BQ24620 Datasheet, PDF (19/30 Pages) Texas Instruments – Stand-Alone Synchronous Switch-Mode Lithium Phosphate Battery Charger with Low Iq

bq24620
www.ti.com
SLUS893 – MARCH 2010
Assuming a 103AT NTC thermistor on the battery pack as shown in the Typical System Schematic, the value
RT1 and RT2 can be determined by using Equation 5 and Equation 6:
RT2 =
V_VREF
´
RTH_COOL
´
RTH_WARM
´
æ₁
ç
è ^VCOOL
-
1^ö
÷
V_{WARM ø}
RTH_WARM
´
æ
ç
è
V_VREF
V_{W ARM}
-
ö
1_÷
-
RTH_COOL
ø
´
æ
ç
V_VREF
ö
- 1_÷
è ^VCOOL ø
(5)
RT1 =
V_VREF
V_COOL
-1
1
1
+
RT2 RTH_COOL
(6)
VREF
bq24620
TS
RT 1
RT 2
RTH
103AT
Figure 14. TS Resistor Network
For example, 103AT NTC thermistor is used to monitor the battery pack temperature. Select T_COOL = 0ºC, T_WARM
= 60ºC. From the calculation and select standard 5% resistor value. We can get R_T1 = 2.2kΩ, R_T2 = 6.8kΩ, and
T_COLD is -17ºC (target -20ºC); T_HOT is 77ºC (target 75ºC), and T_CUT-OFF is 86ºC (target 80ºC). A small RC filter is
suggested to protect TS pin from system-level ESD.
Timer Fault Recovery
The bq24620 provides a recovery method to deal with timer fault conditions. The following summarizes this
method:
Condition 1: The battery voltage is above the recharge threshold and a timeout fault occurs.
Recovery Method: The timer fault will clear when the battery voltage falls below the recharge threshold, and
battery detection will begin. Taking CE low or a POR condition will also clear the fault.
Condition 2: The battery voltage is below the RECHARGE threshold and a timeout fault occurs.
Recovery Method: Under this scenario, the bq24620 applies the IFAULT current to the battery. This small
current is used to detect a battery removal condition and remains on as long as the battery voltage stays below
the recharge threshold. If the battery voltage goes above the recharge threshold, the bq24620 disables the fault
current and executes the recovery method described in Condition 1. Taking CE low or a POR condition will also
clear the fault.
PG Output
The open drain PG(power good) indicates whether the VCC voltage is valid or not. The open drain FET turns on
whenever bq24620 has a valid VCC input ( not in UVLO or ACOV or SLEEP mode). The PGpin can be used to
drive an LED or communicate to the host processor.
Copyright © 2010, Texas Instruments Incorporated
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