BQ25890H Datasheet, PDF (25/66 Pages) Texas Instruments – I2C Controlled Single Cell 5-A Fast Charger

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BQ25890H
SLUSCC5 – SEPTEMBER 2016
The device continuously monitors battery temperature by measuring the voltage between the TS pins and
ground, typically determined by a negative temperature coefficient thermistor (NTC) and an external voltage
divider. The device compares this voltage against its internal thresholds to determine if charging is allowed. To
initiate a charge cycle, the voltage on TS pin must be within the V_T1 to V_T5 thresholds. If TS voltage exceeds the
T1–T5 range, the controller suspends charging and waits until the battery temperature is within the T1 to T5
range. At cool temperature (T1–T2), JEITA recommends the charge current to be reduced to at least half of the
charge current or lower. At warm temperature (T3–T5), JEITA recommends charge voltage below nominal
charge voltage.
The device provides flexible voltage/current settings beyond the JEITA requirement. The voltage setting at warm
temperature (T3–T5) can be 200 mV below charge voltage (JEITA_VSET=0). The current setting at cool
temperature (T1–T2) can be further reduced to 20% or 50% of fast charge current (JEITA_ISET bit).
REGN
bq2589x
TS
RT1
RT2
RTH
103AT
Figure 14. TS Resistor Network
VREG
VREG - 200 mV
Figure 15. Charging Values
Assuming a 103AT NTC thermistor on the battery pack as shown in Figure 14, the value RT1 and RT2 can be
determined by using Equation 2:
RT2 =
V_VREF
´ RTH_COLD
´ RTH_HOT
´
æ
çè
1_-
VT1
1
VT5
ö
÷ø
RTH_HOT
´
æ
çè
V_VREF
VT5
-
ö
1_÷ø
-
RTH_COLD
´
æ
çè
V_VREF
VT1
-
ö
1_÷ø
V_{VREF - 1}
RT1 =
VT1
1₊ 1
RT2 RTH_COLD
Select 0°C to 60°C range for Li-ion or Li-polymer battery,
RTH_T1 = 27.28 kΩ
RTH_T5 = 3.02 kΩ
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