LM4985 Datasheet, PDF (1/29 Pages) National Semiconductor (TI) – Stereo 135mW Low Noise Headphone Amplifier with Selectable Capacitively Coupled or Output Capacitor-less (OCL) Output and Digitally Controlled (I2C) V

May 2006
LM4985
Stereo 135mW Low Noise Headphone Amplifier with
Selectable Capacitively Coupled or Output
Capacitor-less (OCL) Output and Digitally Controlled
(I²C) Volume Control
General Description
The LM4985 is a stereo audio power amplifier with internal
digitally controlled volume control. This amplifier is capable
of delivering 68mW_RMS per channel into a 16Ω load or
38mW_RMS per channel into a 32Ω load at 1% THD when
powered by a 3.6V power supply and operating in the OCL
mode.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. To that end, the LM4985 features two
functions that optimize system cost and minimize PCB area:
an integrated, digitally controlled (I²C bus) volume control
and an operational mode that eliminates output signal cou-
pling capacitors (OCL mode). Since the LM4985 does not
require bootstrap capacitors, snubber networks, or output
coupling capacitors, it is optimally suited for low-power, bat-
tery powered portable systems. For added design flexibility,
the LM4985 can also be configured for single-ended capaci-
tively coupled outputs.
The LM4985 features a current shutdown mode for mi-
cropower dissipation and thermal shutdown protection.
Key Specifications (V_DD = 3.6V)
j PSRR: 217Hz and 1kHz
Output Capacitor-less (OCL)
f_RIPPLE = 217Hz
f_RIPPLE = 1kHz
Capacitor Coupled (C-CUPL)
77dB (typ)
76dB (typ)
f_RIPPLE = 217Hz
f_RIPPLE = 1kHz
j Output Power per channel
(f_IN = 1kHz, THD+N = 1%),
R_L = 16Ω,OCL
V_DD = 2.5V
V_DD = 3.6V
V_DD = 5.0V
j THD+N (f = 1kHz)
63dB (typ)
62dB (typ)
31mW (typ)
68mW (typ)
135mW (typ)
R_LOAD = 16Ω, OCL, P_OUT = 60mW
R_LOAD = 32Ω, OCL, P_OUT = 33mW
j Shutdown Current
0.60
0.031
0.1µA (typ)
Features
n OCL or capacitively coupled outputs (patent pending)
n I²C Digitally Controlled Volume Control
n Available in space-saving 0.4mm lead-pitch micro SMD
package
n Volume control range: –76dB to +18dB
n Ultra low current shutdown mode
n 2.3V - 5.5V operation
n Ultra low noise
Applications
n Mobile Phones
n PDAs
n Portable electronics devices
n MP3 Players
Boomer^® is a registered trademark of National Semiconductor Corporation.
© 2006 National Semiconductor Corporation DS201697
www.national.com