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PDF LTC1759 Data sheet ( Hoja de datos )
| Número de pieza | LTC1759 | |
| Descripción | Smart Battery Charger | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1759
Smart Battery Charger
FEATURES
s Single Chip Smart Battery Charger Controller
s 100% Compliant (Rev 1.0) SMBus Support
Allows for Operation with or without Host
s SMBus Accelerator Improves SMBus Timing
s Hardware Interrupt and SMBAlert Response
Eliminate Interrupt Polling
s High Efficiency Synchronous Buck Charger
s 0.5V Dropout Voltage; Maximum Duty Cycle > 99.5%
s AC Adapter Current Limit Maximizes Charge Rate*
s 1% Voltage Accuracy; 5% Current Accuracy
s Up to 8A Charging Current Capability
s Dual 10-Bit DACs for Charger Voltage and Current
Programming
s User-Selectable Overvoltage and Overcurrent Limits
s High Noise Immunity Thermistor Sensor
s Small 36-Lead Narrow (0.209") SSOP Package
U
APPLICATIO S
s Portable Computers
s Portable Instruments
s Docking Stations
*US Patent Number 5,723,970
DESCRIPTIO
The LTC®1759 Smart Battery Charger is a single chip
charging solution that dramatically simplifies construc-
tion of an SBS compliant system. The LTC1759 imple-
ments a Level 2 charger function whereby the charger can
be programmed by the battery or by the host. A thermistor
on the battery being charged is monitored for tempera-
ture, connectivity and battery type information. The SMBus
interface remains alive when the AC power adapter is
removed and responds to all SMBus activity directed to it,
including thermistor status (via the ChargerStatus com-
mand). The charger also provides an interrupt to the host
whenever a status change is detected (e.g., battery
removal, AC adapter connection).
Charging current and voltage are restricted to chemistry
specific limits for improved system safety and reliability.
Limits are programmable by two external resistors. Addi-
tionally, the maximum average current from the AC adapter
is programmable to avoid overloading the adapter when
simultaneously supplying load current and charging cur-
rent. When supplying system load current, charging cur-
rent is automatically reduced to prevent adapter overload.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
15.8k
AC
ADAPTER
INPUT
+
0.1µF
10µF
35V
Al
VDD
0.1µF
1µF
0.33µF
0.68µF
33k
33k
3.83k
1.5k
1k
VDD
475k
10k
1k
LTC1759
7
UV
DCIN
16
VDD
DCDIV
4
SYNC
INFET
5
SDB
12 CHGEN
VCC
CLP
25
VLIMIT
CLN
24
ILIMIT
TGATE
18
DGND BOOSTC
17
ISET
GBIAS
28
PROG
BOOST
27
VC
SW
11 COMP1 BGATE
6
AGND
SPIN
20
RNR
SENSE
19
THERM
BAT1
14 SDA
BAT2
15
SCL
13
INTB
VSET
PGND
22
21
8
32
9
10
2
33
34
1
3
35
30
29
31
23
26
36
2.2µF
1k
0.033Ω
499Ω
0.47µF
1µF
0.1µF
0.68µF
Figure 1. 4A SMBus Smart Battery Charger
SYSTEM
POWER
22µF
15µH
0.025Ω
+
22µF
SMART
BATTERY
200Ω
200Ω
68Ω
0.047µF 0.015µF
INTB
SCL
SDA
SMBus
TO
HOST
1759 F01
1
1 page  
LTC1759
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full operating temperature range (TJ = 0°C to 100°C), otherwise specifications are
TA = 25°C. VCC = DCIN = 18V, VBAT1, 2 = 12.6V, VDD = 3.3V unless otherwise specified.
PARAMETER
Charger Timing
VTGATE, VBGATE Rise/Fall Time
TGATE, BGATE Peak Drive Current
Regulator Switching Frequency
Synchronization Frequency
CONDITIONS
1nF Load
10nF Load
MIN TYP MAX
25
1
q 170 200 230
q 240
280
UNITS
ns
A
kHz
kHz
Maximum Duty Cycle in Start-Up Mode (Note 9)
tTIMEOUT for Wake-Up Charging a
Cold or Underrange Battery
q 85
90
q 140 175 210
%
sec
SMBus Timing (refer to System Management Bus Specification, Revision 1.0, section 2.1 for timing diagrams) (Note 12)
SCL Serial Clock High Period (tHIGH)
SCL Serial Clock Low Period (tLOW)
SDA/SCL Rise Time (tr)
SDA/SCL Fall Time (tf)
SMBus Accelerator Boosted Pull-Up Current
Start Condition Setup Time (tSU:STA)
Start Condition Hold Time (tHD:STA)
SDA to SCL Rising-Edge Setup Time (tSU:DAT)
SDA to SCL Falling-Edge Hold Time,
Slave Clocking in Data (tHD:DAT)
tTIMEOUT Between Receiving Valid
ChargingCurrent() and ChargingVoltage()
Commands (Note 10)
IPULLUP = 350µA, CLOAD = 150pF
IPULLUP = 350µA, CLOAD = 150pF
CLOAD = 150pF
VDD = 3V
q4
q 4.7
q
q 30
q1
q 4.7
q 4.0
q 250
q 300
q 140
2.5
175
1000
300
210
µs
µs
ns
ns
mA
µs
µs
ns
ns
sec
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: This limit is greater than the absolute maximum for the charger.
Therefore, there is no effective limitation on voltage when this option is
selected. If the charger is requested to charge with a higher voltage than
the nominal limit, the VOLTAGE_OR bit will be set.
Note 3: Total system accuracy from SMBus request to output voltage or
output current.
Note 4: Test Circuit #1.
Note 5: Voltage accuracy is calculated using measured reference voltage,
obtained from VSET pin using Test Circuit #2, and VDAC resistor divider
ratio.
Note 6: When supply and battery voltage differential is low, high oscillator
duty cycle is required. The LTC1759 has a unique design to achieve duty
cycle greater than 99% by skipping cycles. Only when VBOOST drops below
the comparator threshold, will TGATE be turned off. See Applications
Information section.
Note 7: Power failure bit is set when the battery voltage is above 89% of
the power adapter voltage (VDCIN).
Note 8: The charger provides wake-up current when a battery is inserted
into the connector, prior to the battery requesting charging current and
voltage. See Smart Battery Charger Specification (Revision 1.0), section
6.1.3 and 6.1.8.
Note 9: In system start-up, C6 (boost capacitor) has no charge stored in it.
The LTC1759 will keep TGATE off, and turn BGATE on for 0.2µs, thus
charging C6. A comparator senses VBOOST and switches to the normal
PWM mode when VBOOST is above its threshold.
Note 10: Refer to Smart Battery Charge Specification (Revision 1.0),
section 6.1.2.
Note 11: Maximum total external capacitance on RNR and THERM pins
is 75pF.
Note 12: SMBus operation guaranteed by design from –40°C to 85°C.
5
5 Page 
U
OPERATIO
Overview (Refer to Block Diagram and Figure 10)
The LTC1759 is composed of a battery charger section, a
charger controller, two 10-bit DACs to control charger
parameters, a thermistor decoder, limit decoder and an
SMBus controller block. If no battery is present, the
thermistor decoder indicates a THERM_OR condition and
charging is disabled by the charger controller (CHGEN =
Low). Charging will also be disabled if AC_PRESENT is
low, or the battery thermistor is decoded as THERM_HOT.
If a battery is inserted or AC power is connected, the
battery will be charged with an 80mA “wake-up” current.
The wake-up current is discontinued after three minutes
if the thermistor is decoded as THERM_UR or
THERM_COLD, and the battery or host doesn’t transmit
charging commands.
The SMBus controller block receives ChargingCurrent()
and ChargingVoltage() commands via the SMBus. If
ChargingCurrent() and ChargingVoltage() command pairs
are received within a three-minute interval, the values are
stored in the current and voltage DACs and the charger
controller asserts the CHGEN line if the decoded ther-
mistor value will allow charging to commence.
ChargingCurrent () and ChargingVoltage() values are com-
pared against limits programmed by the limit decoder
block; if the commands exceed the programmed limits
these limits are substituted and overrange flags are set.
The charger controller will assert INTB whenever a status
change is detected. The host may query the charger, via
the SMBus, to obtain ChargerStatus() information. INTB
will be deasserted upon a successful read of
ChargerStatus() or a successful Alert Response Address
(ARA) request.
Battery Charger Section
The LTC1759 is synchronous current mode PWM step-
down (Buck) switcher. The battery DC charging current is
programmed with a current DAC via the SMBus interface.
Amplifier CA1 converts the charging current through
RSENSE to a much lower current IPROG (IPROG = IBAT •
RSENSE/RS2) fed into the PROG pin. Amplifier CA2 com-
pares the output of CA1 with the programmed current and
drives the PWM loop to force them to be equal. High DC
LTC1759
accuracy is achieved with averaging capacitor CPROG.
Note that IPROG has both AC and DC components. IPROG
generates a ramp signal that is fed to the PWM control
comparator C1 through buffer B1 and level shift resistors
forming the current mode inner loop. The BOOST pin
supplies the top power switch gate drive. The LTC1759
generates a 8.9V VGBIAS for bootstrapping VBOOST and
VBOOSTC as well as to drive the bottom power FET. The
BOOSTC pin supplies the current amplifier CA1 with a
voltage higher than VCC for low dropout applications.
Amplifier VA reduces the charging current when the bat-
tery voltage reaches the set voltage programmed by the
VDAC and the 2.465V reference voltage.
The amplifier CL1 monitors and limits the input current,
normally from the AC adapter, to a preset level (92mV/
RCL). At input current limit, CL1 will supply the program-
ming current IPROG and thus reduce battery charging
current.
The INFET pin drives an external input P-channel FET for
low dropout applications.
SMBus Interface
All communications over the SMBus are interpreted by the
SMBus controller block. The SMBus controller is an
SMBus slave device. All internal LTC1759 registers may
be updated and accessed through the SMBus controller,
and charger controller as required. The SMBus protocol is
a derivative of the I2CTM bus (Reference “I2C-Bus and How
to Use It, V1.0” by Philips and “System Management Bus
Specification” by the Smart Battery System Organiza-
tion*, for a complete description of the bus protocol
requirements.)
All data is clocked into the shift register on the rising edge
of SCL. All data is clocked out of the shift register on the
falling edge of SCL. Detection of an SMBus Stop condition,
or power-on reset via the VDD undervoltage lockout, will
reset the controller to an initial state at any time.
The LTC1759 command set is interpreted by the SMBus
controller and passed onto the charger controller block as
control signals or updates to internal registers.
I2C is a trademark of Philips Electronics N.V.
*http://www. SBS-FORUM.org
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC1759.PDF ] | |
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