BQ2058T Datasheet, PDF (5/18 Pages) Texas Instruments – Lithium Ion Pack Supervisor For 2-Cell Packs

bq2058T
Low-Power Sleep Mode
The bq2058T enters the low-power sleep mode in two
different ways:
1. On initial power-up.
2. After the detection of an undervoltage condi-
tion–VUV.
When the bq2058T enters the low-power sleep mode,
DSG is driven low and the device consumes 0.7µA (typi-
cal). The bq2058T only comes out of low-power sleep
mode when a valid charge detect condition exists.
Charge Detect
The bq2058T continuously monitors for a charge detect
condition. A valid charge detect condition exists when ei-
ther of the conditions is true:
CSL < BAT2N - 70mV (VCD)
CSH > BAT1P + 70mV (VCD)
A valid charge detect enables the DSG output, allowing
charging of the lithium ion cells. This is accomplished
by applying the charging supply to the pack.
Undervoltage
Undervoltage (or overdischarge) protection is asserted
when any cell voltage drops below the VUV threshold
and remains below the VUV threshold for a time
exceeding a user-configurable delay (tUVD). The DSG
output is driven low, disabling the discharge of the pack.
The bq2058T then enters the low-power sleep mode.
VUV is defined as follows:
VUV = 2.25V
Overvoltage
Overvoltage (or overcharge) protection is asserted when
any cell voltage exceeds the VOV threshold and remains
above the VOV threshold for a time exceeding a user-
configurable delay (tOVD). The CHG pin goes to the
high impedance state, disabling charge into the battery
pack. Since the charge control output is an open drain
output, a pull-down resistor is needed from the CHG pin
to the negative side of the pack. This pulls the gate of
the charge FET low when the CHG pin goes to high im-
pedance. Charging is disabled until a valid charge en-
able exists. See Charge Enable section.
Important note: If any battery pin floats (BAT1P,
BAT1N, BAT2N), the bq2058T assumes an overvolt-
age has occurred.
Because of different manufacturers’ specifications for
overvoltage thresholds, the bq2058T can be available
with different VOV options. Table 1 summarizes these
different voltage thresholds.
July 1997
Table 1. Overvoltage Threshold Options
Part #
bq2058T
bq2058TR
VOV Limit
4.25V
4.35V
The overvoltage threshold limits are programmed
at Benchmarq. The bq2058T is the standard op-
tion that is more readily available for sampling
and prototyping purposes. Please contact Bench-
marq for other voltage threshold and tolerance
options.
Charge Enable
A valid charge enable indicates that an overvoltage
(overcharge) condition no longer exists and that the
pack is ready to accept further charge. Once overvoltage
protection is asserted, charging will not be enabled un-
til all cell voltages fall below VCE. The VCE threshold is
a function of VOV, and changes with different VOV lim-
its.
VCE = VOV - 150mV
Overcurrent
The bq2058T detects an overcurrent (or short circuit)
condition only in the discharge direction. Overcurrent
protection is asserted when either of the conditions oc-
curs and remain for a time exceeding a user-
configurable delay (tOCD):
CSL > BAT2N + VOCL
CSH < BAT1P - VOCH
where:
VOCL = 160mV (low-side detect)
VOCH = 160mV (high-side detect)
When either of these conditions occurs, DSG is driven
low, disconnecting the load from the pack. DSG remains
low until both of the voltage conditions are false, indi-
cating removal of the short-circuit condition. The user
can facilitate clearing these conditions by inserting the
battery pack into a charger.
The high-side overcurrent sense can be disabled by con-
necting CSH to BAT1P. This ensures that CSH is never
greater than BAT1P. If high-side detection is disabled,
low-side detection must be used with CSL.
The FETs in the charge/discharge path controlled by the
CHG and DSG pins affect the overcurrent level. The
on-resistance of these FETs need to be taken into ac-
count when determining overcurrent levels.
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