SLUSA27 – MARCH 2010
• Special charger voltage offset is 4.2V and default special charger voltage is 4.52V.
• Default charge current will be 325mA, if 68-mΩ sensing resistor is used, since default LOW_CHG=1.
Table 9. Safety Limit Register (READ/WRITE, Write only once after reset!)
Memory location: 06, Reset state: 01000000
Maximum charge current sense voltage: 54.4 mV step (default 0) (2)
Maximum charge current sense voltage: 27.2 mV step (default 1)
Maximum charge current sense voltage: 13.6 mV step (default 0)
Maximum charge current sense voltage: 6.8 mV step (default 0)
Maximum battery regulation voltage: 160 mV step (default 0)
Maximum battery regulation voltage: 80 mV step (default 0)
Maximum battery regulation voltage: 40 mV step (default 0)
Maximum battery regulation voltage: 20 mV step (default 0)
(1) Refer to Table 11
• Maximum charge current sense voltage offset is 37.4 mV (550mA), default at 64.6mV (950mA) and the
maximum charge current option is 1.55A (105.4mV), if 68-mΩ sensing resistor is used.
• Maximum battery regulation voltage offset is 4.2V (default at 4.2V) and maximum battery regulation voltage
option is 4.44V.
• Memory location 06H resets only when VCSOUT drops below VSHORT threshold (typ. 2.05V) or SLRST (pin D4,
for bq24156 only) goes to logic ‘0’. After reset, the maximum values for battery regulation voltage and charge
current can be programmed until any writing to other register locks the safety limits. Programmed values
exclude higher values from memory locations 02 (battery regulation voltage), and from memory location 04
(Fast charge current).
• If host accesses (write command) to some other register before Safety limit register, the safety default values
Charge Current Sensing Resistor Selection Guidelines
Both the termination current range and charge current range depend on the sensing resistor (RSNS). The
termination current step (IOTERM_STEP) can be calculated using Equation 1:
Table 10 shows the termination current settings for two sensing resistors.
Table 10. Termination Current Settings for 68-mΩ and 100-mΩ Sense Resistors
R(SNS) = 68mΩ
R(SNS) = 100mΩ
The charge current step (IO(CHARGE_STEP)) is calculated using Equation 2:
Table 11 shows the charge current settings for two sensing resistors.
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