ECIO Voltage Ref- Ref+ for Supply Battery Monitor

[Jay Dee]

Hi all,
Using an ECIO running on an external USB battery supply. I would like to monitor this ~5v power supply.
I believe for the analogue inputs my measurement can either reference VDD (5v supply) or the Vref+ Pin
Using VDD would not work as that's what I trying to measure, any fluctuation would be cancelled out.

So do I have need to take another voltage ref (I have a small 3.3v reg on the board) and feed this to the Vref+ pin ?
I guess I would need to tweak the Vrefvol value to rescale... but can I still monitor 5v if the Vref+ is only at 3.3v ?

Also, Anyone know what the lower side of this measurment is based on? Vss
I'm sure we used to be able to set the Vref- but this option seems to have gone
thanks, J.

[kersing]

According to the datasheet the input voltage should be between Vrefl and Vrefh. So if you are using 3.3V for Vrefh the maximum allowable input voltage would be 3.3V.

[Jay Dee]

Ah.. Thanks Kersing.. very good point.
If a device is battery powered, its supply voltage will drop as the battery discharges. So Vcc is a pretty poor reference.
Umm.. to monitor this the simplest way would be use the 3.3v ref into the Vref+ pin too give a stable reference and then use a voltage divider on the analog input monitoring the supply voltage. A simple 50/50% voltage divider split would allow the input voltage to rise to 6.6v without exceeding the 3.3V voltage ref.
I think this would work. J.

[Benj]

Hi JayDee,

That sounds like a good solution to me. Some chips have an internal voltage reference to avoid needing the voltage regulator but the PIC ECIO chips do not have this functionality.

[Steve001]

Hi,

I made a network cable analyser for patch leads a few years ago that was battery powered , i used a traco power DCDC Convertor with a 3.5 - 5.5v Input and a 5 volt output then measured the dc battery voltage with a adc pin. just had a look farnell do not list it any more tho ,
Power solve electronics are a distributer for traco and they are very helpful.

http://powersolve.co.uk/

Steve

[Jay Dee]

Thanks Steve, handy little brick to give you that buck boost solution. Might be a bit overkill for this project as I'm going down the super small route... well trying too.

[Steve001]

you could use a external ref device and a comparator to drive a input maybe ?

have used this device in a battery monitoring device for a low voltage disconnect (admittedly 24 & 36vdc) it is programmable tho

http://www.ti.com/lit/ds/symlink/tl431.pdf

maybe worth a look

Steve

[Steve001]

there is a range of microprocessor supervision ic's from maxim they list battery monitors

http://www.maximintegrated.com/en/desig ... uits#sc147

http://www.maximintegrated.com/en/app-n ... vp/id/4545

http://www.maximintegrated.com/en/app-n ... mvp/id/655


Steve

[Steve001]

here is another 3.5v - 5.0 DC DC Convertor with a 5.0 v regulated output using Maxim parts - MAX Current 250 MA

MAX256ASA+ this is rated at 500 Ma but you will have to change the transformer also

PLEASE NOTE THESE ARE SMD COMPONENTS AND TINY !

Steve