstalk performance and increases THD+N - a requirement explicitly stated in the PIN DESCRIPTIONS section of the LM1972M/NOPB datasheet.
LM1972M/NOPB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- Product Status:
- Active
- Function:
- Volume Control
- Applications:
- Consumer Audio, Professional Audio
- Number of Channels:
- 2
- Interface:
- SPI
- Voltage - Supply:
- 4.5V ~ 12V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Specifications:
- 78dB
- Mounting Type:
- Surface Mount
- Grade:
- -
LM1972M/NOPB FAQ
1.How can I place an order for LM1972M/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM1972M/NOPB on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LM1972M/NOPB reliable?
The price and inventory of LM1972M/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM1972M/NOPB is usually 5 days.
3.What payment methods are accepted for LM1972M/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM1972M/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM1972M/NOPB?
LM1972M/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM1972M/NOPB order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LM1972M/NOPB?
For technical support, including LM1972M/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM1972M/NOPB requirements.
6.How does Aetrix verify that LM1972M/NOPB is sourced from the original manufacturer or authorized distributors?
All LM1972M/NOPB products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LM1972M/NOPB meets industry standards.
7.What is the process for return or replacement of LM1972M/NOPB?
All LM1972M/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM1972M/NOPB, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LM1972M/NOPB part is unused and in its original packaging.
Return procedure for LM1972M/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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