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PDF ISL88731C Data sheet ( Hoja de datos )
| Número de pieza | ISL88731C | |
| Descripción | SMBus Level 2 Battery Charger | |
| Fabricantes | Intersil Corporation | |
| Logotipo |  |
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SMBus Level 2 Battery Charger
ISL88731C
The ISL88731C is a highly integrated Lithium-ion battery
charger controller, programmable over the SMBus system
management bus (SMBus). The ISL88731C is intended to be
used in a smart battery charger (SBC) within a smart battery
system (SBS) that throttles the charge power such that the
current from the AC-adapter is automatically limited. High
efficiency is achieved with a DC/DC synchronous-rectifier buck
converter, equipped with diode emulation for enhanced light
load efficiency and system bus boosting prevention. The
ISL88731C charges one to four Lithium-ion series cells, and
delivers up to 8A charge current. Integrated MOSFET drivers
and bootstrap diode result in fewer components and smaller
implementation area. Low offset current-sense amplifiers
provide high accuracy with 10mΩ sense resistors. The
ISL88731C provides 0.5% end-of-charge battery voltage
accuracy.
The ISL88731C provides a digital output that indicates the
presence of the AC adapter as well as an analog output which
indicates the adapter current within 4% accuracy.
The ISL88731C is available in a small 5mmx5mm 28 Ld Thin
(0.8mm) QFN package. An evaluation kit is available to reduce
design time. The ISL88731C is available in Pb-Free packages.
Related Literature
• See AN1404 for “ISL88731EVAL2Z and ISL88731CEVAL2Z
Evaluation Boards Setup Procedure”
Features
• 0.5% Battery Voltage Accuracy
• 3% Adapter Current Limit Accuracy
• 3% Charge Current Accuracy
• SMBus 2-Wire Serial Interface
• Battery Short Circuit Protection
• Fast Response for Pulse-Charging
• Fast System-Load Transient Response
• Monitor Outputs
- Adapter Current (3% Accuracy)
- AC-Adapter Detection
• 11-Bit Battery Voltage Setting
• 6 Bit Charge Current/Adapter Current Setting
• 8A Maximum Battery Charger Current
• 11A Maximum Adapter Current
• +8V to +26V Adapter Voltage Range
• Pb-Free (RoHS Compliant)
Applications
• Notebook Computers
• Tablet PCs
• Portable Equipment with Rechargeable Batteries
13.0 3.5
12.5 3.0
2.5
12.0
VCHG (V)
2.0
11.5
1.5
11.0
1.0
10.5
ICHG (A)
0.5
10.0
0
0.0
20 40 60 80 100 120 140 160
CHARGE TIME (MINUTES)
FIGURE 1. TYPICAL CHARGING VOLTAGE AND CURRENT
100
95
90 16.8V BATTERY
12.6V BATTERY
8.4V BATTERY
85
4.2V BATTERY
80
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
IOUT (A)
FIGURE 2. EFFICIENCY vs CHARGE CURRENT AND BATTERY
VOLTAGE
June 8, 2011
FN6978.3
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 |Copyright Intersil Americas Inc. 2010, 2011. All Rights Reserved
Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries.
All other trademarks mentioned are the property of their respective owners.
1 page  
ISL88731C
Table of Contents
Absolute Maximum Ratings ...................................................6
Thermal Information ...............................................................6
Electrical Specifications ........................................................6
SMBus Timing Specifications.................................................8
Typical Operating Performance ...................................................9
Theory of Operation ............................................................. 11
Introduction ..................................................................................11
PWM Control.................................................................................11
AC-Adapter Detection..................................................................11
Current Measurement.................................................................11
VDDP Regulator ...........................................................................11
VDDSMB Supply ...........................................................................11
Short Circuit Protection and 0V Battery Charging ..................11
Undervoltage Detect and Battery Trickle Charging ................11
Over-Temperature Protection ....................................................12
Overvoltage Protection ...............................................................12
The System Management Bus...................................................12
General SMBus Architecture......................................................12
Data Validity .................................................................................12
START and STOP Conditions..............................................................12
Acknowledge......................................................................................... 13
SMBus Transactions............................................................................13
Byte Format .......................................................................... 13
ISL88731C and SMBus ......................................................... 13
Battery Charger Registers................................................... 14
Enabling and Disabling Charging........................................ 14
Setting Charge Voltage........................................................ 14
Setting Charge Current ........................................................ 15
Setting Input-Current Limit.................................................. 16
Charger Timeout ....................................................................17
ISL88731C Data Byte Order..................................................17
Writing to the Internal Registers .........................................17
Reading from the Internal Registers...................................17
Application Information .......................................................17
Inductor Selection ....................................................................... 17
Output Capacitor Selection ........................................................ 18
MOSFET Selection ....................................................................... 18
Snubber Design ........................................................................... 19
Input Capacitor Selection........................................................... 19
Loop Compensation Design....................................................... 19
Transconductance Amplifiers GMV, GMI and GMS ................ 19
PWM Gain Fm .............................................................................. 19
Charge Current Control Loop ..................................................... 20
Adapter Current Limit Control Loop.......................................... 20
Voltage Control Loop................................................................... 21
Output LC Filter Transfer Functions .......................................... 21
Compensation Break Frequency Equations ............................ 22
PCB Layout Considerations................................................. 22
Power and Signal Layers Placement on the PCB ................... 22
Component Placement............................................................... 22
Signal Ground and Power Ground Connection........................ 22
GND and VCC Pin......................................................................... 22
LGATE Pin ..................................................................................... 22
PGND Pin ...................................................................................... 22
PHASE Pin .................................................................................... 23
UGATE Pin..................................................................................... 23
BOOT Pin....................................................................................... 23
CSOP, CSON, CSSP and CSSN Pins .......................................... 23
DCIN Pin........................................................................................ 23
Copper Size for the Phase Node ............................................... 23
Identify the Power and Signal Ground ..................................... 23
Clamping Capacitor for Switching MOSFET............................. 23
Revision History ................................................................... 24
Products................................................................................ 24
Package Outline Drawing .................................................... 25
5 FN6978.3
June 8, 2011
5 Page 
ISL88731C
Theory of Operation
Introduction
The ISL88731C includes all of the functions necessary to charge
1 to 4 cell Li-Ion and Li-polymer batteries. A high efficiency
synchronous buck converter is used to control the charging
voltage up to 19.2V and charging current up to 8A. The
ISL88731C also has input current limiting up to 11A. The Input
current limit, charge current limit and charge voltage limit are set
by internal registers written with SMBus. The ISL88731C “Typical
Application Circuit” is shown in Figure 4.
The ISL88731C charges the battery with constant charge current,
set by the ChargeCurrent register, until the battery voltage rises to
a voltage set by the ChargeVoltage register. The charger will then
operate at a constant voltage. The adapter current is monitored
and if the adapter current rises to the limit set by the InputCurrent
register, battery charge current is reduced so the charger does not
reduce the adapter current available to the system.
The ISL88731C features a voltage regulation loop (VCOMP) and 2
current regulation loops (ICOMP). The VCOMP voltage regulation
loop monitors VFB to limit the battery charge voltage. The ICOMP
current regulation loop limits the battery charging current
delivered to the battery to ensure that it never exceeds the
current set by the ChargeCurrent register. The ICOMP current
regulation loop also limits the input current drawn from the
AC-adapter to ensure that it never exceeds the limit set by the
InputCurrent register, and to prevent a system crash and
AC-adapter overload.
PWM Control
The ISL88731C employs a fixed frequency PWM control
architecture with a feed-forward function. The feed-forward
function maintains a constant modulator gain of 11 to achieve fast
line regulation as the input voltage changes.
The duty cycle of the buck regulator is controlled by the lower of
the voltages on ICOMP and VCOMP. The voltage on ICOMP and
VCOMP are inputs to a Lower Voltage Buffer (LVB) who’s output is
the lower of the 2 inputs. The output of the LVB is compared to an
internal 400kHz ramp to produce the Pulse Width Modulated
signal that controls the UGATE and LGATE drivers. An internal
clamp holds the higher of the 2 voltages (0.3V) above the lower
voltage. This speeds the transition from voltage loop control to
current loop control or vice versa.
The ISL88731C can operate up to 99.6% duty cycle if the input
voltage drops close to or below the battery charge voltage (drop
out mode). The DC/DC converter has a timer to prevent the
frequency from dropping into the audible frequency range.
To prevent boosting of the system bus voltage, the battery
charger drives the lower FET in a way that prevents negative
inductor current.
An adaptive gate drive scheme is used to control the dead time
between two switches. The dead time control circuit monitors the
LGATE output and prevents the upper side MOSFET from turning
on until 20ns after LGATE falls below 1V VGS, preventing
cross-conduction and shoot-through. The same occurs for LGATE
turn on. In order for the deadtime circuit to work properly, there
must be a low resistance, low inductance path from the LGATE
driver to MOSFET gate, and from the source of MOSFET to PGND.
An internal Schottky diode between the VDDP pin and BOOT pin
keeps the bootstrap capacitor charged.
AC-Adapter Detection
Connect the AC-adapter voltage through a resistor divider to ACIN
to detect when AC power is available, as shown in Figure 4. ACOK
is an open-drain output and is active low when ACIN is less than
Vth,fall, and high when ACIN is above Vth,rise. The ACIN rising
threshold is 3.2V (typ) with 60mV hysteresis.
Current Measurement
Use ICM to monitor the adapter current being sensed across
CSSP and CSSN. The output voltage range is 0V to 2.5V. The
voltage of ICM is proportional to the voltage drop across CSSP
and CSSN, and is given by Equation 1:
ICM = 20 ⋅ IINPUT ⋅ RS1
(EQ. 1)
where Iadapter is the DC current drawn from the AC adapter. It is
recommended to have an RC filter at the ICM output for
minimizing the switching noise.
VDDP Regulator
VDDP provides a 5.1V supply voltage from the internal LDO
regulator from DCIN and can deliver up to 30mA of continuous
current. The MOSFET drivers are powered by VDDP. VDDP also
supplies power to VCC through a low pass filter as shown in
“TYPICAL APPLICATION CIRCUIT” on page 2. Bypass VDDP and
VCC with a 1µF capacitor.
VDDSMB Supply
The VDDSMB input provides power to the SMBus interface. Connect
VDDSMB to VCC, or apply an external supply to VDDSMB. Bypass
VDDSMB to GND with a 0.1µF or greater ceramic capacitor.
The typical application connects VDDSMB to the same power source
as the SMBus master. This supply should be active and greater than
2.5V when either the adapter or the battery is present.
ISL88731C does not function when VDDSMB is below its
specified Under Voltage Lockout (UVLO) voltage. All of the SMBus
registers in ISL88731C are powered by VDDSMB and are set to
zero when it is below the UVLO threshold. Other functions are
unpredictable when VDDSMB is below the UVLO threshold.
Short Circuit Protection and 0V Battery
Charging
Since the battery charger will regulate the charge current to the
limit set by the ChargeCurrent register, it automatically has short
circuit protection and is able to provide the charge current to
wake up an extremely discharged battery. Undervoltage trickle
charge folds back current if there is a short circuit on the output.
Undervoltage Detect and Battery Trickle
Charging
If the voltage at CSON falls below 2.5V ISL88731C reduces the
charge current limit to 128mA to trickle charge the battery. When
the voltage rises above 2.7V, the charge current reverts to the
programmed value in the ChargeCurrent register.
11 FN6978.3
June 8, 2011
11 Page | ||
| Páginas | Total 25 Páginas | |
| PDF Descargar | [ Datasheet ISL88731C.PDF ] | |
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