>slow start

That depends almost entirely on the charge current of the capacitors
around the chip. If you can afford place small resistors in series with
the larger ones. This will not save you if the internal resistance of the
supply decreases.

The most direct fix is to place a diode in series with the CPU supply
(before its decoupling caps, one of which should be electrolytic). If your
firmware makes sure that the CPU does not drive (almost) anything at the
moment of the turn-on of the high drain TDA then the decoupling will make
sure that the CPU runs fine across the power sag. Note that the CPU can
sink as much as you want during this time, just make sure it does not
drive anything heavy (and that there is no cap on the MCLR pin).

In my experience a 14 bit PIC with 22 uF + 0.1 uF decoupling survives
serveral msec long power sags (motors and incandescent bulbs run from 4.5V
dry cells near end of life). You can use a shottky diode for better
results. The diode also 'proofs' the CPU against reversed power (but not
other parts of the circuit).

Peter

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