PREVENTING OSCILLATIONS

With the integration of the feedback and bias resistors on-

chip, the LM4752 fits into a very compact package. However,

due to the close proximity of the non-inverting input pins to

the corresponding output pins, the inputs should be AC ter-

minated at all times. If the inputs are left floating, the ampli-

fier will have a positive feedback path through high imped-

ance coupling, resulting in a high frequency oscillation. In

most applications, this termination is typically provided by

the previous stage’s source impedance. If the application will

require an external signal, the inputs should be terminated to

ground with a resistance of 50 k

Ω or less on the AC side of

the input coupling capacitors.

UNDERVOLTAGE SHUTDOWN

If the power supply voltage drops below the minimum oper-

ating supply voltage, the internal under-voltage detection cir-

cuitry pulls down the half-supply bias line, shutting down the

preamp section of the LM4752. Due to the wide operating

supply range of the LM4752, the threshold is set to just un-

der 9V. There may be certain applications where a higher

threshold voltage is desired. One example is a design requir-

ing a high operating supply voltage, with large supply and

bias capacitors, and there is little or no other circuitry con-

nected to the main power supply rail. In this circuit, when the

power is disconnected, the supply and bias capacitors will

discharge at a slower rate, possibly resulting in audible out-

put distortion as the decaying voltage begins to clip the out-

DS100039-30

FIGURE 5. Bridge-Mode Application

DS100039-31

DS100039-37

FIGURE 6. THD+N vs. P

www.national.com

11