Specifications

Smart Battery Charger Specification
SBS Implementers Forum -Page 10- Revision 1.1
5.1. Smart Battery Charger Slave Functions (battery or host-to-charger)
The following functions are performed by the charger operating as a SMBus slave device. They are
required functions for a Smart Battery Charger. Any master device, typically the Smart Battery, or the
system host operating as a master, initiates these functions.
5.1.1. ChargingCurrent() (0x14)
Description:
The Battery, System Host or other master device sends the desired charging rate (mA).
Purpose:
The ChargingCurrent() function sets the maximum current that a Smart Battery Charger may deliver to the
Smart Battery. In combination with the ChargingVoltage() function and the battery's internal impedance,
this function determines the Smart Battery Charger's desired operating point. Together, these functions
permit a Smart Battery Charger to dynamically adjust its charging profile (current/voltage) for optimal
charge. The Smart Battery can effectively turn off the Smart Battery Charger by returning 0 for this
function. Smart Battery Chargers may be operated as a constant voltage source above their maximum
regulated current range by returning a ChargingCurrent() value of 65535.
SMBus Protocol: Write Word
Output: unsigned int -- maximum charger output current in mA
Units: mA
Range: data range is 0 to 65,534 mA
output range is defined by the specific implementation, but not less
than 8 bits within the 16 bit field
Granularity: 0.4% (8 bits) or better, monotonic
Minimum Accuracy: +/-5% of the programmatic maximum current while operating
in constant current mode with sufficient input power to regulate to the
ChargingCurrent () value. If CURRENT_NOTREG or
CURRENT_OR bits in ChargerStatus() are set, the charge current may
be less than (programmatic maximum – 5%). See Appendix E for a
discussion on system design alternatives for improved charging
accuracy.
Invalid Data Indication: 65,535 indicates the battery needs constant voltage at the
ChargingVoltage() value.
Note1: This is the same value as that listed in 5.2.1. In the case shown here, the Smart Battery or other
master device writes the value to the Smart Battery Charger.
Note2: The Smart Battery Charger responds to current requests in one of three ways:
• supply the current requested
• supply the programmatic maximum current if the request is greater than its programmatic
maximum and less than 65535
• supply its maximum safe current if the request is 65535
Note3: The SBS specifications allow a Smart Battery to adjust its ChargingCurrent() and
ChargingVoltage() values in response to the Smart Battery Charger’s output. This technique
allows the Smart Battery to fine tune the Smart Battery Charger’s output, thus reducing the
accuracy requirements of the Smart Battery Charger. The Smart Battery’s algorithm must safely
control the Smart Battery Charger’s output under all conditions.