BQ24085 Datasheet, PDF (9/34 Pages) Texas Instruments – 750 mA SINGLE-CHIP Li-Ion/Li-Pol CHARGE MANAGEMENT IC WITH THERMAL REGULATION

bq24085, bq24086
bq24087, bq24088
www.ti.com .................................................................................................................................................... SLUS784B – DECEMBER 2007 – REVISED MAY 2008
FUNCTIONAL DESCRIPTION
The charge current is programmable using external components (R_ISET resistor). The charge process starts when
an external input power is connected to the system, the charger is enabled by CE = LO and the battery voltage is
below the recharge threshold, V(BAT) < V_(RCH). When the charge cycle starts a safety timer is activated, if the
safety timer function is enabled. The safety timer timeout value is set by an external resistor connected to TMR
pin.
When the charger is enabled two control loops modulate the battery switch drain to source impedance to limit the
BAT pin current to the programmed charge current value (charge current loop) or to regulate the BAT pin voltage
to the programmed charge voltage value (charge voltage loop). If V_(BAT) < V_(LOWV) (3 V typical) the BAT pin
current is internally set to 10% of the programmed charge current value.
A typical charge profile is shown below, for an operation condition that does not cause the IC junction
temperature to exceed T_J(REG), (112°C typical).
V_O(REG)
Pre-
Conditioning
Phase
I_O(OUT)
Current
Regulation
Phase
Voltage Regulation and
Charge Termination
Phase
DONE
FAST-CHARGE
CURRENT
Battery Current,
I_(BAT)
v_(LOWV)
Battery Voltage,
V_(BAT)
Charge
Complete
Status,
Charger
Off
I_O(PRECHG), I_(TERM)
PRE-CHARGE
CURRENT AND
TERMINATION
THRESHOLD
T_(PRECHG)
T_(CHG)
Figure 10. Charging Profile With T_J(REG)
DONE
If the operating conditions cause the IC junction temperature to exceed T_J(REG), the charge cycle is modified, with
the activation of the integrated thermal control loop. The thermal control loop is activated when an internal
voltage reference, which is inversely proportional to the IC junction temperature, is lower than a fixed,
temperature stable internal voltage. The thermal loop overrides the other charger control loops and reduces the
charge current until the IC junction temperature returns to T_J(REG), effectively regulating the IC junction
temperature.
Copyright © 2007–2008, Texas Instruments Incorporated
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