MAXIM DS2788 Technical data

General Description

The DS2788 measures voltage, temperature, and current, and estimates available capacity for rechargeable lithium-ion (Li+) and Li+ polymer batteries. Cell characteristics and application parameters used in the calculations are stored in on-chip EEPROM. The available 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. Capacity estimation is reported in mAh remaining and percentage of full.

LED display drivers and a debounced input make display of the capacity information easy. The LED pins can directly sink current, requiring only a resistor for setting the current in the LED display, thus reducing space and cost.

Applications

Power Tools

Electric Bicycles

Electric Vehicles

Uninterruptible Power Supply

Digital Cameras

Features

♦ Five 30mA Open-Drain Drivers for Driving LED

Fuel-Gauge Display

♦ Debounced Fuel-Gauge Display Enable

♦ Internal Voltage Measurement Gain Register for

Trimming External Voltage-Divider

♦ Pin for Driving FETs to Enable Voltage-Divider

Only During Voltage Measurement, Conserving Power

♦ Precision Voltage, Temperature, and Current

Measurement System

♦ Accurate, Temperature-Stable, Internal Time Base

♦ Absolute and Relative Capacity Estimated from

Coulomb Count, Discharge Rate, Temperature, and Battery Cell Characteristics

♦ Accurate Warning of Low Battery Conditions

♦ Automatic Backup of Coulomb Count and Age

Estimation to Nonvolatile (NV) EEPROM

♦ Gain and Tempco Calibration Allows the Use of

Low-Cost Sense Resistors

♦ 24-Byte Battery/Application Parameter EEPROM

♦ 16-Byte User EEPROM

♦ Unique ID and Multidrop 1-Wire

Interface

♦ 14-Pin TSSOP Package

DS2788

Stand-Alone Fuel-Gauge IC with

LED Display Drivers

________________________________________________________________

Maxim Integrated Products

Pin Configuration

Ordering Information

Rev 1; 6/08

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.

Denotes a lead-free/RoHS-compliant package.

T&R = Tape and reel.

Typical Operating Circuit appears at end of data sheet.

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

TOP VIEW

LED1

5OVD

DS2788

14 LED31LED2

13 LED4

12 LED53DV

PIO

10 V

9 SNS6V

8 VMA7DQ

PART TEMP RANGE PIN-PACKAGE

DS2788E+ -25°C to +70°C 14 TSSOP

DS2788E+T&R -25°C to +70°C 14 TSSOP

TSSOP

DS2788

Stand-Alone Fuel-Gauge IC with LED Display Drivers

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

RECOMMENDED DC OPERATING CHARACTERISTICS

(VDD= 2.5V to 5.5V, TA= -25°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 Any Pin Relative to V

SS..............

-0.3V to +6.0V

Voltage Range on V

, VMA Relative to V

SS ...

-0.3V to VDD+ 0.3V

to V

SS .....................................................................

-0.3V to +0.3V

LED1–5.................................................................60mA each pin

Operating Temperature Range ...........................-40°C to +85°C

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

Soldering Temperature (10s) ................Refer to IPC/JEDEC-020

Specification.

DC ELECTRICAL CHARACTERISTICS

(VDD= 2.5V to 5.5V, TA= -25°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 +5.5 V

VIN, VMA Voltage Range (Note 1) 0 VDD V

DQ, PIO, OVD, LED1–LED5 Voltage Range

(Note 1) 0 +5.5 V

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

ACTIVE Current I

SLEEP Mode Current I

Input Logic-High: DQ, PIO VIH (Note 1) 1.5 V

Input Logic-Low: DQ, PIO VIL (Note 1) 0.6 V

Output Logic-Low: DQ, PIO, VMA VOL IOL = 4mA (Note 1) 0.4 V

Output Logic-High: VMA VOH IOH = 1mA (Note 1)

VMA Precharge Time t

Pulldown Current: DQ, PIO IPD VDQ, V

Output Logic-Low: LED1–LED5 VOL IOL = -30mA (Note 1) 1 V

Input Logic-High: OVD VIH (Note 1)

Input Logic-Low: OVD VIL (Note 1)

VIN Input Resistance RIN 15 M

DQ SLEEP Timeout t

Undervoltage SLEEP Threshold V

PIO Switch Debounce 100 130 m s

LED1 Displa y Blink Rate 50% duty cycle 0.9 1.0 1.1 Hz

LED Display-On Time 3.6 4.0 4.4 s

ACTIVE

SLEEP

PRE

SLEEP

2.5V  VDD 4.2V 70 95

105

1 3 μA

13.3 14.2 ms

= 0.4V 0.2 5 μA

PIO

DQ < VIL 1.8 2.0 2.2 s

(Note 1) 2.40 2.45 2.50 V

0.5

0.2

μA

DS2788

Stand-Alone Fuel-Gauge IC with

LED Display Drivers

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS: TEMPERATURE, VOLTAGE, CURRENT

(VCC= 2.5V to 5.5V, TA= -25°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS: 1-Wire INTERFACE, STANDARD

(VCC= 2.5V to 5.5V, TA= -25°C to +70°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Temperature Reso lution T

Temperature Error T

Voltage Reso lution V

Voltage Full-Scale VFS 0 4.992 V

Voltage Error V

Current Resolution I

Current Ful l-Scale IFS ±51.2 mV

Current Ga in Error I

Current Offset Error I

Accumulated Current Offset q

Timebase Error t

0.125 °C

LSB

±3 °C

ERR

4.88 mV

LSB

±50 mV

ERR

1.56 μV

LSB

(Note 2) ±1

GERR

OERR

ERR

0°C  TA +70°C, 2.5V  VDD 4.2V (Notes 3, 4)

0°C  TA +70°C, 2.5V  VDD 4.2V,

= VSS (Notes 3, 4, 5)

SNS

VDD = 3.8V, TA = +25°C ±1

0°C  TA +70°C, 2.5V  VDD 4.2V ±2

±3

-7.82 +12.5 μV

-188 0

% Full

Scale

μVhr/

day

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Time Slot t

Recovery Time t

Write-0 Low Time t

Write-1 Low Time t

Read Data Valid t

Reset-Time High t

Reset-Time Low t

Presence-Detect High t

Presence-Detect Low t

60 120 μs

SLOT

1 μs

REC

60 120 μs

LOW0

1 15 μs

LOW1

15 μs

RDV

480 μs

RSTH

480 960 μs

RSTL

15 60 μs

PDH

60 240 μs

PDL

DS2788

Stand-Alone Fuel-Gauge IC with LED Display Drivers

4 _______________________________________________________________________________________

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: Parameters guaranteed by design. Note 4: At a constant regulated V

voltage, the Current Offset Bias register can be used to obtain higher accuracy.

Note 5: Accumulation Bias register set to 00h. Note 6: EEPROM data retention is 10 years at +50°C.

ELECTRICAL CHARACTERISTICS: 1-Wire INTERFACE, OVERDRIVE

(VCC= 2.5V to 5.5V, TA= -25°C to +70°C.)

EEPROM RELIABILITY SPECIFICATION

(VCC= 2.5V to 5.5V, TA= -25°C to +70°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Time Slot t

Recovery Time t

Write-0 Low Time t

Write-1 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

EEPROM Copy Time t

EEPROM Copy Endurance N

6 16 μs

SLOT

1 μs

REC

6 16 μs

LOW0

1 2 μs

LOW1

2 μs

RDV

48 μs

RSTH

48 80 μs

RSTL

2 6 μs

PDH

8 24 μs

PDL

10 ms

EEC

TA = +50°C (Note 6) 50,000 Cycles

EEC

DS2788

Stand-Alone Fuel-Gauge IC with

LED Display Drivers

_______________________________________________________________________________________ 5

Pin Description

Figure 1. Block Diagram

PIN NAME FUNCTION

1 LED2 Di spla y Driver. Connect to an LED connected to VDD for display of relative pack capacity.

2 LED1 Display Driver. Connect to an LED connected to VDD for display of relative pack capacity.

3 DVSS Display Ground. Ground connection for the LED display drivers. Connect to VSS.

4 VDD Power-Supply Input. Connect to the positive terminal of the battery cel l through a decoupling networ k.

5 OVD

6 V

7 DQ

8 VMA

9 SNS

10 VIN Voltage Sense Input. The voltage of the battery cell is monitored through thi s input p in.

11 PIO

12 LED5

13 LED4 Displa y Driver. Connect to an LED connected to VDD for display of relative pack capacity.

14 LED3 Displa y Driver. Connect to an LED connected to VDD for display of relative pack capacity.

1-Wire Bus Speed Control. Input logic level selects the speed of the 1-Wire bus. Logic 1 selects overdrive (OVD) and Logic 0 selects standard (STD) timing. On a multidrop bus, all devices must operate at the same speed.

Device Ground. Connect directl y to the negative terminal of the battery cel l. Connect the sen se resi stor

between V

and SNS.

Data Input/Output. 1-Wire data line, open-drain output driver. Connect thi s pin to the DATA terminal of the battery pac k. This pin has a weak internal pulldown (I

) for sensing pack disconnection from host or charger.

Voltage Measurement Active. Output is driven high before the start of a voltage conversion and driven low at the end of the conversion cycle.

Sense Resistor Connection. Connect to the negative terminal of the battery pack. Connect the sense resistor between V

and SNS.

Programmable I/O Pin. Can be configured as input or output to monitor or control u ser-defined external circuitry. Output driver is open drain. This pin has a weak internal pulldown (IPD). When configured as an input, upon recognition of a rising edge, the fuel-gauge displa y is enab led.

Display Driver. Connect to an LED connected to V

for display of relative pack capacity. Leave floating in

LED4 conf iguration.

PIO

OVD

SNS

POR

1-Wire

INTERFACE

EEPROM

STATUS

AND

CONTROL

ACCUMULATED

CURRENT

TIME BASEBIAS/VREF

LED

DRIVERS

TEMP

AND

VOLTAGE

ADC

RATE AND

TEMPERATURE

COMPENSATION

LED5 LED4 LED3 LED2 LED1 DV

VMA V

DS2788

CURRENT ADC

15-BIT + SIGN

DS2788

Detailed Description

The DS2788 operates directly from 2.5V to 5.5V and supports single-cell Li+ battery packs. As shown in Figure 2, the DS2788 accommodates multicell applications by adding a trim resistor for calibration of an external voltage-divider for VIN. NV storage is provided for cell compensation and application parameters. Host-side development of fuel-gauging algorithms is eliminated. On-chip algorithms and convenient status reporting of operating conditions reduce the serial polling required of the host processor.

Additionally, 16 bytes of EEPROM memory are made available for the exclusive use of the host system and/or pack manufacturer. The additional EEPROM memory can be used to facilitate battery lot and date tracking and NV storage of system or battery usage statistics.

A 1-Wire interface provides serial communication at the standard 16kbps or overdrive 140kbps speeds, allowing access to data registers, control registers, and user memory. A unique, factory-programmed, 64-bit regis-

tration number (8-bit family code + 48-bit serial number + 8-bit CRC) assures that no two parts are alike and enables absolute traceability. The 1-Wire interface on the DS2788 supports multidrop capability so that multiple slave devices can be addressed with a single pin.

Power Modes

The DS2788 has two power modes: ACTIVE and SLEEP. On initial power-up, the DS2788 defaults to ACTIVE mode. While in ACTIVE mode, the DS2788 is fully functional with measurements and capacity estimation continuously updated. In SLEEP mode, the DS2788 conserves power by disabling measurement and capacity estimation functions, but preserves register contents. SLEEP mode is entered under two different conditions and an enable bit for each condition makes entry into SLEEP optional. SLEEP mode can be enabled using the power mode (PMOD) bit or the undervoltage enable (UVEN) bit.

The PMOD type SLEEP is entered if the PMOD bit is set and DQ is low for t

SLEEP

(2s nominal). The condition of

DQ low for t

SLEEP

can be used to detect a pack discon-

Stand-Alone Fuel-Gauge IC with LED Display Drivers

6 _______________________________________________________________________________________

Figure 2. Multicell Application Example

PK+

330Ω330Ω330Ω330Ω330Ω

LEDs

LED1

LED2

LED3

LED4

DS2788

LED5

DATA

PK-

150Ω

5.6V

DQ SNS

SNS

20mΩ

VMA

OVD

MAX6765TTLD2+

RST GND

B3F-1000

PIO

IN ENABLE

OUT TIMEOUT

BSS84

10μF 100kΩ

0.1μF

10kΩ

900kΩ

2N7002

0.1μF

PROTECTION

10-CELL Li+ BATTERY

CIRCUIT

nection or system shutdown, in which no charge or discharge current flows. A PMOD SLEEP condition transitions back to ACTIVE mode when DQ is pulled high.

The second option for entering SLEEP is an undervoltage condition. When the UVEN bit is set, the DS2788 transitions to SLEEP if the voltage on V

is less than

SLEEP

(2.45V nominal) and DQ is stable at a low or

high logic level for t

SLEEP

. An undervoltage condition occurs when a pack is fully discharged, where loading on the battery should be minimized. UVEN SLEEP relieves the battery of the I

ACTIVE

load until communi-

cation on DQ resumes.

Note: PMOD and UVEN SLEEP features must be disabled when a battery is charged on an external charger that does not connect to the DQ pin. PMOD SLEEP can be used if the charger pulls DQ high. UVEN SLEEP can be used if the charger toggles DQ. The DS2788 remains in SLEEP and therefore does not measure or accumulate current when a battery is charged on a charger that fails to properly drive DQ.

Initiating Communication

in Sleep

When beginning communication with a DS2788 in PMOD SLEEP, DQ must be pulled up first and then a 1-Wire reset pulse must be issued by the master. In UVEN SLEEP, the procedure depends on the state of DQ when UVEN SLEEP was entered. If DQ was low, DQ must be pulled up and then a 1-Wire reset pulse

must be issued by the master as with PMOD SLEEP. If DQ was high when UVEN SLEEP was entered, then the DS2788 is prepared to receive a 1-Wire reset from the master. In the first two cases with DQ low during SLEEP, the DS2788

does not respond

to the first rising

edge of DQ with a presence pulse.

Voltage Measurement

Battery voltage is measured at the VINinput with respect to VSSover a range of 0 to 4.992V, with a resolution of 4.88mV. The result is updated every 440ms and placed in the Voltage (VOLT) register in two’s complement form. Voltages above the maximum register value are reported at the maximum value; voltages below the minimum register value are reported at the minimum value. Figure 3 shows the format of the Voltage register.

VINis usually connected to the positive terminal of a single-cell Li+ battery by a 1kΩ resistor. The input impedance is sufficiently large (15MΩ) to be connected to a high-impedance voltage-divider in order to support multiple-cell applications. The pack voltage should be divided by the number of series cells to present a single-cell average voltage to the VINinput. In Figure 2, the value of R can be up to 1MΩ without incurring significant error due to input loading. The VMA pin is driven high t

PRE

before the voltage conversion begins. This allows an external switching element to enable the voltage-divider, and allows settling to occur before the start of the conversion.

DS2788

Stand-Alone Fuel-Gauge IC with

LED Display Drivers

_______________________________________________________________________________________ 7

Figure 3. Voltage Register Format

VOLT READ ONLY

MSB—ADDRESS 0Ch LSB—ADD RESS 0Dh

S 2

MSb LSb MSb LSb

“S”: SIGN BIT(S), “X”: RESERVED UNITS: 4.88mV

28 27 26 25 24 23 22 21 20 X X X X X

DS2788

Temperature Measurement

The DS2788 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 (TEMP) register in two’s complement form. Figure 4 shows the format of the Temperature register.

Current Measurement

In the ACTIVE mode of operation, the DS2788 continually measures the current flow into and out of the battery by measuring the voltage drop across a low-value current-sense resistor, R

SNS

. The voltage-sense range

between SNS and V

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 (CURRENT) register at the completion of each conversion cycle.

The Current register is updated every 3.515s with the current conversion result in two’s complement form. Charge currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum register value are reported at the minimum value (8000h = -51.2mV).

Stand-Alone Fuel-Gauge IC with LED Display Drivers

8 _______________________________________________________________________________________

Figure 4. Temperature Register Format

Figure 5. Current Register Format

TEMP READ ONLY

MSB—ADDRESS 0Ah LSB—ADDRESS 0Bh

S 2

MSb LSb MSb LSb

“S”: SIGN BIT(S), “X”: RESERVED UNITS: 0.125°C

28 27 26 25 24 23 22 21 20 X X X X X

CURRENT READ ONLY

MSB—ADDRESS 0Eh LSB—ADDRESS 0Fh

S 2

MSb LSb MSb LSb

“S”: SIGN BIT(S) UNITS: 1.5625μV/R

213 212 211 210 29 28 27 26 25 24 23 22 21 2

CURRENT RESOLUTION (1 LSB)

VSS- V

SNS

1.5625μV 78.13μA 104.2μA 156.3μA 312.5μA

20m 15m 10m 5m

SNS

Average Current Measurement

The Average Current (IAVG) register reports an average current level over the preceding 28 seconds. The register value is updated every 28s in two’s complement form, and is the average of the eight preceding Current register updates. Figure 6 shows the format of the Average Current register. Charge currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum register value are reported at the minimum value (8000h = -51.2mV).

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 (ACR) register is possible; however, to reduce the error, the current measurement made just prior to the offset conversion is displayed in the Current register and is substituted for the dropped current measurement in the current accumulation process. This results in an accumulated current error due to offset correction of less than 1/1024.

Current Offset Bias

The Current Offset Bias (COB) register 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.

COB allows read and write access. 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 nonvolatile memory.

Current Measurement

Calibration

The DS2788’s current measurement gain can be adjusted through the RSGAIN register, which is factorycalibrated 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

DS2788

Stand-Alone Fuel-Gauge IC with

LED Display Drivers

_______________________________________________________________________________________ 9

Figure 6. Average Current Register Format

Figure 7. Current Offset Bias Register Format

IAVG READ ONLY

MSB—ADDRESS 08h LSB—ADDRESS 09h

S 2

MSb LSb MSb LSb

“S”: SIGN BIT(S) UNITS: 1.5625μV/R

COB RW AND EE

ADDRESS 7Bh

S 2

MSb LSb

“S”: SIGN BIT(S) UNITS: 1.56μV/R

213 212 211 210 29 28 27 26 25 24 23 22 21 2

25 24 23 22 21 20

SNS

DS2788

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 read-only FRSGAIN (address B0h and B1h) is provided to preserve the factory value only and is not used in the current measurement.

Sense Resistor Temperature

Compensation

The DS2788 is capable of temperature compensating the current-sense resistor to correct for variation in a sense resistor’s value over temperature. The DS2788 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/°C in steps of

30.5ppm/°C. The user must program RSTC cautiously to ensure accurate current measurement.

Temperature compensation adjustments are made when the Temperature register crosses 0.5°C boundaries. The temperature compensation is most effective with the resistor placed as close as possible to the V

terminal to optimize thermal coupling of the resistor to

the on-chip temperature sensor. If the current shunt is constructed with a copper PCB trace, run the trace under the DS2788 package if possible.

Current Accumulation

Current measurements are internally summed, or accumulated, at the completion of each conversion period with the results displayed 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 (least significant bit) of 6.25µVh. Additional read-only registers (ACRL) hold fractional results of each accumulation to avoid truncation errors. Accumulation of charge current above the maximum register value is reported at the maximum register value (7FFFh); conversely, accumulation of discharge current below the minimum register value is reported at the minimum value (8000h).

Read and write access is allowed to the ACR. The ACR must be written MSB (most significant byte) first, then LSB (least significant byte). The write must be completed within 3.515s (one ACR register update period). A write to the ACR forces the ADC to perform an offset correction conversion and update the internal offset correction factor. Current measurement and accumulation begins with the second conversion following a write to the ACR. Writing the ACR clears the fractional values in ACRL. ACR’s format is shown in Figure 8, and ACRL’s format is shown in Figure 9.

To preserve the ACR value in case of power loss, the ACR value is backed up to EEPROM. The ACR value is recovered from EEPROM on power-up. See the memory map in Table 3 for specific address location and backup frequency.

Stand-Alone Fuel-Gauge IC with LED Display Drivers

10 ______________________________________________________________________________________

Figure 8. Accumulated Current Register (ACR) Format

ACR R/W AND EE

MSB—ADDRESS 10h LSB—ADDRESS 11h

214 213 212 211 210 29 28 27 26 25 24 23 22 21 2

MSb LSb MSb LSb

UNITS: 6.25μVh/R

SNS

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