SM3320-BATT-EV-NOPB Datasheet, PDF (15/21 Pages) Texas Instruments – AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design

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Charging a Li-ion Battery
14.4 Function: send_i2c_command(char number)
Sends an I2C communication string. Each byte sent is stored in the global array “i2c_buffer”. The
argument “number” indicates how many bytes from the buffer will be sent (starting with i2c_buffer[0]).
Refer to the data sheet and I2C and SM_bus standards documentation for complete protocol information.
The main use of this function is to change the voltage limit settings in the SM72442.
14.5 Function: Set_Voutmax()
This will read the “voutmax” variable set in the main and sends the proper I2C command to the SM72442
to regulate that voltage.
14.6 Function: Check_low_current()
This function is called by the “Main” function and controls the start-up circuitry to force the duty cycle of
the converter up if the current becomes close to 0.
Figure 18 summarizes the overall structure of the program: (arrows from the main represent calls to the
functions)
Check_Lead_Acid
- Sense battery voltage
- Return value of battery state
Check_low_current
Check if current is very low
Init()
Setup
registers
Main
- Call proper functions
- Set Voltage Levels
- Enable/disable SM72442
Set_Vout_max
Setup I2C communication words to
change the output voltage level
controlled by the SM72442
Get_i2c_data
- Send request for data through I2C
- Recover and parse data in global variable
Send_i2c_command
Send the content of the communication
buffer on the I2C bus
Figure 18. Microcontroller Code Block Diagram
15 Charging a Li-ion Battery
Although this evaluation board was specifically designed for charging a lead-acid battery, it can be re-
configured to accommodate the Li-ion chemistry battery through a combination of hardware and software
changes. In order to re-configure the board for Li-ion charging, the following steps need to be done:
1. The voltage sensing resistors R103, R104, R51, R52 and R53 and OVP resistors R71 and R72 need
to be changed to the proper values. It is critical for this application that the full scale voltage range for
sensing is as close as possible to the voltage of the battery to maximize the resolution of the sensed
voltage. The level of the OVP circuit needs to be scaled so that it does not trigger when the battery
approaches full SOC but at a voltage slightly higher.
SNOSB76C – December 2010 – Revised May 2013
AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference
15
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