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bq24618
SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
bq24618 Stand-Alone USB-Friendly Synchronous Switched-Mode Li-Ion or Li-Polymer
Battery Charger With System Power Selector and Low Iq
1 Features
2 Applications
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
USB-Friendly 4.7-V to 28-V Input Operating
Range
Stand-Alone Charge Controller to Support 1 to 6
Li-Ion or Li-Polymer Battery Cells
Up to 10-A Charge Current and Adapter Current
600-kHz NMOS-NMOS Synchronous Buck
Converter
High-Accuracy Voltage and Current Regulation
– ±0.5% Charge Voltage Accuracy
– ±3% Charge Current Accuracy
– ±3% Adapter Current Accuracy
Integration
– Automatic System Power Selection From
Adapter or Battery
– Internal Loop Compensation
– Internal Soft Start
– Dynamic Power Management
Safety Protection
– Input Overvoltage Protection
– Battery Thermistor Sense Hot/Cold Charge
Suspend
– Battery Detection
– Reverse-Protection Input FET
– Programmable Safety Timer
– Charge Overcurrent Protection
– Battery Short Protection
– Battery Overvoltage Protection
– Thermal Shutdown
Status Outputs
– Adapter Present
– Charger Operation Status
Charge Enable Pin
6-V Gate Drive for Synchronous Buck Converter
30-ns Driver Dead-Time and 99.5% Maximum
Effective Duty Cycle
Energy Star Low Quiescent Current Iq
– < 15-µA Off-State Battery Discharge Current
– < 1.5-mA Off-State Input Quiescent Current
•
•
•
Tablet PCs
Smart Phones
Portable Media Players, Navigation Devices,
Notebooks and Ultra-Mobile PCs
Personal Digital Assistants
Handheld Terminals
Industrial and Medical Equipment
3 Description
The bq24618 device is highly integrated Li-ion or Lipolymer switched-mode battery-charge controller.
The
bq24618
offers
a
constant-frequency
synchronous switching PWM controller with highaccuracy charge current and voltage regulation,
charge preconditioning, termination, adapter current
regulation and charge status monitoring.
The bq24618 operates from either a USB port or AC
adapter and supports charge currents up to 10 A. The
device charges the battery in three phases:
preconditioning, constant current, and constant
voltage. Charge is terminated when the current
reaches a minimum user-selectable level. A
programmable charge timer provides a safety backup
for charge termination. The bq24618 automatically
restarts the charge cycle if the battery voltage falls
below an internal threshold, and enters a lowquiescent current sleep mode when the input voltage
falls below the battery voltage.
Device Information(1)
PART NUMBER
bq24618
PACKAGE
VQFN (24)
BODY SIZE (NOM)
4.00 mm × 4.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Simplified Schematic
ADAPTER
SYSTEM
ACP
ACDRV
ACN
BATDRV
HIDRV
CE
VREF
ISET1
ISET2
ACSET
VREF
ADAPTER
STAT1
STAT2
PG
TS
PH
bq2461x
1
LODRV
Battery
pack
SRP
SRN
VFB
TTC
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
bq24618
SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Comparison Table.....................................
Pin Configuration and Functions .........................
Specifications.........................................................
7.1
7.2
7.3
7.4
7.5
7.6
8
1
1
1
2
3
4
6
Absolute Maximum Ratings ...................................... 6
ESD Ratings.............................................................. 6
Recommended Operating Conditions....................... 7
Thermal Information .................................................. 7
Electrical Characteristics........................................... 8
Typical Characteristics ............................................ 12
Detailed Description ............................................ 15
8.1 Overview ................................................................. 15
8.2 Functional Block Diagram ....................................... 16
8.3 Feature Description................................................. 17
8.4 Device Functional Modes........................................ 26
9
Application and Implementation ........................ 27
9.1 Application Information............................................ 27
9.2 Typical Application .................................................. 27
10 Power Supply Recommendations ..................... 33
11 Layout................................................................... 33
11.1 Layout Guidelines ................................................. 33
11.2 Layout Example .................................................... 34
12 Device and Documentation Support ................. 35
12.1
12.2
12.3
12.4
12.5
Device Support......................................................
Documentation Support ........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
35
35
35
35
35
13 Mechanical, Packaging, and Orderable
Information ........................................................... 35
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (October 2011) to Revision B
•
Page
Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section. ................................................................................................ 1
Changes from Original (October 2010) to Revision A
Page
•
Changed descriptions for PH and BTST pins......................................................................................................................... 5
•
Corrected Equation 8 ........................................................................................................................................................... 22
2
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SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
5 Device Comparison Table
bq24600
bq24610
bq24616
bq24617
bq24618
bq24650
Li-Ion/Li-Polymer
Li-Ion/Li-Polymer
Li-Ion/Li-Polymer
Li-Ion/Li-Polymer
Li-Ion/Li-Polymer
Li-Ion/Li-Polymer
1 to 6
1 to 6
1 to 6
1 to 5
1 to 6
1 to 6
2.1 to 26
2.1 to 26
2.1 to 26
2.1 to 22
2.1 to 26
2.1 to 26
5 to 28
5 to 28
5 to 28
5 to 24
4.7 to 28
5 to 28
Input overvoltage
(V)
32
32
32
26
32
32
Maximum battery
charging current
(A)
10
10
10
10
10
10
1200
600
600
600
600
600
JEITA charging
temperature profile
No
No
Yes
No
No
No
DPM
No
IIN DPM
IIN DPM
IIN DPM
IIN DPM
VIN DPM
Cell chemistry
Number of cells in
series (minimum to
maximum, 4.2
V/cell)
Charge voltage
(minimum to
maximum) (V)
Input voltage range
(minimum to
maximum) (V)
Switching
frequency (kHz)
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SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
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6 Pin Configuration and Functions
VCC
BATDRV
BTST
HIDRV
PH
LODRV
RGE Package
24-Pin VQFN
Top View
24
23
22
21
20
19
ACN
1
18 REGN
ACP
2
17 GND
16 ACSET
ACDRV 3
TS
6
13 SRN
7
8
9
10
11
12
VFB
14 SRP
ISET1
5
VREF
STAT1
STAT2
15 ISET2
PG
4
TTC
CE
Pin Functions
PIN
NAME
DESCRIPTION
NO.
ACDRV
3
AC adapter to system MOSFET driver output. Connect through a 1-kΩ resistor to the gate of the ACFET P-channel
power MOSFET and the reverse conduction blocking P-channel power MOSFET. The internal gate drive is
asymmetrical, allowing a quick turnoff and slow turnon, in addition to the internal break-before-make logic with
respect to BATDRV. If needed, an optional capacitor from gate to source of the ACFET is used to slow down the ON
and OFF times.
ACN
1
Adapter current sense resistor, negative input. A 0.1-μF ceramic capacitor is placed from ACN to ACP to provide
differential-mode filtering. An optional 0.1-μF ceramic capacitor is placed from the ACN pin to GND for commonmode filtering.
ACP
2
Adapter current sense resistor, positive input. A 0.1-μF ceramic capacitor is placed from ACN to ACP to provide
differential-mode filtering. A 0.1-μF ceramic capacitor is placed from the ACP pin to GND for common-mode filtering.
ACSET
16
Adapter current set input. The voltage on the ACSET pin programs the input current regulation set point during
Dynamic Power Management (DPM).
BATDRV
23
Battery-to-system MOSFET 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. Connect this pin through a 1-kΩ resistor to the gate of the input BAT P-channel
MOSFET. Connect the source of the FET to the system load voltage node. Connect the drain of the FET to the
battery pack positive terminal. The internal gate drive is asymmetrical to allow a quick turnoff and slow turnon, in
addition to the internal break-before-make logic with respect to ACDRV. If needed, an optional capacitor from gate to
source of the BATFET is used to slow down the ON and OFF times.
BTST
22
PWM high-side driver positive supply. Connect to the phase-switching node (junction of the low-side power MOSFET
drain, high-side power MOSFET source, and output inductor). Connect the 0.1-μF bootstrap capacitor from PH to
BTST, and a bootstrap Schottky diode from REGN to BTST.
CE
4
Charge enable active HIGH logic input. HI enables charge. LO disables charge. It has an internal 1-MΩ pulldown
resistor.
GND
17
Low current sensitive analog and digital ground. On PCB layout, connect with thermal pad underneath the IC.
HIDRV
21
PWM high-side driver output. Connect to the gate of the high-side power MOSFET with a short trace.
ISET1
11
Fast charge current set input. The voltage on the ISET1 pin programs the fast charge current regulation set point.
ISET2
15
Precharge and termination current set input. The voltage on the ISET2 pin programs the precharge current regulation
set point and termination current trigger point.
4
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Pin Functions (continued)
PIN
NAME
DESCRIPTION
NO.
LODRV
19
PWM low-side driver output. Connect to the gate of the low-side power MOSFET with a short trace.
PG
8
Open-drain power good status output. Active LOW when IC has a valid VCC (not in UVLO or ACOV or SLEEP
mode). Active HIGH when IC has an invalid VCC. PG can be used to drive an LED or communicate with a host
processor.
PH
20
PWM high-side driver negative supply. Connect to the phase-switching node (junction of the low-side power
MOSFET drain, high-side power MOSFET source, and output inductor).
REGN
18
PWM low-side driver positive 6-V supply output. Connect a 1-μF ceramic capacitor from REGN to the GND pin, close
to the IC. Use for low-side driver and high-side driver bootstrap voltage by connecting a small-signal Schottky diode
from REGN to BTST.
SRN
13
Charge current sense resistor, negative input. A 0.1-μF ceramic capacitor is placed from SRN to SRP to provide
differential-mode filtering. An optional 0.1-μF ceramic capacitor is placed from the SRN pin to GND for commonmode filtering.
SRP
14
Charge current sense resistor, positive input. A 0.1-μF ceramic capacitor is placed from SRN to SRP to provide
differential-mode filtering. A 0.1-μF ceramic capacitor is placed from the SRP pin to GND for common-mode filtering.
STAT1
5
Open-drain charge status pin to indicate various charger operations (see Table 2).
Thermal
Pad
—
Exposed pad beneath the IC. Always solder the thermal pad to the board, and have vias on the thermal-pad plane
star-connecting to GND and to the ground plane for a high-current power converter. It also serves as a thermal pad
to dissipate the heat.
TS
6
Temperature qualification voltage input for battery pack negative temperature coefficient thermistor. Program the hot
and cold temperature window with a resistor divider from VREF to TS to GND (see Figure 15).
TTC
7
Safety Timer and termination control. Connect a capacitor from this node to GND to set the timer. When this input is
LOW, the timer and termination are disabled. When this input is HIGH, the timer is disabled but termination is
allowed.
STAT2
9
Open-drain charge status pin to indicate various charger operations (see Table 2).
VFB
12
Output voltage analog feedback adjustment. Connect the output of a resistive voltage divider from the battery
terminals to this node to adjust the output battery regulation voltage.
VREF
10
3.3-V regulated voltage output. Place a 1-μF ceramic capacitor from VREF to GND pin close to the IC. This voltage
could be used for programming of voltage and current regulation and for programming the TS threshold.
VCC
24
IC power positive supply. Connect through a 10-Ω to the common-source (diode-OR) point: source of high-side Pchannel MOSFET and source of reverse-blocking power P-channel MOSFET. Place a 1-μF ceramic capacitor from
VCC to the GND pin close to the IC.
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SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
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7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
(1) (2) (3)
MIN
MAX
–0.3
33
PH
–2
36
VFB
–0.3
16
REGN, LODRV, ACSET, TS, TTC
–0.3
7
BTST, HIDRV with respect to GND
–0.3
39
VREF, ISET1, ISET2
–0.3
3.6
–0.5
0.5
V
Junction temperature
–40
155
°C
Tstg Storage temperature
–55
155
°C
VCC, ACP, ACN, SRP, SRN, BATDRV, ACDRV, CE, STAT1,
STAT2, PG
Voltage
Maximum difference
voltage
TJ
(1)
(2)
(3)
ACP–ACN, SRP–SRN
UNIT
V
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating
Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to GND if not specified. Currents are positive into, negative out of the specified terminal. Consult Packaging
Section of the data book for thermal limitations and considerations of packages.
If the battery voltage in the application exceeds 16 V, a series resistor between the battery pack and VFB is required. The top resistor of
the resistor-divider on VFB satisfies this requirement.
7.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
6
Electrostatic discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged device model (CDM), per JEDEC specification JESD22C101 (2)
±500
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
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7.3 Recommended Operating Conditions
MIN
VCC, ACP, ACN, SRP, SRN, BATDRV, ACDRV, CE, STAT1, STAT2, PG
28
30
VFB
–0.3
14
REGN, LODRV, ACSET, TS, TTC
–0.3
6.5
BTST, HIDRV with respect to GND
–0.3
34
ISET1, ISET2
–0.3
3.3
VREF
Maximum difference
voltage
MAX UNIT
–2
PH
Voltage
NOM
–0.3
V
3.3
ACP–ACN, SRP–SRN
TJ Junction temperature
–0.2
0.2
V
0
125
°C
7.4 Thermal Information
bq24616
THERMAL METRIC
(1)
RGE [VQFN]
UNIT
24 PINS
RθJA
Junction-to-ambient thermal resistance
43
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
RθJB
Junction-to-board thermal resistance
54.3
°C/W
20
ψJT
°C/W
Junction-to-top characterization parameter
0.6
°C/W
ψJB
Junction-to-board characterization parameter
19
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
4
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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7.5 Electrical Characteristics
4.7 V ≤ VVCC ≤ 28 V, 0°C < TJ < 125°C, typical values are at TA = 25°C, with respect to GND (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
OPERATING CONDITIONS
VVCC_OP
VCC input voltage operating range
4.7
28
V
QUIESCENT CURRENTS
Total battery discharge current (sum of
currents into VCC, BTST, PH, ACP,
ACN, SRP, SRN, VFB), VFB ≤ 2.1 V
IBAT
Battery discharge current (sum of
currents into BTST, PH, SRP, SRN,
VFB), VFB ≤ 2.1 V
Adapter supply current (current into
VCC, ACP, ACN pin)
IAC
VVCC < VSRN, VVCC > VUVLO (SLEEP)
15
VVCC > VSRN, VVCC > VUVLO CE = LOW
5
VVCC > VSRN, VVCC > VVCCLOW CE = HIGH, charge
done
5
VVCC > VSRN, VVCC > VUVLO CE = LOW (IC quiescent
current)
1
1.5
VVCC > VSRN, VVCC > VVCCLOW , CE = HIGH, charge
done
2
5
VVCC > VSRN, VVCC > VVCCLOW , CE = HIGH, charging,
Qg_total = 20 nC
µA
mA
25
CHARGE VOLTAGE REGULATION
VFB
Feedback regulation voltage
Charge voltage regulation accuracy
IVFB
Leakage current into VFB pin
2.1
V
TJ = 0°C to 85°C
–0.5%
0.5%
TJ = –40°C to 125°C
–0.7%
0.7%
VFB = 2.1 V
100
100
nA
CURRENT REGULATION – FAST CHARGE
VISET1
ISET1 voltage range
VIREG_CHG
SRP-SRN current sense voltage range
VIREG_CHG = VSRP – VSRN
KISET1
Charge current set factor (amps of
charge current per volt on ISET1 pin)
RSENSE = 10 mΩ
Charge-current regulation accuracy
IISET1
Leakage current into ISET1 pin
2
5
V
mV
A/V
VIREG_CHG = 40 mV
–3%
VIREG_CHG = 20 mV
–4%
3%
4%
VIREG_CHG = 5 mV
–25%
25%
VIREG_CHG = 1.5 mV (VSRN > 3.1 V)
–40%
40%
VISET1 = 2 V
100
nA
2
V
CURRENT REGULATION – PRECHARGE
VISET2
ISET2 voltage range
KISET2
Precharge current set factor (amps of
Precharge current per volt on ISET2
pin)
Precharge-current regulation accuracy
IISET2
Leakage current into ISET2 pin
RSENSE = 10 mΩ
1
A/V
VIREG_PRECH = 20 mV
–4%
4%
VIREG_PRECH = 5 mV
–25%
25%
VIREG_PRECH = 1.5 mV (VSRN < 3.1 V)
–55%
55%
VISET2 = 2 V
100
nA
CHARGE TERMINATION
Termination current set factor (amps of
termination current per volt on ISET2
pin)
KTERM
Termination current accuracy
RSENSE = 10 mΩ
1
A/V
VITERM = 20 mV
–4%
4%
VITERM = 5 mV
–25%
25%
VITERM = 1.5 mV
–45%
45%
Deglitch time for termination (both
edges)
100
tQUAL
Termination qualification time
VBAT > VRECH and ICHG < ITERM
IQUAL
Termination qualification current
Discharge current once termination is detected
ms
250
ms
2
mA
INPUT CURRENT REGULATION
VACSET
ACSET voltage range
VIREG_DPM
ACP-ACN current sense voltage range
VIREG_DPM = VACP – VACN
KACSET
Input current set factor (amps of input
current per volt on ACSET pin)
RSENSE = 10 mΩ
8
2
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100
5
V
mV
A/V
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Electrical Characteristics (continued)
4.7 V ≤ VVCC ≤ 28 V, 0°C < TJ < 125°C, typical values are at TA = 25°C, with respect to GND (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
VIREG_DPM = 40 mV
Input current regulation accuracy
leakage current into ACSET pin
IACSET
IISET1
Leakage current into ACSET pin
TYP
–3%
MAX
UNIT
3%
VIREG_DPM = 20 mV
–4%
4%
VIREG_DPM = 5 mV
–25%
25%
VACSET = 2 V
100
nA
INPUT UNDERVOLTAGE LOCKOUT COMPARATOR (UVLO)
VUVLO
AC undervoltage rising threshold
VUVLO_HYS
AC undervoltage hysteresis, falling
Measure on VCC
3.65
3.85
4
350
V
mV
VCC LOWV COMPARATOR
Falling threshold, disable charge
Measure on VCC
4.1
Rising threshold, resume charge
V
4.35
4.5
V
100
150
mV
600
mV
SLEEP COMPARATOR (REVERSE DISCHARGING PROTECTION)
VSLEEP
_FALL
VSLEEP_HYS
SLEEP falling threshold
VVCC – VSRN to enter SLEEP
40
SLEEP rising threshold
μs
SLEEP rising delay
VCC falling below SRN, delay to turn off ACFET
1
SLEEP falling delay
VCC rising above SRN, delay to turn on ACFET
30
μs
SLEEP rising shutdown deglitch
VCC falling below SRN, delay to enter SLEEP mode
100
ms
SLEEP falling power up deglitch
VCC rising above SRN, delay to exit SLEEP mode
30
ms
ACN / SRN COMPARATOR
VACN-SRN_FALL
ACN to SRN falling threshold
VACN-SRN_HYS
ACN to SRN rising hysteresis
VACN – VSRN to turn on BATFET
100
200
310
mV
100
mV
ACN to SRN rising deglitch
VACN – VSRN > VACN-SRN_RISE
2
ms
ACN to SRN falling deglitch
VACN – VSRN < VACN-SRN_FALL
50
μs
BAT LOWV COMPARATOR
VLOWV
Precharge to fast charge transition
(LOWV threshold)
VLOWV_HYS
LOWV hysteresis
Measured on VFB pin, Rising
1.534
1.55
1.566
V
100
mV
LOWV rising deglitch
VFB falling below VLOWV
25
ms
LOWV falling deglitch
VFB rising above VLOWV + VLOWV_HYS
25
ms
RECHARGE COMPARATOR
VRECHG
Recharge threshold (with respect to
VREG)
Measured on VFB pin, falling
Recharge rising deglitch
VFB decreasing below VRECHG
10
ms
Recharge falling deglitch
VFB decreasing above VRECHG
10
ms
35
50
65
mV
BAT OVERVOLTAGE COMPARATOR
VOV_RISE
Overvoltage rising threshold
As percentage of VFB
104%
VOV_FALL
Overvoltage falling threshold
As percentage of VFB
102%
INPUT OVERVOLTAGE COMPARATOR (ACOV)
VACOV
AC overvoltage rising threshold on VCC
VACOV_HYS
AC overvoltage falling hysteresis
31.04
32
32.96
V
1
V
1
ms
AC overvoltage deglitch (both edge)
Delay to changing the STAT pins
AC overvoltage rising deglitch
Delay to disable charge
1
ms
AC overvoltage falling deglitch
Delay to resume charge
20
ms
Temperature increasing
145
°C
15
°C
THERMAL SHUTDOWN COMPARATOR
TSHUT
Thermal shutdown rising temperature
TSHUT_HYS
Thermal shutdown hysteresis
Thermal shutdown rising deglitch
Temperature increasing
100
μs
Thermal shutdown falling deglitch
Temperature decreasing
10
ms
THERMISTOR COMPARATOR
VLTF
Cold temperature rising threshold
As percentage of VVREF
72.5%
73.5%
74.5%
VLTF_HYS
Rising hysteresis
As percentage of VVREF
0.2%
0.4%
0.6%
VHTF
Hot temperature rising threshold
As percentage of VVREF
36.2%
37%
37.8%
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Electrical Characteristics (continued)
4.7 V ≤ VVCC ≤ 28 V, 0°C < TJ < 125°C, typical values are at TA = 25°C, with respect to GND (unless otherwise noted)
PARAMETER
VTCO
TEST CONDITIONS
Cut-off temperature rising threshold
As percentage of VVREF
Deglitch time for temperature out-ofrange detection
VTS > VLTF, or VTS < VTCO, or VTS < VHTF
Deglitch time for temperature in-validrange detection
VTS < VLTF – VLTF_HYS or VTS >VTCO, or VTS > VHTF
MIN
TYP
MAX
33.7%
34.4%
35.1%
UNIT
400
ms
20
ms
45.5
mV
CHARGE OVERCURRENT COMPARATOR (CYCLE-BY-CYCLE)
Charge overcurrent falling threshold
VOC
Current rising, in nonsynchronous mode, measure on
V(SRP-SRN), VSRP < 2 V
Current rising, as percentage of V(IREG_CHG), in
synchronous mode, VSRP > 2.2 V
160%
Charge overcurrent threshold floor
Minimum OCP threshold in synchronous mode,
measure on V(SRP-SRN), VSRP > 2.2 V
50
Charge overcurrent threshold ceiling
Maximum OCP threshold in synchronous mode,
measure on V(SRP-SRN), VSRP > 2.2 V
180
mV
CHARGE UNDERCURRENT COMPARATOR (CYCLE-BY-CYCLE)
VISYNSET
Charge undercurrent falling threshold
Switch from SYNCH to NON-SYNCH, VSRP > 2.2 V
1
5
9
mV
BATTERY SHORTED COMPARATOR (BATSHORT)
VBATSHT
BAT short falling threshold, forced
nonsynchronous mode
VBATSHT_HYS
BAT short rising hysteresis
VBATSHT_DEG
Deglitch on both edge
VSRP falling
2
V
200
mV
1
μs
1.25
mV
1.25
mV
1
μs
LOW CHARGE CURRENT COMPARATOR
VLC
Low charge current (average) falling
threshold to force into nonsynchronous
mode
VLC_HYS
Low charge current rising hysteresis
VLC_DEG
Deglitch on both edge
Measure on V(SRP-SRN)
VREF REGULATOR
VVREF_REG
VREF regulator voltage
VVCC > VUVLO, (0- to 35-mA load)
IVREF_LIM
VREF current limit
VVREF = 0 V, VVCC > VUVLO
3.267
35
3.3
3.333
V
mA
REGN REGULATOR
VREGN_REG
REGN regulator voltage
VVCC > 10 V, CE = HIGH, (0- to 40-mA load)
5.7
IREGN_LIM
REGN current limit
VREGN = 0 V, VVCC > VUVLO, CE = HIGH
40
6.0
6.3
V
mA
TTC INPUT AND SAFETY TIMER
TPRECHG
Precharge safety timer range (1)
Precharge time before fault occurs
TCHARGE
Fast-charge safety timer range, with
±10% accuracy (1)
Tchg = CTTC × KTTC
Fast-charge timer accuracy (1)
0.01 μF ≤ CTTC ≤ 0.11 μF
KTTC
1440
2160
sec
1
10
Hr
–10%
10%
Timer multiplier
TTC low threshold
1800
5.6
VTTC below this threshold disables the safety timer and
termination
min/nF
0.4
TTC oscillator high threshold
1.5
TTC oscillator low threshold
V
1
TTC source/sink current
45
50
V
V
55
μA
BATTERY SWITCH (BATFET) DRIVER
RDS_BAT_OFF
BATFET turnoff resistance
VACN > 5 V
150
Ω
RDS_BAT_ON
BATFET turnon resistance
VACN > 5 V
20
kΩ
VBATDRV_REG
BATFET drive voltage
VBATDRV_REG = VACN – VBATDRV when VACN > 5 V and
BATFET is on
4.2
7
V
VBATFET_ACN
ACN voltage to keep BATFET on
BATFET on
2.6
V
AC SWITCH (ACFET) DRIVER
RDS_AC_OFF
ACFET turnoff resistance
VVCC > 5 V
30
Ω
RDS_AC_ON
ACFET turnon resistance
VVCC > 5 V
20
kΩ
(1)
10
Verified by design.
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Electrical Characteristics (continued)
4.7 V ≤ VVCC ≤ 28 V, 0°C < TJ < 125°C, typical values are at TA = 25°C, with respect to GND (unless otherwise noted)
PARAMETER
VACDRV_REG
TEST CONDITIONS
MIN
VACDRV_REG = VVCC – VACDRV when VVCC > 5 V and
ACFET is on
ACFET drive voltage
TYP
4.2
MAX
7
UNIT
V
AC / BAT MOSFET DRIVERS TIMING
Driver dead time
Dead time when switching between AC and BAT
μs
10
BATTERY DETECTION
tWAKE
Wake time
Maximum time charge is enabled
IWAKE
Wake current
RSENSE = 10 mΩ
tDISCHARGE
Discharge time
Maximum time discharge current is applied
IDISCHARGE
Discharge current
IFAULT
Fault current after a time-out fault
VWAKE
Wake threshold (with respect to VREG)
Voltage on VFB to detect battery absent during wake
Discharge threshold
Voltage on VFB to detect battery absent during
discharge
VDISCH
500
50
125
ms
200
mA
1
s
8
mA
2
mA
50
mV
1.55
V
PWM HIGH-SIDE DRIVER (HIDRV)
RDS_HI_ON
High-side driver (HSD) turnon
resistance
VBTST – VPH = 5.5 V
3.3
6
Ω
RDS_HI_OFF
High-side driver turnoff resistance
VBTST – VPH = 5.5 V
1
1.3
Ω
VBTST_REFRESH
Bootstrap refresh comparator threshold
voltage
VBTST – VPH when low side refresh pulse is requested
4.0
4.2
V
PWM LOW-SIDE DRIVER (LODRV)
RDS_LO_ON
Low-side driver (LSD) turnon resistance
RDS_LO_OFF
Low-side driver turnoff resistance
4.1
7
Ω
1
1.4
Ω
PWM DRIVERS TIMING
Driver dead time
Dead time when switching between LSD and HSD, no
load at LSD and HSD
PWM ramp height
As percentage of VCC
30
ns
PWM OSCILLATOR
VRAMP_HEIGHT
7%
PWM switching frequency (1)
510
600
690
kHz
INTERNAL SOFT START (8 steps to regulation current ICHG)
Soft-start steps
Soft-start step time
8
step
1.6
ms
1.5
s
CHARGER SECTION POWER-UP SEQUENCING
Charge enable delay after power up
Delay from CE = 1 until charger is allowed to turn on
LOGIC IO PIN CHARACTERISTICS (CE, STAT1, STAT2, PG)
VIN_LO
CE input-low threshold voltage
VIN_HI
CE input-high threshold voltage
0.8
V
VBIAS_CE
CE input bias current
V = 3.3 V (CE has internal 1-MΩ pulldown resistor)
VOUT_LO
STAT1, STAT2, PG output low
saturation voltage
6
μA
Sink current = 5 mA
0.5
V
IOUT_HI
Leakage current
V = 32 V
1.2
µA
2.1
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7.6 Typical Characteristics
Table 1. Table of Graphs
FIGURE
Figure 1
Charge Enable
Figure 2
Current Soft Start (CE = 1)
Figure 3
Charge Disable
Figure 4
Continuous Conduction Mode Switching Waveforms
Figure 5
Cycle-by-Cycle Synchronous to Nonsynchronous
Figure 6
100% Duty and Refresh Pulse
Figure 7
Transient System Load (DPM)
Figure 8
Battery Insertion
Figure 9
Battery-to-Ground Short Protection
Figure 10
Battery-to-Ground Short Transition
Figure 11
Efficiency vs Output Current
Figure 12
10 V/div
10 V/div
REF, REGN, and PG Power Up (CE = 1)
PH
2 A/div
IBAT
REGN
5 V/div
CE
5 V/div
2 V/div
VREF
5 V/div
/PG
2 V/div
VCC
LODRV
t − Time = 200 ms/div
t − Time = 4 ms/div
Figure 2. Charge Enable
10 V/div
10 V/div
Figure 1. REF, REGN, and PG Power Up (CE = 1)
CE
5 V/div
2 A/div
IBAT
PH
5 V/div 2 A/div
5 V/div
LODRV
5 V/div
PH
LODRV
IL
CE
t − Time = 2 μs/div
t − Time = 4 ms/div
Figure 3. Current Soft Start (CE = 1)
12
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Figure 4. Charge Disable
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5 V/div
PH
HIDRV
LODRV
1 A/div 5 V/div
PH
2 A/div
5 V/div 20 V/div 20 V/div
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IL
LODRV
IL
t − Time = 100 ns/div
t − Time = 100 ns/div
10 V/div
2 A/div
IIN
PH
ISYS
LODRV
2 A/div
0.5 A/div 5 V/div
Figure 6. Cycle-by-Cycle Synchronous to Nonsynchronous
2 A/div
Figure 5. Continuous Conduction Mode Switching
Waveform
IL
IBAT
t − Time = 200 μs/div
t − Time = 400 ns/div
Figure 7. 100% Duty and Refresh Pulse
10 V/div
10 V/div
Figure 8. Transient System Load (DPM)
PH
2 A/div
LODRV
IL
IL
20 V/div
2 A/div
5 V/div
5 V/div
PH
VBAT
VBAT
t − Time = 200 ms/div
Figure 9. Battery Insertion
t − Time = 4 ms/div
Figure 10. Battery-to-GND Short Protection
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10 V/div
98
96
94
20 V/div
20 Vin, 4 cell
Efficiency - %
92
LODRV
2 A/div
5 V/div
PH
12 Vin, 2 cell
20 Vin, 3 cell
90
88
86
IL
12 Vin, 1 cell
VBAT
84
82
t − Time = 10 μs/div
80
0
Figure 11. Battery-to-GND Short Transition
14
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1
2
5
4
3
IBAT - Output Current - A
6
7
8
Figure 12. Efficiency vs Output Current
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8 Detailed Description
8.1 Overview
The bq2461x is a stand-alone, integrated Li-ion or Li-polymer battery charger that accommodates USB
applications with a minimum input voltage of 4.7 V. It employs a switched-mode synchronous buck PWM
controller with constant switching frequency. The device controls external switches to prevent battery discharge
back to the input, to connect the adapter to the system, and to connect the battery to the system using 6-V gate
drives for better system efficiency. The bq2461x features Dynamic Power Management (DPM) which reduces
battery charge current when the input power limit is reached to avoid overloading the AC adapter when supplying
current to the system 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. The input current
limit can be configured through the ACSET pin of the device.
The bq2461x has a battery detect scheme that allows it to automatically detect the presence and absence of a
battery. When the battery is detected, charging begins in one of three phases (depending upon battery voltage):
precharge, constant current (fast charge current regulation), and constant voltage (fast charge voltage
regulation). The device will terminate charging when the termination current threshold has been reached and will
begin a recharge cycle when the battery voltage has dropped below the recharge threshold (VRECHG). Precharge,
constant current, and termination current can be configured through the ISET1 and ISET2 pins, allowing for
flexibility in battery charging profile. During charging, the integrated fault monitors of the device, such as battery
overvoltage protection, battery short detection (VBATSHT), thermal shutdown (internal TSHUT and TS pin), safety
timer expiration (TTC pin), and input voltage protection (VACOV), ensure battery safety.
The bq2461x has three status pins (STAT1, STAT2, and PG) to indicate the charging status and input voltage
(AC adapter) status. These pins can be used to drive LEDs or communicate with a host processor.
Regulation Voltage
VRECH
Regulation Current
Precharge
Current
Regulation
Phase
Fastcharge Current
Regulation Phase
Fastcharge Voltage
Regulation Phase
Termination
Charge
Current
Charge
Voltage
VLOWV
IPRECH
and
ITERM
Precharge
Fastcharge Safety Time
Time
Figure 13. Typical Charging Profile
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8.2 Functional Block Diagram
bq24618
VREF
VCC-6 V
ACN ACN-6 V ACN-6 V
LDO
INTERNAL
REFERENCE
VREF
3.3 V
LDO
VCC
-
SRN+100 mV
+
VCC
-
VUVLO
+
ACN
+
VCC
VCC
SLEEP
UVLO
VCC
VCC-6 V
LDO
SLEEP
SRN+200 mV
UVLO
ACN-SRN
-
ACDRV
SYSTEM
POWER
SELECTOR
LOGIC
VCC-6V
ACN
ACOV
CE
BATDRV
1M
ACN-6V
+
20X
-
V(ACP-ACN)
+
COMP
ERROR
AMPLIFIER
ACN
ACSET
CE
+
1V
+
-
2.1 V
+
+
5 mV -
REGN
2 mA
LODRV
V(SRP-SRN)
160% X IBAT_REG
-
CHG_OCP
GND
TTC
Safety
Timer
IC Tj
+
145 degC
-
CHARGE
FAULT
STAT 1
STAT1
ISET1
IBAT_ REG
ISET2
+
LOWV
104% X VBAT_REG
-
-
BAT
+
ISET2
6 V LDO
REFRESH
4.2V
FAULT
+
ISET1
CE
+
+
-
PH
-
PH
VCC
PWM
CONTROL
LOGIC
BTST
20µA
8 mA
SYNCH
-
IBAT_ REG
SRN
CHARGE
OR
DISCHARGE
+
SRP-SRN
-
V(SRP-SRN)
HIDRV
BAT_OVP
20 µA
+
20X
-
LEVEL
SHIFTER
PWM
-
VFB
SRP
BTST
+
ACP
TSHUT
STATE
MACHINE
LOGIC
BAT_OVP
STAT 2
STAT2
PG
PG
VFB
+
- 1.55V
TTC
-
0.4 V
+
VCC
+
DISABLE
TMR/TERM
BATTERY
DETECTION
LOGIC
ACOV
TTC
TTC
VREF
DISCHARGE
VACOV +-
LTF
+
VFB
-
TS
SUSPEND
RCHRG
HTF
+
+
-
2.05 V +-
RCHRG
V(SRP - SRN)
+
ISET2
-
TERM
TERM
TCO
+
-
TERMINATE CHARGE
16
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8.3 Feature Description
8.3.1 Battery Voltage Regulation
The bq24618 uses a high-accuracy voltage band gap and regulator for the high charging voltage accuracy. The
charge voltage is programmed through a resistor divider from the battery to ground, with the midpoint tied to the
VFB pin. The voltage at the VFB pin is regulated to 2.1 V, giving the following equation for the regulation voltage:
é R2 ù
V
= 2.1 V ´ ê1+
ú,
BAT
ë R1 û
where
•
•
R2 is connected from VFB to the battery.
R1 is connected from VFB to GND.
(1)
8.3.2 Battery Current Regulation
The ISET1 input sets the maximum fast-charging current. Battery charge current is sensed by resistor RSR
connected between SRP and SRN. The full-scale differential voltage between SRP and SRN is 100 mV. Thus,
for a 10-mΩ sense resistor, the maximum charging current is 10 A. The equation for charge current is:
VISET1
ICHARGE =
20 ´ RSR
(2)
VISET1, the input voltage range of ISET1, is from 0 V to 2 V. The SRP and SRN pins are used to sense voltage
across RSR using the default value of 10 mΩ. However, resistors of other values can also be used. A larger
sense resistor gives a larger sense voltage and a higher regulation accuracy, but at the expense of higher
conduction loss.
8.3.3 Input Adapter Current Regulation
The total input from an AC adapter or other DC source is a function of the system supply current and the battery
charging current. System current normally fluctuates as portions of the systems are powered up or down. Without
DPM, the source must be able to supply the maximum system current and the maximum charger input current
simultaneously. By using DPM, the battery charger reduces the charging current when the input current exceeds
the input current limit set by ACSET. The current capability of the AC adaptor can be lowered, reducing system
cost.
Similar to sensing battery regulation current, adaptor current is sensed by resistor RAC connected between ACP
and ACN. Its maximum value is set by ACSET using Equation 3:
VACSET
IDPM =
20 ´ RAC
(3)
VACSET, the input voltage range of ACSET, is from 0 V to 2 V. The ACP and ACN pins are used to sense voltage
across RAC using the default value of 10 mΩ. However, resistors of other values can also be used. A larger
sense resistor gives a larger sense voltage and a higher regulation accuracy, but at the expense of higher
conduction loss.
8.3.4 Precharge
On power up, if the battery voltage is below the VLOWV threshold, the bq24618 applies the precharge current to
the battery. This feature is intended to revive deeply discharged cells. If the VLOWV threshold is not reached within
30 minutes of initiating precharge, the charger turns off and a FAULT is indicated on the status pins.
The precharge current is determined by the voltage on the ISET2 pin, VISET2, according to Equation 4.
VISET2
IPRECHARGE =
100 ´ R SR
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Feature Description (continued)
8.3.5 Charge Termination, Recharge, and Safety Timer
The bq24618 monitors the charging current during the voltage regulation phase. When VTTC is valid, termination
is detected while the voltage on the VFB pin is higher than the VRECH threshold AND the charge current is less
than the ITERM threshold, as calculated in Equation 5:
VISET2
ITERM =
100 ´ RSR
(5)
The input voltage of ISET2 is from 0 V to 2 V. The minimum precharge and termination current is clamped to be
around 125 mA with default 10-mΩ sensing resistor. As a safety backup, the bq24618 also provides a
programmable charge timer. The charge time is programmed by the capacitor connected between the TTC pin
and GND, and is given by Equation 6
tCHARGE = CTTC ´ K TTC
where
•
•
A
•
•
•
CTTC (range from 0.01 µF to 0.11 µF to give 1-h to 10-h safety time) is the capacitor connected from the TTC
pin to GND.
KTTC is the constant multiplier (5.6 min/nF).
(6)
new charge cycle is initiated and the safety timer is reset when any of the following conditions occurs:
The battery voltage falls below the recharge threshold.
A power-on-reset (POR) event occurs.
CE is toggled.
The TTC pin may be taken LOW to disable termination and to disable the safety timer. If TTC is pulled to VREF,
the bq24618 continues to allow termination but disable the safety timer. TTC taken low resets the safety timer.
When ACOV, VCCLOWV, and SLEEP mode resume normal, the safety timer is reset.
8.3.6 Power Up
The bq24618 uses a SLEEP comparator to determine the source of power on the VCC pin, because VCC can be
supplied either from the battery or the adapter. If the VCC voltage is greater than the SRN voltage, the bq24618
enables the ACFET and disables BATFET. If all other conditions are met for charging, the bq24618 then
attempts to charge the battery (see Enable and Disable Charging). If the SRN voltage is greater than VCC,
indicating that the battery is the power source, the bq24618 enables the BATFET and enters a low quiescent
current ( VRECH
Yes
Disable 125-mA
Charge
No
0.5-s timer
expired
No
Yes
Battery Present,
Begin Charge
Battery Absent
Figure 16. Battery-Detection Flow Chart
Once the device has powered up, an 8-mA discharge current is applied to the SRN terminal. If the battery
voltage falls below the LOWV threshold within 1 second, the discharge source is turned off, and the charger is
turned on at low charge current (125 mA). If the battery voltage rises above the recharge threshold within 500
ms, there is no battery present and the cycle restarts. If either the 500-ms or 1-second timer times out before its
respective threshold is hit, a battery is detected and a charge cycle is initiated.
24
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Battery not detected
VREG
VRECH
(VWAKE)
Battery
inserted
VLOWV
Battery detected
(VDISH)
tRECH_DEG
tLOWV_DEG
tWAKE
Figure 17. Battery-Detect Timing Diagram
Ensure that the total output capacitance at the battery node is not so large that the discharge current source
cannot pull the voltage below the LOWV threshold during the 1-second discharge time. The maximum output
capacitance can be calculated as follows:
CMAX =
IDISCH ´ tDISCH
é R ù
0.5 ´ ê1+ 2 ú
ë R1 û
where
•
•
•
•
CMAX is the maximum output capacitance.
IDISCH is the discharge current.
tDISCH is the discharge time.
R2 and R1 are the voltage feedback resistors from the battery to the VFB pin.
(10)
The 0.5 factor is the difference between the RECHARGE and the LOWV thresholds at the VFB pin.
Example
For a three-cell Li+ charger, with R2 = 500 kΩ, R1 = 100 kΩ (giving 12.6 V for voltage regulation), IDISCH = 8 mA,
tDISCH = 1 second,
8mA ´ 1sec
CMAX =
= 2.7 mF
é 500k ù
0.5 ´ ê1+
ú
ë 100k û
(11)
Based on these calculations, no more than 2.7 mF should be allowed on the battery node for proper operation of
the battery detection circuit.
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8.4 Device Functional Modes
Figure 18. Operational Flow Chart
26
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The bq24618 battery charger is ideal for high current charging (up to 10 A) and can charge battery packs
consisting of single cells or multiple cells in series. The bq24610EVM evaluation module is a complete charge
module for evaluating the bq2461x. The application curves were taken using the bq24610EVM. Refer to the EVM
user's guide (SLUU396) for EVM information.
9.2 Typical Application
Q1 (ACFET)
SI7617DN
R17
10Ω
SYSTEM
P
ADAPTER-
P
R14
100 kW
C16
2.2μF
RAC
0.010 W
Q2 (ACFET)
SI7616DN
C14
0.1 mF
C15
0.1 µF
C3
0.1 µF
C2
0.1 µF
ACN
VCC
BATDRV
ACDRV
R5
100 kW
R7
100 kW
R18
1 kΩ
R6
10 kW
R15
100 kW
PH
ISET2
BTST
R8
22.1 kW
REGN
C6
0.1 µF
C5
1 µF
bq24618
VREF
LODRV
C4
1 µF
Q4
SIS412DN
L1
D1
BAT54
D2
R12 10 kW
D3
C10
0.1 µF
D4
VREF
Pack
Thermistor
Sense
103AT
R10
430 kW
PACK+
PACK-
C12
C13
10 µF* 10 µF*
C11
0.1 µF
R2
500 kΩ
Cff
22 pF
STAT1
SRP
ADAPTER +
VBAT
6.8 µH*
Q5
SIS412DN
GND
R9
9.31 kW
RSR
0.010 W
CE
R11 10 kW
R13 10 kW
P
Q3 (BATFET)
SI7617DN
R19
1 kΩ
HIDRV
ISET1
ACSET
R4
32.4 kW
C7
1µF
ACP
VREF
R3
100 kW
C9
10 μF
C8
10 µF
N
R20
2Ω
N
ADAPTER+
R1
100 kW
SRN
STAT2
PG
VFB
R16
100 W
C1
0.1 μF
TS
TTC
PwrPad
CTTC
0.056 μF
VIN = 19 V, 3-cell, Iadapter_limit = 4 A, Icharge = 3 A, Ipre-charge = Iterm = 0.3 A, 5-hour safety timer
Figure 19. Typical System Schematic
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Typical Application (continued)
9.2.1 Design Requirements
For this design example, use the parameters listed in Table 3 as the input parameters.
Table 3. Design Parameters
DESIGN PARAMETER
AC adapter voltage (VIN)
VALUE
19 V
AC adapter current limit
4A
Battery charge voltage (number of cells in series)
Battery charge current (during constant current phase)
Precharge and termination current
12.6 V (3 cells)
3A
0.3 A
Safety timer
5 hours
9.2.2 Detailed Design Procedure
9.2.2.1 Inductor Selection
The bq2461x has 600-kHz switching frequency to allow the use of small inductor and capacitor values. Inductor
saturation current should be higher than the charging current (ICHG) plus half the ripple current (IRIPPLE):
ISAT ³ ICHG + (1/2) IRIPPLE
(12)
The inductor ripple current depends on input voltage (VIN), duty cycle (D = VOUT/VIN), switching frequency (fS) and
inductance (L):
V ´ D ´ (1 - D)
IRIPPLE = IN
fS ´ L
(13)
The maximum inductor ripple current happens with D = 0.5 or close to 0.5. For example, the battery charging
voltage range is from 9 V to 12.6 V for a three-cell battery pack. For 20-V adapter voltage, 10-V battery voltage
gives the maximum inductor ripple current. Another example is a four-cell battery, where the battery voltage
range is from 12 V to 16.8 V, and 12-V battery voltage gives the maximum inductor ripple current.
Usually inductor ripple is designed in the range of 20% to 40% of maximum charging current as a trade-off
between inductor size and efficiency for a practical design.
The bq24618 has cycle-by-cycle charge undercurrent protection (UCP) by monitoring the charge current-sensing
resistor to prevent negative inductor current. The typical UCP threshold is 5 mV falling edge, corresponding to
0.5 A falling edge for a 10-mΩ charge current-sensing resistor.
9.2.2.2 Input Capacitor
The input capacitor should have enough ripple current rating to absorb the input switching ripple current. The
worst-case RMS ripple current is half of the charging current when the duty cycle is 0.5. If the converter does not
operate at 50% duty cycle, then the worst-case capacitor RMS current ICIN occurs where the duty cycle is closest
to 50% and can be estimated by the following equation:
ICIN = ICHG ´
D ´ (1 - D)
(14)
A low-ESR ceramic capacitor such as X7R or X5R is preferred for the input decoupling capacitor and should be
placed as close as possible to the drain of the high-side MOSFET and source of the low-side MOSFET. The
voltage rating of the capacitor must be higher than the normal input voltage level. A 25-V rating or higher
capacitor is preferred for 20-V input voltage. A 10-µF to 20-µF capacitor is suggested for typical 3-A to 4-A
charging current.
9.2.2.3 Output Capacitor
The output capacitor also should have enough ripple current rating to absorb output switching ripple current. The
output capacitor RMS current ICOUT is given:
28
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ICOUT =
IRIPPLE
2 ´
3
» 0.29 ´ IRIPPLE
(15)
The output capacitor voltage ripple can be calculated as follows:
DVo =
1
8LCfs
2
æ
V 2
ç VBAT - BAT
ç
VIN
è
ö
÷
÷
ø
(16)
At certain input/output voltage and switching frequency, the voltage ripple can be reduced by increasing the
output filter LC.
The bq24618 has an internal loop compensator. To get good loop stability, the resonant frequency of the output
inductor and output capacitor should be designed from 12 kHz to 17 kHz. The preferred ceramic capacitor is 25V or higher rating, X7R or X5R for 4-cell applications.
9.2.2.4 Power MOSFET Selection
Two external N-channel MOSFETs are used for a synchronous switching battery charger. The gate drivers are
internally integrated into the IC with 6 V of gate drive voltage. MOSFETs of 30-V or higher voltage rating are
preferred for 20-V input voltage and 40-V or higher rating MOSFETs are preferred for 20-V to 28-V input voltage.
Figure-of-merit (FOM) is usually used for selecting proper the MOSFET, based on a trade-off between the
conduction loss and switching loss. For a top-side MOSFET, FOM is defined as the product of a MOSFET ONresistance, rDS(on), and the gate-to-drain charge, QGD. For a bottom-side MOSFET, FOM is defined as the product
of the MOSFET ON-resistance, rDS(on), and the total gate charge, QG.
FOM top = RDS(on) ´ QG D
FOMbottom = RDS(on) ´ QG
(17)
The lower the FOM value, the lower the total power loss. Usually, lower rDS(on) has higher cost with the same
package size.
The top-side MOSFET loss includes conduction loss and switching loss. It is a function of duty cycle (D =
VOUT/VIN), charging current (ICHG), MOSFET ON-resistance rDS(on)), input voltage (VIN), switching frequency (fS),
turnon time (ton) and turnoff time (toff):
1
Ptop = D ´ ICHG2 ´ RDS(on) +
´ VIN ´ ICHG ´ (t on + t off ) ´ fS
2
(18)
The first item represents the conduction loss. Usually MOSFET rDS(on) increases by 50% with a 100ºC junction
temperature rise. The second term represents the switching loss. The MOSFET turnon and turnoff times are
given by:
Q
Q
ton = SW , t off = SW
Ion
Ioff
where
•
•
•
Qsw is the switching charge.
Ion is the turnon gate-drive current.
Ioff is the turnoff gate-drive current.
(19)
If the switching charge is not given in the MOSFET data sheet, it can be estimated by gate-to-drain charge (QGD)
and gate-to-source charge (QGS):
1
QSW = QGD +
´ QGS
2
(20)
Total gate drive current can be estimated by the REGN voltage (VREGN), MOSFET plateau voltage (Vplt), total
turnon gate resistance (Ron), and turnoff gate resistance (Roff) of the gate driver:
VREG N - Vplt
Vplt
Ion =
, Ioff =
Ron
Roff
(21)
The conduction loss of the bottom-side MOSFET is calculated with the following equation when it operates in
synchronous continuous conduction mode:
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Pbottom = (1 - D) ´ ICHG 2 ´ RDS(on)
(22)
If the SRP-SRN voltage decreases below 5 mV (the charger is also forced into nonsynchronous mode when the
average SRP-SRN voltage is lower than 1.25 mV), the low-side FET is turned off for the remainder of the
switching cycle to prevent negative inductor current.
As a result, all the freewheeling current goes through the body diode of the bottom-side MOSFET. The maximum
charging current in nonsynchronous mode can be up to 0.9 A (0.5 A typical) for a 10-mΩ charging current
sensing resistor, considering IC tolerance. Choose the bottom-side MOSFET with either an internal Schottky or
body diode capable of carrying the maximum nonsynchronous mode charging current.
MOSFET gate driver power loss contributes to the dominant losses on the controller IC when the buck converter
is switching. Choosing a MOSFET with a small Qg_total reduces the IC power loss to avoid thermal shutdown.
PICLoss_driver = VIN × Qg_total × fs
where
•
Qg_total is the total gate charge for both upper and lower MOSFET at 6 V VREGN.
(23)
9.2.2.5 Input Filter Design
During adapter hot plug-in, the parasitic inductance and input capacitor from the adapter cable form a secondorder system. The voltage spike at the VCC pin may be beyond the IC maximum voltage rating and damage the
IC. The input filter must be carefully designed and tested to prevent an overvoltage event on the VCC pin. The
ACP/ACN pin must be placed after the input ACFET in order to avoid overvoltage stress on these pins during hot
plug-in.
There are several methods to damping or limiting the overvoltage spike during adapter hot plug-in. An electrolytic
capacitor with high ESR as an input capacitor can damp the overvoltage spike well below the IC maximum pin
voltage rating. A high current capability TVS Zener diode can also limit the overvoltage level to an IC-safe level.
However, these two solutions may not have low cost or small size.
A cost-effective and small-size solution is shown in Figure 20. R1 and C1 comprise a damping RC network to
damp the hot plug-in oscillation. As a result, the overvoltage spike is limited to a safe level. D1 is used for
reverse voltage protection for the VCC pin (it can be the body diode of the input ACFET). C2 is a VCC pin
decoupling capacitor, and it should be placed as close as possible to the VCC pin. R2 and C2 form a damping
RC network to further protect the IC from high dv/dt and high-voltage spikes. The value of C2 should be less
than the value of C1 so R1 can be dominant over the ESR orf C1 to get enough damping effect for hot plug-in.
The R1 and R2 packages must be sized to handle the inrush current power loss according to the resistor
manufacturer’s data sheet. The filter component values always must be verified with the real application, and
minor adjustments may be needed to fit in the real application circuit.
D1
Adapter
connector
R1
2W
C1
2.2 mF
(2010)
R2 (1206)
4.7 -30W
VCC pin
C2
0.1-1 mF
Figure 20. Input Filter
9.2.2.6 Inductor, Capacitor, and Sense Resistor Selection Guidelines
The bq24618 provides internal loop compensation. With this scheme, best stability occurs when the LC resonant
frequency, fo, is approximately 12 kHz to 17 kHz for the bq24618.
The following table provides a summary of typical LC components for various charge currents:
30
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Table 4. Typical Inductor, Capacitor, and Sense Resistor Values as a Function of Charge Current for
bq24618 (600-kHz Switching Frequency)
CHARGE CURRENT
2A
4A
6A
8A
10 A
Output inductor LO
6.8 μH
6.8 μH
4.7 μH
3.3 μH
3.3 μH
Output capacitor CO
20 μF
20 μF
30 μF
40 μF
40 μF
Sense resistor
10 mΩ
10 mΩ
10 mΩ
10 mΩ
10 mΩ
9.2.2.7 Component List for Typical System Circuit of Figure 19
PART DESIGNATOR
QTY
DESCRIPTION
Q1, Q2, Q3
2
P-channel MOSFET, –30 V, –35 A, PowerPAK 1212-8, Vishay-Siliconix, Si7617DN
Q4, Q5
2
N-channel MOSFET, 30 V, 12 A, PowerPAK 1212-8, Vishay-Siliconix, Sis412DN
D1
1
Diode, dual Schottky, 30 V, 200 mA, SOT23, Fairchild, BAT54C
D2, D3, D4
3
LED diode, green, 2.1 V, 20 mA, LTST-C190GKT
RAC, RSR
2
Sense resistor, 10 mΩ, 2010, Vishay-Dale, WSL2010R0100F
L1
1
Inductor, 6.8 µH, 5.5 A, Vishay-Dale IHLP2525CZ
C8, C9, C12, C13
4
Capacitor, ceramic, 10 µF, 35 V, 20%, X7R
C4, C5
2
Capacitor, ceramic, 1 µF, 16 V, 10%, X7R
C1, C3, C6, C11
4
Capacitor, ceramic, 0.1 µF, 16 V, 10%, X7R
C2, C10
2
Capacitor, ceramic, 0.1 µF, 50 V, 10%, X7R
C7
1
Capacitor, ceramic, 1 µF, 50 V, 10%, X7R
C14, C15 (Optional)
2
Capacitor, ceramic, 0.1 µF, 50 V, 10%, X7R
C16
1
Capacitor, ceramic, 2.2 µF, 35 V, 10%, X7R
Cff
1
Capacitor, ceramic, 22 pF, 25 V, 10%, X7R
CTTC
1
Capacitor, ceramic, 0.056 µF, 16 V, 5%, X7R
R1, R3, R5, R7
4
Resistor, chip, 100 kΩ, 1/16 W, 0.5%
R2
1
Resistor, chip, 500 kΩ, 1/16 W, 0.5%
R4
1
Resistor, chip, 32.4 kΩ, 1/16 W, 0.5%
R6
1
Resistor, chip, 10 kΩ, 1/16 W, 0.5%
R8
1
Resistor, chip, 22.1 kΩ, 1/16 W, 0.5%
R9
1
Resistor, chip, 9.31 kΩ, 1/16 W, 1%
R10
1
Resistor, chip, 430 kΩ, 1/16 W, 1%
R11, R12, R13, R18, R19
5
Resistor, chip, 10 kΩ, 1/16 W, 5%
R14, R15 (optional)
2
Resistor, chip, 100 kΩ, 1/16 W, 5%
R16
1
Resistor, chip, 100 Ω, 1/16 W, 5%
R17
1
Resistor, chip, 10 Ω, 1/4 W, 5%
R20
1
Resistor, chip, 2 Ω, 1 W, 5%
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9.2.3 Application Curves
VIN: 19 V
VBAT: 12 V
ICHG = 4 A
VIN: 19 V
Figure 21. Continuous Conduction Mode Switching
Waveform
32
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VBAT: 12 V
Figure 22. Battery Charging Soft Start
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10 Power Supply Recommendations
For proper operation of bq2461x, VCC must be from 5 V to 28 V (bq24610) or 24 V (bq24617). To begin
charging, VCC must be higher than SRN by at least 500 mV (otherwise, the device will be in sleep mode). TI
recommends an input voltage of at least 1.5 V to 2 V higher than the battery voltage, taking into consideration
the DC losses in the high-side FET (Rdson), inductor (DCR), and input sense resistor (between ACP and ACN),
the body diode drop of RBFET between VCC and input power supply, and battery sense resistor (between SRP
and SRN). Power limit for the input supply must be greater than the max power required by either the system
load or for battery charging (the greater of the two).
11 Layout
11.1 Layout Guidelines
The switching node rise and fall times should be minimized for minimum switching loss. Proper layout of the
components to minimize the high-frequency current-path loop (see Figure 23) is important to prevent electrical
and magnetic field radiation and high-frequency resonance problems. The following is a PCB layout priority list
for proper layout. Layout of the PCB according to this specific order is essential.
1. Place the input capacitor as close as possible to the switching MOSFET supply and ground connections, and
use the shortest-possible copper trace connection. These parts should be placed on the same layer of PCB,
instead of on different layers using vias to make the connection.
2. The IC should be placed close to the switching MOSFET gate terminals to keep the gate-drive signal traces
short for a clean MOSFET drive. The IC can be placed on the other side of the PCB from the switching
MOSFETs.
3. Place the inductor input terminal as close as possible to the switching MOSFET output terminal. Minimize the
copper area of this trace to lower electrical and magnetic field radiation, but make the trace wide enough to
carry the charging current. Do not use multiple layers in parallel for this connection. Minimize parasitic
capacitance from this area to any other trace or plane.
4. The charging-current sensing resistor should be placed right next to the inductor output. Route the sense
leads connected across the sensing resistor back to the IC in the same layer, close to each other (minimize
loop area), and do not route the sense leads through a high-current path (see Figure 24 for the Kelvin
connection for best current accuracy). Place decoupling capacitors on these traces next to the IC.
5. Place the output capacitor next to the sensing resistor output and ground.
6. The output capacitor ground connections must be tied to the same copper that connects to the input
capacitor ground before connecting to system ground.
7. Route the analog ground separately from the power ground and use a single ground connection to tie the
charger power ground to the charger analog ground. Just beneath the IC, use the copper pour for analog
ground, but avoid the power pins to reduce inductive and capacitive noise coupling. Connect the analog
ground to GND. Connect the analog ground and power ground together using the thermal pad as the single
ground connection point. Alternatively, use a 0-Ω resistor to tie the analog ground to power ground (the
thermal pad should tie to analog ground in this case). A star-connection under the thermal pad is highly
recommended.
8. It is critical to solder the exposed thermal pad on the back side of the IC package to the PCB ground. Ensure
that there are sufficient thermal vias directly under the IC connecting to the ground plane on the other layers.
9. Place decoupling capacitors next to the IC pins, and make the trace connection as short as possible.
10. All via sizes and numbers must be adequate for a given current path.
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11.2 Layout Example
SW
L1
V BAT
R1
High
Frequency
VIN
BAT
Current
C1
Path
PGND
C2
C3
Figure 23. High-Frequency Current Path
Current Direction
R SNS
Current Sensing Direction
To SRP - SRN pin or ACP - ACN pin
Figure 24. Sensing Resistor PCB Layout
See the EVM design (SLUU396) for recommended component placement with trace and via locations.
For QFN information, see SCBA017 and SLUA271.
34
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12 Device and Documentation Support
12.1 Device Support
12.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation, see the following:
• EVM user's guide, SLUU396
• EVM design, SLUU396
• QFN information, SCBA017 and SLUA271
12.3 Trademarks
All trademarks are the property of their respective owners.
12.4 Electrostatic Discharge Caution
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.
12.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
BQ24618RGER
ACTIVE
VQFN
RGE
24
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
QWG
BQ24618RGET
ACTIVE
VQFN
RGE
24
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
QWG
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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