Datasheet

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R -k
MTO
W
Pulsewidth-ms
ShowsTolerance
bq2000
www.ti.com SLUS138D –JANUARY 2008–REVISED DECEMBER 2009
During top-off, there are three different temperature faults that can occur. If V
TS
> V
LTF
, top-off is suspended, the
timer is paused, and trickle charge is started. When V
TS
falls below V
LTF
, top-off is resumed. If V
TS
< V
HTF
, all
charging stops, but the timer keeps counting. When V
TS
> V
HTF
, top-off is resumed, if there is still time remaining
on the timer. If there is not time left, trickle maintenance charge is entered. If V
TS
< V
TCO
, all charging stops. Only
trickle maintenance charge may resume after V
TS
> V
HTF
.
Following top-off, the bq2000 trickle-charges the battery by enabling the MOD pin to charge at a rate of once
every 1.0 second. The trickle pulse-width is user-selectable and is set by the value of the resistor R
MTO
,
connected between the RC pin and V
SS
. Figure 8 shows the relationship between the trickle pulse-width and the
value of R
MTO
. The typical tolerance of the pulsewidth below 150kΩ is ±10%.
Figure 8. Relationship Between Trickle Pulse-Width and Value of R
MTO
Note that with an R
MTO
value around 150 kΩ, the trickle charge pulse width is nearly identical to the top-off pulse
width of 62.5 ms (1/16 of a second). With R
MTO
values near 150 kΩ, it can be difficult to tell which state the IC is
in (top-off or trickle charge). The best way to tell if the bq2000 is in top-off or trickle charge is to look at the RC
pin when the temperature is between the LTF and HTF. In top-off, the RC pin will be counting and will have a
sawtooth waveform on it. In trickle charge, there is no timer and the RC pin will be at a DC value.
The RC pin contains valuable information in determining what state the bq2000 is in, since it always operates in
one of three modes. If the RC pin is low (around V
SS
potential), the IC is in sleep mode. (If the RC pin is low for
brief instants during fast charge, the bq2000 is sampling the BAT pin for PVD). If the RC pin is at some DC value
(usually around 1-2V), then the IC has paused the timer or the timer is inactive. If the RC pin is a sawtooth
waveform (similar to Figure 15), then the timer is running and the RC pin is considered “active.” Lastly, the RC
pin can be loaded by too large of a C or too small of an R. This will sometimes make the usual sawtooth
waveform look like a triangle waveform on an oscilloscope (the rise time is lengthened), or the RC signal could
have the appearance of being clipped (flat top or bottom). The timer will be unreliable under these conditions and
the bq2000 should not be operated in this manner. Table 2 summarizes the different states of the RC pin.
Table 2. RC Pin Status
bq2000 CHARGE STATE TS PIN STATE RC PIN BEHAVIOR
Battery absent N/A 1-2V DC level
Sleep mode N/A Ground (Vss)
Charge qualification (including battery
conditioning (trickle charge) and charge N/A 1-2V DC level
suspended)
V
TS
< V
LTF
Active
Fast charge (current and voltage regulation)
V
TS
> V
LTF
(in battery conditioning state) 1-2V DC level (timer is paused and will
resume when V
TS
< V
LTF
)
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