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uC controlled 3.3V@2A PS unit w/ 2 cell Li-ion Li-pol charger w/ fuel gauge


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Hello, I wanted to put this project into Projects area but couldn't find the link so here it is.
This schematic is part of a bigger project that was never completed. That means it's not complete, meaning that even though I believe that it will work ok, it has not been constructed. The firmware is not done also.
Think of it more as a base or a starting point, if you want to start a project like this.
The main functional requirements were
1. A regulated 3.3V @ 800mA power supply
2. Embedded 2 cell Li-ion battery pack 8.2V or 8.4V
3. Device should be usable even when battery is charging
4. User should have detailed information about battery status
5. Visual indication of status (On wall adapter/charging/charged/fault)
7. SPI interface w/ firmware update capability

Description
This circuit uses the MAX17015 Li-ion multicell battery charger. It charges a battery pack while providing current to the load. When it detects an external power source it switches the load to this source bu means of Q1 and N1 FETs.
The output goes to 2 regulators. The MAX8718 acts as an always-on source for the internal circuits. You can shut it down if you want but I chose not to, because the stand-by current of the circuit is minimum. But if you let it running, finally it will drain the battery because it will switch off when the battery voltage will be less than 4V which is too late. If you don't want this, you can place a switch circuit to the /SHDN pin.
The MAX1791 is a 3.3V/5V regulator and is controlled by the uC.
The uC controlls the charge current by using PWM on pin PB1 or lets the default setting if PB1 is set as input. The default setting is controlled by R9. IINP is an analog voltage depending on the current drawn by the circuit so that the uC can calculate the power consumption. I'm really bored right now, so if you want to see what the other pins do, please read the datasheet of the 17015.
The uC also controls 4 LEDs that indicate the power status of the device. The ISP pins are connected to the system header that goes to the system. That's why it's called a system header.
Finally, the MAX17041 is a really cool fuel gauge. It communicates with the uC using I2C and can give detailed data about the battery status, aging etc.

If you finally decide that you want to build this device, download the evaluation kit manuals for the maxim ICs because they provide schematics and other information about routing etc that will be very helpful.

Bill of Materials
C1 1uF 25V
C2 4,7uF 25V
C3 0.1uF
C4 0.68uF
C5 4.7uF 25V
C6 4.7uF 25V
C7 1uF
C8 0.01uF
C9 10uF 25V
C10 1uF
C11 0.1uF
C12 10uF
C13 1000pF
C14 10nF
C15 1000pF
C16 1uF
C17 10uF
C18 10uF
C19 1uF
C20 0,1uF
C21 220uF 10V
C22 100nF
C23 10uF
D1 BAT54WS
D2 BAT54WS
D3 AC_OK LED WHITE
D4 CH LED ORANGE
D5 FAULT LED RED
D6 CH_OK LED RED
D9 ON LED GREEN
J2 Power adapter mini jack
J3 Battery connector 2 pin
J4 System connector 10 pin
L1 2uH
L2 7uH
N1 IRF9410PBF
N2 2N7002K
N3 FDS8884
N4 FDS6690AS
N5 FDS8958A
P1 FDS8958A
Q1-A IRF7319PBF
Q1-B IRF7319PBF
R1 0.015
R2 100K
R3 1K
R4 100K
R5 49.9K
R6 22.5K
R7 113K
R8 2M
R9 50K
R10 10K
R11 1K
R12 4.7K
R13 660R
R14 150K
R15 660R
R16 0R02
R17 30.1K
R18 10K
R19 130K
R20 30K
R21 100K
R22 660R
R23 4.7K
R24 10K
R25 1K
R26 660R
R28 1M
SW1 ON/OFF Switch Momentary contact N.O.
U1 MAX17015B
U2 MAX8718
U3 ATtiny48 ATtiny48 TQFP-32
U4 MAX17041
U5 MAX1791

post-66992-14279144368436_thumb.png

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