BQ29311_15 Datasheet, PDF (10/24 Pages) Texas Instruments – FOUR-CELL LITHIUM-ION

Not Recommended for New Designs
bq29311
SLUS487D − DECEMBER 2001 − REVISED NOVEMBER 2003
www.ti.com
FUNCTIONAL DESCRIPTION
INTEGRATED REGULATOR
The input for this regulator is derived from the battery cell
stack or the pack positive terminal, with a valid range of
V_SD to 25 V. These two source inputs are ORed internally.
An external diode is required to protect uncontrolled
charging. The output is typically 3.3 V ±5% (T_A = −25_C to
85_C) with a maximum output current of 25 mA. The output
capacitance for stable operation is typically 1 µF. The
output voltage line regulation is ±20 mV (max) between
V_SD and 25 V. The load regulation is ±20 mV (max) over
the current range of 0. 1 mA to 25 mA.
The regulator output starts up only when VPACK reaches
the valid input voltage. After this voltage is reached, the
bios of the regulator is supplied through VBAT from the
battery, even if VPACK voltage is removed.
SHUTDOWN AND BROWNOUT
If the voltage at VBAT falls below 7.975 V± 5%(default), the
bq29311 sets the BRWO bit to 1 in STATUS (b4) and
triggers the XALERT output. The value in the SDV register
(b4−b7) determines the threshold value and this can be
programmed from 7.975 V to 12.475 V in 0.3-V steps (with
an accuracy of ±5% at the falling edge) and has 50 mV
±30% of hysteresis.
The overcurrent, overload, and short-circuit thresholds are
set in the OCVD/C and SCV registers with defaults of
50 mV and 100 mV respectively. The individual
overcurrent (charge) , and overload (discharge) thresholds
can be programmed from 50 mV to 205 mV in 5-mV steps
with a hysteresis of 10 mV ±30%. The single short-circuit
threshold can be programmed from 100 mV to 475 mV in
25-mV steps with a hysteresis of 50 mV ±20%.
OVERCURRENT, OVERLOAD AND
SHORT-CIRCUIT DELAY
The overcurrent and overload delays allow the system to
momentarily accept a high current condition. The default
overcurrent delay is 1 ms. The delay time can be increased
via the OCD register, where the overcurrent and overload
delays can be independently defined. The OCD register
can be programmed for a range of 1 ms to 31 ms with steps
of 2 ms.
The short-circuit delay has a default value of 0 ms and is
also programmable in the SCD register. This register can
be programmed from 0 to 915 µs with steps of 61 µs.
OVERCURRENT, OVERLOAD AND
SHORT-CIRCUIT RESPONSE
Reading the STATUS register clears XALERT in a
brownout, but OCL (CONTROL, b0) must be taken from
0 to 1 to 0; then STATUS must be read, to clear the BRWO
bit.
If the voltage at VBAT is below 6.475V ±5% (default) the
regulator can be shut down. The value in the SDV register
(b0−3) determines the threshold value, which can be
programmed from 6.475 V to 10.975 V in 0.3-V steps with
an accuracy of ±5% at the falling edge and has 50 mV
±30% of hysteresis.
When the input voltage is below the shutdown threshold
and a higher voltage at VPACK is not present, then SHDN
(STATUS, b5) is set and the bq29311 enters the sleep
mode and turns off CHG, DSG, and PCHG. The current
consumption in this mode is under 1 µA. SHDN is cleared
when the input voltage rises above the shutdown
threshold. XALERT does not respond to shutdown.
OVERCURRENT, OVERLOAD,AND
SHORT-CIRCUIT DETECTION
The overcurrent, overload, and short-circuit detection is
used to detect abnormal current in either the charge or
discharge direction. This safety feature is used to protect
the pass FETs, cells, and any other inline components
from excessive current conditions. The detection circuit
also incorporates a blanking delay before driving the
control for the pass FETs to turn off.
When an overcurrent, overload, or short-circuit condition
is detected, the CHG and DSG FETs are turned off and the
PCHG FET turned on, limiting the charge current to the
pre-charge rate. The STATUS (b0...b3) register reports the
details of discharge short circuit, charge short circuit,
overload (discharge overcurrent) and overcurrent. The
respective STATUS (b0...b3) bits are set to 1 and the
XALERT output changes state. This condition is latched
until the CONTROL (b0) is set and then reset. If a FET is
turned on by resetting CONTROL (b0) and the error
condition is still on the system, then the device again
enters the protection response state.
CELL VOLTAGE
The cell voltage is translated to allow a system host to
measure individual series elements of the battery.
The series element voltage is translated to a GND-based
voltage equal to 0.15 of the series element voltage. This
provides a range from 0 V to 4.5 V. The translation output
is inversely proportional to the input.
V_{(CELL_OUT)} = −K × V_{(CELL_IN)} + 0.975 (V)
Programming CELL_SEL (b0...b1) selects the individual
series element. The CELL_SEL (b2 . . . b3) selects the
measurement mode for the series elements. This allows
the offset to be determined for each element in the string.
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