topic Re: '908AB32 Power Supplies in 8-bit Microcontrollers

'908AB32 Power Supplies

J_Gordon — Sat, 10 Mar 2007 00:18:11 GMT

I am interested in understanding if there is any compelling reason to provide power to the analog section of the Clock Generator Module (CGM) or Analog-to-Digital Converter (ADC) section of the HC908AB32 if my application does not make use of the PLL or the ADC? If it is not necessary to power the unused modules, should the associated power, reference and ground pins be left all unterminated, all terminated to Vss or some combination?

Additionally - Is there any reason to provide the external filter capacitor for the CGM PLL (pin CGMXFC) if the PLL is unused and off?

I look forward to knowledgable replies and thank you in advance.

Re: '908AB32 Power Supplies

bigmac — Sat, 10 Mar 2007 13:01:33 GMT

Hello,

I think it would be safer to connect the various Vdd and Vss pins according to the data sheet. I can't see that there is anything to be gained by not doing so, and this may avoid side effects that may not be immediately apparent. We don't know what intrinsic diodes may be present between the internal modules. The power required by the CGM PLL and the ADC should already be reduced when not enabled.

You can probably omit the CGMXFC filter capacitor when the PLL is not used.

Regards,

Mac

Re: '908AB32 Power Supplies

J_Gordon — Tue, 13 Mar 2007 21:54:34 GMT

Thanks for your insight.