ISL88731C Datasheet, PDF (15/25 Pages) Intersil Corporation – SMBus Level 2 Battery Charger

ISL88731C
Setting Charge Current
ISL88731C has a 16-bit ChargeCurrent register that sets
the battery charging current. ISL88731C controls the
charge current by controlling the CSOP-CSON voltage.
The register’s LSB translates to 10µV at CSON-CSOP.
With a 10mΩ charge current R_sense resistor (RS2 in
”Typical Application Circuit” on page 2), the LSB
translates to 1mA charge current. The ISL88731C
ignores the first 7 LSBs and uses the next 6 bits to
control the current DAC. The charge-current range of the
ISL88731C is 0A to 8.064A (using a 10mΩ current-sense
resistor). All numbers requesting charge current above
8.064A result in a current setting of 8.064A. All numbers
requesting charge current between 0mA to 128mA result
in a current setting of 0mA. The default charge current
setting at Power-On Reset (POR) is 0mA. To stop
charging, set ChargeCurrent to 0. Upon initial power up,
the ChargeVoltage and ChargeCurrent registers are reset
to 0 and the charger is disabled. To start the charger,
write valid numbers to the ChargeVoltage and
ChargeCurrent registers. The ChargeCurrent register
uses the Write-Word protocol (Figure 20). The register
code for ChargeCurrent is 0x14 (0b00010100). Table 3
shows the mapping between the charge current set point
and the ChargeCurrent number. The ChargeCurrent
register can be read back to verify its contents.
The ISL88731C includes a fault limiter for low battery
conditions. If the battery voltage is less than 2.5V, the
charge current is temporarily set to 128mA. The
ChargeCurrent register is preserved and becomes active
again when the battery voltage is higher than 2.7V. This
function effectively provides a foldback current limit,
which protects the charger during short circuit and
overload.
BIT
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
TABLE 3. CHARGE CURRENT (REGISTER 0x14) (10mΩ SENSE RESISTOR, RS2)
BIT NAME
DESCRIPTION
Not used.
Not used.
Not used.
Not used.
Not used.
Not used.
Not used.
Charge Current, DACI 0
0 = Adds 0mA of charger current.
1 = Adds 128mA of charger current.
Charge Current, DACI 1
0 = Adds 0mA of charger current.
1 = Adds 256mA of charger current.
Charge Current, DACI 2
0 = Adds 0mA of charger current.
1 = Adds 512mA of charger current.
Charge Current, DACI 3
0 = Adds 0mA of charger current.
1 = Adds 1024mA of charger current.
Charge Current, DACI 4
0 = Adds 0mA of charger current.
1 = Adds 2048mA of charger current.
Charge Current, DACI 5
0 = Adds 0mA of charger current.
1 = Adds 4096mA of charger current, 8064mA max.
Not used.
Not used.
Not used.
15
FN6978.0
March 8, 2010