[sdiy] uPD444 RAM battery power

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sat May 30 00:40:41 CEST 2015

On May 29, 2015, at 3:20 PM, Adam Inglis <21pointy at tpg.com.au> wrote:
> On 29/05/2015, at 6:10 PM, rsdio at audiobanshee.com wrote:
>> What are the specs on that protection diode? What's the part number?
>> One thing I notice is that it seems you're increasing the reverse voltage on that protection diode from 0.5 V to 2.0 V (that's quadrupled). I did a quick search, and very few diodes have a maximum reverse voltage of only 2 or 3 Volts, but it's possible that you might be getting close to its limit. If there's any question, another diode with higher reverse voltage capacity would be a good idea.
> The diode is quoted as DS442. Datasheets show reverse current 1 uA at 4 volts. I'm measuring about 0.3 volts forward drop in circuit. So I should be ok.

Repetitive Peak Reverse Voltage is rated as 35 V !  I don't think you'll have any problem with 2.0 V reverse, although I didn't find an official data sheet.

> The RAM datasheet quotes "Data Retention Supply Current - 0.01 uA typical, 10 uA max" - a rather large variation!

Yeah, your battery could drain 1000x faster on one chip than another. I seem to recall that this confusing spec was discussed on the list, either here or Analogue Heaven.

Brian Willoughby

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