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'[EE] MCP73831 Battery Charger'
2010\02\27@103221 by Marcelo Rodrigues

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Hi all,

I'm designing a product using the MCP73831 Battery Charger. I need to check
if the MCP73831 is working properly, but i can't wait it to make a complete
battery charge, because it takes about 5 hours.

Thus i've decided to connect a single resistor (4K) at the VBAT pin without
the battery and verify if the current at this pin have the expected value
(1mA).

My question is: Connecting a resistor at the VBAT pin can damage the
MCP73831?

Or maybe do you know another better and simple way to test this IC?

Thanks in advance.

--
Marcelo dos Santos Rodrigues


'[EE] MCP73831 Battery Charger'
2010\03\01@091517 by Ariel Rocholl
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If you understand the logic behind CV/CC charging steps, you can see how bad
a single resistor will work simulating a Lipo battery. Internal logic of the
MCP73831 will not work properly with a single resistor.

Why do you need to wait 5hs? it is because of the autoshutdown timer? At a
specified 1C charging rate, a battery should be charged in 1hr or less, and
that assuming it was fully depleted. You will measure different charging
currents at different times on the charging curve, but you can start
measuring it as soon as you feed some power to the circuit.

To test the autoshutdown timer you have to wait till timer expires, MCP
doesn't offer any simpler method.

2010/2/27 Marcelo Rodrigues <spam_OUTmsrmailTakeThisOuTspamgmail.com>

{Quote hidden}

> -

2010\03\01@112249 by Marcelo Rodrigues

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Hi, arocholl

The MCP73831 charges with 0,1C until the battery reaches 66.7% of the
nominal voltage, then it charge with 1C (CC) until the nominal voltage. The
last step is to charge with
the nominal voltage (CV).

I have measured the charge time several times and it takes about 5 hours
until the MCP73831 signals that the battery is fully charged.

The MCP73831 doesns't have a timer to control the end of charge, only the
MCP73833.

About my question, i want to use the resistor only to verify if the tracks
around the IC are not open or shorted. Actually i don't need to simulate all
CV/CC charging steps. But i'm worried if the resistor can damge the IC.


arocholl wrote:
{Quote hidden}

>> --

2010\03\01@114230 by Ariel Rocholl

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2010/3/1 Marcelo Rodrigues <msrmailspamKILLspamgmail.com>

>
> Hi, arocholl
>
> The MCP73831 charges with 0,1C until the battery reaches 66.7% of the
> nominal voltage, then it charge with 1C (CC) until the nominal voltage. The
> last step is to charge with
> the nominal voltage (CV).
>

The 0.1C step is needed only for deeply discharged battery, you shouldn't
get into that step with a Lipo in normal situations. In any case, this step
takes almost no time.

For the 1C step, It will charge to whatever current you program it to with
the external PROG resistor, limited to the max MCP device charge current.


>
> I have measured the charge time several times and it takes about 5 hours
> until the MCP73831 signals that the battery is fully charged.
>

Perhaps hat is because you selected a wrong PROG resistor. What is the mAh
capacity of your battery and what is the PROG resistor you selected for the
circuit?


>
> The MCP73831 doesns't have a timer to control the end of charge, only the
> MCP73833.
>

You're right. So how do you know then the battery gets fully charged? By led
status indicator?


>
> About my question, i want to use the resistor only to verify if the tracks
> around the IC are not open or shorted. Actually i don't need to simulate
> all
> CV/CC charging steps. But i'm worried if the resistor can damge the IC.
>
>
I don't think it can damage the IC based on internal circuit modular
diagram. However, it may quickly shutdown charge as I guess it will get
nominal voltage immediately. Why you don't just plug a Lipo battery and
check whatever you need to check?



--
Ariel Rocholl
Madrid, Spain

2010\03\01@120121 by Marcelo Rodrigues

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Hi, arocholl,

I'm using the LIR2032 battery (Nominal C = 35mAh and standard charging
method = CC 17mA (0.5C)). Thus the PROG resistor i'm using is 60K4 (aprox.
16mA).

I can't just plug a battery and check the current value. It will be tested
in the production
and must be a fast method. The people that will make it, must just verify if
threre is a known current value. As the current depends on the battery
voltage, i can't use it.



arocholl wrote:
{Quote hidden}

> --

2010\03\01@122111 by Michael Rigby-Jones

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> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On
Behalf
> Of Marcelo Rodrigues
> Sent: 01 March 2010 17:01
> To: @spam@piclistKILLspamspammit.edu
> Subject: Re: [EE] MCP73831 Battery Charger
>
>
> Hi, arocholl,
>
> I'm using the LIR2032 battery (Nominal C = 35mAh and standard charging
> method = CC 17mA (0.5C)). Thus the PROG resistor i'm using is 60K4
(aprox.
> 16mA).
>
> I can't just plug a battery and check the current value. It will be
tested
> in the production
> and must be a fast method. The people that will make it, must just
verify
> if
> threre is a known current value. As the current depends on the battery
> voltage, i can't use it.
>

It sounds like you need a voltage source that can sink current which
could be used to emulate a battery in this context.  A resistor is
unlikely to do what you want, I'd be surprised if the charger didn't
shutdown with zero volts on it's output.

Mike

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2010\03\01@124401 by Ariel Rocholl

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face
2010/3/1 Marcelo Rodrigues <KILLspammsrmailKILLspamspamgmail.com>

>
> Hi, arocholl,
>
> I'm using the LIR2032 battery (Nominal C = 35mAh and standard charging
> method = CC 17mA (0.5C)). Thus the PROG resistor i'm using is 60K4 (aprox.
> 16mA).
>
>
You can get faster charge with a smaller value resistor. Except there is a
good reason not to, you can charge with up to 1C any standard lipo.


> I can't just plug a battery and check the current value. It will be tested
> in the production
> and must be a fast method. The people that will make it, must just verify
> if
> threre is a known current value. As the current depends on the battery
> voltage, i can't use it.
>
>
I see what you mean. So someone will plug something in and will measure
current?  would vote for a 3V3 zener with some limiting resistor. Do some
math, it should work on the CC region.

--
Ariel Rocholl
Madrid, Spain

2010\03\01@211401 by Russell McMahon

face picon face
> I'm using the LIR2032 battery (Nominal C = 35mAh and standard charging
> method = CC 17mA (0.5C)). Thus the PROG resistor i'm using is 60K4 (aprox.
> 16mA).

> I can't just plug a battery and check the current value. It will be tested
> in the production
> and must be a fast method. The people that will make it, must just verify
if
> there is a known current value. As the current depends on the battery
> voltage, i can't use it.

OK. You just provided (probably) enough information to make sense of your
questions.
If you had provided all relevant (and some irrelevant ;-) ) information at
the start we'd be home by now.

Apparently the issue is that you wish to production test chargers to ensure
that  there are no gross PCB faults and to ensure that the circuit performs
major tasks correctly.

This sounds 'not too hard' [tm] BUT you really need a custom battery
emulator that speeds up the process.
You also need a good understanding of what the charger IC does at each stage
and why.

It seems likely that  a capacitor possibly with a resistor network, would
test the low battery and constant current parts of the cycle.

Provide a capacitor of sufficient capacitance that it will charge to full
voltage at 1C in an acceptable time. YOU define what the acceptable time is.
Let's suppose it is 10 seconds.

Precharge the cap to slightly under the low voltage trickle up voltage.
Connect the charger. The cap will be charged at 0.1C until it reaches the
low voltage thresh-hold, then jump to 1C and charge until Vmax is reached.
It will now go into constant voltage mode.

If a single cap is used as above it will immediately stop accepting current
and the charge cycle will terminate. To emulate the constant voltage,
declining current "tail" you could try adding a second smaller cap in series
with a resistor with time constant that it is still not fully charged when
the main cap reaches Vmax. It will now accept current via the resistor and
current will fall off exponentially. by suitable sizing of the two caps and
the R a suitable length 'tail" will be obtainable.

Problems may occur if the IC is "too smart" and tries to put finite delays
into the system between phases. In such a  case you either need a better
battery emulator OR it's not doable due to IC constraints.

Note that the 5 hour fully charged period is a function of at least 2
factors. The LiPo cell will slowly reduce current when held at vmax. The
charger IC will have some C/X value where it deems the current to be low
enough to show that charging is complete. These two interact.

Note that if you want maximum battery life you should set the current tail
cutoff  current as HIGH as possible. eg when current falls to say C/4 you
stop charge. Some use C/10 or C/20. The longer you run the more capacity you
get, but the gains are small and it severely affects battery life.

Note also that for best life you can reduce Vmax by about 0.1V below
manufacturer's maximum recommendation. this also takes something off gross
capacity (maybe 5%-10%) but increases cell lifetime substantially.

Precise results of the above life extension methods depend somewhat on
precise chemistry and manufacturer. Still quite a lot of arcane art in Lixxx
batteries.

Note that when you transition from CC to CV cell is in the 65%-80% charged
range and typically is about 1 hour into charging at C. In you case you get
the remaining 20%-35% over the next 4 hours.

THE optimum charge point for lifetime is at the CC/CV transition. If you
terminate charging there (say when current falls to 90% of CC) you get a
much longer battery life in exchange for reduced capacity.

Terminating lowest cutoff at a slightly higher voltage also helps.


         Russell McMahon

2010\03\02@091910 by Artem Zezyulinskiy

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> I can't just plug a battery and check the current value. It will be tested
> in the production and must be a fast method. The people that will make it, must just verify if
> threre is a known current value. As the current depends on the battery voltage, i can't use it.
>
>    

Hi,

I use a battery to verify the charger circuit. My Li-ion battery has a
voltage range of 2.7-4.2 V... Below this it is depleted. All battery
that is this range is charged with a 1C (fast charge). If the battery
has a voltage near 4.2V => current decrease.

So, you can use a battery to verify your circuit. You must just use a
not completely depleted and not very charged battery. We use a simple
circuit, that discharge the battery to the needed level of voltage. And
it's ok.

A cicuit to emulate the Li-ion battery is very complicated and is costly.

Hope, it is will help you.

Artem

2010\03\02@114751 by Russell McMahon

face picon face
> A circuit to emulate the Li-ion battery is very complicated and is costly.

Did you see my suggestion?

C1 1 x capacitor to ground.
C2 Smaller capacitor via resistor R1 to ground.

Charge C1 to say 2V (switch to 2V supply).

Connect C1 + C2 to device under test.

C1 V is < Vmin so is charged at 0.1C until it reaches Vmin when charge
rate increases to C.
C2 is charging via R1.

C1 reaches Vmax and charger switches to CV mode.
C1 draws no current as it is at Vmax.

C2 charges via R1 and current decreases as V_C2 approaches Vmax.
At some limit set by the charger the charging terminates.

By choosing suitable values of C1, C2 and R1 the whole simulation is
doable with a switch or two added.

Using batteries works - but arguably less well, as they change state
with time and the transition from CCC to CV is not easily handled -
the charger IC may terminate charge as you attempt to swap them over
AND CV termination is not easily tested.


regards


            Russell McMahon

2010\03\03@014233 by kim taylor

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Hi

Sorry I haven't read all responses to this so this might have been suggested but have you read the microchip
document DS51596. This tells you on page nine how to make a battery emulator. Which consists of a 1000uf 10v
alu capacitor and 5ohm 2w resistor.You also need a diode and a 0-6v variable supply.
If you don't have this document it would be well worth getting.
http://ww1.microchip.com/downloads/en/DeviceDoc/51596a.pdf

regards
Mike Seiler


                                           
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2010\03\03@084917 by Peter Bindels

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Hi,

On 1 March 2010 15:15, Ariel Rocholl <RemoveMEforosTakeThisOuTspamarocholl.com> wrote:
> Why do you need to wait 5hs?

5 hectosecond? Is "our" so much work to type between the h and the s
to make clear what you're trying?

2010\03\03@104820 by Russell McMahon

face picon face
> 5 hectosecond? Is "our" so much work to type between the h and the s
> to make clear what you're trying?

I'll not ask 'what's it to you', though one may wonder.
And, he was not the one trying but the one questioning the need.
I wot its' clear what he wanted :-).
I posit that perhaps he missed only an r, or substituted an s for an
r, arguably then a typo, as both would have been a widely accepted
abbreviation.

And, it dinna be hectosecond as anything that large would be capitalised ie Hs.
As in eg MPa, TB, GB.
(Pa having a capital P due to its eponymous nominative association).
The only valid candidate seems to be hour.second. Time squared.
= Distance per acceleration!
Or in MKSA, 5 h.s  =  18,000 metres per g, E&OE..
Definitely too long to wait to test a battery charger.

FWIW

              RM

2010\03\05@085117 by Artem Zezyulinskiy

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Excellent, never seem this before.

Thank you!

Artem ZEZYULINSKIY

Le 03/03/2010 07:42, kim taylor a écrit :
{Quote hidden}

>

2010\03\05@094522 by Michael Rigby-Jones

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face
> Le 03/03/2010 07:42, kim taylor a écrit :
> > Hi
> >
> > Sorry I haven't read all responses to this so this might have been
> suggested but have you read the microchip
> > document DS51596. This tells you on page nine how to make a battery
> emulator. Which consists of a 1000uf 10v
> > alu capacitor and 5ohm 2w resistor.You also need a diode and a 0-6v
> variable supply.
> > If you don't have this document it would be well worth getting.
> > ww1.microchip.com/downloads/en/DeviceDoc/51596a.pdf
> >
> > regards
> > Mike Seiler

> {Original Message removed}

2010\03\05@101747 by Russell McMahon

face picon face
>> > Sorry I haven't read all responses to this so this might have been
>> suggested but have you read the microchip
>> > document DS51596. This tells you on page nine how to make a battery
>> emulator. Which consists of a 1000uf 10v
>> > alu capacitor and 5ohm 2w resistor.You also need a diode and a 0-6v
>> variable supply.

>> > http://ww1.microchip.com/downloads/en/DeviceDoc/51596a.pdf

> Be aware that the 2W rating for the load resistor is rather optimistic.  With 6v from the supply and assuming a silicon diode, the resistor will be seeing ~5.4v across it and dissipating almost 6 Watts.

Also note that the manner of use of the simulator may not be as it appears
The charger is intended to supply 500 mA maximum.
At 4.2 V the 5R resistor passes 840 mA, so the charger cannot pull it
to full battery voltage by itself.
At 500 mA the IC will be limited to 2.5V and, as the preconditioning
voltage is 2.8V, if the external supply is not used the IC will not
pull the resistor to much above 0.25V (assuming C/10 trickle up
current).

So, the external supply provides "makeup" current and the battery
voltage is largely controlled by the external supply. Which is a good
feature, as long as what is happening is understood.

For Icharge = 5-- MA and Itrickle = 50 mA say, then an eg 1 Farad
supercap connected to the battery terminals, when below 2V8 would ramp
by about about 50 mV/second, and when above 2V8 by about 0.5V /
second. So if the cap was precharged to say 2V6 it would charge to 2V8
in 4 seconds and then to 4V2 in (4.2-2.8) / 0.5 = 2.8 more seconds. A
simple analog voltmetetr on the cap or an oscilloscope on
appropriately slow sweep would rapidly show if the system was working
as intended with no intervention other than turning it on.

For a smaller charging current adjust cap size to suit.
A second cap with a series R could then provide a declining CV "tail".

An almost fully automatic functional test in as many or as few seconds
as desired.

Doing the same with a processor controlled load would also be easy and
more flexible.


R

2010\03\05@103230 by Ariel Rocholl

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Nice emulator.

I think you would use it only in case you really need to test the charger IC
is doing what is expected to do in all charge phases, which seems to be more
than Marcelo was apparently asking for (just to confirm the circuit
basically works, looking at charge current in CC stage for instance should
be enough in that case).

Unfortunately we don't have any more answers from him...

2010/3/3 kim taylor <spamBeGonems767210spamBeGonespamhotmail.com>

{Quote hidden}

--
Ariel Rocholl
Madrid, Spain

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