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| BQ24085_17 Datasheet, PDF (11/42 Pages) Texas Instruments – 750-mA Single-Chip Li-Ion and Li-Pol Charge Management IC With Thermal Regulation | |||
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8 Detailed Description
bq24085, bq24086, bq24087, bq24088
SLUS784E â DECEMBER 2007 â REVISED DECEMBER 2015
8.1 Overview
The charge current is programmable using external components (RISET 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 for an operation condition that does not cause the IC junction temperature to exceed
TJ(REG), (112°C typical), is shown in Figure 8.
VO(REG)
Pre-
Conditioning
Phase
IO(OUT)
FAST-CHARGE
CURRENT
Current
Regulation
Phase
Voltage Regulation and
Charge Termination
Phase
DONE
Battery Current,
I(BAT)
v(LOWV)
Battery Voltage,
V(BAT)
Charge
Complete
Status,
Charger
Off
IO(PRECHG), I(TERM)
PRE-CHARGE
CURRENT AND
TERMINATION
THRESHOLD
T(PRECHG)
T(CHG)
Figure 8. Charging Profile With TJ(REG)
DONE
If the operating conditions cause the IC junction temperature to exceed TJ(REG), the charge cycle is modified, with
the activation of the integrated thermal control loop. The thermal control loop is activated when a internal junction
temperature monitoring voltage is lower than a fixed, temperature stable internal voltage. The junction
temperature monitoring voltage is inversely proportional to the IC junction temperature. The thermal loop
overrides the other charger control loops and reduces the charge current until the IC junction temperature returns
to TJ(REG), effectively regulating the IC junction temperature.
Copyright © 2007â2015, Texas Instruments Incorporated
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Product Folder Links: bq24085 bq24086 bq24087 bq24088
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