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Adafruit USB Li-Ion/LiPoly Charger - v1.2
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Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Wed Dec 12, 2018 10:51 am

Good day Adafruit community

I am having some difficulty understanding and extracting the information i need from the datasheet for the MCP73833 chip that this charge controller is based on. The datasheet is available as a link on the same adafruit webpage as the product itself:

https://www.adafruit.com/product/259

-I would like to know what is the threshold charge current that will cause the device to automatically terminate charging a? Under the "DC Characteristics" , 'Charge termination' is 5% (page 4) Does this mean,with Prog at 1kohm, that when the charge current is 1000*5%=50mA?
If PROG was 2kohm will the charge termination ratio change to 7.5% ? And 5kohm 10% etc ? Since the adafruit board already comes with a 2kohm resistor soldered on

-At what voltage will the charge controller automatically begin charging the battery after it terminates charging? The datasheet states it has "Automatic Recharge" at 94% (page 4). Does this mean if i have the PROG resistor to be 1kohm than that threshold voltage is 4.2*94%=3.948V?
For a 2kohm PROG what will the % be, will still be 94% or will it be 96.5%

-If there is no power applied to the charge controller and the battery is supplying the load via the charge controller, is there a threshold voltage that when reached will result in this controller automatically cutting of the battery from supplying the load? There datasheet states that it has "Under voltage lockout". What is this threshold voltage? Where is it indicated in the datasheet ? What is ment by Vstart and Vstop (page 3)?

-Is there a temperature threshold sensed by the charge controller that when reached will automatically cut off the charger from charging the battery? If so is this the die temperature 150℃ (page 5)

-Is there a threshold temperature that when reached will prevent the battery from supplying the load? Is that when the device goes into shutdown mode?

Can some one please assist by pointing out if i am correct if not please correct me and please point out where these values are shown on the datasheet. Thank you in advance.

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Thu Dec 13, 2018 3:05 am

Alli wrote:I would like to know what is the threshold charge current that will cause the device to automatically terminate charging a?

The constant-voltage phase of the charging cycle ends when the current flowing into the LiPo falls to 5% of the constant-current level. If you've configured the MCP73833 for 100mA during the constant-current phase, the end-of-charging-cycle current level will be 5mA.

Alli wrote:At what voltage will the charge controller automatically begin charging the battery after it terminates charging?

About 3.95V for a LiPo whose full-charge voltage is 4.2V.

Alli wrote:If there is no power applied to the charge controller and the battery is supplying the load via the charge controller,

That isn't possible. The MCP73833 sends power to the LiPo, but the LiPo doesn't send power back.

As far as the MCP73833 is concerned, the LiPo and the circuit powered by the LiPo are two loads operating in parallel. The MCP73833 can't control the current flowing from the LiPo to the load because the LiPo's positive output terminal is usually VCC for the load that takes power from the LiPo.

Most LiPos have built-in protection circuits that will cut power when the LiPo voltage falls below 2.5V, but you'll have to check the datasheet for the LiPo you're using to make sure.

Alli wrote:There datasheet states that it has "Under voltage lockout". What is this threshold voltage?

That means the MCP73833 will automatically shut off if its input voltage falls below 3.3V, and won't try to turn on again until its input voltage rises above 3.4V.

Assuming the MCP73833's input voltage is higher than 3.4V, the MCP73833 won't start a charging cycle unless its input voltage is at least 150mV higher than the LiPo voltage.

Alli wrote:Where is it indicated in the datasheet ?

Section 4.1, page 11 in the copy of the datasheet I have.

Alli wrote:What is ment by Vstart and Vstop (page 3)?

Vstop means the MCP73833 will automatically shut off if its supply voltage falls below 3.3V. Vstart means it won't turn on unless the supply voltage is at least 3.4V.

Alli wrote:Is there a temperature threshold sensed by the charge controller that when reached will automatically cut off the charger from charging the battery?

Yes, but the sensor isn't built into the MCP73833. It's a thermistor built into the LiPo.

Alli wrote:If so is this the die temperature 150℃ (page 5)

Those are the temperatures where the MCP73833 is guaranteed to operate as specified in the datasheet. They don't have anything to do with the LiPo, and they don't have any control over the charging cycle.

Silicon behaves differently as the temperature changes, becoming more conductive as it gets hotter, and less conductive as it gets colder. The MCP73833 is specified to function at all between the temperatures of -40C and 125C, and to operate within the parameters specified in the datasheet between the temperatures of -40C and 85C. The physical chip can be stored between the temperatures of -65C and 150C without being damaged.

Alli wrote:Is there a threshold temperature that when reached will prevent the battery from supplying the load?

Not in the MCP73833. As mentioned above, the MCP73833 doesn't have any control over the connection between the LiPo and the load. The LiPo's internal protection circuit might have a high-temperature cutoff, but that's something you'll find in the LiPo's datasheet.

Alli wrote:Is that when the device goes into shutdown mode?

The 'shutdown mode' state shown in section 4.0 of the datasheet has no connection to temperature. The MCP73833 always shuts down if its input voltage is less than 3.3V (Vstop), and will optionally shut down any time its input voltage is less than 150mV higher than the LiPo voltage.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Thu Dec 13, 2018 8:39 am

Good day Mike

Thank you very much for taking the time to reply to all my questions. It has helped me determine if i am on the right track and where i have strayed from it.
I would like clarity on a few points you mentioned:


Yes, but the sensor isn't built into the MCP73833. It's a thermistor built into the LiPo.

I saw on page 17 section 5.1.4, that the NTC will cut off charge to the battery when its voltage is outside of the specified range But it does not specify the actual temperature vlues representing that voltage range. Is it mentioned elsewhere?

The constant-voltage phase of the charging cycle ends when the current flowing into the LiPo falls to 5% of the constant-current level. If you've configured the MCP73733 for 100mA during the constant-current phase, the end-of-charging-cycle current level will be 5mA.


If PROG was 2kohm will the charge termination ratio change to 7.5% ? And 5kohm 10% etc ? Since the adafruit board already comes with a 2kohm resistor soldered on

I tested the resistor used in the case of the USB charger from adafruit to be 2kohms which means the charge current is 200mA. Now under the section where is specifies the current level before charge termination occurs, what will that threshold current be i.e 5% or 7.5% for a 200mA charge current ?


About 3.95V for a LiPo whose full-charge voltage is 4.2V.

How did you come to this voltage value? Did you use the 94% recharge voltage threshold or the 96.5%? which one of the two would apply if the charge current was selected to be 200mA and the Vreg to be 4.2V? How do you know which one applies?

Vstop means the MCP73833 will automatically shut off if its supply voltage falls below 3.3V. Vstart means it won't turn on unless the supply voltage is at least 3.4V.

What is the benefit of this feature? Whats the purpose of it?
When it is said that the MCP73833 shuts off does that it means it does not charge the batteries with the low supply voltage? (but the battery will still discharges into the load as you mentioned that the Charger has no control over the battery supplying the load)

i would like to know how to use the STAT1 and STAT2 pins. i would like to connect them to my micro-controller. Can i remove the LEDs and connect the pins as a Digital inputs to my micro-controller? The datasheet says that they are "open drain logic" section 3.2. If i understood section 5.2.1 correctly, if i connected the STAT pins to my micro-controller, with pull up resisters, i would see the state of STAT 1 go Low while STAT2 remains High than the battery is being charged? And if STAT1 remains High but STAT2 goes Low than battery has completed charging?

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Fri Dec 14, 2018 1:29 am

Alli wrote:I saw on page 17 section 5.1.4, that the NTC will cut off charge to the battery when its voltage is outside of the specified range But it does not specify the actual temperature vlues representing that voltage range. Is it mentioned elsewhere?

You'd have to calculate the temperatures from the thermal response curve of a 10k thermistor and the MCP73833's 0.25v/1.2V cutoff thresholds. The corresponding thermistor values would be 5k and 24k.

Alli wrote:tested the resistor used in the case of the USB charger from adafruit to be 2kohms which means the charge current is 200mA. Now under the section where is specifies the current level before charge termination occurs, what will that threshold current

For the version of the MCP73833 we use, it would be 5% of 200mA, or 10mA.

Alli wrote:How did you come to this voltage value? Did you use the 94% recharge voltage threshold or the 96.5%?

94% of 4.2V.

Alli wrote:which one of the two would apply if the charge current was selected to be 200mA and the Vreg to be 4.2V? How do you know which one applies?

The datasheet lists two percentages because there are different versions of the MCP73833 for different LiPo chemistries. For any version, the percentage is fixed and independent of the charging current. For the version of the MCP73833 we use, the percentage is 94% no matter what current-setting resistor value you choose.

Alli wrote:What is the benefit of this feature?

It's simply good planning.

Every circuit is designed for a certain set of operating conditions. One of those conditions is the minimum voltage necessary for the circuit to work at all. Responsible circuit designers plan for that, and include a circuit that checks for the minimum necessary operating voltage before letting the rest of the circuit start up. It's standard practice to design those circuits with hysteresis, or a gap between the minimum-turn-on voltage and the mandatory-turn-off voltage. Cutoff circuits with a single threshold become unstable if you hold the supply voltage too close to the threshold value.

The datasheet's job is to describe the chip's specified behavior, and the startup/shutoff circuit is a feature designers need to know.

Alli wrote:When it is said that the MCP73833 shuts off does that it means it does not charge the batteries with the low supply voltage?

Yes.

Alli wrote:i would like to know how to use the STAT1 and STAT2 pins

See table 5.1 on page 13.

Alli wrote:Can i remove the LEDs and connect the pins as a Digital inputs to my micro-controller?

Yes, but they'll need pull-up resistors. Open-drain output means that instead of producing a high or low output voltage, the pin controls a high or low resistance connection to GND. If a pin is listed as 'Hi-Z' in table 5.1, it means the resistance to GND is very high (usually around 10M). Where the pins are listed as 'L', it means the resistance to GND is low.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Sun Dec 16, 2018 4:38 am

@Mike

Okay perfect. Thanks once again for taking the time to reply to all my questions. It was great help.

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Thu Jan 24, 2019 11:05 am

@Mike

I have come across one more thing. It seems that battery with an NTC wire is not necessary since this charge controller has a built in NTC for battery temperature monitoring. That being said, would it still be possible to use a 3.7V cell that has 3 wires, the third being an NTC, can i still use such a cell with this charge controller? If so, where would the 3rd wire connect to?

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Fri Jan 25, 2019 2:24 am

The charger doesn't have its own thermistor, but it does have a space where you can connect a thermistor. We put a standard 10k resistor on the board so the MCP73833 would see a reasonable value.

Even if you have a LiPo with a built-in thermistor, connecting it is optional. High-current chargers monitor the cell temperature because heat is an early warning sign that a cell could go boom, but a cell charging at moderate current shouldn't get warm enough to notice.

If you have a 3-wire LiPo and only connect the positive and negative terminals to the charger, the LiPo will charge normally. If you do want to connect the thermistor, remove the surface-mount 10k resistor or cut one of the traces that connects it to the THERM pads, then solder the LiPo's thermistor wire into the hole next to the silkscreen marking.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Fri Jan 25, 2019 2:52 am

@Mike

Great, thanks again Mike.

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Mon Feb 04, 2019 4:11 pm

@Mike

I apologize in advance if this is a silly question but is it necessary to remove the LEDs associated with STAT1 and STAT2? They are quite tiny and I am afraid i may not be able to remove them without damaging the board if I am not too careful. There are separate STAT pins on the side of the board so can i just connect those to my micro-controller without removing the LEDs?

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Tue Feb 05, 2019 4:07 am

If you don't specifically want to remove the LEDs, you can leave them as-is and use the STAT pins at the edge of the board. The signals are the same, and the pins are easier to get to.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Tue Feb 05, 2019 9:52 am

@Mike
Excellent. Thanks Mike.

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Thu Feb 07, 2019 1:57 pm

@Mike

What is the state of the STAT pins when there is no supply voltage connected to the charge controller? (When there is a supply voltage the STAT pins have Hi-Z and L to indicate chargin and charge complete etc but what are their states when there no supply voltage connected i.e the battery is not charging etc)

I know that this charge controller is able to tell if the battery voltage has reached a low state and that it needs to be charged. Is there any way that it indicates that the voltage of the battery is low, similar to the leds that indicate when the battery is charging and when charging is complete. Is there any point that i can tap off to feed into my micro-controller that would indicate that the battery voltage is low?

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Fri Feb 08, 2019 1:59 am

Alli wrote:What is the state of the STAT pins when there is no supply voltage connected to the charge controller?

Off.

The chip's pin states aren't defined when the chip doesn't have power. That would probably put them in a high-impedance state, but there are no guarantees for that. The good news is that it shouldn't matter: the LEDs on the charger are connected to the MCP73833's supply power, so there's no voltage or current to the STAT pins when the MCP73833 doesn't have power.

Alli wrote:Is there any point that i can tap off to feed into my micro-controller that would indicate that the battery voltage is low?

An MCP73833 without power won't have anything you can use.

You could use an external voltage monitor like the KA75330:

https://www.adafruit.com/product/3428

whose output goes low when its input falls below 3.3V. The sensor itself operates down to 0.8V, so its signal will be valid before a microcontroller boots and after it shuts down from low voltage.

You could also put a 150k-150k voltage divider between the BAT pin and GND, and connect the center to an ADC pin on the microcontroller. Read the divider voltage every minute or so and you'll have a good track of the LiPo's discharge curve.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Sat Feb 09, 2019 10:53 am

@Mike
Thanks again.

You could also put a 150k-150k voltage divider between the BAT pin and GND, and connect the center to an ADC pin on the microcontroller.


Why this specific value of resistance?

Alli
 
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by luke1976 on Sat Feb 09, 2019 12:48 pm

Hello, I don't know if anyone will see this as the thread is so old, but I have this USB charger (https://www.adafruit.com/product/259), but it is not charging the battery. Power flows through so when plugged in, the device works, but the battery (Adafruit 2500mAh LiPo Battery 3.7V) is not charging, so does not work when not plugged in.

I have had my speaker project half made for far too long, but don't know how to fix this issue, and I would love to get it over the line!

Could anybody suggest why this might be the case?

Much appreciated.

Luke

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