MAXIM MAX6620 User Manual

General Description

The MAX6620 controls the speeds of up to four fans using four independent linear voltage outputs. The drive voltages for the fans are controlled directly over the I

C interface. Each output drives the base of an external bipolar transistor or the gate of a FET in highside drive configuration. Voltage feedback at the fan’s power-supply terminal is used to force the correct output voltage.

The MAX6620 offers two methods for fan control. In RPM mode, the MAX6620 monitors four fan tachometer logic outputs for precise (±1%) control of fan RPM and detection of fan failure. In DAC mode, each fan is driven with a voltage resolution of 9 bits and the tachometer outputs of the fans are monitored for failure.

The DAC_START input selects the fan power-supply voltage at startup to ensure appropriate fan drive when power is first applied. A watchdog feature turns the fans fully on to protect the system if there are no valid I

C communications within a preset timeout period.

The MAX6620 operates from a 3.0V to 5.5V power supply with low 250µA supply current, and the I

C-compatible interface makes it ideal for fan control in a wide range of cooling applications. The MAX6620 is available in a 28-pin TQFN package and operates over the

-40°C to +125°C automotive temperature range.

Applications

Consumer Products

Servers

Communications Equipment

Storage Equipment

Features

♦ Controls Up to Four Independent Fans With

Linear (DC) Drive

♦ Uses Four External Low-Cost Pass Transistors ♦ 1% Accuracy Precision RPM Control ♦ Controlled Voltage Rate-Of-Change for Best

Acoustics

♦ I

C Bus Interface

♦ 3.0V to 5.5V Supply Voltage Range ♦ 250µA (typ) Operating Supply Current ♦ 3µA (typ) Shutdown Supply Current ♦ Small 5mm x 5mm Footprint

MAX6620

Quad Linear Fan-Speed Controller

________________________________________________________________

Maxim Integrated Products

Pin Configuration

Ordering Information

19-4039; Rev 0; 3/08

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.

EVALUATION KIT

AVAILABLE

Denotes a lead-free package.

EP = Exposed paddle.

PART

PINPACKAGE

PKG

CODE

MAX6620ATI+

T2855-8

Typical Application Circuit appears at end of data sheet.

TEMP RANGE

-40°C to +125°C 28 TQFN-EP*

TOP VIEW

TACH1

DACFB1

DACOUT1

GND

FAN

VCC

FAN_FAIL

DACFB2

TACH2

2021 19 17 16 15

SCL

(5mm

GND

DACOUT2

MAX6620

4567

SDA

GND

WD_START

THIN QFN

5mm × 0.8mm)

DACOUT3

DACFB3

ADDR

DAC_START

TACH3

TACH4

DACFB4

DACOUT4

GND

SPINUP_START

MAX6620

Quad Linear Fan-Speed Controller

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(TA= -40°C to +125°C, VCC= 3.0V to 5.5V, unless otherwise noted. Typical values are at TA= +25°C, VCC= 3.3V.) (Note 3)

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.

VCC to GND ..........................................................-0.3V to +6.0V

FAN_FAIL, SDA, SCL to GND ...............................-0.3V to +6.0V

ADDR, SPINUP_START, DAC_START, WD_START,

X1, X2 to GND ........................................-0.3V to (V

+ 0.3V)

All Other Pins to GND..........................................-0.3V to +13.5V

Input Current at DACOUT_ Pins (Note 1) ...............+5mA/-50mA

Input Current at Any Pin (Note 1)..........................................5mA

ESD Protection (all pins, Human Body Model) (Note 2) ...±2000V

Continuous Power Dissipation (T

= +70°C)

28-Pin TQFN (derate 34.5mW/°C above +70°C) ....2758.6mW

Operating Temperature Range .........................-40°C to +125°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

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

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifica-

tions do not apply when operating the device beyond its rated operating conditions.

Note 2: Human Body Model, 100pF discharged through a 1.5kΩ resistor.

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS

Operating Supply Voltage V

Operating Supply Current I

Quiescent Supply Current

Supply Voltage

FAN

DACOUT_ Output Current I

DACOUT_ Output Voltage V

DAC Feedback Voltage at Half Scale

DAC Feedback Voltage at Full Scale

Drive Voltage Resolution 9 Bit

DACFB_ Impedance R

TACH Minimum Input Pulse Width 25 µs

Internal Reference Frequency Accuracy

TACH Count Accuracy (Note 4)

VCC = 5.5V 0.25 0.60 mA

I2C inactive 0.2 0.5 mA

Shutdown mode 3 20 µA

FANHI

FANLO

GND

DACOUT_

DACOUT_IDACOUT_

V V

FAN

GND

FAN

At DACFB_,

FBHS

FBFS

code = 0x100, I

DACOUT_

At DACFB_,

DAC

code = 0x1FF, I

DACFB511

DACFB

DACOUT_

(Note 4) -3 +3 %

Using 32.768kHz crystal -0.1 +0.1

Using on-chip oscillator -2 +2

+ 10V < V

DACOUT_

< 11.5V,

= 12V

+ 3V < V

DACOUT_

< 10V,

= 12V

= 5mA 0.05

= V

FAN

FANHI

= V

FAN

FANLO

= 12V 5.54 5.74 5.94

= 5mA

FAN

= 5V 2.05 2.25 2.45

FAN

= V

FAN

FANHI

= V

FAN

FANLO

= 12V 11.25 11.45 11.65

FAN

= 5V 4.3 4.5 4.7

FAN

3.0 5.5 V

10 12 13.5

4.0 5.0 5.5

-18

-16

FAN

0.1

256/535

256/567

511/535

511/567

1MΩ

MAX6620

Quad Linear Fan-Speed Controller

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(TA= -40°C to +125°C, VCC= 3.0V to 5.5V, unless otherwise noted. Typical values are at TA= +25°C, VCC= 3.3V.) (Note 3)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS

Fan Control Accuracy (Note 4)

Using 32.768kHz crystal, test at 850RPM -1 +1

Using on-chip oscillator -3 +3

XTAL Oscillator Startup Time 2s

X1 Input Threshold 0.7 V

POR Threshold

FAN

3.5

LOGIC (SDA, SCL, FAN_FAIL, WD_START, TACH_)

Input High Voltage V

Input Low Voltage V

Input High Current I

Input Low Current I

VCC x

0.7

VCC x

0.3

1.0 µA

-1.0 µA

Input Capacitance All digital inputs 6 pF

Output High Current 100 µA

Output Low Voltage IOL = 3mA 0.4 V

LOGIC (DAC_START, SPIN_START, ADDR)

Input High Voltage V

Input Low Voltage V

Input High Current I

Input Low Current I

0.5

0.5 V

1.0 µA

-1.0 µA

Input Capacitance All digital inputs 6 pF

I2C-COMPATIBLE TIMING (Notes 5, 6)

Serial Clock Frequency f

Bus Free Time Between STOP and START Conditions

START Condition Hold Time t

STOP Condition Setup Time t

Clock Low Period t

Clock High Period t

START Condition Setup Time t

Data Setup Time t

Data Out Hold Time t

Data In Hold Time t

Maximum Receive SCL/SDA Rise Time

Minimum Receive SCL/SDA Rise Time

SCL

BUF

HD:STA

SU:STO

LOW

HIGH

SU:STA

SU:DAT

HD:DAT

1.3 µs

0.6 µs

600 ns

1.3 µs

0.6 µs

600 ns

100 ns

(Note 6) 0 0.9 µs

(Note 8) 300 ns

(Note 7)

20 + 0.1

x C

400 kHz

MAX6620

Quad Linear Fan-Speed Controller

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(TA= -40°C to +125°C, VCC= 3.0V to 5.5V, unless otherwise noted. Typical values are at TA= +25°C, VCC= 3.3V.) (Note 3)

Note 3: All parts will operate properly over the VCCsupply voltage range of 3.0V to 5.5V. Note 4: Guaranteed by design and characterization. Note 5: All timing specifications are guaranteed by design. Note 6: A master device must provide a hold time of at least 300ns for the SDA signal to bridge the undefined region of SCL’s falling edge. Note 7: C

= total capacitance of one bus line in pF. Tested with CB= 400pF.

Note 8: Input filters on SDA and SCL suppress noise spikes less than 50ns. Note 9: Holding the SDA line low for a time greater than t

TIMEOUT

will cause the devices to reset SDA to the idle state of the serial

bus communication (SDA set high).

HD,STA

HIGH

HD,STA

S Sr A

SCL

SDA

SU,STA

SU,STO

BUF

LOW

SU,DAT

HD,DAT

Figure 1. I2C Serial Interface Timing

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS

Maximum Receive SCL/SDA Fall Time

Minimum Receive SCL/SDA Fall Time

Transmit SDA Fall Time t

Pulse Width of Suppressed Spike t

Output Fall Time CL = 400pF, I

SDA Time Low for Reset of Serial Interface

TIMEOUT

(Note 7)

20 + 0.1

x C

(Note 8) 0 50 ns

= 3mA 250 ns

OUT

(Note 9) 20 50 ms

300 ns

20 + 0.1

x C

250 ns

MAX6620

Quad Linear Fan-Speed Controller

_______________________________________________________________________________________ 5

Typical Operating Characteristics

(VCC= 3.3V, V

FAN

= 12V, TA= +25°C, unless otherwise noted.)

TACH COUNT ACCURACY WITH INT CLK

vs. SUPPLY VOLTAGE

2.0 V

= 12V

FAN

1.5

1.0

0.5

TA = +25°C

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH INT CLK (%)

-2.0

3.0 5.5

TA = 0°C

TA = +125°C

SUPPLY VOLTAGE (V)

TACH COUNT ACCURACY WITH EXT CLK

vs. TEMPERATURE

2.0 V

= 12V

FAN

1.5

1.0

0.5

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH EXT CLK (%)

-2.0

-55 125

VCC = 3.3V, 5.0V

TEMPERATURE (°C)

TA = +70°C

TACH COUNT ACCURACY WITH EXT CLK

vs. SUPPLY VOLTAGE

2.0 V

= 12V

FAN

1.5

MAX6620 toc01

1.0

0.5

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH EXT CLK (%)

-2.0

5.04.53.5 4.0

3.0 5.5

TA = 0°C, +70°C, +125°C

TA = +25°C

5.04.53.5 4.0

SUPPLY VOLTAGE (V)

MAX6620 toc02

DACFB_ VOLTAGE ACCURACY

vs. TEMPERATURE

2.0 V

= 12V

FAN

1.5

MAX6620 toc04

1.0

0.5

-0.5

-1.0

DACFB VOLTAGE ACCURACY (%)

-1.5

-2.0

8035-10

-55 125

VCC = 3.0V, 3.3V, 5.0V

TEMPERATURE (°C)

MAX6620 toc05

8035-10

TACH COUNT ACCURACY WITH INT CLK

vs. TEMPERATURE

2.0 V

= 12V

FAN

1.5

1.0

0.5

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH INT CLK (%)

-2.0

-55 125

VCC = 5.0V

VCC = 3.3V

TEMPERATURE (°C)

DACFB_ VOLTAGE ACCURACY

vs. SUPPLY VOLTAGE

2.0 V

= 12V

FAN

1.5

1.0

0.5

-0.5

-1.0

DACFB VOLTAGE ACCURACY (%)

-1.5

-2.0

3.0 5.5 SUPPLY VOLTAGE (V)

MAX6620 toc03

8035-10

MAX6620 toc06

5.04.54.03.5

DACFB_ VOLTAGE ACCURACY

vs. OUTPUT CURRENT

2.0 V

= 12V

FAN

1.5

1.0

0.5

-0.5

-1.0

DACFB VOLTAGE ACCURACY (%)

-1.5

-2.0

5.0 10.08.57.56.55.5 9.5

VCC = 3.0V, 3.3V

VCC = 5.5V

OUTPUT CURRENT (mA)

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

500

= 12V

FAN

450

MAX6620 toc07

400

350

300

250

200

150

100

STANDBY SUPPLY CURRENT (μA)

9.08.07.06.0

3.0 5.5

INT CLK

EXT CLK

5.04.54.03.5

SUPPLY VOLTAGE (V)

MAX6620 toc08

OPERATING SUPPLY CURRENT (mA)

OPERATING SUPPLY CURRENT

vs. SUPPLY VOLTAGE

0.6 V

= 12V

FAN

0.5

0.4

0.3

0.2

0.1

3.0 5.5

INT CLK

EXT CLK

5.04.54.03.5

SUPPLY VOLTAGE (V)

MAX6620 toc09

MAX6620

Quad Linear Fan-Speed Controller

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VCC= 3.3V, V

FAN

= 12V, TA= +25°C, unless otherwise noted.)

TACH COUNT ACCURACY WITH INT CLK

vs. SUPPLY VOLTAGE

2.0 V

= 5.0V

FAN

1.5

1.0

0.5

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH INT CLK (%)

-2.0

3.0 5.5

TA = +25°C

TA = +125°C

SUPPLY VOLTAGE (V)

TACH COUNT ACCURACY WITH EXT CLK

vs. TEMPERATURE

2.0 V

= 5.0V

FAN

1.5

1.0

0.5

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH EXT CLK (%)

-2.0

-55 125

VCC = 3.3V, 5.0V

TEMPERATURE (°C)

TA = 0°C

TA = +70°C

TACH COUNT ACCURACY WITH EXT CLK

vs. SUPPLY VOLTAGE

2.0 V

= 5.0V

FAN

1.5

MAX6620 toc10

1.0

0.5

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH EXT CLK (%)

5.04.54.03.5

-2.0

TA = 0°C, +70°C, +125°C

TA = +25°C

3.0 5.5 SUPPLY VOLTAGE (V)

5.04.54.03.5

MAX6620 toc11

DACFB_ VOLTAGE ACCURACY

vs. TEMPERATURE

4.5 V

= 5.0V

FAN

3.5

MAX6620 toc13

2.5

1.5

0.5

-0.5

-1.5

-2.5

DACFB VOLTAGE ACCURACY (%)

-3.5

8035-10

-4.5

VCC = 3.0V

VCC = 3.3V

-55 125 TEMPERATURE (°C)

VCC = 5.5V

8035-10

MAX6620 toc14

TACH COUNT ACCURACY WITH INT CLK

vs. TEMPERATURE

2.0 V

= 5.0V

FAN

1.5

1.0

0.5

-0.5

-1.0

-1.5

TACH COUNT ACCURACY WITH INT CLK (%)

-2.0

-55 125

VCC = 3.3V

VCC = 5.0V

TEMPERATURE (°C)

DACFB_ VOLTAGE ACCURACY

vs. SUPPLY VOLTAGE

4.5 V

= 5.0V

FAN

3.5

2.5

1.5

0.5

-0.5

-1.5

-2.5

DACFB VOLTAGE ACCURACY (%)

-3.5

-4.5

3.0 5.5 SUPPLY VOLTAGE (V)

MAX6620 toc12

8035-10

MAX6620 toc15

5.04.54.03.5

DACFB_ VOLTAGE ACCURACY

vs. OUTPUT CURRENT

4.5 V

= 5.0V

FAN

3.5

2.5

1.5

0.5

-0.5

-1.5

-2.5

DACFB VOLTAGE ACCURACY (%)

-3.5

-4.5

5.0 10.08.57.56.55.5 9.5

VCC = 3.0V, 3.3V

VCC = 5.5V

OUTPUT CURRENT (mA)

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

500

= 5.0V

FAN

450

MAX6620 toc16

400

350

300

250

200

150

100

STANDBY SUPPLY CURRENT (μA)

9.08.07.06.0

3.0 5.5

INT CLK

EXT CLK

5.04.54.03.5

SUPPLY VOLTAGE (V)

MAX6620 toc17

OPERATING SUPPLY CURRENT (mA)

OPERATING SUPPLY CURRENT

vs. SUPPLY VOLTAGE

0.6 V

= 5.0V

FAN

0.5

0.4

0.3

0.2

0.1

3.0 SUPPLY VOLTAGE (V)

MAX6620 toc18

INT CLK

EXT CLK

5.0 5.54.54.03.5

MAX6620

Quad Linear Fan-Speed Controller

_______________________________________________________________________________________ 7

Pin Description

PIN NAME FUNCTION

1 SCL I2C Serial-Clock Input. Can be pulled up to 5.5V regardless of VCC. Open circuit when VCC = 0V.

2 SDA

3 WD_START

4, 10, 11, 18,

5 ADDR

6 DAC_START

7S P IN U P _S TART

8, 9 X1, X2

12, 17, 19, 24

13, 16, 20, 23

14, 15, 21, 22 TACH4–TACH1 Fan Tachometer Logic Inputs. These inputs accept input voltages up to V

26 FAN

27 VCC Power-Supply Input. 3.3V nominal. Bypass VCC to GND with a 0.1µF capacitor.

28 FAN_FAIL

—EP

GND Ground

DACOUT4–

DACOUT1

DACFB4–

DACFB1

Open-Drain, I circuit when V

Startup Watchdog Set Input. This input is sampled when power is first applied and sets the initial

C watchdog behavior. When connected to GND, the watchdog function is disabled. When

I connected to V fan drive goes to 100%.

C Address Set Input. This input is sampled when power is first applied and sets the I2C slave

I address. When connected to GND, the slave address will be 0x50. When unconnected, the slave address will be 0x52. When connected to V

Startup Fan Drive DAC Set Input. This input is sampled when power is first applied and sets the power-up value for the fan drive voltage. When connected to GND, the fan drive voltage will be 0%. When unconnected, the fan drive voltage will be 75%. When connected to V voltage will be 100%.

Startup Spin-Up Set Input. This input is sampled when power is first applied and sets the initial spin-up behavior. When connected to GND, spin-up is disabled. When connected to V power-up, the fan is driven with a full-scale drive voltage until two tachometer pulses have been detected, or 1s has elapsed. When unconnected, the fan is driven with a full-scale drive voltage until two tachometer pulses have been detected, or 0.5s has elapsed. Spin-up behavior may be modified by writing appropriate settings to the MAX6620’s registers.

Crystal Oscillator Inputs. Connections for a standard 32.768kHz quartz crystal. The internal oscillator circuitry is designed for operation with a crystal having a specified load capacitance (CL) of 12pF. Connect an external 32.768kHz oscillator across X1 and X2 for operation with the external oscillator. If no crystal or external oscillator is connected, the MAX6620 will use its internal oscillator.

Fan Drive DAC Outputs. Connect to the gate of a p-channel MOSFET or base of a PNP bipolar transistor.

D AC Feed b ack Inp uts. C onnect a 0.1µF cap aci tor b etw een these p i ns and GN D . C onnect to the sup p l y p i n of the fan and to the d r ai n of a p - channel M O S FE T or col l ector of a P N P b i p ol ar tr ansi stor .

Fan Power-Supply Voltage Input. Connect to the fan power supply (V capacitor to GND.

Active-Low, Open-Drain Fan Failure Output. Active only when fault is present; open-circuit when

= 0V. This pin can be pulled up to 5.5V regardless of VCC.

Exposed Paddle. Internally connected to GND. Connect to a large ground plane to maximize thermal performance. Not intended as an electrical connection point.

C Serial-Data Input/Output. Can be pulled up to 5.5V regardless of VCC. Open

= 0V.

, the MAX6620 monitors SDA. If 10s elapse without a valid I2C transaction, the

, the slave address will be 0x54.

FAN

). Bypass with a 0.1µF

FAN

, the fan drive

MAX6620

Quad Linear Fan-Speed Controller

8 _______________________________________________________________________________________

Write Byte Format

Read Byte Format

Send Byte Format

Receive Byte Format

Slave Address: equivalent to chip-select line of a 3-wire interface

Command Byte: selects which register you are writing to

Data Byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate)

Slave Address: equivalent to chip-select line

Command Byte: selects which register you are reading from

Slave Address: repeated due to change in dataflow direction

Data Byte: reads from the register set by the command byte

Command Byte: sends command with no data, usually used for one-shot command

Data Byte: reads data from the register commanded by the last read byte or write byte transmission; also used for SMBus alert response return address

S = START CONDITION SHADED = SLAVE TRANSMISSION P = STOP CONDITION A = NOT ACKNOWLEDGED

Figure 2. I2C Protocols

S ADDRESS RD A DATA

7 bits 8 bits

WRS A COMMAND A P

8 bits

ADDRESS

7 bits

ADATA

8 bits

ACOMMAND

8 bits

AWRADDRESS

7 bits

S ADDRESS WR A COMMAND A S ADDRESS

7 bits8 bits7 bits

RD A DATA

8 bits

Detailed Description

The MAX6620 controls the speeds of up to four fans using four independent linear voltage outputs. The drive voltages for the fans are controlled directly over the I

C interface. Each of the outputs (DACOUT1– DACOUT4) drive the base of an external PNP or the gate of a p-channel MOSFET. Voltage feedback at the fan’s power-supply terminal is used to force the output voltage.

The MAX6620 monitors fan tachometer logic outputs for precise (1%) control of fan RPM and detection of fan failure. When the MAX6620 is used with 2-wire fans, these inputs are not used, and the fans can be driven to the desired voltage without using tachometer feedback.

Three inputs set the fan drive status on application of power. The DAC_START input selects the fan-supply voltage (100%, 75%, or 0%) at startup to ensure appropriate fan drive when power is first applied. The SPIN_START input selects whether spin-up will be applied to the fans at power-up. WD_START selects

whether lack of I

C activity will force the fans to full speed. When the watchdog function is enabled, the fans will be driven to full speed if there is no I2C activity for a period of 2s, 6s, or 10s.

Digital Interface

The MAX6620 features an I2C-compatible, 2-wire serial interface consisting of a bidirectional serial data line (SDA) and a serial clock line (SCL). SDA and SCL facilitate bidirectional communication between the MAX6620 and the master at rates up to 400kHz. The master (typically a microcontroller) initiates data transfer on the bus and generates SCL. SDA and SCL require 4.7kΩ (typ) pullup resistors.

Bit Transfer

One data bit is transferred during each SCL clock cycle. Nine clock cycles are required to transfer the data into or out of the MAX6620. The data on SDA must remain stable during the high period of the SCL clock pulse, as changes in SDA while SCL is high are control signals (see the

START and STOP Conditions

section).

Both SDA and SCL idle high.

MAX6620

Quad Linear Fan-Speed Controller

_______________________________________________________________________________________ 9

START and STOP Conditions

The master initiates a transmission with a START condition (S), a high-to-low transition on SDA with SCL high. The master terminates a transmission with a STOP condition (P), a low-to-high transition on SDA while SCL is high (Figure 3). The STOP condition frees the bus and places all devices in F/S mode (Figure 1). Use a repeated START condition (Sr) in place of a STOP condition to leave the bus active and in its current timing mode.

Acknowledge Bits

Successful data transfers are acknowledged with an acknowledge bit (A) or a not-acknowledge bit (A). Both the master and the MAX6620 (slave) generate acknowl-

edge bits. To generate an acknowledge, the receiving device must pull SDA low before the rising edge of the acknowledge-related clock pulse (9th pulse), and keep it low during the high period of the clock pulse (Figure 4). To generate a not acknowledge, the receiver allows SDA to be pulled high before the rising edge of the acknowledge-related clock pulse, and leaves it high during the high period of the clock pulse. Monitoring the acknowledge bits allows for detection of unsuccessful data transfers. An unsuccessful data transfer happens if a receiving device is busy or if a system fault has occurred. In the event of an unsuccessful data transfer, the master should reattempt communication at a later time.

A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE

I = MASTER PULLS DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION

SCL

AB CDEFG HIJ

SDA

SU:STA

HD:STA

LOWtHIGH

SU:DAT

HD:DAT

SU:STO

BUF

Figure 3. I2C Write Timing Diagram

A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER I = MASTER PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION M = NEW START CONDITION

SCL

AB CDEFG

HIJ

SDA

SU:STAtHD:STA

LOW

HIGH

SU:DAT

SU:STOtBUF

LMK

Figure 4. I2C Read Timing Diagram

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