Datasheet

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CE Input (Charge Enable)
Thermal Shutdown and Protection
Timer Fault Recovery
DC-DC CONVERTER
Power Save Mode Operation
bq25010
bq25011
bq25012
SLUS615B – DECEMBER 2004 – REVISED JULY 2007
The CE digital input is used to enable or disable the charge process. A low-level signal on this pin enables the
charge and a high-level signal disables the charge and places the device into a low-power mode. A high-to-low
transition on this pin also resets all timers and timer fault conditions. Note that this applies to both AC and USB
charging.
The bq2501x monitors the junction temperature, T
J
, of the die and suspends charging if T
J
exceeds T
(SHTDWN)
.
Charging resumes when T
J
falls below T
(SHTDWN)
by approximately 15 ° C.
As shown in Figure 5 , bq2501x provides a recovery method to deal with timer fault conditions. The following
summarizes this method:
Condition 1: Charge voltage above recharge threshold (V
(RCH)
) and timeout fault occurs.
Recovery method: bq2501x waits for the battery voltage to fall below the recharge threshold. This could happen
as a result of a load on the battery, self-discharge or battery removal. Once the battery falls below the recharge
threshold, the bq2501x clears the fault and starts a new charge cycle. A POR or CE toggle also clears the fault.
Condition 2: Charge voltage below recharge threshold (V
(RCH)
) and timeout fault occurs.
Recovery method: Under this scenario, the bq2501x applies the I
(FAULT)
current. This small current is used to
detect a battery removal condition and remains on as long as the battery voltage stays below the recharge
threshold. If the battery voltage goes above the recharge threshold, then the bq2501x disables the I
(FAULT)
current
and executes the recovery method described for Condition 1. Once the battery falls below the recharge
threshold, the bq2501x clears the fault and starts a new charge cycle. A POR or CE toggle also clears the fault.
The bq2501x provides a low quiescent-current synchronous DC-DC converter. The internally compensated
converter is designed to operate over the entire voltage range of a single-cell Li-Ion or Li-Pol battery. Under
nominal load current, the device operates with a fixed PWM switching frequency of typically 1 MHz. At light load
currents, the device enters the power save mode of operation; the switching frequency is reduced and the
quiescent current drawn by the converter from the BAT/OUT pin is typically only 15 μ A.
During PWM operation the converter uses a unique fast-response voltage mode controller scheme with input
voltage feedforward to achieve good line and load regulation allowing the use of small ceramic input and output
capacitors. At the beginning of each clock cycle initiated by the clock signal (S), the P-channel MOSFET switch
is turned on and the inductor current ramps up until the comparator trips and the control logic turns off the switch.
The current limit comparator also turns off the switch in case the current limit of the P-channel switch is
exceeded. After the dead time preventing current shoot through the N-cannel MOSFET rectifier is turned on and
the inductor current ramps down. The next cycle is initiated by the clock signal again turning off the N-channel
rectifier and turning on the on the P-channel switch. The g
M
amplifier as well as the input voltage determines the
rise time of the saw-tooth generator and therefore any change in input voltage or output voltage directly controls
the duty cycle of the converter giving a very good line and load transient regulation.
As the load current decreases, the converter enters the power save mode operation. During power save mode,
the converter operates with reduced switching frequency in PFM mode and with a minimum quiescent current to
maintain high efficiency.
Two conditions allow the converter to enter the power save mode operation. One is the detection of
discontinuous conduction mode. The other is when the peak switch current in the P-channel switch goes below
the skip current limit. The typical skip current limit can be calculated as:
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