BQ2054 Datasheet, PDF (6/16 Pages) Texas Instruments – Lithium Ion Fast-Charge IC

bq2054
Fast charge terminates when the charging current drops
below a minimum current threshold programmed by the
value of ITERM (see Table 2) and remains below that
level for 120 ± 40ms.
Table 2. I_MIN Termination Thresholds
ITERM
0
1
Float
IMIN
IMAX/10
IMAX/20
IMAX/30
Figure 3 shows the bq2054 configured for display mode 2
and IMIN = IMAX/10.
Voltage and Current Monitoring
The bq2054 monitors battery pack voltage at the BAT
pin. The user must implement a voltage divider be-
tween the positive and negative terminals of the battery
pack to present a scaled battery pack voltage to the BAT
pin. The bq2054 also uses the voltage across a sense re-
sistor (RSNS) between the negative terminal of the bat-
tery pack and ground to monitor the current into the
pack. See Figure 4 for the configuration of this network.
The resistor values are calculated from the following:
Equation 1
RB1 ₌ N * V_{REG − 1}
RB2 2.05V
These parameters are typically specified by the battery
manufacturer. The total resistance presented across the
battery pack by RB1 + RB2 should be between 150kΩ
and 1MΩ. The minimum value ensures that the divider
network does not drain the battery excessively when the
power source is disconnected. Exceeding the maximum
value increases the noise susceptibility of the BAT pin.
The current sense resistor, RSNS (see Figure 5), deter-
mines the fast charge current. The value of RSNS is
given by the following:
Equation 2
I _MAX
=
0.250 V
R _SNS
where:
n IMAX = Desired maximum charge current
Hold-Off Period
Both VHCO and IMIN terminations are ignored during
the first 1.33 ± 0.19 seconds of both the Charge Qualifi-
cation and Fast Charge phases. This condition prevents
premature termination due to voltage spikes that may
occur when charge is first applied.
where:
n N = Number of cells in series
n VREG = Desired fast-charging voltage per cell
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