LME49610 Datasheet, PDF (12/21 Pages) National Semiconductor (TI) – High Performance, High Fidelity, High Current Audio Buffer

LME49610
SNAS435B – APRIL 2008 – REVISED APRIL 2013
V+
10 PF
+
V_CC
IN
OUT
LME49610
R_S
V_EE
BW
10 PF
R_L
+
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V-
Figure 30. Buffer Connections
OUTPUT CURRENT
The LME49610 can continuously source or sink 250mA. Internal circuitry limits the short circuit output current to
approximately ±450mA. For many applications that fully utilize the LME49610’s current source and sink
capabilities, thermal dissipation may be the factor that limits the continuous output current.
The maximum output voltage swing magnitude varies with junction temperature and output current. Using
sufficient PCB copper area as a heatsink when the metal tab of the LME49610’s surface mount DDPAK/TO-263
package is soldered directly to the circuit board reduces thermal impedance. This in turn reduces junction
temperature. The PCB copper area should be in the range of 2in² to 6in².
THERMAL PROTECTION
LME49610 power dissipated will cause the buffer’s junction temperature to rise. A thermal protection circuit in the
LME49610 will disable the output when the junction temperature exceeds 150°C. When the thermal protection is
activated, the output stage is disabled, allowing the device to cool. The output circuitry is enabled when the
junction temperature drops below 150°C.
The DSDPAK/TO-263 package has excellent thermal characteristics. To minimize thermal impedance, its
exposed die attach paddle should be soldered to a circuit board copper area for good heat dissipation. Figure 31
shows typical thermal resistance from junction to ambient as a function of the copper area. The DDPAK/TO-
263’s exposed die attach paddle is electrically connected to the V_EE power supply pin.
LOAD IMPEDANCE
The LME49610 is stable under any capacitive load when driven by a source that has an impedance of 50Ω or
less. When driving capacitive loads, any overshoot that is present on the output signal can be reduced by
shunting the load capacitance with a resistor.
OVERVOLTAGE PROTECTION
If the input-to-output differential voltage exceeds the LME49610’s Absolute Maximum Rating of 3V, the internal
diode clamps shown in Figure 1 conduct, diverting current around the compound emitter followers of Q1/Q5
(D1 – D7 for positive input), or around Q2/Q6 (D8 – D14 for negative inputs). Without this clamp, the input
transistors Q1/Q2 and Q5/Q6 will zener and damage the buffer.
To ensure that the current flow through the diodes is held to a save level, the internal 200Ω resistor in series with
the input limits the current through these clamps. If the additional current that flows during this situation can
damage the source that drives the LME49610’s input, add an external resistor in series with the input see
Figure 30.
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