BQ25070 Datasheet, PDF (12/21 Pages) Texas Instruments – 1A, Single-Input, Single-Cell LiFePO4 Linear Battery Charger with 50mA LDO

bq25070
SLUSA66 – JULY 2011
V_COLD
+
V_HOT
+
LDO
TS
R1
TEMP
PACK +
R2
PACK -
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bq25070
For applications that do not require the TS monitoring function, set R1 = 490kΩ and R2 = 100kΩ to set the TS voltage
at a valid level and maintain charging.
Figure 14. NTC Monitoring Function
50 mA LDO (LDO)
The LDO output of the bq25070 is a low dropout linear regulator (LDO) that supplies up to 50mA while regulating
to V_LDO. The LDO is active whenever the input voltage is above V_UVLO and below V_OVP. It is not affected by the
CTRL input. The LDO output is used to power and protect circuitry such as USB transceivers from transients on
the input supply.
CHARGE STATUS INDICATOR (CHG)
The bq25070 contains an open drain CHG output that indicates when charge cycles and faults. When charging a
battery in precharge or fastcharge mode, the CHG output is pulled to GND. Once the BAT output reaches the
overcharge voltage threshold, CHG goes high impedance to signal the battery is fully charged. The CHG output
goes low during battery recharge cycles to signal the host.
Additionally, CHG notifies the host if a NTC temperature fault has occurred. CHG pulses with a period of 100ms
and a 50% duty cycle if a TS faults occurs. Connect CHG to the required logic level voltage through a 1kΩ to
100kΩ resistor to use the signal with a microprocessor. I_CHG must be below 5mA.
The IC monitors the CHG pin when no input is connected to verify if the system circuitry is active. If the voltage
at CHG is logic being drive low when no input is connected, the TS circuit is turned off for a low quiescent current
state. Once the voltage at CHG increases above logic high, the TS circuit is turned on.
SINGLE INPUT INTERFACE (CTRL)
CTRL is used to enable/disable the device as well as select the input current limit, enable/disable charge, extend
the TS operation range and disable V_IN-DPM mode. CTRL is pulled low to enable the device. After the 50μs
deglitch expires, the IC enters the 32ms WAIT state. CTRL may be used to program the bq25070 during this
time. Once t_WAIT expires, the IC starts up. If no command is sent to CTRL during t_WAIT, the IC starts up with a
default 285mA current limit.
Programming the different modes is done by pulsing the CTRL input. See Table 1 for a map of the different
modes. The width of the CTRL pulses is unimportant as long as they are between 50μs and 1000μs long. The
time between pulses must be between 50μs and 1000μs to be properly read. Once CTRL is held low for 2ms,
the number of pulses is passed to the control logic and decoded and then the mode changes. To ensure proper
operation, do not send more than 16 pulses in one programming cycle.
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