BQ2000 datasheet(11/29 Pages) TI1

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SLUS138D – JANUARY 2008 – REVISED DECEMBER 2009

During top-off, there are three different temperature faults that can occur. If VTS > VLTF, top-off is suspended, the

timer is paused, and trickle charge is started. When VTS falls below VLTF, top-off is resumed. If VTS < VHTF, all

charging stops, but the timer keeps counting. When VTS > VHTF, 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 VTS < VTCO, all charging stops. Only

trickle maintenance charge may resume after VTS > VHTF.

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 RMTO,

connected between the RC pin and VSS. Figure 8 shows the relationship between the trickle pulse-width and the

value of RMTO. The typical tolerance of the pulsewidth below 150kΩ is ±10%.

Figure 8. Relationship Between Trickle Pulse-Width and Value of RMTO

Note that with an RMTO 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 RMTO 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 VSS 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)

VTS < VLTF

Active

Fast charge (current and voltage regulation)

VTS > VLTF (in battery conditioning state)

1-2V DC level (timer is paused and will

resume when VTS < VLTF)

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