Datasheet

Low-Dropout Regulators (REG1 and REG2)
Initialization
bq77PL900
www.ti.com ...................................................................................................................................................... SLUS844B – JUNE 2008 – REVISED JANUARY 2009
Table 5. Detection and Recovery Condition Summary (Stand-Alone Mode)
OVERCURRENT IN SHORT CIRCUIT IN
CELL OVERVOLTAGE CELL UNDERVOLTAGE
DISCHARGE DISCHARGE
Detection condition Any cell voltage > V
OV
Any cell voltage < V
UV
(V
SRP
– V
SRN
) > V
OCD
(V
SRP
– V
SRN
) > V
SCD
CHG FET ON → OFF ON ON → OFF ON → OFF
DSG FET ON ON → OFF ON → OFF ON → OFF
SOR = 0: Attach a SOR = 0: Attach a
All cell voltage < All cell voltages > charger charger
Recovery condition 1
(V
OV
– Δ V
OVH
) (V
UV
+ Δ V
UVH
) SOR = 1: OC condition is SOR = 1: SC condition is
released released
All cell voltages > V
UV
Recovery condition 2 AND
PACK+ – V
BAT
> 0.1 V
CHG FET OFF → ON ON OFF → ON OFF → ON
DSG FET ON OFF → ON OFF → ON OFF → ON
Table 6. Detection and Recovery Condition Summary (Host-Control Mode)
OVERCURRENT IN SHORT CIRCUIT IN
CELL OVERVOLTAGE CELL UNDERVOLTAGE
DISCHARGE DISCHARGE
Detection condition Any cell voltage > V
OV
Any cell voltage < V
UV
(V
SRP
– V
SRN
) > V
OCD
(V
SRP
– V
SRN
) > V
SCD
CHG FET ON → OFF ON ON → OFF ON → OFF
ON → OFF
DSG FET ON ON → OFF ON → OFF
(UVFET_DIS = 0)
All cell voltage < V
OV
All cell voltage >
Recovery condition 1 None None
(ignore the hysteresis) (V
UV
+ Δ V
UVH
)
All cell voltage > V
UV
Recovery condition 2 AND
VPACK – VBAT > 0.1 V
CHG FET
(1)
OFF → ON ON OFF → ON OFF → ON
DSG FET
(1)
ON OFF → ON OFF → ON OFF → ON
(1) Host is required to set and clear LTCLR, then turn on the FETs.
The bq77PL900 has two low dropout (LDO) regulators that provide power to both internal and external circuitry.
The inputs for these regulators can be derived from the PACK or BAT terminals (see the Initialization section for
further details). The output of REG1 is typically 5 V, with a minimum output capacitance of 2.2 µ F required for
stable operation. It is also internally current-limited. During normal operation, the regulator limits the output
current, typically to 25 mA. The output of REG2 is typically 3.3 V, also with a minimum output capacitance of 2.2
µ F for stable operation, and it is also internally current-limited.
Until the internal regulator circuit is correctly powered, the DSG and CHG FETs are driven OFF.
From a shutdown situation, the bq77PL900 requires a voltage greater that the start-up voltage (V
STARTUP
) applied
to the PACK pin to enable its integrated regulator and provide the regulator power source. Once the REG1 and
REG2 outputs become stable, the power source of the regulator is switched to BAT.
After the regulators have started, they then continue to operate through the BAT input. If the BAT input is below
the minimum operating range, then the bq77PL900 does not operate until the supply to the PACK input is
applied.
If the voltage at REG2 falls, the internal circuit turns off the CHG and DSG FETs and disables all controllable
functions, including the REG1, REG2, and TOUT outputs.
Copyright © 2008 – 2009, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Link(s): bq77PL900