Datasheet

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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
ChargeCurrent
4-cell16.8V
3-cell12.6V
2-cell8.4V
Efficiency-%
V =20V,
f=750kHz,
L =4.7 H
I
m
Not Recommended for New Designs
bq24725
SLUS702A –JULY 2010–REVISED NOVEMBER 2010 www.ti.com
CH1: PHASE, 20V/div, CH2: LODRV, 10V/div, CH3: battery voltage,
5V/div, CH4: inductor current, 2A/div, 4us/div
Figure 14. Battery to Ground Short Transition Figure 15. Efficiency vs Output Current
PIN FUNCTIONS – 20-PIN QFN
PIN FUNCTION DESCRIPTION
NO. NAME
1 ACN Input current sense resistor negative input. Place an optional 0.1 µF ceramic capacitor from ACN to GND for common-
mode filtering. Place a 0.1µF ceramic capacitor from ACN to ACP to provide differential mode filtering.
2 ACP Input current sense resistor positive input. Place a 0.1µF ceramic capacitor from ACP to GND for common-mode
filtering. Place a 0.1 µF ceramic capacitor from ACN to ACP to provide differential-mode filtering.
3 CMSRC ACDRV charge pump source input. Place a 4kΩ resistor from CMSRC to the common source of ACFET (Q1) and
RBFET (Q2) limit the in-rush current on the CMSRC pin.
4 ACDRV Charge pump output to drive both adapter input n-channel MOSFET (ACFET) and reverse blocking n-channel MOSFET
(RBFET). ACDRV voltage is 6V above CMSRC when voltage on ACDET pin is between 2.4V to 3.15V, voltage on VCC
pin is above UVLO and voltage on VCC pin is 275mV above voltage on SRN pin so that ACFET and RBFET can be
turned on to power the system by AC adapter. Place a 4kΩ resistor from ACDRV to the gate of ACFET and RBFET
limits the in-rush current on ACDRV pin.
5 ACOK AC adapter detection open drain output. It is pulled HIGH to external pull-up supply rail by external pull-up resistor when
voltage on ACDET pin is between 2.4V and 3.15V, and voltage on VCC is above UVLO and voltage on VCC pin is
275mV above voltage on SRN pin, indicating a valid adapter is present to start charge. If any one of the above
conditions can not meet, it is pulled LOW to GND by internal MOSFET. Connect a 10kΩ pull up resistor from ACOK to
the pull-up supply rail.
6 ACDET Adapter detection input. Program adapter valid input threshold by connecting a resistor divider from adapter input to
ACDET pin to GND pin. When ACDET pin is above 0.6V and VCC is above UVLO, REGN LDO is present, ACOK
comparator and IOUT are both active.
7 IOUT Buffered adapter or charge current output, selectable with SMBus command ChargeOption(). IOUT voltage is 20 times
the differential voltage across sense resistor. Place a 100pF or less ceramic decoupling capacitor from IOUT pin to
GND.
8 SDA SMBus open-drain data I/O. Connect to SMBus data line from the host controller or smart battery. Connect a 10kΩ pull-
up resistor according to SMBus specifications.
9 SCL SMBus open-drain clock input. Connect to SMBus clock line from the host controller or smart battery. Connect a 10kΩ
pull-up resistor according to SMBus specifications.
10 ILIM Charge current limit input. Program ILIM voltage by connecting a resistor divider from system reference 3.3V rail to ILIM
pin to GND pin. The lower of ILIM voltage or DAC limit voltage sets charge current regulation limit. To disable the
control on ILIM, set ILIM above 1.6V. Once voltage on ILIM pin falls below 75mV, charge is disabled. Charge is enabled
when ILIM pin rises above 105mV.
11 BATDRV Charge pump output to drive Battery to System n-channel MOSFET (BATFET). BATDRV voltage is 6V above SRN to
turn on BATFET (Q5) to power the system from battery. BATDRV voltage is SRN voltage to turn off BATFET to power
system from AC adapter. Place a 4kΩ resistor from BATDRV to the gate of BATFET limits the in-rush current on
BATDRV pin.
12 SRN Charge current sense resistor negative input. SRN pin is for battery voltage sensing as well. Connect the SRN pin to a
7.5Ω resistor first then from resistor another terminal connect a 0.1µF ceramic capacitor to GND for common-mode
filtering and connect to current sensing resistor. Connect a 0.1µF ceramic capacitor between current sensing resistor to
provide differential mode filtering. See the application information about negative output voltage protection for hard
shorts on battery to ground or battery reverse connection by adding small resistor.
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