BQ27505-J4 Datasheet, PDF (31/38 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

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bq27505-J4
SLVSA40 – DECEMBER 2009
5.7.5 HIBERNATE MODE
HIBERNATE mode should be used when the system equipment needs to enter a low-power state, and
minimal gauge power consumption is required. This mode is ideal when a system equipment is set to its
own HIBERNATE, SHUTDOWN, or OFF modes.
Before the fuel gauge can enter HIBERNATE mode, the system must set the [HIBERNATE] bit of the
CONTROL_STATUS register. The gauge waits to enter HIBERNATE mode until it has taken a valid OCV
measurement and the magnitude of the average cell current has fallen below Hibernate Current. The
gauge can also enter HIBERNATE mode if the cell voltage falls below Hibernate Voltage and a valid
OCV measurement has been taken. The gauge will remain in HIBERNATE mode until the system issues a
direct I²C command to the gauge or a POR occurs. I²C Communication that is not directed to the gauge
will not wake the gauge (or at least for very long).
It is important that /BAT_GD be set to disable status (no battery charging/discharging). This prevents a
charger application from inadvertently charging the battery before an OCV reading can be taken. It is the
system’s responsibility to wake the bq27505-J4 after it has gone into HIBERNATE mode. After waking, the
gauge can proceed with the initialization of the battery information (OCV, profile selection, etc.)
5.8 POWER CONTROL
5.8.1 Reset Functions
When the bq27505-J4 detects a software reset ([RESET] bit of Control( ) initiated), it increments the reset
counter.
5.8.2 WAKE-UP COMPARATOR
The wake up comparator is used to indicate a change in cell current while the bq27505-J4 is SLEEP or
HIBERNATE modes. Operation Configuration uses bits [RSNS1–RSNS0] to set the sense resistor
selection. Operation Configuration also uses the [IWAKE] bit to select one of two possible voltage
threshold ranges for the given sense resistor selection. An internal interrupt is generated when the
threshold is breached in either the charge or discharge direction. Setting both [RSNS1] and [RSNS0] to 0
disables this feature.
Table 5-6. I_WAKE Threshold Settings⁽¹⁾
RSNS1
0
0
0
0
1
1
1
1
RSNS0
0
0
1
1
0
0
1
1
IWAKE
0
1
0
1
0
1
0
1
Vth(SRP–SRN)
Disabled
Disabled
+1.25 mV or –1.25 mV
+2.5 mV or –2.5 mV
+2.5 mV or –2.5 mV
+5 mV or –5 mV
+5 mV or –5 mV
+10 mV or –10 mV
(1) The actual resistance value vs the setting of the sense resistor is not important, just the actual voltage
threshold when calculating the configuration.
5.8.3 FLASH UPDATES
Data Flash can only be updated if Voltage( ) ≥ Flash Update OK Voltage. Flash programming current can
cause an increase in LDO dropout. The value of Flash Update OK Voltage should be selected such that
the bq27505-J4 V_CC voltage does not fall below its minimum of 2.4 V during Flash write operations.
Copyright © 2009, Texas Instruments Incorporated
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FUNCTIONAL DESCRIPTION
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