Datasheet

DS2780 Standalone Fuel Gauge IC
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fuel gauge data to EEPROM, but some data loss can occur depending on the timing of the protection event and the
backup. When the protection circuit is connected directly to the battery the protection is absolute, no charging will
occur during a protection event. With the protection circuit located outside, see Figure 3, the DS2780 will remain
powered up during a protection event. The disadvantage to this configuration is that you run the risk of
overcharging the battery by creating an unintentional charge path from PK+ to DATA or PIO (V
PK+
> V
CELL
+ V
DIODE
).
Communication to the DS2780 is broken during a protection event regardless of protector location.
POWER MODES
The DS2780 has two power modes: ACTIVE and SLEEP. On initial power up, the DS2780 defaults to ACTIVE
mode. While in ACTIVE mode, the DS2780 is fully functional with measurements and capacity estimation
continuously updated. In SLEEP mode, the DS2780 conserves power by disabling measurement and capacity
estimation functions, but preserves register contents. SLEEP mode is entered under two different conditions and
an enable bit for each condition makes entry into SLEEP optional. SLEEP mode can be enabled using the Power
Mode (PMOD) bit or the Under Voltage Enable (UVEN) bit.
The PMOD type SLEEP is entered if the PMOD bit is set AND DQ is low for t
SLEEP
(2s nominal). The condition of
DQ low for t
SLEEP
can be used to detect a pack disconnection or system shutdown, in which no charge or discharge
current will flow. A PMOD SLEEP condition transitions back to ACTIVE mode when DQ is pulled high.
The second option for entering SLEEP is an under voltage condition. When the UVEN bit is set, the DS2780
transitions to SLEEP if the voltage on VIN is less than V
SLEEP
(2.45V nominal) AND DQ is stable at a low or high
logic level for t
SLEEP
. An under-voltage condition occurs when a pack is fully discharged, where loading on the
battery should be minimized. UVEN type SLEEP relieves the battery of the I
ACTIVE
load until communication on DQ
resumes.
NOTE: PMOD and UVEN SLEEP features must be disabled when a battery is charged on an external charger that
does not connect to the DQ pin. PMOD SLEEP can be used if the charger pulls DQ high. UVEN SLEEP can be
used if the charger toggles DQ. The DS2780 remains in SLEEP on a charger that fails to properly drive DQ and
therefore does not measure or accumulate current when a battery is charged.
INITIATING COMMUNICATION IN SLEEP
When beginning communication with a DS2780 in PMOD SLEEP, DQ must be pulled up first and then a 1-Wire
Reset pulse must be issued by the master. In UVEN SLEEP, the procedure depends on the state of DQ when
UVEN SLEEP was entered. If DQ was low, DQ must be pulled up and then a 1-Wire Reset pulse must be issued
by the master as with PMOD SLEEP. If DQ was high when UVEN SLEEP was entered, then the DS2780 is
prepared to receive a 1-Wire reset from the master. In the first two cases with DQ low during SLEEP, the DS2780
does not respond to the first rising edge of DQ with a presence pulse.
VOLTAGE MEASUREMENT
Battery voltage is measured at the VIN input with respect to VSS. It has a range of 0V to 4.992V (pin voltage
limited to 4.5V) and a resolution of 4.88mV. The measurement is stored in the VOLTAGE register in two’s
compliment form and is updated every 440ms. Voltages above the maximum register value are reported at the
maximum value; voltages below the minimum register value are reported at the minimum value. The format of the
voltage register is shown in Figure 4.
Figure 4. Voltage Register Format
VOLT
Read Only
MSB—Address 0Ch LSB—Address 0Dh
S 2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
X X X X X
MSb LSb MSb LSb
“S”: sign bit(s), “X”: reserved
Units: 4.88mV