BQ24618 Datasheet, PDF (22/36 Pages) Texas Instruments – Stand-Alone USB-Friendly Synchronous Switch-Mode Li-Ion or Li-Polymer Battery Charger

bq24618
SLUSA55 – OCTOBER 2010
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For example, 103AT NTC thermistors are used to monitor the battery pack temperature. Select T_COLD = 0ºC and
T_HOT = 40ºC then we get R_T2 = 430kΩ, R_T1 = 9.31kΩ and T_CUT-OFF is around 45ºC. A small RC filter is suggested
to use for system-level ESD protection.
Timer Fault Recovery
The bq24618 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 bq24618 applies the I_FAULT 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 bq24618 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) output indicates whether the VCC voltage is valid or not. The open drain FET
turns on whenever bq24618 has a valid VCC input ( not in UVLO or ACOV or SLEEP mode). The PG pin can be
used to drive an LED or communicate to the host processor.
CE (Charge Enable)
The CE digital input is used to disable or enable the charge process. A high-level signal on this pin enables
charge, provided all the other conditions for charge are met (see Enabling and Disabling Charge). A high to low
transition on this pin also resets all timers and fault conditions. There is an internal 1MΩ pulldown resistor on the
CE pin, so if CE is floated the charge will not turn on.
Inductor, Capacitor, and Sense Resistor Selection Guidelines
The bq24618 provides internal loop compensation. With this scheme, best stability occurs when the LC resonant
frequency, f_o, is approximately 12kHz–17kHz for bq24618.
The following table provides a summary of typical LC components for various charge currents:
Table 2. Typical Inductor, Capacitor, and Sense Resistor Values as a Function of Charge Current for
bq24618 (600 kHz Switching Frequency)
CHARGE CURRENT
Output Inductor Lo
Output Capacitor Co
Sense Resistor
2A
6.8 mH
20 mF
10 mΩ
4A
6.8 mH
20 mF
10 mΩ
6A
4.7 mH
30 mF
10 mΩ
8A
3.3 mH
40 mF
10 mΩ
10A
3.3 mH
40 mF
10 mΩ
Charge Status Outputs
The open-drain STAT1 and STAT2 outputs indicate various charger operations as shown in the table below.
These status pins can be used to drive LEDs or communicate with the host processor. Note that OFF indicates
that the open-drain transistor is turned off.
Table 3. STAT Pin Definition for bq24618
CHARGE STATE
Charge in progress
Charge complete
Charge suspend, timer fault, over-voltage, sleep mode, battery absent
STAT1
ON
OFF
OFF
STAT2
OFF
ON
OFF
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