Understanding a datasheet

[ethrbunny]

Ive been working (struggling) to understand some problems Im having with the ISD2560.


Two big questions:

1) why are there 2 different +5 inputs to the chip? The datasheet says "single +5V power supply" yet there are 2 distinct (analog and digital) lines. Does this mean I need to supply two distinct 7805s?

2) these lines are supposed to be 'decoupled as close to the pin as possible.' Does this mean I should trim off extra wire from the capacitors? How close should I be aiming for? Can I use a common ground for these?

[toneman]

page 7.
Vcca is analog power
Vccd is digital power
chip maker elected to keep them separate.
also watch out for analog & digital *gnd*s.
keep them separate until U tie them 2gether *at only one point*.
this would B @ the pwr input 2 the pcb.
staysampled
tone

[ethrbunny]

So making them common through the whole board? no go?

EDIT: on the sample page the grounds *appear* to be common. There is a single line Vcc for feeding both the Vd and Va.

Im way confused.

[Paul Perry (Frostwave)]

I wouldn't worry about it too much.
You only need one 5v regulator.
For this kind of thing, the separate grounds & supplies are only important when you are getting the last bits of noise out of the system, & it will only matter if the PCB layout is pretty well 'optimum', which is unlikely to be the case.
I don't think it would be worth cutting legs off caps either.

[ethrbunny]

Ok. Im asking as Im getting terrible noise on mine. The chip is recording and playing back ok but there is a strong background hum with several periodic elements. Makes me wonder if the chip isn't properly 'decoupled'.