LM4851ITL – National Semiconductor Boomer® Audio Power Amplifier
Comprehensive Datasheet Summary

1. Device IdentificationOrderable Part Number: LM4851ITLPackage: 18-bump micro-SMD (TLA18AAA) – 1.996 mm × 2.225 mm × 0.600 mm max heightDate Code Format: XY-TT (X = year digit, Y = month code, TT = traceability)Family Marking: “G 52” (Boomer family identifier & die revision)
2. Key Features

• Mono 1.1 W (typ) into 8 Ω BTL, 1 % THD+N @ 5 V
• Stereo 115 mW (typ) per channel into 32 Ω BTL, 0.5 % THD+N @ 5 V
• 32-step SPI-programmable volume control (–40.5 dB → +6 dB, 1.5 dB/step)
• Eight distinct output modes (mono/stereo mix, speaker/headphone path routing)
• 2.6 V – 5.0 V single-supply operation
• “Click-and-pop” suppression, thermal shutdown, 0.1 µA shutdown current
• Space-saving 18-bump micro-SMD (2 mm × 2.3 mm effective PCB footprint)

1. Absolute Maximum RatingsVDD ............................................... –0.3 V to 6.0 VTJ (Junction Temperature) ....................... 150 °CTstg ............................................... –65 °C to +150 °CESD ToleranceHuman-body model ............................. 2 kVMachine model ................................ 200 V
2. Operating ConditionsAmbient ........................................... –40 °C to +85 °CVDD ............................................... 2.6 V – 5.0 VThermal resistance θJA (micro-SMD, no airflow) .... 48 °C/W
3. Electrical Characteristics @ 25 °C, VDD = 5 V (unless noted)
4. SUPPLY
   IDD (no load, modes 1-6) ........................ 5 mA typ, 9 mA max
   IDD (mode 7) .................................... 7.5 mA typ, 14 mA max
   ISD (shutdown, mode 0) .......................... 0.1 µA typ, 2 µA max
5. OUTPUT POWER
   Speaker BTL (SPKROUT)
   RL = 8 Ω, THD+N = 1 % ........................ 1.1 W typ, 0.8 W min
   RL = 4 Ω, THD+N = 1 % ........................ 1.5 W typ (LQ pkg only)
   Headphone BTL (ROUT/LOUT)
   RL = 32 Ω, THD+N = 0.5 % .................... 115 mW typ, 80 mW min
6. DISTORTION & NOISE
   THD+N @ 1 kHz
   1 W into 8 Ω .................................. 1 % max
   80 mW into 32 Ω .............................. 0.5 % max
   Output noise (A-weighted) ........................ 29 µV typ
   PSRR @ 217 Hz, 200 mVPP ripple
   Input floating ................................ 70 dB typ
   Input terminated 50 Ω ........................ 62 dB typ
7. OUTPUT OFFSET .................................... 5 mV typ, 50 mV max
8. LOGIC INPUTS (SPI)
   VIH .............................................. 1.4 V min
   VIL .............................................. 0.4 V max
   CLK frequency .................................... DC – 10 MHz
9. SPI Control SummaryData word: 8 bits, LSB first, rising-edge clocking

• Bits 2-0 → output mode (0-7)
• Bits 7-3 → volume gain (00000b = –40.5 dB … 11111b = +6 dB)Latch occurs when ENB goes LOW after 8th clock.Timing: setup/hold 20 ns min, clock high/low 50 ns min, ENB low ≥30 ns after 8th clock.

1. Output Mode OverviewMode 0: full shutdown (all outputs muted)Mode 1: SPKROUT only, 6 dB gain, stereo mutedMode 2: stereo headphones only (ROUT/LOUT), speaker mutedMode 3: SPKROUT = R+L mix, stereo mutedMode 4: stereo headphones only, volume-controlledMode 5: SPKROUT = R+L + 6 dB Phone-In boostMode 6: stereo headphones + Phone-In mixed on each channelMode 7: simultaneous speaker (6 dB) + headphone (R+L+Phone) – most common for hands-free call.
2. External Components (typical, Fig. 1)Cin ................ 0.22 µF (input coupling & high-pass)Cbypass ........... 1 µF (BYPASS pin, sets turn-on pop & PSRR)Csupply .......... 1 µF + 0.1 µF (local VDD bypass)No output coupling capacitors required (BTL outputs biased at VDD/2).
3. Thermal & Layout NotesMicro-SMD die-attach paddle (DAP) must solder to PCB copper pad.Recommended copper area: ≥2.5 in² (same layer) or ≥5 in² (inner layer) for 5 V, 8 Ω full-power operation.Keep output traces short & wide to minimise trace-resistance loss (<100 mΩ recommended for 4 Ω loads).Junction temperature must stay <150 °C under all conditions; device includes thermal shutdown at ≈150 °C.
4. Typical Application Diagram[Refer to Figure 1 in datasheet]

• Stereo line inputs (LIN/RIN) via 0.22 µF to pins 6/7
• Phone input (single-ended) via 0.22 µF to pin 3
• Speaker connected differentially to SPKROUT+ (pin 17) / SPKROUT– (pin 16)
• 32 Ω headphones to ROUT+ (pin 19) / ROUT– (pin 18) and LOUT+ (pin 14) / LOUT– (pin 13)
• SPI bus (DATA, CLK, ENB) to system MCU; pull-up on ENB optional.

1. Packing & OrderingShipping Media: 8 mm embossed tape, 7-in reel, 3 k pcs/reel standardMSL Rating: 3 (floor life 168 h @ ≤30 °C/60 % RH)Lead Finish: SnAgCu (RoHS-compliant), NiPdAu bump pads
2. Related Documentation

• AN-1187 “LLP & micro-SMD Thermal Design Guide”
• AN-450 “SMT Assembly and Reliability”
• SPI Timing & Mode tables (datasheet pages 13-14)