Dear Friends [ specially Kai ],

I have just finished the routing of a battery powered dual supply [+5V -5V ] mixed signal current measuring device.

The schematic and pcb layouts are attached.
- The +9V shown in schematic refers to 7.2V Ni-MH battery.
- Though schematic shows 7805 I am going to use LM2937 +5V LDO.
- Schematic shows 7905 but LM2990 -5V LDOs will be used.

- For analog +5V supply the +7.2 is given to input of LM2937 and output filtered with filter formed by shown capacitors bead etc. The filtered +5V is called F+5V. This filtered +5V goes to Opamp +Vcc and to micro [ Atmega48 ] AVcc.

- For analog -5V generation the +7.2V from battery is inverted by ICL7660 to produce output of -6.5V. This is then applied to LM2990 -5V LDO. The output of this LDO is also filtered and is given to Opamp -Vcc.

- For generating +5V for digital section the +7.2V battery trace is taken to digital gnd plane this trace is filtered with pi filter at interace of AGND and DGND.

- This pi filtered filtered +7.2V is applied to another LM2937 LDO and output is given to micro DVcc and LCD Vcc. LCD and Micro supply lines are fitlered using two separate beads tantal and a 100nF ceramic as shown.

http://www.8052.com/users/prahlad/wcbatsch.GIF [schematic link]





This is the first time I have used so heavy filtering on a PCB. There appears to be more filtering components then other parts. Is this filtering adequate or too much? Do i need to make changes in it? I have used ICL7660 charge pump voltage invertor for generating -ve supply for amp can this create trouble? What can be done to keep noise problems minimum with this design? I am targetting 10 bit accuracy.

Thanks & Regards,
Prahlad Purohit