DS2731E+ ,Cache-Memory Battery-Backup Management ICApplications+Denotes a lead(Pb)-free/RoHS-compliant package.T&R = Tape and reel.RAID Controller Car ..
DS2740B ,High-Precision Coulomb Counterapplications. Current is measured bidirectionally over a dynamic range of 15bits (DS2740U) or 13 bi ..
DS2740B ,High-Precision Coulomb CounterPIN DESCRIPTIONRangeOVD- 1-Wire Bus Speed Select 312A LSB and ±2.56A DynamicPIO - Programmable I/ ..
DS2740BU ,High-Precision Coulomb CounterPin Descriptions.(DS2740B) 6.25V LSB and ±51.2mV Dynamic
DS2740BU ,High-Precision Coulomb CounterBLOCK DIAGRAMVDDPIOSTATUS/CONTROL1-WIREACCUMULATEDDQINTERFACETIMEBASECURRENTANDADDRESSCURRENT15-Bit ..
DS2740BU ,High-Precision Coulomb CounterFEATURES 15-Bit Bidirectional Current Measurement(DS2740)1 8 VOVD DD 1.56V LSB and ±51.2mV Dynam ..
E53NA50 ,NABSOLUTE MAXIMUM RATINGSSymbol Parameter Value UnitV Drain-source Voltage (V =0) 500 VDS GSV 500 VD ..
EA2-12 ,COMPACT AND LIGHTWEIGHTAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..
EA2-12NU ,COMPACT AND LIGHTWEIGHTFEATURESª Low power consumptionª Compact and light weightª 2 form c contact arrangementª Low magnet ..
EA2-12S ,COMPACT AND LIGHTWEIGHTFEATURESª Low power consumptionª Compact and light weightª 2 form c contact arrangementª Low magnet ..
EA2-12TNU ,COMPACT AND LIGHTWEIGHTAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..
EA2-4.5NU ,COMPACT AND LIGHTWEIGHTAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..
DS2731E+
Cache-Memory Battery-Backup Management IC
General DescriptionThe DS2731 is a complete power-management solution
for modular backup applications. It is well-suited for 2.5V
and below memory bus voltages, with an input voltage of
12V. The DS2731 includes an internal MOSFET switching
power stage for charging a one-cell lithium chemistry bat-
tery. It has a fully integrated synchronous buck regulator
capable of supplying up to 450mA of cache backup sup-
ply current, and the necessary logic and power devices
for handling the switchover from system power to battery
power. The battery charging method of the DS2731 is
constant current/constant voltage (CCCV). Output voltage
can be margined from 3.8V to 4.6V using a resistor-
divider. Charge is terminated when the charging current
falls below 5% of full charge current. Switchover to battery
backup is initiated by an internal comparator and occurs
automatically when a sensed-input voltage drops below
2.93V. At light loads, the 2MHz internal synchronous buck
regulator operates in burst mode for maximum efficiency.
All nonessential functions of the DS2731 are disabled
while supplying holdup current to the cache memory, and
the IC goes into very low-current dormant mode when the
battery voltage drops below a user-settable threshold.
The DS2731 keeps track of charge status and signals the
user through open-drain I/O pins that can be used to
drive LEDs.
ApplicationsRAID Controller Card
FeaturesLithium Chemistry CCCV ChargerAdjustable Regulated Charging Up to 1.5A DCAdjustable Charge Voltage from 3.8V to 4.6VExternal and Internal Thermal ProtectionSafety Timer Secondary TerminationLED Indicator OutputsDetects Power Outage and Switches Between
Normal Power and Backup BatteryAdjustable High-Efficiency Synchronous Buck
Regulator with Skip Mode at Light LoadsLow-Power Consumption in Discharge Mode
DS2731
Cache-Memory Battery-Backup Management ICTOP VIEW
DS2731
TSSOP4SNSAUX3BATT+CTG2RSETSTMR1THMMARGIN7CHG1CIN6VINVREG8CHG2LX9CGND1SGND10CGND2AGND11CHARGEREF12FAULTLO_BATT13DONEDIV5CGATECBIAS14ENCENS
*EP
*EXPOSED PAD
Pin Configuration
Ordering InformationSWITCH MODE
CHARGER
(CCCV)LITHIUM
BACKUP
CELL
CACHE
MEMORY
POWER
MANAGEMENT
AUXILIARY
POWER
SWITCHING
REGULATOR
DS2731
MAIN
POWER
Typical Operating CircuitRev 1; 1/09
+Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
*EP = Exposed pad.
PARTTEMP RANGEPIN-
PACKAGE
TOP
MARKDS2731E+ -20°C to +70°C 28 TSSOP-EP*
(173 mils) DS2731
DS2731E+T&R -20°C to +70°C 28 TSSOP-EP*
(173 mils) DS2731
DS2731
Cache-Memory Battery-Backup Management IC
ABSOLUTE MAXIMUM RATINGS
RECOMMENDED OPERATING CONDITIONS (VIN= +10.8V to +13.2V, TA= -20°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)
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 in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage Range on CGND1, CGND2, and
SGND Pins Relative to AGND...........................-0.3V to +0.3V
Voltage Range on VIN, CHG1, CHG2, and
CGATE Pins Relative to AGND........................-0.3V to +16.0V
Voltage Range on CHARGE, FAULT, and
DONE Pins Relative to AGND.........................-0.3V to +16.0V
Voltage Range on Any Other Pin Relative
to AGND............................................................-0.3V to +6.0V
Continuous Sink Current on VIN, CGND1,
CGND2, SGND, AUX, BATT+ Pins......................750mA each
Continuous Source Current on CHG1,
CHG2, and LX Pins..............................................750mA each
Continuous Sink Current on CHARGE,
FAULT, and DONE Pins.........................................20mA each
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-55°C to +125°C
Soldering Temperature...........................Refer to the IPC/JEDEC
J-STD-020 Specification.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS Charger Supply Voltage VIN (Note 1) 10.8 12.0 13.2 V
Auxiliary Supply Voltage VAUX (Note 1) 3.0 3.6 V
Battery Voltage VBATT+ Operating as input (Note 1) 2.7 5.0 V
LED Voltage
(CHARGE, FAULT, DONE Pins) (Note 1) 0 VIN
+ 0.3 V
Charger Enable (ENC) (Notes 1, 2) 0 VCBIAS
+ 0.3 V
Switcher Enable (ENS) (Notes 1, 2) 0 VCIN
+ 0.3 V
CHARGER CIRCUIT ELECTRICAL CHARACTERISTICS(VIN= +10.8V to +13.2V, TA= -20°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS Charger Idle Supply Current IINVIN > VUVLO-CHG (Note 3),
VAUX = 3.3V 1 mA
IAUX VAUX > VTRIP 100 µA
IBATT+VAUX < VTRIP,
VBATT+ > VSLEEP,ENS disabled 100 150 µA Regulator Supply Current
(Note 3)
ISLEEPVIN = VAUX = 0.0V,
VBATT+ < VSLEEP 10 µA
CBIAS Regulator Voltage VCBIAS 3.3 V
CGATE Regulator Voltage VCGATE VIN - 4.0 V
CGATE Capacitance CCGATE 2.2 µF
CBIAS Capacitance CCBIAS 0.22 µF
Enable Logic-Low (ENS, ENC) VIL (Notes 4, 5) 0.4 V
DS2731
Cache-Memory Battery-Backup Management IC
CHARGER CIRCUIT ELECTRICAL CHARACTERISTICS (continued)(VIN= +10.8V to +13.2V, TA= -20°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS Enable Hysteresis (ENS, ENC) VHYS-EN 35 70 140 mV
Pulldown Resistance (ENS, ENC) RPD 100 200 300 k
LED Outputs Low
(CHARGE, DONE, FAULT) VOL IOL = 10mA 1.0 V
Fault LED Flash Rate fFAULT 4 Hz
Preconditioning Charge
Threshold VMIN (Note 1) 2.55 2.60 2.70 V
Preconditioning Hysteresis VHYS 50 100 mV
Preconditioning Charge Current IPRE VBATT+ < VMIN 5.0 10.0 15.0 % of
ICHG
Precondition Timeout tPRE 27 30 33 min
0.5 1.5 A Charge-Current Range
(RSET Resistance) ICHGCharge current determined by RSET
(Note 7) 5.0 1.6 k
Charge-Current Accuracy IERR-CHGRSET resistor tolerance 0.1%,
RSNS = 0.050-5 +5 %
Overcurrent Clamp IOVERCURRENT RSET = 0 or RSNS = 0 1.7 2.5 A
Constant-Voltage Threshold
Range VCVCharge voltage determined by MARGIN
pin voltage 3.6 4.2 4.6 V
MARGIN Pin Leakage ILEAKAGE -2 +2 µA
Constant-Voltage Charge
Accuracy VERR-CV -25.0 +25.0 mV
Charge Termination (CV) Current ITERMINATE In constant-voltage mode 4.0 5.0 6.0 % of
ICHG
Charge-Restart Threshold VDELTA (Note 8) 94 95 96 % of
VCV
1 10 hr Safety Timeout Range
(STMR Resistance) tSAFETY22 220 k
Safety Timeout Error tERR-SAFETY RSTMR = 22,000 -5 +5 %
Battery Charger Switching Period tSW-CHG Full load (1.5A) (Note 9) 0.83 1.00 µs
Charger Undervoltage Lockout VUVLO-CHG 8 10 V
High-Side MOSFET
On-ResistanceRDSON-CPICHG = 1A, VIN = 10.8V
(Note 10) 0.4
Low-Side MOSFET On-Resistance RDSON-CN ICHG = 1A, VIN = 10.8V (Note 10) 0.15
Reverse Leakage of Charge FET
(CHG1, CHG2) IREVERSE VIN= 0V, VCV = 4.2V, ENC = 0V 10 µA
Forward Leakage of Charge FET
(CHG1, CHG2) IFORWARD VIN= 12V, VCV = 4.2V, ENC = 0V 10 µA
SNS Leakage Current ILKG-CHG No charge current, VIN= 12V -2 +2 µA
Startup Time tSTART Using typical application components 1 ms
DS2731
Cache-Memory Battery-Backup Management IC
BUCK REGULATOR AND POWER MUX CIRCUIT ELECTRICAL CHARACTERISTICS(VIN= +10.8V to +13.2V, TA= -20°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS Auxiliary Input Trip Threshold VTRIP (Note 1) 2.85 2.93 3.00 V
Auxiliary Input Trip Hysteresis VHYS-TRIP Relative to actual VTRIP 50 80 150 mV
Multiplexer Delay
Break-Before-Make tBREAKSwitching to/from BATT+
(Note 11) 1 µs
Power Multiplexer On-Resistance RMUX IMUX = 10mA, BATT+ or AUX source 0.6 1.0
Regulator Output Voltage Range VREG Set by VDIV pin voltage 0.9 2.5 V
DIV Pin Voltage Range VDIV 0.4 VREF V
Regulator Output Voltage Error VERR-REG (Note 9) -5.0 +5.0 %
Low-Battery Threshold
Adjustment Range VSLEEP 2.75 3.00 V
LO_BATT Pin Voltage Range VLO-BATT 0.6 VREF V
VREF Voltage VREF 1.220 1.238 1.260 V
1.22 126.00 µA VREF Load Range
(Equivalent Resistance) IREF1000 10 k
Buck Regulator Switching Period tSW-REG 50mA (Note 9) 500 ns
Regulator Undervoltage Lockout VUVLO-REG 2.45 2.70 V
Switching Power
pFET Resistance RDSON-SPIOUT = 100mADC
BATT+ = 3.0V, VAUX = 0 (Note 10) 0.6
Switching Power
nFET Resistance RDSON-SNIOUT = 100mADC
BATT+ = 3.0V, VAUX = 0 (Note 10) 1.2
nFET Off Threshold IOFFN0 40 80 mA
Switching Power
pFET Overcurrent Limit IOCLP 500 750 1000 mA
Switching Power
nFET Overcurrent Limit IOCLN 400 650 900 mA
VREGPin Leakage ILKG-REG -2 +2 µA
DS2731
Cache-Memory Battery-Backup Management IC
THERMAL PROTECTION CHARACTERISTICS(VIN= +10.8V to +13.2V, TA= -20°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS THM Pin Internal Pullup Voltage VTHM (Notes 1, 12) VCBIAS V
THM Pin Internal Resistance RTHM THM to CBIAS (Note 12) 9.8 10.0 10.2 k
Thermistor Overtemperature
HALT Threshold VHOT (Notes 12, 13) 0.271 0.283 0.292 Ratio to
VCBIAS
Thermistor Overtemperature
Resume Threshold VHYS-HOT (Notes 12, 13) 0.3055 Ratio to
VCBIAS
Thermistor Undertemperature
HALT Threshold VCOLD (Notes 12, 13) 0.727 0.739 0.748 Ratio to
VCBIAS
Thermistor Undertemperature
Resume Threshold VHYS-COLD (Notes 12, 13) 0.714 Ratio to
VCBIAS
Thermistor Disable
Threshold VDISABLE (Notes 12, 13) 0.02 0.03 0.04 Ratio to
VCBIAS
Internal Overtemperature
Protection Threshold CCCV TPROTECT_CCCV (Note 12) 160 °C
Internal Overtemperature
Hysteresis CCCV THYS-PROTECT_CCCV (Note 12) -20 °C
Internal Overtemperature
Protection Threshold MEM_REG TPROTECT_MEMREG (Note 14) 165 °C
Internal Overtemperature
Hysteresis MEM_REG
THYS-PROTECT_
MEMREG(Note 14) -15 °C
Charging Current Reduction
Threshold TCHOKE (Note 12) 100 °C
Charging Current Reduction Rate TCHOKE_RATE (Note 12) 133 mA/°C
Note 1:All voltages referenced to AGND pin.
Note 2:VCINis equivalent to VAUXwhen VAUXis greater than VTRIP, otherwise VCINis equivalent to VBATT+.
Note 3:Supply-current specification is only for current drain of the IC and does not include cell-charge current, load-supply cur-
rent, or any external resistor bias currents. The only exception is ISLEEP, which does account for complete current drain of
the lithium cell during low-battery conditions.
Note 4:Below this voltage, the input is guaranteed to be logic-low.
Note 5:Operating from 3.3V ±10%.
Note 6:Above this voltage, the input is guaranteed to be logic-high.
Note 7:Assumes an RSNSvalue of 0.05Ω.
Note 8:Relative to VCV.
Note 9:With recommended application circuit.
Note 10:Includes complete package resistance.
Note 11:This specification is from the rising or falling edge of ENSto the closure of the switch and includes whatever delay is in the
internal logic and FET drivers.
Note 12:Applies to charger.
Note 13:Multiply these values by CBIASvoltage to get value in volts. Recommended value of resistor in divider network is 10kΩ±1%.
Tolerance includes tolerances of internal resistance and CBIASvoltage.
Note 14:Applies to memory buck regulator.
DS2731
Cache-Memory Battery-Backup Management ICDS2731CHG1CHG
6.8μH
CHG2SNSSNS
AGND
CTG
10μF
0.050Ω
360kΩ
240kΩ
590kΩCHARGECLED
CHARGE
4.7kΩFAULTFLED
FAULT
4.7kΩDONEDLED
DONE
4.7kΩVINVINCGATECGNDCGATE
THMI
10kΩ OR 103AT-2
10μF
22μF
22μF
VIN
47μF
BATTERY+
BATTERY-
TEST
MEM+
J10
MEM-AUXAUXENCENC-RESENCENSENS-RESENSCBIASCBIASLO_BATTLO_BATTDIVDIVREFREF
AUX+
ENC
ENS
CGND
10.2kΩ
R13
2.49kΩ
56.2kΩMARGINMARGINSTMRSTMRRSETRSETCGND119CGNDCGND2THMTHMBATT+BATT+
ISOLATED GROUND AREA
ISOLATED GROUND AREAVREG
8LX
VREG
2.2μHCINCINSGND
47μF
47μF
SYSTEM
CONTROL
SYSTEM CONTROL
Figure 1. Typical Application Diagram
DS2731
Cache-Memory Battery-Backup Management IC
Pin Description
PINNAMEFUNCTION1 MARGIN Voltage-Margining Input. Selects regulation voltage of charging circuit. Connect to the STMR pin through
a resistor-divider. STMR Voltage Safety-Timer Input. Sets timeout period for a charge cycle based on external resistance to AGND. CTG Connect To Ground. Must be connected to AGND externally. AUX Auxiliary. External supply input to switching supply. Connect to system 3.3V supply.
5 CBIAS Internal Regulator Output. Internal supply for the charging circuit generated from the VIN input. Bypass
with a capacitor to AGND.
6 VREG Cache Voltage-Sense Input. Feedback for regulation of the switching circuit voltage. Connect to the
positive side of the switching output load.
7 CIN Holdup/Bypass Capacitor. Internal supply for the switching regulator. Bypass with a 4.7µF capacitor to
AGND.
8 LX Switching Node, Backup Supply. Output from the switching regulator. Connect to the switching
regulator’s external coil. SGND Switcher Ground. Ground reference for the switching regulator. Connect to the negative side of the load.
10 AGND Analog Ground. Ground reference for the charging circuit. Connect to the negative side of the battery.
11 REF Voltage Reference for Backup. 1.238V voltage reference used to set regulation voltage and low-battery-
detection threshold. Connect to AGND through a resistor network.
12 LO_BATT Low-Battery Detection. Selects the low-battery shutdown threshold of the switching regulator. Connect to
the REF pin through a resistor-divider.
13 DIV Voltage Divider for Backup. Controls the voltage output level of the switching regulator. Connect to the
REF pin through a resistor-divider. ENS Enable Switcher. Active-low enable for the switching regulator.
15 ENC Enable Charger. Active-high enable for the charging circuit.
16 DONE Charge-Done Indicator. Open-drain active-low output indicating successful charge completion of the
external cell.
17 FAULT Charger-Fault Indicator. Open-drain active-low output indicating failure during charge of the external cell.
18 CHARGE Charge Indicator. Open-drain active-low output indicating charge of the external cell in progress.
19 CGND2 Charger Ground 2. Ground reference for battery-charging circuit. Connect to negative side of external cell.
20 CGND1 Charger Ground 1. Ground reference for battery-charging circuit. Connect to negative side of external cell.
21 CHG2 High-Current Charger Output 2. Output from the charging circuit. Connect to charging circuit’s external coil.
22 CHG1 High-Current Charger Output 1. Output from the charging circuit. Connect to charging circuit’s external coil.
23 VIN Charge-Supply Input. Connect to 10.8V to 13.2V system supply.
24 CGATE Floating Gate Drive Bypass. Internal supply for the charger gate control. Bypass with a 2.2µF capacitor to VIN.
25 SNS Current-Sense Input. Feedback for regulator of charger current. Connect a 0.050 sense resistor
between SNS and BATT+.
26 BATT+ Battery Terminal Voltage. Feedback for regulation of charger voltage and supply to switching regulator
during power loss.
27 RSET Charge-Setting Resistor Intput. Selects CC charge rate for external lithium cell. Connect to AGND
through an external resistor.
28 THM Thermistor Input. Connect to 10k NTC thermistor with good thermal contact to the external lithium cell. EP Exposed Paddle. It is recommended the exposed pad be connected to system ground.
DS2731
Cache-Memory Battery-Backup Management IC0.4Ω MAX
GATE DRIVERS
0.15Ω
MAX
0.6Ω
0.7Ω
0.3Ω
BATT+
SUPPLY CONTROL
OCLP
GATE REGULATOR
VIN12V
INPUT
CCCV CONTROLLERV
2MHz PWM
SWITCHING
REGULATOR
SAFETY TIMER
PRECONDITION
TIMER
INTERNAL
THERMAL SENSE
BIAS
REGULATOR
2.93V REFERENCE
CGATE
STMR
1.238V
REFERENCE
UVLO
HYSTERESIS
REF
DIV
LO_BATT
BATT+4.5:1
SCALER
ENS
MARGIN
THM
RSET
CBIAS
ENC
CIN
10kΩ
CHG1
CHG2
SNS
CGND1
CGND2
AGND
BATT+
AUX
CHARGE
FAULT
DONE
0.3Ω
1.0Ω
OCLN
1MΩ
1MΩ
10pF
VREG
SGNDS
LOAD
3.3V
INPUT
DS2731
Figure 2. Block Diagram
Detailed DescriptionThe DS2731 is a complete power-management solution
for modular backup applications. It is well suited for
2.5V and below memory bus voltages. It has a 12V
supply input for battery charging and a 3.3V aux supply
input for power failure circuitry and memory voltage
regulation. The DS2731 includes an internal MOSFET-
switching power stage for charging a lithium-ion (Li+)
cell. It has a fully integrated synchronous-buck regula-
tor capable of supplying up to 450mA of cache-backup
supply current. It also handles switching from system
power to battery power.
The battery-charging method is CCCV. Charging can
be broken into three different modes: precondition,
constant-current (CC) charge, and constant-voltage
(CV) charge. Precondition mode charges at a reduced
rate for a severely depleted cell. CC mode charge rate
is user selectable from 0.5A to 1.5A. In CV mode,
charge is terminated when the charging current falls
below 5% of CC mode charge rate. The CV mode out-
put is also user selectable from 3.8V to 4.6V. Charge
status is signaled to the user through three open-drain
pins that can be used to drive LEDs. A thermistor input
is provided to prevent charging outside of temperature
specifications and a safety timer prevents the contin-
ued charging of a damaged cell.
Switchover to battery backup is initiated by an internal
comparator and occurs automatically when a sensed
input voltage drops below 2.93V. The power failure
switching circuitry can be disabled by the user.
Memory voltage is user selectable from 0.9V to 2.5V. At
light loads, the 2MHz internal synchronous buck regu-
lator operates in burst mode for maximum efficiency. All
nonessential functions of the DS2731 are disabled dur-
ing a power failure while supplying holdup current to
the cache memory. To prevent damaging the battery,
the regulator shuts down and the IC goes into a very
low-current dormant mode when the battery voltage
drops below a user-settable threshold (LO_BATT).
Li+ ChargerThe CCCV charger circuitry is powered by the 12V
input supply. When the charger circuitry is enabled,
battery voltage is continuously monitored at the BATT+
pin. Charging begins when the battery voltage drops
below the charge restart threshold. Accurate charge
current measurements are achieved by the Kelvin
remote-sense connections at the SNS and BATT+ pins.
Measuring the voltage through a Kelvin remote-sense
connection eliminates offset error caused by small
trace resistances at high current.
Charging AlgorithmFrom initiate, CC charging proceeds if ENC is high, the
UVLO-CHG is false, the die temperature is below
TPROTECT_CCCV,and the battery is above the minimum
voltage. If the battery is below the minimum voltage, the
charger goes into preconditioning charge. Once the
battery voltage exceeds VMIN, the charger proceeds to
CC mode. Precondition charge has a default 30-minute
timer. If the timer expires before the battery voltage
exceeds VMIN, the charger goes to fault. For CC charg-
ing, the charge safety timer starts. CC charging pro-
ceeds until the output voltage reaches the CV set point.
The charger then proceeds to CV mode. Charging ter-
minates when the current drops below 5% of the CC
charge rate. The charge-safety timer duration is the
sum of the CC and CV charge times and should be set
to about 15% above the expected maximum charge
time. If the charge-safety timer expires, the charger
goes to fault. After charge termination, the charger
monitors the battery voltage for self-discharge. When it
drops 200mV below the CV charge threshold, the
charger enters Initiate and a new charge cycle begins.
Note:VAUXmust be above 3.08V for the charger to
operate.
Precharge ModePrecharge mode is intended to restore severely deplet-
ed cells. Batteries with a voltage < VMINcharge at a
reduced rate, 10% x ICHG, to prevent damaging the
cell. Precharge mode has a fixed safety timer of 30
minutes. This timer is independent of the STMR pin. If
the battery voltage has not exceeded VMINwithin 30
minutes, the charger goes to the fault state. The charge
pin is active during precharge mode.
DS2731
Cache-Memory Battery-Backup Management IC
DS2731
Cache-Memory Battery-Backup Management IC
INITIATE*DONE LED ACTIVE
TIMERS RESET
NO CURRENT FLOW
PRECONDITIONCHARGE LED ACTIVE
PRECONDITION TIMER ACTIVE
CURRENT REGULATED TO IPRE
DONEDONE LED ACTIVE
TIMERS RESET
NO CURRENT FLOW
CONSTANT-CURRENT CHARGECHARGE LED ACTIVE
SAFETY TIMER ACTIVE
CURRENT REGULATED BY RSET**
CONSTANT-VOLTAGE CHARGECHARGE LED ACTIVE
SAFETY TIMER ACTIVE
CURRENT REGULATED BY RMARGIN
FAULTFAULT LED ACTIVE, TIMERS INACTIVE,
NO CURRENT FLOW
SAFETY TIMER FAULT CONDITION
TEMPERATURE FAULT CONDITION
ASYNCHRONOUS
FROM ANY STATE
ENC TRUE OR
POWER-ON RESET (POR)
RETURN TO
PREVIOUS STATE
TTHERMISTOR = THYS-HOT AND
TTHERMISTOR = THYS-COLD AND
TDS2731 = THYS-PROTECT
ASYNCHRONOUS
FROM ANY STATE
TTHERMISTOR > THOT OR
TTHERMISTOR < TCOLD OR
TDS2731 > TPROTECT
VBATT+ < VMINVBATT+ < VMIN
VBATT+ < VDIVVBATT+ < VDIV
VBATT+ = VMINVBATT+ ≥ VMIN
VBATT+ = VMARGINVBATT+ ≥ VMARGIN
ISNS < ITERMINATEISNS < ITERMINATE
VBATT+ = VMINVBATT+ ≥ VMIN
SAFETY TIMEOUTSAFETY TIMEOUT
SAFETY TIMEOUTSAFETY TIMEOUT
PRECONDITION
TIMEOUT
PRECONDITION
TIMEOUT
ENC TOGGLED FALSE
THEN TRUE OR POR
*VIN > VUVLO-CHG, VAUX > 3.08V MUST EXIST BEFORE CHARGER OPERATES.
**IF THE DS2731 DIE TEMPERATURE EXCEEDS TCHOKE, THE DS2731 BEGINS REDUCING CHARGE CURRENT BELOW THE RSET VALUE TO PROTECT THE IC.
VBATT > VDIV
Figure 3. Charger State Diagram
