LME49610 Datasheet, PDF (13/21 Pages) National Semiconductor (TI) – High Performance, High Fidelity, High Current Audio Buffer

LME49610
www.ti.com
SNAS435B – APRIL 2008 – REVISED APRIL 2013
BANDWIDTH CONTROL PIN
The LME49610’s –3dB bandwidth is approximately 110MHz in the low quiescent-current mode (13mA typical).
Select this mode by leaving the BW pin unconnected.
Connect the BW pin to the V_EE pin to extend the LME49610’s bandwidth to a nominal value of 180MHz. In this
mode, the quiescent current increases to approximately 19mA. Bandwidths between these two limits are easily
selected by connecting a series resistor between the BW pin and V_EE .
Regardless of the connection to the LME49610’s BW pin, the rated output current and slew rate remain constant.
With the power supply voltage held constant, the wide-bandwidth mode’s increased quiescent current causes a
corresponding increase in quiescent power dissipation. For all values of the BW pin voltage, the quiescent power
dissipation is equal to the total supply voltage times the quiescent current (I_Q * (V_CC + |V_EE |)).
BOOSTING OP AMP OUTPUT CURRENT
When placed in the feedback loop, the LME49610 will increase an operational amplifier’s output current. The
operational amplifier’s open loop gain will correct any LME49610 errors while operating inside the feedback loop.
To ensure that the operational amplifier and buffer system are closed loop stable, the phase shift must be low.
For a system gain of one, the LME49610 must contribute less than 20° at the operational amplifier’s unity-gain
frequency. Various operating conditions may change or increase the total system phase shift. These phase shift
changes may affect the operational amplifier's stability.
Unity gain stability is preserved when the LME49610 is placed in the feedback loop of most general-purpose or
precision op amps. When the LME46900 is driving high value capacitive loads, the BW pin should be connected
to the V_EE pin for wide bandwidth and stable operation. The wide bandwidth mode is also suggested for high
speed or fast-settling operational amplifiers. This preserves their stability and the ability to faithfully amplify high
frequency, fast-changing signals. Stability is ensured when pulsed signals exhibit no oscillations and ringing is
minimized while driving the intended load and operating in the worst-case conditions that perturb the
LME49610’s phase response.
HIGH FREQUENCY APPLICATIONS
The LME49610’s wide bandwidth and very high slew rate make it ideal for a variety of high-frequency open-loop
applications such as an ADC input driver, 75Ω stepped volume attenuator driver, and other low impedance loads.
Circuit board layout and bypassing techniques affect high frequency, fast signal dynamic performance when the
LME49610 operates open-loop.
A ground plane type circuit board layout is best for very high frequency performance results. Bypass the power
supply pins (V_CC and V_EE) with 0.1μF ceramic chip capacitors in parallel with solid tantalum 10μF capacitors
placed as close as possible to the respective pins.
Source resistance can affect high-frequency peaking and step response overshoot and ringing. Depending on
the signal source, source impedance and layout, best nominal response may require an additional resistance of
25Ω to 200Ω in series with the input. Response with some loads (especially capacitive) can be improved with an
output series resistor in the range of 10Ω to 150Ω.
THERMAL MANAGEMENT
Heat Sinking
For some applications, the LME49610 may require a heat sink. The use of a heat sink is dependent on the
maximum LME49610 power dissipation and a given application’s maximum ambient temperature. In the
DDPAK/TO-263 package, heat sinking the LME49610 is easily accomplished by soldering the package’s tab to a
copper plane on the PCB. (Note: The tab on the LME49610’s DDPAK/TO-263 package is electrically connected
to V_EE.)
Through the mechanisms of convection, heat conducts from the LME49610 in all directions. A large percentage
moves to the surrounding air, some is absorbed by the circuit board material and some is absorbed by the
copper traces connected to the package’s pins. From the PCB material and the copper, it then moves to the air.
Natural convection depends on the amount of surface area that contacts the air.
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LME49610
Submit Documentation Feedback
13