BQ24232HA Datasheet, PDF (21/36 Pages) Texas Instruments – USB-Friendly Lithium-Ion Battery Charger

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bq24232HA
SLUSCG4 – MAY 2016
Device Functional Modes (continued)
7.4.1.1 Charge Current Translator
When the charger is enabled, internal circuits generate a current proportional to the charge current at the ISET
input. The current out of ISET is 1/400 (±10%) of the charge current. This current, when applied to the external
charge current programming resistor, R_ISET, generates an analog voltage that can be monitored by an external
host to calculate the current sourced from BAT.
V_ISET = (I_CHARGE / 400) × R_ISET
(5)
7.4.1.2 Battery Detection and Recharge
The bq24232HA 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.
7.4.1.3 Adjustable Termination Threshold (ITERM Input)
The termination current threshold for the bq24232HA 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
(6)
In the other input current limit modes (EN1 ≠ EN2), the termination current value is calculated as:
I_TERM = 0.03 × R_ITERM / R_ISET
(7)
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.
7.4.1.4 Dynamic Charge Timers (TMR Input)
The bq24232HA device contains 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
(8)
t_MAXCHG = 10 × K_TMR × R_TMR
(9)
Leave TMR unconnected to select the internal default timers. Disable the timers by connecting TMR to VSS.
Reset the timers by toggling CE pin.
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.
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.
Copyright © 2016, Texas Instruments Incorporated
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