BQ24165_14 Datasheet, PDF (23/38 Pages) Texas Instruments – 2.5A, Dual-Input, Single Cell Switch Mode Li-Ion Battery Charger with Power Path Management

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SLUSAP4B – DECEMBER 2011 – REVISED MARCH 2013
Input Over-Voltage Protection
The bq24165/6/7 provides over-voltage protection on the input that protects downstream circuitry. The built-in
input over-voltage protection to protect the device and other components against damage from overvoltage on
the input supply (Voltage from V_USB or V_IN to PGND). When V_SUPPLY > V_OVP, the bq24165/6/7 turns off the PWM
converter, suspends the charging cycle and turns the battery FET and BGATE on. Once the OVP fault is
removed, the device returns to the operation it was in prior to the OVP fault.
Reverse Boost (Boost Back) Prevention Circuit
Figure 25. Reverse Boost
A buck converter has two operating states, continuous conduction mode (CCM) and discontinuous conduction
mode (DCM). In DCM, the inductor current ramps down to zero during the switching cycle while in CCM the
inductor maintains a DC level of current. Transitioning from DCM to CCM during load transients, slows down the
converter's transient response for those load steps, which can result in the SYS rail drooping. To achieve the
fastest possible transient reponse for this charger, this charger's synchronous buck converter is forced to run in
CCM even at light loads when the buck converter would typically revert to DCM. The challenge that presents
itself when forcing CCM with a charger is that the output of the buck converter now has a power source. Thus, if
the battery voltage, V_BAT, is ever greater than V_BATREG, the inductor current goes fully negative and pushes
current back to the input supply. This effect causes the input source voltage to rise if the input source cannot sink
current. The input over-voltage protection circuit protects the IC from damage however some input sources may
be damaged if the voltage rises. To prevent this, this charger has implemented a reverse boost prevention circuit.
When reverse current is sensed that is not a result of the supplement comparator tripping, this circuit disables
the internal battery FET and changes the feedback point to V_SYSREG for 1ms. After the 1ms timeout, the BATFET
is turned on again and the battery is tested to see if it is higher than V_BATREG (negative current). The reverse
current protection is only active when V_BOVP > VBAT > VBATREG - V_RCH. Having V_BOVP > V_BAT > V_BATREG - V_RCH
and termination disabled (e.g., when CE1 = 1 and CE2 = 0 but VBAT > 4.06V) results in an approximately
100mV, 1000Hz ripple on SYS as seen in Figure 25. With termination enabled and ITERM > 150mA or with a
high line impedance to the battery, the likelihood of activating reverse boost protection circuit is greatly reduced
even if V_BAT > VBATREG - V_RCH. The IC stops charging and can exit charge done after entering reverse boost
due to a SYS load transient causing a battery supplement event. Charging resumes after V_BAT drops below
V_BATREG - V_RCH. Therefore, large SYS load transients may result in the battery reaching slightly less than full
charge.
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