Maxim Integrated Producs DS2784G+, DS2784 Datasheet

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REV: 092507

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 Dallas Semiconductor, a wholly owned subsidiary of Maxim Integrated Products, Inc.

DS2784

1-Cell Stand-Alone Fuel Gauge IC with

Li+ Protector and SHA-1 Authentication

www.maxim-ic.com

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  Dallas 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

ORDERING INFORMATION

PART TEMP RANGE TOP MARK PIN PACKAGE

DS2784G+ -40°C to +85°C DS2784 14 TDFN (3mm x 5mm) DS2784G+T&R -40°C to +85°C DS2784 14 TDFN (3mm x 5mm)

+ Denotes a lead-free package. T&R = tape and reel

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication

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ABSOLUTE MAXIMUM RATINGS

Voltage Range on PLS Pin Relative to V

-0.3V to +18V

Voltage Range on CP Pin Relative to V

-0.3V to +12V

Voltage Range on DC Pin Relative to V

-0.3V to (CP + 0.3V)

Voltage Range on CC Pin Relative to V

VDD - 0.3V to CP + 0.3V

Voltage Range on All Other Pins Relative to V

-0.3V to +6.0V

Maximum Voltage Range on V

Pin Relative to V

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 Soldering Temperature (10s) See IPC/JEDEC J-STD-020

*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 V

(Note 1) 2.5 4.6 V

DD0

Sleep mode 1 4

DD1

Sleep mode, VDD = 2.5V 0°C to +50°C

0.4 1.5

DD2

Active mode 85 125

μA

Supply Current

DD3

Active mode during SHA computation

300 500

μA

Temperature Accuracy -3 +3 Temperature Resolution 0.125 Temperature Range -128.000 +127.875

4.0 ≤ V

≤ 4.6,

≤ VDD + 0.3V

-30 30

Voltage Accuracy, V

2.5 ≤ V

≤ 4.6V,

≤ VDD + 0.3V

-50 +50

Voltage Resolution, V

4.88 mV

Voltage Range, V

0 4.99 V

Input Resistance, V

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

0ºC ≤ TA ≤ +50ºC -2 +2

Time Base Error

-3 +3

CP Output Voltage V

ICC + I

= 0.9µA 8.50 9.25 10.00 V

CP Startup Time t

SCP

CE = 0, DE = 0, C

= 0.1µF, Active mode

200 ms

Output High: CC, DC

OHCC

OHDC

IOH = -100µA (Note 5) V

- 0.4 V

Output Low: CC V

OLCC

IOL = 100µA VDD + 0.1 V

Output Low: DC V

OLDC

IOL = 100µA 0.1 V

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PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DQ, PIO Voltage Range -0.3 +5.5 V

DQ, PIO Input-Logic High V

1.5 V

DQ, PIO Input-Logic Low V

0.6 V

DQ, PIO Output-Logic Low V

IOL = 4mA 0.4 V

DQ, PIO Pullup Current I

Sleep mode, V

= VDD - 0.4V

0.2

μA

DQ, PIO Pulldown Current I

Active mode, V

= 0.4V

0.2

μA

DQ Input Capacitance C

50 pF

DQ Sleep Timeout t

SLEEP

DQ < V

2 9 s

PIO, DQ Wake Debounce t

WDB

B Sleep mode 100 ms

SHA-1 COMPUTATION TIMING

Computation Time t

SHA

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

VOV = 11000b 4.457 4.482 4.507

Overvoltage Detect V

= 00011b 4.252 4.277 4.302

Charge-Enable Voltage V

Relative to V

-75 -100 -125 mV

Undervoltage Detect V

2.40 2.45 2.50 V

OC = 11b -57 -72 -87

Overcurrent Detect: Charge V

COC

OC = 00b -15.5 -23.5 -31.5

OC = 11b 76 96 116

Overcurrent Detect: Discharge V

DOC

OC = 00b 23.5 35.5 47.5

SC = 1b 240 300 360 mV

Short-Circuit Current Detect V

SC = 0b 120 150 180 mV

Overvoltage Delay t

OVD

(Note 6) 425 1150 ms

Undervoltage Delay t

UVD

(Notes 6, 7) 84 680 ms

Overcurrent Delay t

OCD

8 10 12 ms

Short-Circuit Delay t

SCD

80 120 160

μs

Test Threshold V

COC, DOC conditions 0.3 0.8 1.5 V

Test Current I

TST

SC, COC, DOC condition 10 20 40

μA

PLS Pulldown Current I

PPD

Sleep mode 30 200 600

μA

Recovery Current I

VUV condition, max: V

PLS

= 15V,

= 1V

min: V

PLS

= 4.2V,

= 2V

2.5 5.0 10.00 mA

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EEPROM RELIABILITY SPECIFICATION

(VDD = 2.5V to 5.5V, TA = -20°C to +70°C, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

EEPROM Copy Time t

EEC

10 ms

EEPROM Copy Endurance N

EEC

TA = +50°C 50,000 cycles

ELECTRICAL CHARACTERISTICS: 1-Wire Interface, Standard

(VDD = 2.5V to 5.5V, TA = -20°C to +70°C, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Time Slot t

SLOT

60 120

μs

Recovery Time t

REC

μs

Write-0 Low Time t

LOW0

60 120

μs

Write-1 Low Time t

LOW1

1 15

μs

Read-Data Valid t

RDV

μs

Reset-Time High t

RSTH

480

μs

Reset-Time Low t

RSTL

480 960

μs

Presence-Detect High t

PDH

15 60

μs

Presence-Detect Low t

PDL

60 240

μs

ELECTRICAL CHARACTERISTICS: 1-Wire Interface, Overdrive

(VDD = 2.5V to 5.5V, TA = -20°C to +70°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Time Slot t

SLOT

6 16

μs

Recovery Time t

REC

μs

Write-0 Low Time t

LOW0

6 16

μs

Write-1 Low Time t

LOW1

1 2

μs

Read-Data Valid t

RDV

μs

Reset-Time High t

RSTH

μs

Reset-Time Low t

RSTL

48 80

μs

Presence-Detect High t

PDH

2 6

μs

Presence-Detect Low t

PDL

8 24

μs

Note 1: All voltages are referenced to V

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 (t

OVD

, t

UVD

) are reduced to 0s if the OV or UV condition is detected within 100ms of entering

Active mode.

Note 7: t

UVD

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 OPERATING CIRCUIT

PIN DESCRIPTION

PIN NAME FUNCTION

1 V

Power-Supply Input. Chip supply input. Bypass with 0.1µF to VSS. 2 CTG Connect to Ground 3 V

Device Ground. Chip ground and battery-side sense resistor input.

4 V

Battery Voltage-Sense Input. Connect to positive cell terminal through decoupling

network.

5, 9, 10 N.C. No Connection

6 PLS

Pack Plus Terminal-Sense Input. Used to detect the removal of short-circuit, discharge

overcurrent, and charge overcurrent conditions.

7 CC Charge Control. Charge FET control output. 8 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.

PAD PAD Exposed Pad. Connect to V

or float.

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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication

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 currentmeasurement 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 9V charge pump that increase gate drive as the cell voltage decreases. The high-side topology preserves the ground path for serial communication while eliminating the parasitic charge path formed when the fuel gauge IC is 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

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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 I

DD3

for t

SHA

. 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 (V

PLS

> VDD + 50mV) or if a

charge current of 1.6mV / R

SNS

is measured from SNS to VSS. The DS2784 exits Sleep mode upon charger

connection and V

≥ VUV or a low to high transition on DQ.

The bus-low condition, where the DQ pin is low for t

SLEEP

, indicates pack removal or system shutdown in which the

1-Wire bus pullup voltage, V

PULLUP

, 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 V

voltage is less

than V

(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 t

SLEEP

. 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.

Figure 1. Sleep Mode State Diagram

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication

PMOD = 0

UVEN = 0

PMOD = 1

UVEN = 1

PMOD = 1

UVEN = 0

PMOD = 0

UVEN = 1

PSIO = 1

PSDQ = 1

PSIO = 1

PSDQ = 0

PSIO = 0

PSDQ = 1

PSIO = 0

PSDQ = 0

Vin < V

DQ low for t

SLEEP

DQ low for t

SLEEP

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

is less than V

and DQ is stable at either logic level for t

SLEEP

. A value of 0 disables transitions to Sleep mode in an

undervoltage condition.

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PMOD—Power Mode Enable. A value of 1 allows the DS2784 to enter Sleep mode when DQ is low for t

SLEEP

. A

value of 0 disables DQ related transitions to Sleep mode.

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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 V

PLS

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

ACTIVATION

CONDITION

THRESHOLD DELAY RESPONSE

(2)

RELEASE THRESHOLD

Overvoltage V

> V

OVD

CC Off

VIN < VCE or (V

SNS

> 1.2mV

and V

< VOV)

Undervoltage VIN < V

UVD

CC Off, DC Off,

Sleep Mode

PLS

> V

(3)

(charger connected)

Overcurrent, Charge V

SNS

< V

COC

OCD

CC Off, DC Off

PLS

< VDD - V

(4)

(charger removed)

Overcurrent, Discharge V

SNS

> V

DOC

OCD

DC Off

PLS

> VDD - V

(5)

(load removed)

Short Circuit V

SNS

> V

SCD

DC Off

PLS

> VDD - V

(5)

(load removed)

Note 1: All voltages are with respect to V

Note 2: CC pin driven to V

OLCC

(VDD) for CC off response. DC pin driven to V

OLDC

(VSS) for DC off response.

Note 3: If V

< VUV when charger connection is detected, release is delayed until VIN ≥ VUV. The recovery charge path provides an internal

current limit (I

) to safely charge the battery.

Note 4: With test current I

TST

flowing from PLS to V

(pulldown on PLS) enabled.

Note 5: With test current I

TST

flowing from V

to PLS (pullup on PLS).

Overvoltage. If the voltage on V

exceeds the overvoltage threshold (VOV) for a period longer than overvoltage

delay (t

OVD

), 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 V

falls below the charge enable

threshold, V

, the DS2784 turns the charge FET on by driving CC high. The DS2784 drives CC high before

< VCE if a discharge condition persists with V

SNS

≥ 1.2mV and VIN < VOV.

Undervoltage. If V

drops below the undervoltage threshold (VUV) for a period longer than undervoltage delay

UVD

), 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 (I

) from

PLS to V

to gently charge severely depleted cells. The recovery charge path is enabled when

0 ≤ V

< (VOV - 100mV). Once VDD reaches 2.45V (typ), the DS2784 returns to normal operation and begins

monitoring V

. Once V

> VUV, the DS2784 transitions from Sleep to Active mode and the CC and DC outputs are

driven high to turn on the charge and discharge FETs.

Overcurrent, Charge Direction (COC). Charge current develops a negative voltage on V

SNS

with respect to VSS. If

SNS

is less than the charge overcurrent threshold (V

COC

) for a period longer than overcurrent delay (t

OCD

), the

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication

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 V

- VTP. The DS2784 provides a pulldown current

TST

) 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 V

SNS

with respect to

. If V

SNS

exceeds the discharge overcurrent threshold (V

DOC

) for a period longer than t

OCD

, the DS2784 shuts off the external discharge FET and sets the DOC flag in the protection register. The discharge current path is not reestablished until the voltage on PLS rises above V

- VTP. The DS2784 provides a test current (I

TST

) from VDD to

PLS to pull PLS up in order to detect the removal of the offending low-impedance load.

Short Circuit. If V

SNS

exceeds short-circuit threshold VSC for a period longer than short-circuit delay (t

SCD

), 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 V

- VTP. The DS2784 provides a test

current of value (I

TST

) 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

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

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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

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 V

has persisted above the V

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 V

< V

. 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 V

COC

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 V

DOC

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 V

. 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

as an enable input to the safety circuit. If all safety conditions are met AND DE is set, the DC pin drives to V

. If

DE is cleared, the DC pin is driven low to disable the charge FET.

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

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication

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Table 2. VOV Threshold

VOV BIT FIELD V

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 V

COC

(mV) V

DOC

(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 V

(mV)

0 150

1 300

VOLTAGE MEASUREMENT

Battery voltage is measured every 440ms on the VIN pin with respect to VSS. Measurements have a 0 to 4.99V 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

S 2

28272625242

22212

X X X X X

MSb LSb MSb LSb

“S”: Sign Bit(s), “X”: Reserved

Units: 4.886mV

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