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BQ24751 Datasheet(PDF) 4 Page - Texas Instruments

Part No. BQ24751
Description  Host-controlled Multi-chemistry Battery Charger with System Power Selector, AC Over-Power Protection, and Programmable OVP
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Maker  TI [Texas Instruments]
Homepage  http://www.ti.com
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BQ24751 Datasheet(HTML) 4 Page - Texas Instruments

 
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bq24751
SLUS734 – DECEMBER 2006
Table 1. TERMINAL FUNCTIONS – 28-PIN QFN
TERMINAL
DESCRIPTION
NAME
NO.
CHGEN
1
Charge enable active-low logic input. LO enables charge. HI disables charge.
Adapter current sense resistor, negative input. An optional 0.1-
µF ceramic capacitor is placed from ACN pin to AGND
ACN
2
for common-mode filtering. An optional 0.1-
µF ceramic capacitor is placed from ACN to ACP to provide
differential-mode filtering.
ACP
3
Adapter current sense resistor, positive input. (See comments with ACN description)
AC adapter to system-switch driver output. Connect directly to the gate of the ACFET P-channel power MOSFET and
the reverse conduction blocking P-channel power MOSFET. Connect both FETs as common-source. Connect the
ACFET drain to the system-load side. The PVCC should be connected to the common-source node to ensure that the
driver logic is always active when needed. If needed, an optional capacitor from gate to source of the ACFET is used
ACDRV
4
to slow down the ON and OFF times. The internal gate drive is asymmetrical, allowing a quick turn-off and slower
turn-on in addition to the internal break-before-make logic with respect to the BATDRV. The output goes into linear
regulation mode when the input sensed current exceeds the ACOC threshold. ACDRV is latched off after ACOP
voltage exceeds 2 V, to protect the charging system from an ACFET-overpower condition.
Adapter detected voltage set input. Program the adapter detect threshold by connecting a resistor divider from
ACDET
5
adapter input to ACDET pin to AGND pin. Adapter voltage is detected if ACDET-pin voltage is greater than 2.4 V. The
IADAPT current sense amplifier is active when the ACDET pin voltage is greater than 0.6 V.
Adapter current set input. The voltage ratio of ACSET voltage versus VDAC voltage programs the input current
regulation set-point during Dynamic Power Management (DPM). Program by connecting a resistor divider from VDAC
ACSET
6
to ACSET to AGND; or by connecting the output of an external DAC to the ACSET pin and connect the DAC supply
to the VDAC pin.
Input power limit set input. Program the input over-power time constant by placing a ceramic capacitor from ACOP to
AGND. The capacitor sets the time that the input current limit, ACOC, can be sustained before exceeding the
ACOP
7
power-MOSFET power limit. When the ACOP voltage exceeds 2 V, then the ACDRV latches off to protect the charge
system from an over-power condition, ACOP. Reset latch by toggling ACDET or PVCC_UVLO.
Set input over voltage protection threshold. Charge is disabled and ACDRV is turned off if adapter input voltage is
higher than the OVPSET programmed threshold. Input overvoltage, ACOV, disables charge and ACDRV when
OVPSET
8
OVPSET > 3.1 V. ACOV does not latch. Program the overvoltage protection threshold by connecting a resistor divider
from adapter input to OVPSET pin to AGND pin.
Analog ground. On PCB layout, connect to the analog ground plane, and only connect to PGND through the power
AGND
9
pad underneath the IC.
3.3-V regulated voltage output. Place a 1-
µF ceramic capacitor from VREF to AGND pin close to the IC. This voltage
VREF
10
could be used for ratiometric programming of voltage and current regulation.
Charge voltage set reference input. Connect the VREF or external DAC voltage source to the VDAC pin. Battery
voltage, charge current, and input current are programmed as a ratio of the VDAC pin voltage versus the VADJ,
VDAC
11
SRSET, and ACSET pin voltages, respectively. Place resistor dividers from VDAC to VADJ, SRSET, and ACSET pins
to AGND for programming. A DAC could be used by connecting the DAC supply to VDAC and connecting the output
to VADJ, SRSET, or ACSET.
Charge voltage set input. The voltage ratio of VADJ voltage versus VDAC voltage programs the battery voltage
regulation set-point. Program by connecting a resistor divider from VDAC to VADJ, to AGND; or, by connecting the
VADJ
12
output of an external DAC to VADJ, and connect the DAC supply to VDAC. VADJ connected to REGN programs the
default of 4.2 V per cell.
Valid adapter active-low detect logic open-drain output. Pulled low when Input voltage is above programmed ACDET.
ACGOOD
13
Connect a 10-k
Ω pullup resistor from ACGOOD to VREF, or to a different pullup-supply rail.
Battery to system switch driver output. Gate drive for the battery to system load BAT PMOS power FET to isolate the
system from the battery to prevent current flow from the system to the battery, while allowing a low impedance path
from battery to system and while discharging the battery pack to the system load. Connect this pin directly to the gate
BATDRV
14
of the input BAT P-channel power MOSFET. Connect the source of the FET to the system load voltage node.
Connect the drain of the FET to the battery pack positive node. An optional capacitor is placed from the gate to the
source to slow down the switching times. The internal gate drive is asymmetrical to allow a quick turn-off and slower
turn-on, in addition to the internal break-before-make logic with respect to ACDRV.
Adapter current sense amplifier output. IADAPT voltage is 20 times the differential voltage across ACP-ACN. Place a
IADAPT
15
100-pF or less ceramic decoupling capacitor from IADAPT to AGND.
Charge current set input. The voltage ratio of SRSET voltage versus VDAC voltage programs the charge current
SRSET
16
regulation set-point. Program by connecting a resistor divider from VDAC to SRSET to AGND; or by connecting the
output of an external DAC to SRSET pin and connect the DAC supply to VDAC pin.
Battery voltage remote sense. Directly connect a kelvin sense trace from the battery pack positive terminal to the BAT
BAT
17
pin to accurately sense the battery pack voltage. Place a 0.1-
µF capacitor from BAT to AGND close to the IC to filter
high-frequency noise.
4
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