LTC6802-2
15
68022fa
applicaTions inForMaTion
MODES OF OPERATION
The LTC6802-2 has three modes of operation: standby,
measure and monitor. Standby mode is a power saving state
where all circuits except the serial interface are turned off.
In measure mode, the LTC6802-2 is used to measure cell
voltages and store the results in memory. Measure mode
will also monitor each cell voltage for overvoltage (OV)
and undervoltage (UV) conditions. In monitor mode, the
device will only monitor cells for UV and OV conditions.
A signal is output on the SDO pin to indicate the UV/OV
status. The serial interface is disabled.
Standby Mode
The LTC6802-2 defaults (powers up) to standby mode.
Standby mode is the lowest possible supply current state.
All circuits are turned off except the serial interface and
the voltage regulator. The LTC6802-2 can be programmed
for standby mode by setting configuration bits CDC[2:0]
to 0. If the part is put into standby mode while ADC
measurements are in progress, the measurements will
be interrupted and the cell voltage registers will be in an
indeterminate state. To exit standby mode, the CDC bits
must be written to a value other than 0.
Measure Mode
The LTC6802-2 is in measure mode when the CDC bits are
programmed with a value from 1 to 7. The IC monitors
each cell voltage and produces an interrupt signal on the
SDO pin indicating all cell voltages are within the UV and
OV limits. There are two methods for indicating the UV/OV
interrupt status: toggle polling (using a 1kHz output signal)
and level polling (using a high or low output signal). The
polling methods are described in the Serial Port section.
The UV/OV limits are set by the VUV and VOV values in
the configuration registers. When a cell voltage exceeds
the UV/OV limits a bit is set in the flag register. The UV
and OV flag status for each cell can be determined using
the Read Flag Register Group.
If fewer than 12 cells are connected to the LTC6802-2
then it is necessary to mask the unused input channels.
The MCxI bits in the configuration registers are used to
mask channels. If the CELL10 bit is high, then the inputs
for cells 11 and 12 are automatically masked.
The LTC6802-2 can monitor UV and OV conditions con-
tinuously. Alternatively, the duty cycle of the UV and OV
comparisons can be reduced or turned off to lower the
overall power consumption. The CDC bits are used to
control the duty cycle.
To initiate cell voltage measurements while in measure
mode, a Start A/D Conversion and Poll Status command
must be sent. After the command has been sent, the
LTC6802-2 will send the A/D converter status using either
the toggle polling or the level polling method, as described
in the Serial Port section. If the CELL10 bit is high, then
only the bottom 10 cell voltages will be measured, thereby
reducing power consumption and measurement time. By
default the CELL10 bit is low, enabling measurement of all
12 cell voltages. During cell voltage measurement com-
mands, UV and OV flag conditions, reflected in the flag
register group, are also updated. When the measurements
are complete, the part will go back to monitoring UV and
OV conditions at the rate designated by the CDC bits.
Monitor Mode
The LTC6802-2 can be used as a simple monitoring circuit
with no serial interface by pulling the MMB pin low. When
in this mode, the interrupt status is indicated on the SDO
pin using the toggle polling mode described in the Serial
Port section. Unlike serial port polling commands, however,
the toggling is independent of the state of the CSBI pin.
When the MMB pin is low, all the device configuration
values are reset to the default states shown in Table 15
Memory Bit Descriptions. When MMB is held low the
VUV, VOV, and CDC register values are ignored. Instead
VUV and VOV use factory-programmed setings. CDC is
set
to
state 5. The number of cells to be monitored is set
by the logic levels on the WDTB and GPIO pins, as shown
in Table 1.
