SM3320-BATT-EV/NOPB National Semiconductor, SM3320-BATT-EV/NOPB Datasheet - Page 11

• Manufacturer Part Number: SM3320-BATT-EV/NOPB
• Description: EVAL CHARGE CONTROL BATTERY
• Manufacturer: National Semiconductor
• Series: SolarMagic™r

Specifications of SM3320-BATT-EV/NOPB

• Main Purpose: Power Management, Battery Charger
• Embedded: No
• Utilized Ic / Part: SM72295, SM72442
• Primary Attributes: Lead Acid, Solar Power
• Secondary Attributes: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Charging a Li-ion Battery
Although this evaluation board was specifically designed for
charging a lead-acid battery, it can be re-configured to ac-
commodate the Li-ion chemistry battery through a combina-
tion 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.
R103 and R104 set the voltage at the input of the
microcontroller. The voltage at the input of the
microcontroller is:
R103 and R104 should be chosen so that the maximum
expected battery voltage creates a voltage close to 5V to
maximize resolution (but less than 5V to avoid saturating
the measure).
R51, R52 and R53 are for the voltage measurement of
the SM72442 and should be modified in the same way:
R21 needs to be set to zero ohm (short).
FIGURE 20. Microcontroller Code Block Diagram
11
2.
3.
4.
5.
Once the values are picked, the proper threshold needs
to be programmed through I2C. The maximum level
(0x3FF) is now V
Finally, the overvoltage protection should be adjusted to:
The OVP level is set at V
The proper voltage setpoints and charging curve need to
be programmed in the microcontroller. The initial voltage
limit is set by R28 and R38. Voltage limit setpoint is
AVOUT = A0. Once overridden through I2C, the voltage
at A0 is not used anymore. Hence, there is the option of
setting the value through resistors R28 and R38 or by
programming it from the microcontroller into SM72442
through I2C each time the SM72442 is reset/powered.
Proper current limits also need to be set if required by the
battery model. The current limit value is set when the
voltage at pin 3 of U11A equals the voltage at at pin 2.
Hence, R111 and R112 will need to be adjusted
accordingly.
The software needs to be changed to follow the Li-ion
charge control profile: battery voltage is set either by
hardware as stated above, which requires no action from
the software, or it is set from the microcontroller through
the I2C interface similar to the Lead Acid battery.
Finally, the software needs to include the full State-Of-
Charge charge cut-off: When the battery reaches its full
voltage and current has dropped below 500mA (can vary
depending on battery), charge is cut-off and the battery
is considered fully charged (no trickle charge of Li-ion
batteries should be done). It is important to remember
that current can drop below 500mA during the charge
when solar power becomes unavailable (low light
intensity). Therefore the charge cut-off needs to be
programmed to occur only when the battery voltage is at
AVOUT
= 5V at the input of the SM72442.
HARD_OVP
30138226
= 5v.
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