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Texas Instruments
Texas Instruments

BQ24751A Datasheet

Host-controlled Multi-Chemistry Battery Charger


BQ24751A Datasheet Preview


www.ti.com
bq24751A
SLUS756 – SEPTEMBER 2007
Host-controlled Multi-Chemistry Battery Charger With System Power Selector, AC
Over-Power Protection, Programmable OVP and Low Iq
FEATURES
1
NMOS-NMOS Synchronous Buck Converter
with 300 kHz Frequency and >95% Efficiency
30-ns Minimum Driver Dead-time and 99.5%
Maximum Effective Duty Cycle
High-Accuracy Voltage and Current Regulation
– ±0.5% Charge Voltage Accuracy
– ±3% Charge Current Accuracy
– ±3% Adapter Current Accuracy
– ±2% Input Current Sense Amp Accuracy
Integration
– Automatic System Power Selection From
AC/DC Adapter or Battery
– Internal Loop Compensation
– Internal Soft Start
Safety
– Programmable Input Overvoltage
Protection (OVP)
– Dynamic Power Management (DPM) with
Status Indicator
– Programmable Inrush Adapter Power
(ACOP) and Overcurrent (ACOC) Limits
– Reverse-Conduction Protection Input FET
Supports Two, Three, or Four Li+ Cells
5 – 24 V AC/DC-Adapter Operating Range
Analog Inputs with Ratiometric Programming
via Resistors or DAC/GPIO Host Control
28-pin, 5x5-mm QFN package
Energy Star Low Iq
– < 10-μA Off-State Battery Discharge Current
– < 1.5-mA Off-State Input Quiescent Current
APPLICATIONS
Notebook and Ultra-Mobile Computers
Portable Data Capture Terminals
Portable Printers
Medical Diagnostics Equipment
Battery Bay Chargers
Battery Back-up Systems
DESCRIPTION
The bq24751A is a high-efficiency, synchronous
battery charger with integrated compensation and
system power selector logic, offering low component
count for space-constrained multi-chemistry battery
charging applications. Ratiometric charge current and
voltage programming allows very high regulation
accuracies, and can be either hardwired with resistors
or programmed by the system power-management
microcontroller using a DAC or GPIOs.
The bq24751A charges two, three, or four series Li+
cells, supporting up to 10 A of charge current, and is
available in a 28-pin, 5x5-mm thin QFN package.
– Charge Voltage (4-4.512 V/cell)
– Charge Current (up to 10 A, with 10-m
sense resistor)
CHGEN
ACN
28 27 26 25 24 23 22
1 21
2 20
LEARN
CELLS
– Adapter Current Limit (DPM)
Status and Monitoring Outputs
– AC/DC Adapter Present with Programmable
Voltage Threshold
– Current Drawn from Input Source
Battery Learn Cycle Control
Supports Any Battery Chemistry: Li+, NiCd,
NiMH, Lead Acid, etc.
Charge Enable
ACP
ACDRV
ACDET
3
4
5
bq24751A
28 LD QFN
TOP VIEW
19 SRP
18 SRN
17 BAT
ACSET 6
16 SRSET
ACOP 7
15 IADAPT
8 9 10 11 12 13 14
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1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2007, Texas Instruments Incorporated
Page 1

bq24751A
SLUS756 – SEPTEMBER 2007
www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
DESCRIPTION (CONTINUED)
The bq24751A controls external switches to prevent battery discharge back to the input, connect the adapter to
the system, and to connect the battery to the system using 6-V gate drives for better system efficiency. For
maximum system safety, inrush-power limiting provides instantaneous response to high input voltage multiplied
by current. This AC Over-Power protection (ACOP) feature limits the input-switch power to the programmed level
on the ACOP pin, and latches off if the high-power condition persists to prevent overheating.
The bq24751A features Dynamic Power Management (DPM) and input power limiting. These features reduce
battery charge current when the input power limit is reached to avoid overloading the AC adapter when supplying
the load and the battery charger simultaneously. A highly-accurate current-sense amplifier enables precise
measurement of input current from the AC adapter to monitor the overall system power.
TYPICAL APPLICATION
C17 C18
10 mF 10 mF
C19
10 mF
ADAPTER+
ADAPTER-
P
Q1 (ACFET)
SI4435
P
Q2 (ACFET)
SI4435
C2
0.1 mF
RAC
0.010 W
C3
0.1 mF
ACGOOD
R1
432 kW 1%
R2
66.5
kW
VREF
R4 10 kW
R3 422 kW
DAC
R5 71 kW
HOST
C4 1 mF
DAC
ACN
PVCC
ACP
ACDRV
ACDET
AGND
BATDRV
HIDRV
bq24751A PH
ACGOOD
OVPSET
BTST
REGN
SRSET
ACSET
VREF
LEARN
CELLS
CHGEN
VDAC
VADJ
LODRV
PGND
SRP
SRN
BAT
ACOP
C6 C7
10 mF 10 mF
C8 1 mF
R6 100 kW
Q4
FDS6680A
P
RSR
C9 L1 0.010 W
D1 BAT54 0.1 mF
8.2 mH
C11
C10 1 mF
10 mF
C13
0.1 mF
Q5
FDS6680A
C4
0.1 mF
C16
0.47 mF
C15
0.1 mF
SYSTEM
Q3(BATFET)
SI4435
C12
10 mF
PACK+
PACK-
ADC
C5 100 pH
IADAPT
PowerPad
(1) Pull-up rail could be either VREF or other system rail .
(2) SRSET/ACSET could come from either DAC or resistor dividers .
VIN = 20 V, VBAT = 3-cell Li-Ion, Icharge = 3 A, Iadapter_limit = 4 A
Figure 1. Typical System Schematic, Voltage and Current Programmed by DAC
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Copyright © 2007, Texas Instruments Incorporated
Page 2

www.ti.com
bq24751A
SLUS756 – SEPTEMBER 2007
C17 C18
10 mF 10 mF
C19
10 mF
ADAPTER+
ADAPTER-
P
Q1 (ACFET)
C1 SI4435
10 mF
P
Q2 (ACFET)
SI4435
C2
0.1 mF
RAC
0.010 W
C3
0.1 mF
ACGOOD
HOST
R1 432 kW
R2
66.5
kW
VREF
R4 10 kW
R3 422 kW
R5 71 kW
R7 43 kW
R6
R8 100 kW
100 kW
R9
66.5 kW
C4
1 mF
GPIO
ADC
C5
100 pF
C6 C7
10 mF 10 mF
SYSTEM
ACN
PVCC
ACP
ACDRV
ACDET
BATDRV
AGND
HIDRV
bq24751A PH
ACGOOD
OVPSET
BTST
REGN
SRSET
ACSET
VREF
LODRV
PGND
C8 1 mF
R10 100 kW
Q4
FDS6680A
C9
D1 BAT54 0.1 mF
C10
1 mF
L1
8.2 mH
C11
10 mF
C13
0.1 mF
Q5
FDS6680A
P
RSR
0.010 W
C4
0.1 mF
Q3(BATFET)
SI4435
C12
10 mF
PACK+
PACK-
LEARN
CELLS
CHGEN
VDAC
VADJ
SRP
SRN
BAT
ACOP
C16
0.47 mF
C15
0.1 mF
IADAPT
PowerPad
(1) Pull-up rail could be either VREF or other system rail .
(2) SRSET/ACSET could come from either DAC or resistor dividers .
VIN = 20 V, VBAT = 3-cell Li-Ion, Icharge = 3 A, Iadapter_limit = 4 A
Figure 2. Typical System Schematic, Voltage and Current Programmed by Resistor
PART NUMBER
bq24751A
ORDERING INFORMATION
PACKAGE
28-PIN 5 x 5 mm QFN
ORDERING NUMBER
(Tape and Reel)
bq24751ARHDR
bq24751ARHDT
QUANTITY
3000
250
PACKAGE THERMAL DATA
PACKAGE
QFN – RHD(1)(2)
θJA
39°C/W
TA = 70°C POWER RATING
2.36 W
DERATING FACTOR ABOVE TA = 25°C
0.028 W/°C
(1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
Web site at www.ti.com.
(2) This data is based on using the JEDEC High-K board and the exposed die pad is connected to a Cu pad on the board. This is
connected to the ground plane by a 2x3 via matrix.
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Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s) :bq24751A
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3
Page 3

bq24751A
SLUS756 – SEPTEMBER 2007
www.ti.com
Table 1. TERMINAL FUNCTIONS – 28-PIN QFN
TERMINAL
NAME
NO.
DESCRIPTION
CHGEN
1 Charge enable active-low logic input. LO enables charge. HI disables charge.
ACN
Adapter current sense resistor, negative input. An optional 0.1-μF ceramic capacitor is placed from ACN pin to AGND
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)
ACDRV
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
4
driver logic is always active when needed. If needed, an optional capacitor from gate to source of the ACFET is used
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.
ACDET
Adapter detected voltage set input. Program the adapter detect threshold by connecting a resistor divider from adapter
5 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.
ACSET
Adapter current set input. The voltage ratio of ACSET voltage versus VDAC voltage programs the input current
6
regulation set-point during Dynamic Power Management (DPM). Program by connecting a resistor divider from VDAC
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.
ACOP
Input power limit set input. Program the input over-power time constant by placing a ceramic capacitor from ACOP to
7
AGND. The capacitor sets the time that the input current limit, ACOC, can be sustained before exceeding the
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.
OVPSET
Set input over voltage protection threshold. Charge is disabled and ACDRV is turned off if adapter input voltage is
8
higher than the OVPSET programmed threshold. Input overvoltage, ACOV, disables charge and ACDRV when
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.
AGND
9
Analog ground. On PCB layout, connect to the analog ground plane, and only connect to PGND through the power
pad underneath the IC.
VREF
10
3.3-V regulated voltage output. Place a 1-μF ceramic capacitor from VREF to AGND pin close to the IC. This voltage
could be used for ratiometric programming of voltage and current regulation.
VDAC
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,
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.
VADJ
Charge voltage set input. The voltage ratio of VADJ voltage versus VDAC voltage programs the battery voltage
12
regulation set-point. Program by connecting a resistor divider from VDAC to VADJ, to AGND; or, by connecting the
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.
ACGOOD
13
Valid adapter active-low detect logic open-drain output. Pulled low when Input voltage is above programmed ACDET.
Connect a 10-kpullup resistor from ACGOOD to VREF, or to a different pullup-supply rail.
BATDRV
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
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.
IADAPT
15
Adapter current sense amplifier output. IADAPT voltage is 20 times the differential voltage across ACP-ACN. Place a
100-pF or less ceramic decoupling capacitor from IADAPT to AGND.
SRSET
Charge current set input. The voltage ratio of SRSET voltage versus VDAC voltage programs the charge current
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.
eehSataD.wwwBAT
Battery voltage remote sense. Directly connect a kelvin sense trace from the battery pack positive terminal to the 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 Submit Documentation Feedback
Product Folder Link(s) :bq24751A
Copyright © 2007, Texas Instruments Incorporated
Page 4
Part Number BQ24751A
Manufactur Texas Instruments
Description Host-controlled Multi-Chemistry Battery Charger
Total Page 30 Pages
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