BQ24230 Datasheet, PDF (20/33 Pages) Texas Instruments – USB-FRIENDLY LITHIUM-ION BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

bq24230
bq24232
SLUS821A – OCTOBER 2008 – REVISED DECEMBER 2008 .......................................................................................................................................... www.ti.com
BATTERY DETECTION AND RECHARGE
The bq2423x automatically detects if a battery is connected or removed. Once a charge cycle is complete, the
battery voltage is monitored. When the battery voltage falls below V_RCH, the battery detection routine is run. The
detection routine first applies I_BAT(DET) for t_DET to see if V_BAT drops below V_LOWV. If not, it indicates that the battery
is still connected, but has discharged. If CE is low, the charger is turned on again to top off the battery. During
this recharge cycle, the CHG output remains high-impedance as recharge cycles are not indicated by the CHG
pin. If the BAT voltage falls below V_LOWV during the battery detection test, it indicates that the battery has been
removed or the protector is open. Next, the precharge current is applied for t_DET to close the protector if possible.
If the battery voltage does not rise above V_RCH, it indicates that the protector is closed, or a battery has been
inserted, and a new charge cycle begins. If the voltage rises above V_RCH, the battery is determined missing and
the detection routine continues. The battery detection runs until a battery is detected.
TERMINATION DISABLE (TD Input, bq24230)
The bq24230 contains a TD input that allows termination to be enabled/disabled. Connect TD to a logic high to
disable charge termination. When termination is disabled, the device goes through the precharge, fast-charge,
and CV phases, then remains in the CV phase. During the CV phase, the charger maintains the output voltage at
BAT equal to V_BAT(REG), and charging current does not terminate. BAT sources currents up to I_CHG or I_IN-MAX,
whichever is less. Battery detection is not performed. The CHG output is high impedance once the current falls
below I_TERM and does not go low until the input power or CE are toggled. When termination is disabled, the
precharge and fast-charge safety timers are also disabled. Battery pack temperature sensing (TS pin
functionality) is also disabled if the TD pin is high and the TS pin is unconnected.
ADJUSTABLE TERMINATION THRESHOLD (ITERM Input, bq24232)
The termination current threshold for the bq24232 is user-programmable. Set the termination current by
connecting a resistor from ITERM to VSS. For USB100, mode (EN1 = EN2 = VSS), the termination current value
is calculated as:
I_TERM = 0.01 × R_ITERM / R_ISET
In the other input current limit modes (EN1 ≠ EN2), the termination current value is calculated as:
I_TERM = 0.03 × R_ITERM / R_ISET
The termination current is programmable up to 50% of the fast-charge current. The R_ITERM resistor must be less
than 15 kΩ. Leave ITERM unconnected to select the default internally set termination current.
DYNAMIC CHARGE TIMERS (TMR Input)
The bq2423x devices contain internal safety timers for the precharge and fast-charge phases to prevent potential
damage to the battery and the system. The timers begin at the start of the respective charge cycles. The timer
values are programmed by connecting a resistor from TMR to VSS. The resistor value is calculated using the
following equation:
t_PRECHG = K_TMR × R_TMR
t_MAXCHG = 10 × K_TMR × R_TMR
Leave TMR unconnected to select the internal default timers. Disable the timers by connecting TMR to VSS.
Note that timers are suspended when the device is in thermal shutdown, and the timers are slowed proportionally
to the charge current when the device enters thermal regulation. For the bq24230, the timers are disabled when
TD is connected to a high logic level.
During the fast-charge phase, several events increase the timer durations.
1. The system load current activates the DPPM loop which reduces the available charging current
2. The input current is reduced because the input voltage has fallen to V_IN(LOW)
3. The device has entered thermal regulation because the IC junction temperature has exceeded T_J(REG)
During each of these events, the internal timers are slowed down proportionately to the reduction in charging
current. For example, if the charging current is reduced by half for two minutes, the timer clock is reduced to half
the frequency and the counter counts half as fast resulting in only one minute of counted time.
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