LA8519M Datasheet, PDF (23/29 Pages) Sanyo Semicon Device – I/O Switch/Voice Signal-Processing IC for Cordless Telephones

LA8519M
• Power amplifier VREF (pin 24) line
Pin 24 is the reference voltage pin for the power amplifier, and is connected to pin 23 (the input) by an internal bias
resistor. This means that pin 24 is part of the power amplifier plus input line system. If this line is affected by the
power amplifier output or the V_CC line, the resultant positive feedback can cause oscillation.
Therefore, if at all possible, the pin 24 line should not be routed around other lines. If it must be routed around
other lines, do not rout it adjacent to output or V_CC lines, but rout it adjacent to ground lines to prevent
interference.
• LA8519M ground line rerouting (See the figure on the next page.)
The LA8519M circuit blocks can be classified into three systems: (1) power amplifier, (2) speech network system,
and (3) crosspoint switch and other small-signal processing systems. Since the IC itself, naturally, has a three-block
structure, each block has independent V_CC and ground pins. The best possible ground system design, is for external
components that are connected to ground to be connected to the ground for the block to which they belong, and for
the pattern to be formed so that these three lines are independent and connect to the ground of the power supply
(regulator) that is the reference.
However, since there are limitations on the area available on the printed circuit board, there are cases where a
single line is connected to the reference ground. In this case, ground lines must be routed so that the ground lines
that carry larger currents (power amplifier and line connection blocks) are closer to the power supply ground (and
thus have a lower impedance)than ground lines for circuits with a lower current drain.
If the large currents used by the power amplifier or other high-current system flow in the ground lines that handle
the smaller currents from small-signal system or other low-current system, a loop may be formed and low band
oscillation may occur.
Therefore we recommend that the ground lines are designed, as described above, so that lines in which large
currents flow are routed closest to the power supply ground.
IC Usage Notes
1. If the LA8519M is used in the vicinity of its maximum ratings, even slight variations in operating conditions may
result in the maximum ratings being exceeded. Since this can lead to damage to or destruction of the device,
provide adequate margin in the fluctuations in the supply voltage and other parameters, and do not allow the
maximum ratings to be exceeded.
2. Pin shorting
If the LA8519M is left with output loads shorted for extended periods, it may be damaged or destroyed. Always
use this device in a manner such that output loads are never shorted.
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