Datasheet

bq24278
SLUSB04 –JUNE 2012 www.ti.com
PIN FUNCTIONS
PIN
NAME NUMBER I/O DESCRIPTION
YFF RGE
Input power supply. IN is connected to the external DC supply (AC adapter or alternate power
IN A1-A4 21 I
source). Bypass IN to PGND with at least a 1μF ceramic capacitor.
AGND A5-A7 22 I Ground terminal. Connect to the thermal pad (for QFN only) and the ground plane of the circuit.
Reverse Blocking MOSFET and High Side MOSFET Connection Point for High Power Input.
Bypass PMID to PGND with at least a 4.7μF ceramic capacitor. Use caution when connecting
PMID B1-B4 20 O
an external load to PMID. The PMID output is not current limited. Any short on PMID will result
in damage to the IC.
BYP B5-B7 23 O Bypass for internal supply. Bypass BYP to GND with at least a 0.1µF ceramic capacitor.
SW C1–C7 18 O Inductor Connection. Connect to the switched side of the external inductor.
Ground terminal for Switching FET. Connect to the thermal pad (for QFN only) and the ground
PGND D1–D7 16, 17 —
plane of the circuit.
IN Input Current Limit Programming Input. Connect a resistor from ILIM to GND to program the
ILIM E1 15 I
input current limit for IN. The current limit is programmable from 1A to 2.5A.
IC Hardware Disable Input. Drive CD high to place the bq24278 in high-z mode. Drive CD low
CD E2 2 I
for normal operation.
Input DPM Programming Input. Connect a resistor divider from IN to PGND with VDPM
connected to the center tap to program the Input Voltage based Dynamic Power Management
VDPM E3 1 I
(VIN_DPM) threshold. The input current is reduced to maintain the supply voltage at V
IN_
DPM.
See the Input Voltage based Dynamic Power Management section for a detailed explanation.
Charge Enable Input. CE is used to disable or enable the charge process. A low logic level (0)
enables charging and a high logic level (1) disables charging. When charging is disabled, the
CE E4 24 I
SYS output remains in regulation, but BAT is disconnected from SYS. Supplement mode is still
available if the system load demands cannot be met by the supply.
DRV_S E5, E6 3, 4 I Supply for Internal Circuits. Connect DRV_S to DRV directly.
High Side MOSFET Gate Driver Supply. Connect a 0.01μF ceramic capacitor (voltage rating >
BOOT E7 19 I
10V) from BOOT to SW to supply the gate drive for the high side MOSFETs.
System Voltage Sense and Charger FET Connection. Connect SYS to the system output at the
SYS F1–F4 13,14 I/O
output bulk capacitors. Bypass SYS locally with 1μF.
External Discharge MOSFET Gate Connection. BGATE drives an external P-Channel MOSFET
BGATE F5 10 O to provide a very low resistance discharge path. Connect BGATE to the gate of the external
MOSFET. BGATE is low during supplement mode and when no input is connected.
Power Good Open Drain Output. /PG is pulled low when a valid supply is connected to IN. A
PG F6 7 I valid supply is between V
BAT
+V
SLP
and V
OVP
. If no supply is connected or the supply is out of
this range, PG is high impedance.
Gate Drive Supply. DRV is the bias supply for the gate drive of the internal MOSFETs. bypass
DRV to PGND with a 1μF ceramic capacitor. DRV may be used to drive external loads up to
DRV F7 6 O
10mA. DRV is active whenever the input is connected and V
SUPPLY
> V
UVLO
and V
SUPPLY
>
(V
BAT
+ V
SLP
)
Battery Connection. Connect to the positive terminal of the battery. Additionally, bypass BAT to
BAT G1–G4 11, 12 I/O
GND with a 1μF capacitor.
Battery Pack NTC Monitor. Connect TS to the center tap of a resistor divider from DRV to
GND. The NTC is connected from TS to GND. The TS function in the bq24278 provides 2
TS G5 9 I
thresholds for Hot/ Cold shutoff, with 2 additional thresholds for JEITA compliance. See the
NTC Monitor section for more details on operation and selecting the resistor values.
Charge Status Open Drain Output. CHG is pulled low when a charge cycle starts and remains
CHG G6 8 O low while charging. CHG is high impedance when the charging terminates and when no supply
exists. CHG does not indicate recharge cycles.
Charge Current Programming Input. Connect a resistor from ISET to GND to program the fast
ISET G7 5 I
charge current. The charge current is programmable from 550mA to 2.5A.
There is an internal electrical connection between the exposed thermal pad and the VSS pin of
Thermal the device. The thermal pad must be connected to the same potential as the VSS pin on the
— Pad —
Pad printed circuit board. Do not use the thermal pad as the primary ground input for the device.
VSS pin must be connected to ground at all times.
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