LME49810 Datasheet, PDF (11/21 Pages) National Semiconductor (TI) – 200V Audio Power Amplifier Driver with Baker Clamp

LME49810
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APPLICATION INFORMATION
SNAS391C – MAY 2007 – REVISED APRIL 2013
MUTE FUNCTION
The mute function of the LME49810 is controlled by the amount of current that flows into the MUTE pin.
LME49810 typically requires 50μA to 100μA of mute current flowing in order to be in “play” mode. This can be
done by connecting a reference voltage (V_MUTE) to the MUTE pin through a resistor (R_M). The following formula
can be used to calculate the mute current.
I_MUTE = (V_MUTE-0.7V) / (R_M+10kΩ) (A)
(1)
The 10kΩ resistor value in Equation (1) is internal. Please refer to Figure 3, LME49810 Simplified Schematic, for
additional details. For example, if a 5V voltage is connected through a 33kΩ resistor to the MUTE pin, then the
mute current will be 100μA, according to Equation (1). Consequently, R_M can be changed to suit any other
reference voltage requirement. The LME49810 will enter Mute mode if I_MUTE is less than 1μA which can be
accomplished by shorting the MUTE pin to ground or by floating the MUTE pin. It is not recommended that more
than 200μA flow into the MUTE pin because damage to LME49810 may occur and device may not function
properly.
BAKER CLAMP AND CLAMP FLAG OUTPUT
The LME49810 features a Baker Clamp function with corresponding CLPFLAG output pin. The clamp function
keeps all transistors in linear operation when the output goes into clipping. In addition, when the output goes into
clipping, a logic low level appears at the CLPFLAG pin. The CLPFLGAG pin can be used to drive an LED or
some other visual display as shown by Figure 1. The value of logic low voltage varies and depends on I_FLAG. For
example, if I_FLAG is 4.7mA then a voltage (V_BC) of 0.4V will appear at the CLPFLAG output pin. The smooth
response of the Baker Clamp and the corresponding CLPFLAG logic output is shown in the scope photo below:
+V_CC = -V_EE = 100V,
V_IN = 4V_RMS,
f_IN = 1kHz,
R_C = 1kΩ Ch1: Output,
Ch2: CLPFLAG Output
Figure 34.
The CLPFLAG pin can source up to 10mA, and since the CLPFLAG output is an open collector output as shown
by Figure 3, LME49810 Simplified Schematic, it should never be left to float under normal operation. If CLPFLAG
pin is not used, then it should be connected through a resistor to a reference voltage so that I_FLAG is below
10mA. For example, a resistor of 1k can be used with a 5V reference voltage. This will give the I_FLAG of 4.7mA. In
a typical LED setup, if +5V reference voltage is not available, the following circuit using a Zener diode can be
used to power the CLPFLAG pin from the higher supply voltage rails of the LME49810. The power dissipation
rating of R_Z will need to be at-least ½W if using a 5V Zener Diode. Alternately, the following basic formula can be
used to find the proper power rating of R_Z : P_DZ = (V_CC - V_Z)²/R_Z (W). This formula can also be used to meet the
design requirements of any other reference voltage that the user desires.
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