Rainbow Electronics MAX17047 - Manual (Page 28)

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MAX17047
ModelGauge m3 Fuel Gauge
Note that some registers are application outputs, some
registers are for internal calculations, and some are
characterization setup registers. Registers that are not
internal are described in their own sections. These values
should be stored by the application at periodic intervals.
Some recommended back-up events are:
• End-of-charge
• End-of-discharge
• Prior to application entering shutdown state
The host is responsible for loading the default character-
ization data at first power-up of the device, and restoring
the default characterization data plus learned information
on subsequent power-up events.
Battery Removal and Insertion
The device detects when a cell has been removed or
inserted into the application. This allows the device to
adjust to the new cell to maintain accuracy. The removal-
detection feature also allows the device to quickly warn the
host processor through interrupt of impending power loss
if enabled.
Detection occurs by monitoring the AIN pin voltage com-
pared to the THRM pin. Whenever a cell is present, the
external resistor-divider network sets the voltage of AIN.
When the cell is removed, the remaining external resistor
pulls AIN to the THRM pin voltage level. Whenever V
AIN
< V
THRM
- V
DETF
, the device determines that a cell is
present in the application. If V
AIN
> V
THRM
- V
DETR
, the
device determines that no cell is present at that time.
Cell Insertion (IC Already Powered)
The device is ready to detect a cell insertion if either the
ETHRM or FTHRM bits of the CONFIG register are set
to enable the THRM pin output. See
Figure 37 . When a
cell insertion is detected, the fuel gauge is reset and all
fuel-gauge outputs are updated to reflect the SOC of the
newly inserted cell. This process can take up to 1.845s
(FTHRM = 0) or 620ms (FTHRM = 1) from time of inser-
tion. Note that the device uses the cell voltage as a start-
ing point for the fuel gauge. If the cell voltage is not fully
relaxed at time of insertion, the fuel gauge begins with
some initial error. See the Fuel-Gauge Learning section
for details. The host can disable this feature by clearing
the enBi1 bit in the MiscCFG register.
The device can also be configured to alert the host when
cell insertion occurs. When Bei = 1 in the CONFIG reg-
ister, the device generates an interrupt on the ALRT pin
at the start of the first temperature conversion after inser-
tion. This could take up to 1.4s to occur. This feature is
useful if the application uses more than one cell type and
the IC must be reconfigured at each insertion.
Cell Removal
The device detects a cell removal if either the ETHRM or
FTHRM bits of the CONFIG register are set to enable the
THRM pin output. Cell removal does not affect IC opera-
tion. The device continues to update fuel-gauge outputs.
The host should monitor the Br and Bst bits of the Status
register to determine if the fuel-gauge outputs are valid.
The device can also be configured to alert the host when
cell removal occurs. When Ber = 1 in the CONFIG reg-
ister, the device generates an interrupt on the ALRT pin
at the start of the first temperature conversion after inser-
tion. This could take up to 1.4s to occur. This feature is
useful if the application uses more than one cell type and
the IC must be reconfigured at each insertion.
Fast Detection of Cell Removal
The device can be configured to quickly alert the host of
impending power loss on cell removal. This fast response
allows the system to quickly and gracefully hibernate to
prevent power loss during battery swap. When Ber = 1 and
FTHRM = 1 in the CONFIG register, an interrupt on the
ALRT pin is generated within 100Fs after V
AIN
becomes
greater than V
THRM
- V
DETR
. If fast detection is used, it
is recommended that all other IC interrupts are disabled
to prevent the host from spending time determining the
cause of the interrupt. Fast detection of cell removal has
no affect on fuel-gauge operation, but leaving the exter-
nal resistor-divider active increases current consumption
of the application. See
Figure 38 .