BQ2054 Datasheet, PDF (9/16 Pages) Texas Instruments – Lithium Ion Fast-Charge IC

bq2054
A resistor-divider network can be implemented that
presents the defined voltage levels to the TS pin at the
desired temperatures (see Figure 6).
The equations for determining RT1 and RT2 are:
Equation 3
0.6
*
V_CC
=
1
+
(V_CC
RT1 *
− 0.250)
(RT2 + R _LTF )
(RT2 * R _LTF )
Equation 4
R
1
TM
C
VCC
VCC ¹³
12
VSS
0.44 =
1
1 + ^{RT1 * (RT2 + R HTF )}
(RT2 * R _HTF )
bq2054
where:
n RLTF = thermistor resistance at LTF
n RHTF = thermistor resistance at HTF
TCO is determined by the values of RT1 and RT2. 1%
resistors are recommended.
Disabling Temperature Sensing
Temperature sensing can be disabled by placing 10kΩ
resistors between TS and SNS and between SNS and
VCC.
Maximum Time-Out
MTO is programmed from 1 to 24 hours by an R-C net-
work on the TM pin (see Figure 7) per the equation:
Equation 5
tMTO = 0.5 * R * C
Where R is in kΩ and C is in µF, tMTO is in hours. The
maximum value for C (0.1µF) is typically used.
The MTO timer is reset at the beginning of fast charge
and when fast charge transitions from the current regu-
lated to the voltage regulated mode. If MTO expires dur-
ing the current regulated phase, the bq2054 enters the
Fault state and terminates charge. If the MTO timer ex-
pires during the voltage regulated phase, fast charging
terminates and the bq2054 enters the Charge Complete
state.
The MTO timer is suspended (but not reset) during the
out-of-range temperature (Charge Pending) state.
VSS
FG205406.eps
Figure 7. R-C Network for Setting MTO
Charge Regulation
The bq2054 controls charging through pulse-width
modulation of the MOD output pin, supporting both
constant-current and constant-voltage regulation.
Charge current is monitored at the SNS pin, and charge
voltage is monitored at the BAT pin. These voltages are
compared to an internal reference, and the MOD output
modulated to maintain the desired value.
Voltage at the SNS pin is determined by the value of re-
sistor RSNS, so nominal regulated current is set by:
Equation 6
IMAX = 0.250V/RSNS
The switching frequency of the MOD output is deter-
mined by an external capacitor (CPWM) between the
pin TPWM and ground, per the following:
Equation 7
FPWM = 0.1/CPWM
Where C is in µF and F is in kHz. A typical switching
rate is 100kHz, implying CPWM = 0.001µF. MOD pulse
width is modulated between 0 and 90% of the switching
period.
To prevent oscillation in the voltage and current control
loops, frequency compensation networks (C or R-C) are typi-
cally required on the VCOMP and ICOMP pins (respectively).
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