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DS2784G-CP1+-DS2784K
1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
GENERAL DESCRIPTION The DS2784 operates from 2.5V to 4.6V for integration
in battery packs using a single lithium-ion (Li+) or Li+
polymer cell. Available capacity is reported in mAh and
as a percentage. Safe operation is ensured with the
included Li+ protection function and SHA-1-based
challenge-response authentication.
Precision measurements of voltage, temperature, and
current, along with cell characteristics and application
parameters are used to estimate capacity. The
available capacity registers report a conservative
estimate of the amount of charge that can be removed
given the current temperature and discharge rate.
In addition to the nonvolatile (NV) storage for cell
compensation and application parameters, 16 bytes of
EEPROM memory is made available for the exclusive
use of the host system and/or pack manufacturer. This
facilitates battery lot and date tracking or NV storage of
system or battery usage statistics.
A 1-Wire® interface provides serial communication at
16kbps or 143kbps to access data registers, control
registers, and user memory. Additionally, 1-Wire
communication enables challenge-response pack
authentication using SHA-1 as the hash algorithm in a
hash-based message authentication code (HMAC)
authentication protocol.
APPLICATIONS Smartphones/PDAs
Digital Still and Video Cameras
Cordless VoIP Phones
Portable GPS Navigation
Modes and commands are capitalized for clarity.
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
FEATURES
Precision Voltage, Temperature, and Current
Measurement System
Available Capacity Estimated from Coulomb
Count, Discharge Rate, Temperature, and Cell
Characteristics
Estimates Cell Aging Using Learn Cycles
Uses Low-Cost Sense Resistor
Allows for Calibration of Gain and
Temperature Coefficient
Li+ Safety Circuitry—Overvoltage,
Undervoltage, Overcurrent, Short-Circuit
Protection
Programmable Safety Thresholds for
Overvoltage and Overcurrent
Authentication Using SHA-1 Algorithm and
64-Bit Secret
32-Byte Parameter EEPROM
16-Byte User EEPROM
Maxim 1-Wire Interface with 64-Bit Unique ID
Tiny, Pb-Free, 14-Pin TDFN Package Embeds
Easily in Battery Packs Using Thin Prismatic
Cells
PIN CONFIGURATION VDD
CTG
VSS
VIN
PLS
PIO
SNS
3mm x 5mm TDFN – 14
Top View
PAD
ORDERING INFORMATION
PART TEMP RANGE TOP MARK PIN PACKAGE DS2784G+ -40°C to +85°C D2784 14 TDFN-EP*
DS2784G+T&R -40°C to +85°C D2784 14 TDFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
19-4636; Rev 3/12
DS2784
1-Cell Stand-Alone Fuel Gauge IC with
Li+ Protector and SHA-1 Authentication
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
ABSOLUTE MAXIMUM RATINGS Voltage Range on PLS Pin Relative to VSS -0.3V to +18V
Voltage Range on CP Pin Relative to VSS -0.3V to +12V
Voltage Range on DC Pin Relative to VSS -0.3V to (VCP + 0.3V)
Voltage Range on CC Pin Relative to VSS VDD - 0.3V to VCP + 0.3V
Voltage Range on All Other Pins Relative to VSS -0.3V to +6.0V
Maximum Voltage Range on VIN Pin Relative to VDD VDD + 0.3V
Continuous Sink Current, PIO, DQ 20mA
Continuous Sink Current, CC, DC 10mA
Operating Temperature Range -40°C to +85°C
Storage Temperature Range -55°C to +125°C
Lead Temperature (soldering,10s)
Soldering Temperature (reflow)
+300°C
+260°C
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections
of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
ELECTRICAL CHARACTERISTICS (VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Voltage VDD (Note 1) +2.5 +4.6 V
Supply Current
IDD0 Sleep mode 1 4 µA IDD1 Sleep mode, VDD = 2.5V
0°C to +50°C 0.4 1.5
IDD2 Active mode 85 125
IDD3 Active mode during SHA
computation 300 500 µA
Temperature Accuracy -3 +3 C Temperature Resolution 0.125
Temperature Range -128.000 +127.875
Voltage Accuracy, VIN
4.0 ≤ VIN ≤ 4.6,
VIN ≤ VDD + 0.3V -30 30
mV 2.5 ≤ VIN ≤ 4.6V,
VIN ≤ VDD + 0.3V -50 +50
Voltage Resolution, VIN 4.88 mV
Voltage Range, VIN 0 4.6 V
Input Resistance, VIN 15 MΩ
Current Resolution 1.56 µV
Current Full Scale -51.2 +51.2 mV
Current Gain Error -1 +1 % full
scale
Current Offset (Notes 2, 3, 4) -15 +25 µV
Accumulated Current Offset (Notes 2, 3, 4) -360 0 µVh/day
Time Base Error 0ºC ≤ TA ≤ +50ºC -2 +2 -3 +3
CP Output Voltage VCP ICC + IDC = 0.9µA 8.50 9.25 10.00 V
CP Startup Time tSCP CE = 0, DE = 0,
CCP = 0.1µF, Active mode 200 ms
Output High: CC, DC VOHCC IOH = -100µA (Note 5) VCP - 0.4 V
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Output Low: DC VOLDC IOL = 100µA 0.1 V
DQ, PIO Voltage Range -0.3 +5.5 V
DQ, PIO Input-Logic High VIH 1.5 V
DQ, PIO Input-Logic Low VIL 0.6 V
DQ, PIO Output-Logic Low VOL IOL = 4mA 0.4 V
DQ, PIO Pullup Current IPU Sleep mode,
VPIN = VDD - 0.4V 0.2 µA
DQ, PIO Pulldown Current IPD Active mode,
VPIN = 0.4V 0.2 µA
DQ Input Capacitance CDQ 50 pF
DQ Sleep Timeout tSLEEP VDQ < VIL 2 9 s
PIO, DQ Wake Debounce tWDB Sleep mode 100 ms
SHA-1 COMPUTATION TIMING Computation Time tSHA 30 ms
ELECTRICAL CHARACTERISTICS: Protection Circuit (VDD = 2.5V to 4.6V, TA = 0°C to +50°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Overvoltage Detect VOV
VOV = 11000b 4.457 4.482 4.507 VOV = 00011b 4.252 4.277 4.302
Charge-Enable Voltage VCE Relative to VOV -75 -100 -125 mV
Undervoltage Detect VUV 2.40 2.45 2.50 V
Overcurrent Detect: Charge VCOC
OC = 11b -57 -72 -87
mV OC = 00b -15.5 -23.5 -31.5
Overcurrent Detect: Discharge VDOC OC = 11b 76 96 116 mV OC = 00b 23.5 35.5 47.5
Short-Circuit Current Detect VSC
SC = 1b 240 300 360 mV
SC = 0b 120 150 180 mV
Overvoltage Delay tOVD (Note 6) 425 1150 ms
Undervoltage Delay tUVD (Notes 6, 7) 84 680 ms
Overcurrent Delay tOCD 8 10 12 ms
Short-Circuit Delay tSCD 80 120 160 µs
Test Threshold VTP COC, DOC conditions 0.3 0.8 1.5 V
Test Current ITST SC, COC, DOC condition 10 20 40 µA
PLS Pulldown Current IPPD Sleep mode 30 200 600 µA
VUV condition,
max: VPLS = 15V,
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
EEPROM RELIABILITY SPECIFICATION (VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS EEPROM Copy Time tEEC 10 ms
EEPROM Copy Endurance NEEC TA = +50°C 50,000 cycles
ELECTRICAL CHARACTERISTICS: 1-Wire Interface, Standard (VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Time Slot tSLOT 60 120 µs
Recovery Time tREC 1 µs
Write-0 Low Time tLOW0 60 120 µs
Write-1 Low Time tLOW1 1 15 µs
Read-Data Valid tRDV 15 µs
Reset-Time High tRSTH 480 µs
Reset-Time Low tRSTL 480 960 µs
Presence-Detect High tPDH 15 60 µs
Presence-Detect Low tPDL 60 240 µs
ELECTRICAL CHARACTERISTICS: 1-Wire Interface, Overdrive (VDD = 2.5V to 4.6V, TA = -20°C to +70°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Time Slot tSLOT 6 16 µs
Recovery Time tREC 1 µs
Write-0 Low Time tLOW0 6 16 µs
Write-1 Low Time tLOW1 1 2 µs
Read-Data Valid tRDV 2 µs
Reset-Time High tRSTH 48 µs
Reset-Time Low tRSTL 48 80 µs
Presence-Detect High tPDH 2 6 µs
Presence-Detect Low tPDL 8 24 µs
Note 1: All voltages are referenced to VSS.
Note 2: Factory-calibrated accuracy. Higher accuracy can be achieved by in-system calibration by the user.
Note 3: Accumulation bias and offset bias registers set to 00h. NBEN bit set to 0.
Note 4: Parameters guaranteed by design.
Note 5: CP pin externally driven to 10V.
Note 6: Overvoltage and undervoltage delays (tOVD, tUVD) are reduced to 0s if the OV or UV condition is detected within 100ms of entering
Active mode.
Note 7: tUVD MIN determined by stepping the voltage on VIN from VUV + 250mV to VUV - 250mV.
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
TYPICAL OPERATION CHARACTERISTICS
CC FET Turn Off
DC FET Turn Off
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
COC Delay
DOC Delay
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
SC Delay
OV Delay
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
UV Delay
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
TYPICAL OPERATING CIRCUIT
PIN DESCRIPTION
PIN NAME FUNCTION VDD Power-Supply Input. Chip supply input. Bypass with 0.1µF to VSS. CTG Connect to Ground VSS Device Ground. Chip ground and battery-side sense resistor input. VIN Battery Voltage-Sense Input. Connect to positive cell terminal through decoupling
network.
5, 9, 10 N.C. No Connection PLS Pack Plus Terminal-Sense Input. Used to detect the removal of short-circuit, discharge
overcurrent, and charge overcurrent conditions. CC Charge Control. Charge FET control output. DC Discharge Control. Discharge FET control output.
11 DQ Data Input/Output. Serial data I/O, includes weak pulldown to detect battery disconnect
and can be configured as wake input.
12 SNS Sense Resistor Connection. Pack minus terminal and pack-side sense resistor sense
input.
13 CP Charge Pump Output. Bypass with 0.1µF to VSS.
14 PIO Programmable I/O Pin. Can be configured as wake input. EP Exposed Pad. Connect to VSS or leave unconnected.
DETAILED DESCRIPTION The DS2784 functions as an accurate fuel gauge, Li+ protector, and SHA-1-based authentication token. The fuel
gauge provides accurate estimates of remaining capacity and reports timely voltage, temperature, and current-
measurement data. Capacity estimates are calculated from a piecewise-linear model of the battery performance
over load and temperature, and system parameters for full and empty conditions. The algorithm parameters are
user programmable and can be modified in pack. Critical capacity and aging data are periodically saved to
EEPROM in case of loss of power due to a short circuit or deep depletion.
The Li+ protection function ensures safe, high-performance operation. nFET protection switches are driven with a
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
located inside the protection FETs in a low-side configuration. The thresholds for overvoltage, overcurrent, and
short-circuit current are user programmable for easy customization to each cell and application.
The 32-bit wide SHA-1 engine with 64-bit secret and 64-bit challenge words resists brute force and other attacks
with financial-level HMAC security. The challenge of managing secrets in the supply chain is addressed with the
compute next secret feature. The unique serial number or ROM ID can be used to assign a unique secret to each
battery.
BLOCK DIAGRAM FuelPack™
Algorithm
POWER MODE
Control
PRECISION
ANALOG
OSCILLATOR
16 Byte User
EEPROM
1-Wire Interface
CHARGE
PUMPVDD
VDD_INT
CURRENT
(VSS -SNS)
TEMPERATURE
VOLTAGE
(VIN -VSSA)
VIN
VREF
DS2784
10-Bit + sign
ADC/MUX
SNS
VSS
PIO
WKP, WKD
LITHIUM ION
PROTECTOR
PLS
FET DRIVERS
UV, CD
32 Byte
Parameter
EEPROM
Pin Drivers
and Pwr
Switch
Control
PIO Logic
15-Bit + sign
ADC
Control and
Status Registers
FuelPack™
ALGORITHM
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
POWER MODES The DS2784 has two power modes: Active and Sleep. On initial power-up, the DS2784 defaults to Active mode. In
Active mode, the DS2784 is fully functional with measurements and capacity estimation registers continuously
updated. The protector circuit monitors the battery voltages and current for unsafe conditions. The protection FET
gate drivers are enabled when conditions are deemed safe. Also, the SHA-1 authentication function is available in
Active mode. When a SHA-1 computation is performed, the supply current increases to IDD3 for tSHA. In Sleep mode,
the DS2784 conserves power by disabling measurement and capacity estimation functions, but preserves register
contents. Gate drive to the protection FETs is disabled in Sleep. And the SHA-1 authentication feature is not
operational.
Sleep mode is entered under two different conditions: bus low and undervoltage. An enable bit makes entry into
Sleep optional for each condition. Sleep mode is not entered if a charger is connected (VPLS > VDD + 50mV) or if a
charge current of 1.6mV / RSNS is measured from SNS to VSS. The DS2784 exits Sleep mode upon charger
connection and VIN ≥ VUV or a low to high transition on DQ.
The bus-low condition, where the DQ pin is low for tSLEEP, indicates pack removal or system shutdown in which the
1-Wire bus pullup voltage, VPULLUP, is not present. The Power mode (PMOD) bit must be set to enter Sleep when a
bus-low condition occurs. After the DS2784 enters Sleep due to a bus-low condition, it is assumed that no charge
or discharge current will flow and that coulomb counting is unnecessary.
The second condition to enter Sleep is an undervoltage condition, which reduces battery drain due to the DS2784
supply current and prevents over discharging the cell. The DS2784 transitions to Sleep if the VIN voltage is less
than VUV (2.45V typical) and the undervoltage enable (UVEN) bit is set. The 1-Wire bus must be in a static state,
that is, with DQ either high or low for tSLEEP. The DS2784 transitions from UVEN Sleep to Active mode when DQ
changes logic state.
The DS2784 has the “power switch” capability for waking the device and enabling the protection FETs when the
host system is powered down. A simple dry-contact switch on the PIO pin or DQ pin can be used to wake up the
battery pack. The power switch function is enabled using the PSPIO and PSDQ configuration bits in the control
register. When PSPIO or PSDQ is set and a Sleep condition is satisfied, the PIO and DQ pins pull high weakly,
then become armed to detect a low-going transition. A 100ms debounce period filters out glitches that can be
caused when a sleeping battery is inserted into a system.
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
Figure 1. Sleep Mode State Diagram Active
PMOD = 0
UVEN = 0
Active
PMOD = 1
UVEN = 1
Active
PMOD = 1
UVEN = 0
Active
PMOD = 0
UVEN = 1
SLEEP
PSIO = 1
PSDQ = 1
SLEEP
PSIO = 1
PSDQ = 0
SLEEP
PSIO = 0
PSDQ = 1
SLEEP
PSIO = 0
PSDQ = 0
Vin < VUV
Vin < VUV
DQ low for tSLEEP
DQ low for tSLEEP
I/O Communication or
Charger Connection
I/O Communication or
Charger Connection
Pull DQ Low
Pull PIO Low
Pull PIO low
Pull DQ low
I/O Communication or
Charger Connection
I/O Communication or
Charger Connection
CONTROL REGISTER FORMAT All control register bits are read and write accessible. The control register is recalled from parameter EEPROM
memory at power-up. Register bit values can be modified in shadow RAM after power-up. Power-up default values
are saved using the Copy Data command.
ADDRESS 60h
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NBEN UVEN PMOD RNAOP 0 PSPIO PSDQ X
NBEN—Negative Blanking Enable. A value of 1 enables blanking of negative current values up to 25µV. A value of 0 disables blanking of negative currents. The power-up default of NBEN = 0.
UVEN—Undervoltage Enable. A value of 1 allows the DS2784 to enter Sleep mode when the voltage register value
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
PMOD—Power Mode Enable. A value of 1 allows the DS2784 to enter Sleep mode when DQ is low for tSLEEP. A value of 0 disables DQ related transitions to Sleep mode.
RNAOP—Read Net Address Op Code. A value of 0 selects 33h as the op code value for the Read Net Address command. A value of 1 selects 39h as the Read Net Address opcode value.
0—Reserved bit, must be programmed to 0 for proper operation.
PSPIO—Power-Switch PIO Enable. A value of 1 enables the PIO pin as a power-switch input. A value of 0 disables the power-switch input function on PIO pin. This control is independent of the PSDQ state.
PSDQ—Power-Switch DQ Enable. A value of 1 enables the DQ pin as a power-switch input. A value of 0 disables the power-switch input function on DQ pin. This control is independent of the PSPIO state.
X—Reserved Bit.
Li+ PROTECTION CIRCUITRY During Active mode, the DS2784 constantly monitors SNS, VIN, and VPLS to protect the battery from overvoltage
(overcharge), undervoltage (overdischarge), and excessive charge and discharge currents (overcurrent, short
circuit). Table 1 summarizes the conditions that activate the protection circuit, the response of the DS2784, and the
thresholds that release the DS2784 from a protection state.
Table 1. Li+ Protection Conditions and DS2784 Responses
CONDITION
ACTIVATION
RELEASE THRESHOLD THRESHOLD DELAY RESPONSE(2)
Overvoltage VIN > VOV tOVD CC Off VIN < VCE or (VSNS > 1.2mV
and VIN < VOV)
Undervoltage VIN < VUV tUVD CC Off, DC Off,
Sleep Mode
VPLS > VIN (3)
(charger connected)
Overcurrent, Charge VSNS < VCOC tOCD CC Off, DC Off VPLS < VDD - VTP (4)
(charger removed)
Overcurrent, Discharge VSNS > VDOC tOCD DC Off VPLS > VDD - VTP (5)
(load removed)
Short Circuit VSNS > VSC tSCD DC Off VPLS > VDD - VTP (5)
(load removed)
Note 1: All voltages are with respect to VSS.
Note 2: CC pin driven to VOLCC (VDD) for CC off response. DC pin driven to VOLDC (VSS) for DC off response.
Note 3: If VIN < VUV when charger connection is detected, release is delayed until VIN ≥ VUV. The recovery charge path provides an internal
current limit (IRC) to safely charge the battery. If the device does not enter sleep mode for an UV condition (UVEN=0) then the
FETs will turn on once VIN > VUV.
Note 4: With test current ITST flowing from PLS to VSS (pulldown on PLS) enabled.
Note 5: With test current ITST flowing from VDD to PLS (pullup on PLS).
Overvoltage. If the voltage on VIN exceeds the overvoltage threshold (VOV) for a period longer than overvoltage
delay (tOVD), the CC pin is driven low to shut off the external-charge FET, and the OV flag in the protection register
is set. The DC output remains high during overvoltage to allow discharging. When VIN falls below the charge enable
threshold, VCE, the DS2784 turns the charge FET on by driving CC high. The DS2784 drives CC high before
VIN < VCE if a discharge condition persists with VSNS ≥ 1.2mV and VIN < VOV.
Undervoltage. If VIN drops below the undervoltage threshold (VUV) for a period longer than undervoltage delay
(tUVD), the DS2784 shuts off the charge and discharge FETs and sets the UV flag in the protection register. If UVEN
is set, the DS2784 also enters Sleep mode. The DS2784 provides a current-limited recovery charge path (IRC) from
PLS to VDD to gently charge severely depleted cells. The recovery charge path is enabled when
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
discharge FETs. . If the device does not enter sleep mode for an UV condition (UVEN=0) then the FETs will turn
on once VIN > VUV.
Overcurrent, Charge Direction (COC). Charge current develops a negative voltage on VSNS with respect to VSS. If VSNS is less than the charge overcurrent threshold (VCOC) for a period longer than overcurrent delay (tOCD), the
DS2784 shuts off both external FETs and sets the COC flag in the protection register. The charge current path is
not re-established until the voltage on the PLS pin drops below VDD - VTP. The DS2784 provides a pulldown current
(ITST) from PLS to VSS to pull PLS down in order to detect the removal of the offending charge current source.
Overcurrent, Discharge Direction (DOC). Discharge current develops a positive voltage on VSNS with respect to VSS. If VSNS exceeds the discharge overcurrent threshold (VDOC) for a period longer than tOCD, the DS2784 shuts off
the external discharge FET and sets the DOC flag in the protection register. The discharge current path is not re-
established until the voltage on PLS rises above VDD - VTP. The DS2784 provides a test current (ITST) from VDD to
PLS to pull PLS up in order to detect the removal of the offending low-impedance load.
Short Circuit. If VSNS exceeds short-circuit threshold VSC for a period longer than short-circuit delay (tSCD), the
DS2784 shuts off the external discharge FET and sets the DOC flag in the protection register. The discharge
current path is not re-established until the voltage on PLS rises above VDD - VTP. The DS2784 provides a test
current of value (ITST) from VDD to PLS to pull PLS up in order to detect the removal of the short circuit.
Figure 2. Li+ Protection Circuitry Example Waveforms OVDtOCDSCDOVCEUVINSNSSCDOCCOCOVDtUVD
Charge
Discharge
Power
Mode
ACTIVE
SLEEPUVDtOCDCPDDPLSCP
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
Summary. All the protection conditions previously described are logic ANDed to affect the CC and DC outputs. CC = (Overvoltage) AND (Undervoltage) AND (Overcurrent, Charge Direction)
AND (Protection Register Bit CE)
DC = (Undervoltage) AND (Overcurrent, Either Direction) AND (Short Circuit)
AND (Protection Register Bit DE)
PROTECTION REGISTER FORMAT The protection register reports events detected by the Li+ safety circuit on bits 2 to 7. Bits 0 and 1 are used to
disable the charge and discharge FET gate drivers. Bits 2 to 7 are set by internal hardware only. Bits 2 and 3 are
cleared by hardware only. Bits 4 to 7 are cleared by writing the register with a 0 in the bit position of interest. Writing
a 1 to bits 4 to 7 has no effect on the register. Bits 0 and 1 are set on power-up and a transition from Sleep to
Active modes. While in Active mode, these bits can be cleared to disable the FET gate drive of either or both FETs.
Setting these bits only turns on the FETs if there are no protection faults.
ADDRESS 00h
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
OV UV COC DOC CC DC CE DE
OV—Overvoltage Flag. OV is set to indicate that an overvoltage condition has been detected. The voltage on VIN has persisted above the VOV threshold for tOV. OV remains set until written to a 0 or cleared by a power-on reset or
transition to Sleep mode.
UV—Undervoltage Flag. UV is a read-only mirror of the UVF flag located in the status register. UVF is set to
indicate that VIN < VUV . The UVF bit must be written to 0 to clear UV and UVF.
COC—Charge Overcurrent Flag. COC is set to indicate that an overcurrent condition has occurred during a charge. The sense-resistor voltage has persisted above the VCOC threshold for tOC. COC remains set until written to a 0,
cleared by a power-on reset, or transition to Sleep mode.
DOC—Discharge Overcurrent Flag. DOC is set to indicate that an overcurrent condition has occurred during a
discharge. The sense-resistor voltage has persisted above the VDOC threshold for tOC. DOC remains set until written
to a 0, cleared by a power-on reset, or transition to Sleep mode.
CC—Charge Control Flag. CC indicates the logic state of the CC pin driver. CC flag is set to indicate CC high. CC flag is cleared to indicate CC low. CC flag is read only.
DC—Discharge Control Flag. DC indicates the logic state of the DC pin driver. DC flag is set to indicate DC high. DC flag is cleared to indicate DC low. DC flag is read only.
CE—Charge Enable Bit. CE must be set to allow the CC pin to drive the charge FET to the on state. CE acts as an enable input to the safety circuit. If all safety conditions are met AND CE is set, the CC pin drives to VCP. If CE is
cleared, the CC pin is driven low to disable the charge FET.
DE—Discharge Enable Bit. DE must be set to allow the DC pin to drive the discharge FET to the on state. DE acts
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
PROTECTOR THRESHOLD REGISTER FORMAT The 8-bit threshold register consists of bit fields for setting the overvoltage threshold, charge overcurrent threshold,
discharge overcurrent threshold, and short-circuit threshold for the protection circuit.
ADDRESS 7Fh
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
VOV4 VOV3 VOV2 VOV1 VOV0 SC0 OC1 OC0
Table 2. VOV Threshold
VOV BIT FIELD VOV VOV BIT FIELD VOV 0 0 0 0 0 4.248 1 0 0 0 0 4.404
0 0 0 0 1 4.258 1 0 0 0 1 4.414
0 0 0 1 0 4.268 1 0 0 1 0 4.424
0 0 0 1 1 4.277 1 0 0 1 1 4.434
0 0 1 0 0 4.287 1 0 1 0 0 4.443
0 0 1 0 1 4.297 1 0 1 0 1 4.453
0 0 1 1 0 4.307 1 0 1 1 0 4.463
0 0 1 1 1 4.316 1 0 1 1 1 4.473
0 1 0 0 0 4.326 1 1 0 0 0 4.482
0 1 0 0 1 4.336 1 1 0 0 1 4.492
0 1 0 1 0 4.346 1 1 0 1 0 4.502
0 1 0 1 1 4.356 1 1 0 1 1 4.512
0 1 1 0 0 4.365 1 1 1 0 0 4.522
0 1 1 0 1 4.375 1 1 1 0 1 4.531
0 1 1 1 0 4.385 1 1 1 1 0 4.541
0 1 1 1 1 4.395 1 1 1 1 1 4.551
Table 3. COC, DOC Threshold
OC[1:0] BIT FIELD VCOC (mV) VDOC (mV) 0 0 -23.5 35.5
0 1 -36 48
1 0 -48 72
1 1 -72 96
Table 4. SC Threshold
SC0 BIT FIELD VSC (mV) 150 300
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
VOLTAGE MEASUREMENT Battery voltage is measured every 440ms on the VIN pin with respect to VSS. Measurements have a 0 to 4.6V range
and a 4.88mV resolution. The value is stored in the voltage register in two’s complement form and is updated every
440ms. Voltages above the maximum register value are reported at the maximum value; voltages below the
minimum register value are reported at the minimum value.
VOLTAGE REGISTER FORMAT MSB—ADDRESS 0Ch LSB—ADDRESS 0Dh 29 28 27 26 25 24 23 22 21 20 X X X X X
MSb LSb MSb LSb
“S”: Sign Bit(s), “X”: Reserved Units: 4.886mV
TEMPERATURE MEASUREMENT The DS2784 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C.
Temperature measurements are updated every 440ms and placed in the temperature register in two’s complement
form.
TEMPERATURE REGISTER FORMAT MSB—ADDRESS 0Ah LSB—ADDRESS 0Bh 29 28 27 26 25 24 23 22 21 20 X X X X X
MSb LSb MSb LSb
“S”: Sign Bit(s), “X”: Reserved Units: 0.125°C
Note: Temperature and battery voltage (VIN) are measured using the same ADC. Therefore, measurements are a 220ms average updated every 440ms.
CURRENT MEASUREMENT The DS2784 continually measures the current flow into and out of the battery by measuring the voltage drop across
a low-value current-sense resistor, RSNS. The voltage-sense range between SNS and VSS is ±51.2mV. The input
linearly converts peak-signal amplitudes up to 102.4mV as long as the continuous signal level (average over the
conversion cycle period) does not exceed ±51.2mV. The ADC samples the input differentially at 18.6kHz and
updates the current register at the completion of each conversion cycle (3.52s). Charge currents above the
maximum register value are reported as 7FFFh. Discharge currents below the minimum register value are reported
as 8000h.
CURRENT REGISTER FORMAT MSB—ADDRESS 0Eh LSB—ADDRESS 0Fh 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb
“S”: Sign Bit(s) Units: 1.5625µV/RSNS
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
The average current register reports an average current level over the preceding 28s. The register value is updated
every 28s in two’s complement form, and represents an average of the eight preceding current register values.
AVERAGE CURRENT REGISTER FORMAT MSB—ADDRESS 08h LSB—ADDRESS 09h 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb
“S”: Sign Bit(s) Units: 1.5625µV/RSNS
CURRENT OFFSET CORRECTION Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs
approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements.
During the offset correction conversion, the ADC does not measure the sense-resistor signal. A maximum error of
1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current
measurement made just prior to the offset conversion is retained in the current register and is substituted for the
dropped current measurement in the current accumulation process. Therefore, the accumulated current error due
to offset correction is typically much less than 1/1024.
CURRENT OFFSET BIAS The current offset bias (COB) value allows a programmable offset value to be added to raw current measurements.
The result of the raw current measurement plus COB is displayed as the current measurement result in the current
register, and is used for current accumulation. COB can be used to correct for a static offset error, or can be used
to intentionally skew the current results and, therefore, the current accumulation.
Read and write access is allowed to COB. Whenever the COB is written, the new value is applied to all subsequent
current measurements. COB can be programmed in 1.56µV steps to any value between +198.1µV and -199.7µV.
The COB value is stored as a two’s complement value in EEPROM. The COB is loaded on power-up from
EEPROM memory. The factory default value is 00h.
The difference between the CAB and COB is that the CAB is not subject to current blanking. Offset currents
between 100µV and -25µV are not accumulated if the offset is made by the COB. Offset currents between 100µV
and -25µV are accumulated if they are made by the CAB.
CURRENT OFFSET BIAS REGISTER FORMAT ADDRESS 7Bh S 26 25 24 23 22 21 20 MSb LSb “S”: Sign Bit(s) Units: 1.56µV/RSNS
CURRENT BLANKING The current blanking feature modifies current measurement result prior to being accumulated in the ACR. Current
blanking occurs conditionally when a current measurement (raw current + COBR) falls in one of two defined
ranges. The first range prevents charge currents less than 100µV from being accumulated. The second range
prevents discharge currents less than 25µV in magnitude from being accumulated. Charge current blanking is
always performed; however, discharge current blanking must be enabled by setting the NBEN bit in the control
register. See the register description for additional information.
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
CURRENT MEASUREMENT CALIBRATION The DS2784’s current measurement gain can be adjusted through the RSGAIN register, which is factory calibrated
to meet the data sheet-specified accuracy. RSGAIN is user accessible and can be reprogrammed after module or
pack manufacture to improve the current measurement accuracy. Adjusting RSGAIN can correct for variation in an
external sense resistor’s nominal value, and allows the use of low-cost, nonprecision, current-sense resistors.
RSGAIN is an 11-bit value stored in 2 bytes of the parameter EEPROM memory block. The RSGAIN value adjusts
the gain from 0 to 1.999 in steps of 0.001 (precisely 2-10). The user must program RSGAIN cautiously to ensure
accurate current measurement. When shipped from the factory, the gain calibration value is stored in two separate
locations in the parameter EEPROM block: RSGAIN, which is reprogrammable, and FRSGAIN, which is read only.
RSGAIN determines the gain used in the current measurement. The FRSGAIN value is provided to preserve the
factory calibration value only and is not used to calibrate the current measurement. The 16-bit FRSGAIN value is
readable from addresses B0h and B1h.
CURRENT MEASUREMENT GAIN REGISTER FORMAT MSB—ADDRESS 78h LSB—ADDRESS 79h X X X X 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb Units: 2
-10
SENSE RESISTOR TEMPERATURE COMPENSATION The DS2784 can temperature compensate the current-sense resistor to correct for variation in a sense resistor’s
value overtemperature. The DS2784 is factory programmed with the sense-resistor temperature coefficient, RSTC,
set to zero, which turns off the temperature compensation function. RSTC is user accessible and can be
reprogrammed after module or pack manufacture to improve the current accuracy when using a high-temperature
coefficient current-sense resistor. RSTC is an 8-bit value stored in the parameter EEPROM memory block. The
RSTC value sets the temperature coefficient from 0 to +7782ppm/ºC in steps of 30.5ppm/ºC. The user must
program RSTC cautiously to ensure accurate current measurement.
Temperature compensation adjustments are made when the temperature register crosses 0.5oC boundaries. The
temperature compensation is most effective with the resistor placed as close as possible to the VSS terminal. This
optimizes thermal coupling of the resistor to the on-chip temperature sensor.
SENSE RESISTOR TEMPERATURE COMPENSATION REGISTER FORMAT ADDRESS 7Ah 27 26 25 24 23 22 21 20 MSb LSb Units: 30.5ppm/ºC
CURRENT ACCUMULATION Current measurements are internally summed, or accumulated, at the completion of each conversion period and
the results are stored in the ACR. The accuracy of the ACR is dependent on both the current measurement and the
conversion time base. The ACR has a range of 0 to 409.6mVh with an LSb of 6.25µVh. Additional registers hold
fractional results of each accumulation to avoid truncation errors. The fractional result bits are not user accessible.
Accumulation of charge current above the maximum register value is reported at the maximum value; conversely,
accumulation of discharge current below the minimum register value is reported at the minimum value.
Charge currents (positive current register values) less than 100µV are not accumulated in order to mask the effect
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
Read and write access is allowed to the ACR. The ACR must be written MSB first then LSB. Whenever the ACR is
written, the fractional accumulation result bits are cleared. The write must be completed in 3.5s (one ACR update
period). A write to the ACR forces the ADC to perform an offset correction conversion and update the internal offset
correction factor. The current measurement and accumulation begin with the second conversion following a write to
the ACR.
The ACR value is backed up to EEPROM in case of power loss. The ACR value is recovered from EEPROM on
power-up. See Table 8 for specific address location and backup frequency.
ACCUMULATED CURRENT REGISTER FORMAT MSB—ADDRESS 10h LSB—ADDRESS 11h 15 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20
MSb LSb MSb LSb Units: 6.25µVh/RSNS
Table 5. Resolution and Range vs. Sense Resistor VSS - VSNS RSNS
20mΩ 15mΩ 10mΩ 5mΩ
Current Resolution 1.5625µV 78.13µA 104.2µA 156.3µA 312.5µA
Current Range ±51.2mV ±2.56A ±3.41A ±5.12A ±10.24A
ACR Resolution 6.25µVh 312.5µAh 416.7µAh 625µAh 1.250mAh
ACR Range 409.6mVh 20.48Ah 27.31Ah 40.96Ah 81.92Ah
ACCUMULATION BIAS In some designs a systematic error or an application preference requires the application of an arbitrary bias to the
current accumulation process. The current accumulation bias register (CAB) allows a user-programmed constant
positive or negative polarity bias to be included in the current accumulation process. The value in CAB can be used
to estimate battery currents that do not flow through the sense resistor, estimate battery self-discharge or estimate
current levels below the current measurement resolution. The user programmed two’s complement value, with bit
weighting the same as the current register, is added to the ACR once per current conversion cycle. The CAB is
loaded on power-up from EEPROM memory.
The difference between the CAB and COB is that the CAB is not subject to current blanking. Offset currents
between 100µV and -25µV are not accumulated if the offset is made by the COB. Offset currents between 100µV
and -25µV are accumulated if they are made by the CAB.
CURRENT ACCUMULATION BIAS REGISTER FORMAT ADDRESS 61h S 26 25 24 23 22 21 20 MSb LSb
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
CAPACITY ESTIMATION ALGORITHM Remaining capacity estimation uses real-time measured values, stored parameters describing the cell
characteristics, and application operating limits. Figure 3 describes the algorithm inputs and outputs.
Figure 3. Top-Level Algorithm Diagram
MODELING CELL CHARACTERISTICS To achieve reasonable accuracy in estimating remaining capacity, the cell performance characteristics
overtemperature, load current, and charge-termination point must be considered. Since the behavior of Li+ cells is
nonlinear, these characteristics must be included in the capacity estimation to achieve an acceptable level of
accuracy in the capacity estimation. The FuelPack™ method used in the DS2784 is described in general in
Application Note 131: Lithium-Ion Cell Fuel Gauging with Maxim Battery Monitor ICs. To facilitate efficient
implementation in hardware, a modified version of the method outlined in AN131 is used to store cell characteristics
in the DS2784. Full and empty points are retrieved in a lookup process which retraces a piece-wise linear model
consisting of three model curves named full, active empty, and standby empty. Each model curve is constructed
with 5-line segments, numbered 1 through 5. Above 40°C, the segment 5 model curves extend infinitely with zero
slope, approximating the nearly flat change in capacity of Li+ cells at temperatures above 40°C. Segment 4 of each
model curves originates at +40°C on its upper end and extends downward in temperature to the junction with
segment 3. Segment 3 joins with segment 2, which in turn joins with segment 1. Segment 1 of each model curve
extends from the junction with segment 2 to infinitely colder temperatures. The three junctions or breakpoints that
join the segments (labeled TBP12, TBP23, and TBP34 in Figure 4) are programmable in 1°C increments from -
128°C to +40°C. The slope or derivative for segments 1, 2, 3, and 4 are also programmable over a range of 0 to
15,555ppm, in steps of 61ppm.
Capacity Look-up
Available Capacity Calculation
ACR Housekeeping
Age Estimator
Learn Function
Cell
Model
Parameters
(EEPROM)
FULL(T) (R)
Active Empty (T) (R)
Standby Empty (T) (R)
Remaining Active Absolute
Capacity (RAAC) mAh (R)
Sense Resistor’
(RSNSP) (1byte EE)
Voltage (R)
Temperature (R)
Current (R)
Accumulated
Current (ACR) (R/W)
User Memory (EEPROM)
16 bytes
Aging Cap (AC)
(2 bytes EE)
Charge Voltage
(VCHG) (1 byte EE)
Remaining Standby Absolute
Capacity (RSAC) mAh (R)
Remaining Active Relative
Capacity (RARC) % (R)
Remaining Standby Relative
Capacity (RSRC) % (R)
Age Scalar (AS)
(1 bytes EE)
Min Chg Current
(IMIN) (1 byte EE)
Empty Voltage
(VAE) (1 byte EE)
Empty Current (IAE)
(1 byte EE)
Average Current (R)
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
Figure 4. Cell Model Example Diagram
Full—The full curve defines how the full point of a given cell varies over temperature for a given charge termination. The application’s charge termination method should be used to determine the table values. The DS2784
reconstructs the full line from the cell characteristic table to determine the full capacity of the battery at each
temperature. Reconstruction occurs in one-degree temperature increments.
Active Empty—The active-empty curve defines the variation of the active-empty point over temperature. The
active-empty point is defined as the minimum voltage required for system operation at a discharge rate based on a
high-level load current (one that is sustained during a high-power operating mode). This load current is
programmed as the active-empty current (IAE), and should be a 3.5s average value to correspond to values read
from the current register. The specified minimum voltage, or active empty voltage (VAE), should be a 220ms
average value to correspond to the values read from the voltage register. The DS2784 reconstructs the active
empty line from the cell characteristic table to determine the active empty capacity of the battery at each
temperature. Reconstruction occurs in one-degree temperature increments.
Standby Empty—The standby-empty curve defines the variation of the standby-empty point over temperature. The standby-empty point is defined as the minimum voltage required for standby operation at a discharge rate dictated
by the application standby current. In typical handheld applications, standby empty represents the point that the
battery can no longer support DRAM refresh and thus the standby voltage is set by the minimum DRAM voltage-
supply requirements. In other applications, standby empty can represent the point that the battery can no longer
support a subset of the full application operation, such as games or organizer functions. The standby load current
and voltage are used for determining the cell characteristics but are not programmed into the DS2784. The DS2784
reconstructs the standby-empty line from the cell characteristic table to determine the standby-empty capacity of
the battery at each temperature. Reconstruction occurs in one-degree temperature increments.
CELL MODEL CONSTRUCTION The model is constructed with all points normalized to the fully charged state at +40°C. All values are stored in the
cell parameter EEPROM block. The +40°C full value is stored in µVhr with an LSB of 6.25µVhr. The +40°C active
empty value is stored as a percentage of +40°C full with a resolution of 2-10. Standby empty at +40°C is, by
definition, zero and, therefore, no storage is required. The slopes (derivatives) of the 4 segments for each model
curve are stored in the cell parameter EEPROM block as ppm/°C. The breakpoint temperatures of each segment
are stored there also (see Application Note 3584: Storing Battery Fuel Gauge Parameters in DS2780 for more TBP12 TBP23 TBP34 40°C
100%
SEGMENT 1
DERIVATIVE
[PPM/°C]
ACTIVE
EMPTY
STANDBY
EMPTY
FULL
CELL
CHARACTERIZATION
DATA POINTS
SEG. 2 SEG. 3 SEG. 4 SEG. 5
