MAXIM DS2775, DS2776, DS2777, DS2778 User Manual

General Description

The DS2775–DS2778 report available capacity for
rechargeable lithium-ion (Li+) and Li+ polymer (Li-Poly)
batteries in mAh and as a percentage of full. Safe oper­ation is ensured by the integrated Li+ protector. The
DS2776/DS2778 support SHA-1-based challenge­response authentication in addition to all other DS2775/
DS2777 features.

Precision measurements of voltage, temperature, and
current, along with a cell characteristics table and
application parameters, are used for capacity estima­tion calculations. The capacity registers report a con­servative estimate of the amount of charge that can be
removed given the current temperature, discharge rate,
stored charge, and application parameters.

The DS2775–DS2778 operate from +4.0V to +9.2V for
direct integration into battery packs with two Li+ or Li­Poly cells.

In addition to nonvolatile storage for cell compensation
and application parameters, the DS2775–DS2778 offer
16 bytes of EEPROM for use by the host system and/or
pack manufacturer to store battery lot and date tracking
information. The EEPROM can also be used for non­volatile storage of system and/or battery usage statis­tics. A Maxim 1-Wire

®

(DS2775/DS2776) or 2-wire
(DS2777/DS2778) interface provides serial communica­tion to access measurement and capacity data regis­ters, control registers, and user memory. The
DS2776/DS2778 use the SHA-1 hash algorithm in a
challenge-response pack authentication protocol for
battery-pack verification.

Applications

Low-Cost Notebooks

UMPCs

DSLR Cameras

Video Cameras

Commercial and Military Radios

Portable Medical Equipment

Features

♦ High-Side nFET Drivers and Protection Circuitry

♦ Precision Voltage, Temperature, and Current

Measurement System

♦ Cell-Capacity Estimation from Coulomb Count,

Discharge Rate, Temperature, and Cell
Characteristics

♦ Estimates Cell Aging Between Learn Cycles

♦ Uses Low-Cost Sense Resistor

♦ Allows Calibration of Gain and Temperature

Coefficient

♦ Programmable Thresholds for Overvoltage and

Overcurrent

♦ Pack Authentication Using SHA-1 Algorithm

(DS2776/DS2778)

♦ 32-Byte Parameter EEPROM

♦ 16-Byte User EEPROM

♦ Maxim 1-Wire Interface with 64-Bit Unique ID

(DS2775/DS2776)

♦ 2-Wire Interface with 64-Bit Unique ID

(DS2777/DS2778)

♦ 3mm x 5mm, 14-Pin TDFN Lead-Free Package

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with

Protector and Optional SHA-1 Authentication

________________________________________________________________

Maxim Integrated Products

1

Ordering Information

19-4688; Rev 4; 6/11

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

PART PIN-PACKAGE TOP MARK

DS2775G+ 14 TDFN-EP* D2775

DS2775G+T& R 14 TDFN-EP* D2775

DS2776G+ 14 TDFN-EP* D2776

DS776G+T&R 14 TDFN-EP* D2776

DS2777G+ 14 TDFN-EP* D2777

DS2777G+T& R 14 TDFN-EP* D2777

DS2778G+ 14 TDFN-EP* D2778

DS2778G+T& R 14 TDFN-EP* D2778

Note: All devices are specified over the -20°C to +70°C oper­ating temperature range.

+

Denotes a lead(Pb)-free/RoHS-compliant package.

T&R = Tape and reel.

*

EP = Exposed pad.

Selector Guide appears at end of data sheet.

1-Wire is a registered trademark of Maxim Integrated Products, Inc.

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= +4.0V to +9.2V, 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 PLS, CP, CC, DC Pins

Relative to V

SS

.....................................................-0.3V to +18V

Voltage Range on V

DD

, V

IN1

, V

IN2

, SRC Pins

Relative to VSS....................................................-0.3V to +9.2V

Voltage Range on All Other Pins Relative to V

SS

..-0.3V to +6.0V

Continuous Sink Current, PIO, DQ......................................20mA

Continuous Sink Current, CC, DC.......................................10mA

Operating Temperature Range ...........................-20°C to +70°C

Storage Temperature Range .............................-55°C to +125°C

Lead Temperature (soldering, 10s) .................................+300°C

Soldering Temperature (reflow) .......................................+260°C

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

I

DD0

Supply Current

Temperature Accuracy T

I

DD1

I

DD2

ERR

Voltage Accuracy

Input Resistance (V

Current Resolut ion I

Current Ful l Scale I

Current Gain Error I

Current Offset I

Accumulated Current Offset q

Time-Base Error t

CP Output Voltage (VCP - V

CP Startup Time t

Output High: CC, DC V

Output Low: CC V

Output Low: DC V

IN1

, V

) 15 M

IN2

LSB

FS

GERR

OERR

OERR

ERR

) VGS I

SRC

SCP

OHCP IOH

OLCC IOL

OLDC IOL

DQ, PIO Voltage Range -0.3 +5.5 V

DQ, PIO, SDA, SCL Input
Logic-High

DQ, PIO, SDA, SCL Input
Logic-Low

V

V

OVD Input Logic-High V

OVD Input Logic-Low V

Sleep mode, TA +50°C 3 5

Sleep mode, TA> +50°C 10

Active mode 80 135

Active mode during SHA-1 computation 120 300

-3 +3 °C

2.0V  V

IN1

4.6V, 0°C  T

2.0V  V

4.6V, T

2.0V  V

IN1

= +25°C

A

IN1

1.56 μV

-51.2 +51.2 mV

-1 +1 % FS

0°C  TA +70°C (Note 1) -9.375 9.375 μVh

0°C  TA +70°C (Note 1) -255 0 μVh/Day

0°C  TA +50°C -2 +2

-3 +3

= 0.9μA 4.4 4.7 5 V

OUT

CE = 0, DE = 0, CCP = 0.1μF, acti ve mode 200 ms

= 100μA (Note 2) VCP - 0.4 V

= 100μA V

= 100μA V

1.5 V

IH

0.6 V

IL

V

IH

V

IL

 4.6V, 2.0V  (V

 +50°C

A

 4.6V, 2.0V  (V

 4.6V, 2.0V  (V

IN2

- V

IN2

IN2

) 

IN1

– V

) 

IN1

- V

)  4.6V -50 +50

IN1

-35 +35

-22 22

- 0.2 V

BAT

SRC

SRC

SS

+ 0.1 V

+ 0.1 V

+ 0.2 V

μA

mV

%

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with

Protector and Optional SHA-1 Authentication

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDD= +4.0V to +9.2V, TA= -20°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)

SHA-1 COMPUTATION TIMING (DS2776/DS2778 ONLY)

(VDD= +4.0V to +9.2V, TA= 0°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS: PROTECTION CIRCUIT

(VDD= +4.0V to +9.2V, TA= 0°C to +50°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DQ, PIO, SDA Output Logic-Low V

DQ, PIO Pullup Current I

DQ, PIO, SDA, SCL Pulldown
Current

DQ Input Capacitance C

DQ Sleep Timeout t

PIO, DQ Wake Debounce t

OL

PU

I

PD

DQ

SLEEP

WDB

IOL = 4mA 0.4 V

Sleep mode, V

Active mode, V

50 pF

DQ < VIL 2 9 s

Sleep mode 100 ms

= (VDD - 0.4V) 30 100 200 nA

PIN

= 0.4V 30 100 200 nA

PIN

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Computation Time t

COMP

30 m s

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Overvoltage Detect V

Charge-Enable Voltage V

Undervoltage Detect V

Overcurrent Detect: Charge V

Overcurrent Detect: Discharge V

Short-Circuit Current Detect V

Overvoltage Delay t

Undervoltage Delay t

Overcurrent Delay t

Short-Circuit Delay t

Charger-Detect Hysteresis V

Test Threshold V

Test Current I

PLS Pulldown Current I

Recovery Current I

OV

CE

UV

COC

DOC

SC

OVD

UVD

OCD

SCD

CD

TST

PPD

RC

VOV = 1110111b 4.438 4.473 4.508

VOV = 1100011b 4.242 4.277 4.312

Relative to VOV -100 mV

Programmable in Control register 0x60h,
UV[1:0] = 10

OC = 11b -60 -75 -90

OC = 00b -12.5 -25 -38

OC = 11b 80 100 120

OC = 00b 25 38 50

SC =1b 240 300 360

SC = 0b 120 150 180

(Note 3) 600 1400 ms

(Note 3) 600 1400 ms

8 10 12 ms

80 120 160 μs

VUV condition 50 mV

COC, DOC condition 0.4 1.0 1.2 V

TP

DOC condition 20 40 80

COC condition -45 -60 -95

Sleep mode 200 400 630 μA

VUV condition, max: V
min: V

= 4.2V, VDD = 2V

PLS

= 15V, VDD = 1.4V;

PLS

2.415 2.450 2.485 V

3.3 8 13 mA

V

mV

mV

mV

μA

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication

4 _______________________________________________________________________________________

EEPROM RELIABILITY SPECIFICATION

(VDD= +4.0V to +9.2V, TA= -20°C to +70°C, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS: 1-Wire INTERFACE, STANDARD (DS2775/DS2776 ONLY)

(VDD= +4.0V to +9.2V, TA= -20°C to +70°C.)

ELECTRICAL CHARACTERISTICS: 1-Wire INTERFACE, OVERDRIVE (DS2775/DS2776 ONLY)

(VDD= +4.0V to +9.2V, TA= -20°C to +70°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

EEPROM Copy Time t

EEPROM Copy Endurance N

EEC

EEC

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Time Slot t

Recovery Time t

Write-Zero Low Time t

Write-One Low Time t

Read Data Valid t

Reset Time High t

Reset Time Low t

Presence-Detect High t

Presence-Detect Low t

SLOT

REC

LOW0

LOW1

RDV

RSTH

RSTL

PDH

PDL

10 ms

TA = +50°C 50,000 Cycles

60 120 μs

1 μs

60 120 μs

1 15 μs

15 μs

480 μs

480 960 μs

15 60 μs

60 240 μs

Time Slot t

Recovery Time t

Write-Zero Low Time t

Write-One Low Time t

Read Data Valid t

Reset Time High t

Reset Time Low t

Presence-Detect High t

Presence-Detect Low t

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

SLOT

REC

LOW0

LOW1

RDV

RSTH

RSTL

PDH

PDL

6 16 μs

1 μs

6 16 μs

1 2 μs

2 μs

48 μs

48 80 μs

2 6 μs

8 24 μs

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with

Protector and Optional SHA-1 Authentication

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (DS2777/DS2778 ONLY)

(VDD= +4.0V to +9.2V, TA= -20°C to +70°C.)

Note 1: Accumulation bias and offset bias registers set to 00h. NBEN bit set to 0.
Note 2: Measurement made with V

SRC

= +8V, VGSdriven with external +4.5V supply.

Note 3: Overvoltage (OV) and undervoltage (UV) delays (t

OVD

, t

UVD

) are reduced to zero seconds if the OV or UV condition is

detected within 100ms of entering active mode.

Note 4: Timing must be fast enough to prevent the DS2777/DS2778 from entering sleep mode due to bus low for period > t

SLEEP

.

Note 5: f

SCL

must meet the minimum clock low time plus the rise/fall times.

Note 6: The maximum t

HD:DAT

need only be met if the device does not stretch the low period (t

LOW

) of the SCL signal.

Note 7: This device internally provides a hold time of at least 75ns for the SDA signal (referred to the V

IHMIN

of the SCL signal) to

bridge the undefined region of the falling edge of SCL.

Note 8: Filters on SDA and SCL suppress noise spikes at the input buffers and delay the sampling instant.
Note 9: C

B

is total capacitance of one bus line in pF.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

SCL Clock Frequency f

Bus-Free Time Between a STOP
and START Condition

Hold Time (Repeated) START
Condition

Low Period of SCL Clock t

High Period of SCL Clock t

Setup Time for a Repeated
START Condition

Data Hold Time t

Data Setup Time t

Rise Time of Both SDA and SCL
Signals

Fal l Time of Both SDA and SCL
Signals

Setup Time for STOP Condition t

Spike Pulse Widths Suppressed
by Input Filter

Capacitive Load for Each Bus
Line

SCL, SDA Input Capacitance C

(Note 4) 0 400 kHz

SCL

t

1.3 μs

BUF

t

(Note 5) 0.6 μs

HD: STA

1.3 μs

LOW

0.6 μs

HIGH

t

0.6 μs

SU:STA

(Notes 6, 7) 0 0.9 μs

HD:DAT

(Note 6) 100 ns

SU:DAT

t

R

t

F

0.6 μs

SU:STO

(Note 8) 0 50 ns

t

SP

C

(Note 9) 400 pF

B

60 pF

BIN

20 +

0.1C

20 +

0.1C

300 ns

B

300 ns

B

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication

6 _______________________________________________________________________________________

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

DISCHARGE-OVERCURRENT

PROTECTION DELAY

DS2775/6/7/8 toc01

DC FET
GATE

2V/div

2V/div

0V

0V

0V

0V

1V/div

20mV/div

DC FET
SOURCE

V

GS

V

SNS

25mΩ
SENSE RESISTOR
WITH DISCHARGE­OVERCURRENT
THRESHOLD = 38mV

TIME (ms)

18

161412108642020

CC FET GATE TURN-OFF DURING

CHARGE-OVERCURRENT EVENT

DS2775/6/7/8 toc02

CC FET
GATE

2V/div

2V/div

0V

0V

0V

0V

1V/div

20mV/div

CC FET
SOURCE

V

GS

CC FET

V

SNS

25mΩ
SENSE RESISTOR
WITH CHARGE­OVERCURRENT
THRESHOLD = 25mV

TIME (μs)

45

403530252015105050

DC FET GATE TURN-OFF DURING

SHORT-CIRCUIT EVENT

DS2775/6/7/8 toc03

DC FET
GATE

2V/div

0V

0V

0V

0V

2V/div

1V/div

50mV/div

DC FET
SOURCE

V

GS

DC FET

V

SNS

25mΩ
SENSE RESISTOR
WITH SHORT-CIRCUIT
THRESHOLD = 150mV

TIME (μs)

18

161412108642020

SHORT-CIRCUIT PROTECTION

DELAY

DS2775/6/7/8 toc04

DC FET
GATE

2V/div

0V

0V

0V

0V

2V/div

1V/div

100mV/div

DC FET
SOURCE

V

GS

DC FET

V

SNS

25mΩ
SENSE RESISTOR
WITH SHORT-CIRCUIT
THRESHOLD = 150mV

TIME (μs)

180

160140120100806040200 200

VOLTAGE MEASUREMENT

ACCURACY

DS2775/6/7/8 toc05

V

INX

(V)

ACCURACY (mV)

4321

2

4

6

8

10

12

14

16

18

20

0

0

+70°C

-20°C

+25°C

CHARGE-PUMP STARTUP EXITING SLEEP

MODE (V

DD

= 8V NO LOAD ON PK+)

DS2775/6/7/8 toc06

TIME (ms)

VOLTAGE (V)

908010 20 30 50 6040 70

0

2

3

4

5

6

7

8

-2
0 100

2.75V

12.6V

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with

Protector and Optional SHA-1 Authentication

_______________________________________________________________________________________

7

Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

CURRENT MEASUREMENT

ACCURACY

125

75

25

-25

ACCURACY (μV)

-75

-125

-0.052

-20°C

+25°C

+70°C

V

(mV)

SNS

0.0480.0280.008-0.012-0.032

CURRENT MEASUREMENT OFFSET

vs. TEMPERATURE

2

1

0

-1

-2

LSB (1.5625μV)

-3

-4

-5

-20
TEMPERATURE (°C)

DS2775/6/7/8 toc07

(mA)

RC

I

IRC vs. V

7

1kΩ RESISTOR FROM PLS TO PK+

6

5

4

3

2

1

0

06

DD

DS2775/6/7/8 toc08

54321

VDD (V)

DS2775/6/7/8 toc09

6040200

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication

8 _______________________________________________________________________________________

Pin Description

×

Pin Configuration

TOP VIEW

1CC

+

2V

DD

3DC
4V

IN2

5V

IN1

6VB
7V

SS

PIN NAME FUNCTION

1 CC Charge Control. Charge FET control output.

2 VDD Chip-Supply Input. Bypa ss with 0.1μF to VSS.

3 DC Discharge Control. Discharge FET control output.

4 V

5 V

6 VB Regulated Operating Voltage. B ypas s with 0.1μF to VSS.

Battery Voltage Sense Input 2. Connect to highest voltage potential positive cell terminal through

IN2

decoupl ing network.

Battery Voltage Sense Input 1. Connect to lowe st voltage potential po sit ive cel l terminal through

IN1

decoupl ing network.

DS2775
DS2776
DS2777
DS2778

TDFN

(3mm

5mm)

EP

14 CP
13 SRC
12 SCL/OVD
11 SDA/DQ
10 PLS

9 PIO
8 SNS

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

8 SNS Sense Resistor Connection. Pack-side sense resistor sense input.

9 PIO Programmable I/O. Can be configured as wake input.

10 PLS

11 SDA/DQ

12 SCL/OVD

13 SRC Protection MOSFET Source Connection. U sed a s a reference for the charge pump.

14 CP Charge Pump Output. Generates gate drive voltage for protection FETs. Bypass with 0.47μF to SRC.

— EP Exposed Pad. Connect to ground or leave unconnected.

Pack Plus Terminal Sense Input. Used to detect the removal of short-circuit, discharge overcurrent, and
charge overcurrent condition s.

Data Input/Output. Serial data I/O, includes weak pulldown to detect system disconnect and can be
configured as wa ke input for 1-Wire devices.

Serial Clock Input/Overdrive Select. Communication clock for 2-wire devices/overdrive select pin for
1-Wire devices.

DS2775/DS2776/DS2777/DS2778

Block Diagram

FuelPack is a trademark of Maxim Integrated Products, Inc.

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with

Protector and Optional SHA-1 Authentication

_______________________________________________________________________________________ 9

PLS

CC

DC

CP

V

VOLTAGE

POWER-MODE

CONTROL

Li+

PROTECTOR

FuelPack™

ALGORITHM

FET DRIVERS

CONTROL AND

STATUS REGISTERS

DD

VB

CHARGE

PUMP

VOLTAGE

REGULATOR

VB INTERNAL

32-BYTE

PARAMETER

EEPROM

16-BYTE USER

EEPROM

TEMPERATURE

CURRENT

PRECISION ANALOG

OSCILLATOR

PIO LOGIC

COMMUNICATION

INTERFACE

DS2775–DS2778

10-BIT + SIGN

ADC/MUX

15-BIT + SIGN

ADC

VREF

PIN

DRIVERS

AND

POWER

SWITCH

CONTROL

V

IN2

V

IN1

SNS

V

SS

SDA/DQ

SCL/OVD

PIO

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication

10 ______________________________________________________________________________________

DS2775/DS2776 Typical Application Circuit

DS2777/DS2778 Typical Application Circuit

PK+

1kΩ 150Ω

150Ω

DATA

5.1V

0.1μF

PK-

1kΩ

CC SRC DC

PLS

DQ

DS2775

PIO

VB

DS2776

R

SNS

1kΩ470Ω

V

DD

V

IN2

V

IN1

CP

V

OVDSNS

SS

SRC

PK+

1kΩ 150Ω

1kΩ

1kΩ470Ω

0.47μF

1kΩ

1kΩ

0.1μF

1kΩ

CC SRC DC

SDA

SCL

PK-

150Ω

150Ω

PLS

SDA

SCL

PIO

5.1V5.1V

0.1μF

VB

SNS

DS2777
DS2778

R

SNS

V

DD

V

IN2

V

IN1

CP

SRC

0.47μF

0.1μF

V

SS

1kΩ

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with

Protector and Optional SHA-1 Authentication

______________________________________________________________________________________ 11

Detailed Description

The DS2775–DS2778 function as an accurate fuel
gauge, Li+ protector, and SHA-1-based authentication
token (SHA-1-based authentication available only on
the DS2776/DS2778). 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 along with system parameters for charge
and end-of-discharge conditions. The algorithm para­meters are user programmable and can be modified
within the pack. Critical capacity and aging data are
periodically saved to EEPROM in case of short-circuit
or deep-depletion events.

The Li+ protection function ensures safe, high-perfor­mance operation. nFET protection switches are driven
with a charge pump that maintains 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,
undervoltage, overcurrent, and short-circuit current are
user programmable for 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.

Power Modes

The DS2775–DS2778 have two power modes: active
and sleep. On initial power-up, the DS2775–DS2778
default to active mode. In active mode, the DS2775–
DS2778 are fully functional with measurements and
capacity estimation registers continuously updated.
The protector circuit monitors battery pack, cell volt­ages, and battery current for safe 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 an SHA-1 com­putation is performed, the supply current increases to
I

DD2

for t

SHA

. In sleep mode, the DS2775–DS2778 con-

serve power by disabling measurement and capacity
estimation functions, but preserve register contents.
Gate drive to the protection FETs is disabled in sleep;
the SHA-1 authentication feature is not operational.

The IC enters sleep mode 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+

V

CD

) or if a charge current of 1.6mV/R

SNS

measured

from SNS to V

SS

. The DS2775–DS2778 exit sleep mode
upon charger connection or a low-to-high transition on
any communication line. The bus-low condition, where
all communication lines are low for t

SLEEP

, indicates
pack removal or system shutdown in which the 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 DS2775–DS2778
enter sleep due to a bus-low condition, it is assumed
that no charge or discharge current flows and that
coulomb counting is unnecessary.

The second condition to enter sleep is an undervoltage
condition, which reduces battery drain due to the
DS2775–DS2778 supply current and prevents overdis­charging the cell. The DS2775–DS2778 transition to
sleep mode if the V

IN1

or V

IN2

voltage is less than V

UV

and the undervoltage enable (UVEN) bit is set. The
communication bus must be in a static state, that is,
with DQ (SDA and SCL for 2-wire) either high or low for
t

SLEEP

. The DS2775–DS2778 transition from sleep
mode to active mode when DQ (SDA and SCL for
2-wire) changes logic state. See Figures 1 and 2 for
more information on sleep-mode state.

The DS2775–DS2778 have a “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 are set and sleep mode is
entered through the PMOD condition*, the PIO and DQ
pins pull high, respectively. Sleep mode is exited upon
the detection of a low-going transition on PIO or DQ.
PIO has a 100ms debounce period to filter out glitches
that can be caused when a sleeping battery is inserted
into a system.

*

The “power switch” feature is disabled if sleep mode is

entered because of a UV condition.

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication

12 ______________________________________________________________________________________

Li+ Protection Circuitry

During active mode, the DS2775–DS2778 constantly
monitor SNS, V

IN1

, V

IN2

, and 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 DS2775–DS2778, and the thresholds
that release the DS2775–DS2778 from a protection
state. Figure 3 shows Li+ protection circuitry example
waveforms.

Overvoltage (OV)

If either of the voltages on (V

IN2

- V

IN1

) or (V

IN1

- VSS)
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. The DC out­put remains high during overvoltage to allow
discharging. When (V

IN2

- V

IN1

) and (V

IN1

- VSS) falls
below the charge-enable threshold, VCE, the
DS2775–DS2778 turn the charge FET on by driving CC
high. The DS2775–DS2778 drive CC high before
[(V

IN2-VIN1

) and (V

IN1

- VSS)] < VCEif a discharge

condition persists with V

SNS

≥ 1.2mV and [(V

IN2

- V

IN1

)

and (V

IN1

- VSS)] < VOV.

ACTIVE

PMOD = 0

UVEN = 0

SLEEP

PSPIO = 0

PSDQ = 0

RISING EDGE ON DQ

CHARGER DETECT

PULL DQ LOW

CHARGER DETECT

ACTIVE

PMOD = 0

UVEN = 1

SLEEP

PSPIO = 0

PSDQ = 1

V

IN1

OR V

IN2

< V

UV

PULL PIO LOW

RISING EDGE ON DQ

CHARGER DETECT

ACTIVE

PMOD = 1

UVEN = 0

SLEEP

PSPIO = 1

PSDQ = 0

PULL DQ LOW FOR t

SLEEP

PULL DQ LOW FOR t

SLEEP

PULL DQ LOW

PULL PIO LOW

CHARGER DETECT

ACTIVE

PMOD = 1

UVEN = 1

SLEEP

PSPIO = 1

PSDQ = 1

V

IN1

OR V

IN2

< V

UV

Figure 1. Sleep-Mode State Diagram for DS2775/DS2776

ACTIVE

PMOD = 0

UVEN = 0

SLEEP

PSPIO = 0
PSDQ = X

RISING EDGE ON SDA OR SCL

CHARGER DETECT

V

IN1

OR V

IN2

< V

UV

CHARGER DETECT

ACTIVE

PMOD = 0

UVEN = 1

SLEEP

PSPIO = 0
PSDQ = X

RISING EDGE ON SDA OR SCL

PULL PIO LOW

CHARGER DETECT

PULL SDA AND SCL LOW

FOR t

SLEEP

ACTIVE

PMOD = 1

UVEN = 0

SLEEP

PSPIO = 1
PSDQ = X

RISING EDGE ON SDA OR SCL

PULL SDA AND SCL LOW

FOR t

SLEEP

PULL PIO LOW

CHARGER DETECT

V

IN1

OR V

IN2

< V

UV

ACTIVE

PMOD = 1

UVEN = 1

SLEEP

PSPIO = 1
PSDQ = X

RISING EDGE ON SDA OR SCL

Figure 2. Sleep-Mode State Diagram for DS2777/DS2778

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with

Protector and Optional SHA-1 Authentication

______________________________________________________________________________________ 13

Table 1. Li+ Protection Conditions and DS2775/DS2776 Responses

Note 1: V

CELL

is defined as (V

IN1

- VSS) or (V

IN2

- V

IN1

).

Note 2: Sleep mode is only entered if UVEN = 1.
Note 3: If V

CELL

< VUVwhen a charger connection is detected, release is delayed until V

CELL

≥

V

UV

. The recovery charge path pro-

vides an internal current limit (I

RC

) to safely charge the battery.

Note 4: With test current I

PPD

flowing from PLS to VSS(pulldown on PLS) enabled.

Note 5: With test current I

TST

flowing from VDDto PLS (pullup on PLS).

V

OV

V

CE

V

UV

V

IN

V

SNS

-V

COC

0

V

DOC

V

SC

t

OVD

t

OVD

t

OCD

t

UVD

t

UVD

t

OCD

t

SCO

DISCHARGE

CHARGE

POWER

MODE

ACTIVE

SLEEP*

*IF UVEN = 1.

CC

DC

V

OHCC

V

CP

V

DD

V

CP

V

PLS

Figure 3. Li+ Protection Circuitry Example Waveforms

ACTIVATION

CC Off

OVD

UVD

CC Off, DC Off

OCD

DC Off

OCD

DC Off V

SCD

CC Off, DC Off,

Sleep Mode (Note 2)

CONDITION

Overvoltage (OV) (Note 1) V

Undervoltage (UV) (Note 1) V

Overcurrent, Charge (COC) V

Overcurrent, Discharge
(DOC)

Short Circuit (SC) V

THRESHOLD DELAY RESPONSE

> VOV t

CELL

< VUV t

CELL

< V

SNS

COC

V

> V

SNS

DOC

> VSC t

SNS

t

t

RELEASE THRESHOLD

< VCE or

CELL

 1.2mV and both

< VOV) (Note 1)

(charger connected)

> VUV and

CELL

V

PLS

Both V

(V

SNS

V

CELL

> V

IN2

or (both V

UVEN = 0) (Note 3)

V

< VDD – V

PLS

TP

(charger removed) (Note 4)

> VDD – V

V

PLS

TP

(load removed) (Note 5)

> VDD – VTP (Note 5)

PLS

DS2775/DS2776/DS2777/DS2778

2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
Protector and Optional SHA-1 Authentication

14 ______________________________________________________________________________________

Undervoltage (UV)

If the average of the voltages on (V

IN2

- V

IN1

) or

(V

IN1

- VSS) drops below the undervoltage threshold,

VUV, for a period longer than undervoltage delay, t

UVD

,
the DS2775–DS2778 shut off the charge and discharge
FETs. If UVEN is set, the DS2775–DS2778 also enter
sleep mode. When a charger is detected and V

PLS

>

V

IN2

, the DS2775–DS2778 provide a current-limited
recovery charge path (IRC) from PLS to VDDto gently
charge severely depleted cells. The recovery charge
path is enabled when 0 ≤ [(V

IN2

- V

IN1

) and (V

IN1

-

V

SS

)] < VCE. The FETs remain off until (V

IN2

- V

IN1

) and

(V

IN1

- VSS) exceed VUV.

Overcurrent, Charge Direction (COC)

Charge current develops a negative voltage on V

SNS

with respect to VSS. If V

SNS

is less than the charge

overcurrent threshold, V

COC

, for a period longer than

overcurrent delay, t

OCD

, the DS2775–DS2778 shut off
both external FETs. The charge current path is not re­established until the voltage on the PLS pin drops
below (VDD- VTP). The DS2775–DS2778 provide a test
current of value I

PPD

from PLS to VSS, pulling 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 VSS. If V

SNS

exceeds the discharge

overcurrent threshold, V

DOC

, for a period longer than

t

OCD

, the DS2775–DS2778 shut off the external dis­charge FET. The discharge current path is not reestab­lished until the voltage on PLS rises above (VDD- VTP).

The DS2775–DS2778 provide a test current of value
I

TST

from V

DD

to PLS, pulling PLS up, in order to detect

the removal of the offending low-impedance load.

Short Circuit (SC)

If V

SNS

exceeds short-circuit threshold, VSC, for a

period longer than short-circuit delay, t

SCD

, the
DS2775–DS2778 shut off the external discharge FET.
The discharge current path is not reestablished until
the voltage on PLS rises above (VDD- VTP). The
DS2775–DS2778 provide a test current of value I

TST

from VDDto PLS, pulling PLS up, in order to detect the
removal of the short circuit.

All the protection conditions described are logic
ANDed to affect the CC and DC outputs.

CC = (overvoltage) AND (undervoltage) AND

(overcurrent, charge direction) AND (Protection register

bit CE = 0)

DC = (undervoltage) AND (overcurrent, either direction)

AND (short circuit) AND (Protection register bit

DE = 0)

Voltage Measurements

Cell voltages are measured every 440ms. The lowest
potential cell, V

IN1

, is measured with respect to VSS.

The highest potential cell, V

IN2

, is measured with

respect to V

IN1

. Battery voltages are measured with a
range of -5V to +4.9951V and a resolution of 4.8828mV
and placed in the Result register in two’s complement
form. Voltages above the maximum register value are
reported as 7FE0h.

MSB - ADDRESS 0Ch, V

IN1

- V

SS

LSB - ADDRESS 0Dh, V

IN1

- V

SS

MSB - ADDRESS 1Ch, V

IN2

- V

IN1

LSB - ADDRESS 1Dh, V

IN2

- V

IN1

S 29 28 27 26 25 24 2

3

22 21 20 X X X X X

MSb LSb MSb LSb

“S”: SIGN BIT(S), “X”: RESERVED UNITS: 4.883mV

Figure 4. Voltage Register Format