ASC7511M8 - Andigilog, Inc.

Fully Released Specification

- 1 -

LOW-OLTAGE 2-WIRE DIGITAL TEMPERATURE SENSOR

WITH THERMAL ALARM

aSC7511

PRODUCT SPECIFICATION

Product Description

The aSC7511 is a high-precision CMOS temperature

sensor with SMBus compatible serial digital interface,

intended for use in PC thermal management applications.

The aSC7511 can measure temperature of a remote

thermal diode to an accuracy of ±1°C. Internal temperature

can be measured to ±3°C.

Communication of configuration, temperature and alarm

status takes place over the PC standard System

Management Bus (SMBus).

The aSC7511 features thermal alarm functions with a user-

programmable trip and turn-off temperatures. The THERM

output comparator can be set to control a fan while

ALERT signals that the remote or local temperature is

outside of a range of temperatures. ALERT pin may be

optionally configured as a second THERM output,

THERM2 , controlling a second fan.

The aSC7511 is available in SOP-8 and MSOP-8 surface

mount packages.

Features

• Local and remote temperature sensors

• 0.25°C resolution, ±1°C accuracy on remote diode

• 1°C resolution, ±3°C accuracy on local sensor

• Extended temperature measurement range 0°C to

+127°C (default) or –55°C to +150°C

• 2-wire SMBus serial interface with SMBus alert

• Programmable over / under temperature limits

• Offset registers for system calibration

• One or two over-temperature fail-safe THERM

outputs

• 8-lead, Pb-free, SOIC (SOP) or MSOP package

Applications

Desktop Computers – Motherboards and Graphics Cards

Laptop Computers

Pin Configuration

SOP-8 and MSOP-8

SCL

4 5

THERM

VDD

D+ SD

Application Diagram

Ordering Information

Part Number Package Temperature Range

and Operating Voltage Marking How Supplied

aSC7511D8 8-Lead SOP -40°C to +125°C, 3.3V aSC7511

Ayww 2500 units Tape & Reel

aSC7511M8 8-Lead MSOP -40°C to +125°C, 3.3V 7511

Ayww 2500 units Tape & Reel

Ayww – Assembly site, year, workweek

GND

LERT /

THERM2

aSC7511

D-

CPU

3.3V

aSC7511

SMBus

Interface

SDA

SCL

6 ALERT /

THERM2

THERM

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aSC7511

Absolute Maximum Ratings1

Parameter Rating

Supply Voltage, VDD, 3.3V nom. -0.3, +3.6V

Output Voltage VDD + 0.5V

D+ -0.3V to VDD +

0.5V

D- to GND -0.3V to 0.6V

SDA, SCL, ALERT , THERM -0.3V to 5.5V

I/O Current, SCL, SDA,

ALERT , THERM -1mA

Input Current, D- ±1mA

Continuous Current,

any other terminal 10mA

Storage Temperature Range -60°C to +150°C

IR Reflow Peak Temperature 260°C

Lead Soldering

Temperature (10 sec.) 300°C

Human Body Model > 2000 V

Machine Model > 250 V

ESD2

Charged Device Model > 2000 V

Notes:

1. Absolute maximum ratings are limits beyond which

operation may cause permanent damage to the device.

These are stress ratings only; functional operation at or

above these limits is not implied.

2. Human Body Model: 100pF capacitor discharged through

a 1.5kΩ resistor into each pin. Machine Model: 200pF

capacitor discharged directly into each pin. Charged

Device Model is per JESD22-C101C.

3. These specifications are guaranteed only for the test

conditions listed.

4. Accuracy (expressed in °C) = Difference between the

aSC7511 reported output temperature and the

temperature being measured.

5. Guaranteed by characterization but not production tested.

6. The accuracy of the aSC7511 is guaranteed when using

the thermal diode of a processor or any thermal diode with

a non-ideality of 1.008 and internal series resistance of

3.52. When using a 2N3904 type transistor as a thermal

diode the error band will be typically shifted depending on

transistor characteristics.

7. The aSC7511 can be read at any time without interrupting

the temperature conversion process.

Electrical Characteristics3

(-40°C≤TA≤+125°C, VDD= 3.3V unless otherwise noted. Specifications subject to change without notice)

Parameter Conditions Min Typ Max Units

Supply Voltage VDD 3.0 3.3 3.6 V

0.0625 Conversions-per-second rate 170 215 µA

Standby Mode, -40°C ≤TA<+85°C 6 10 µA Operating Supply Current IDD

Standby Mode, +85°C≤TA≤+120°C 6 20 µA

Local Sensor Accuracy4 -40°C ≤TA≤+100°C, 3V≤VDD≤3.6V ±1 ±3 °C

Local Sensor Resolution 1 °C

+60°C ≤TA≤+100°C,

-55°C≤TD ≤+150°C, 3V≤VDD≤3.6V ±1 ±2 °C

Remote Sensor Accuracy4,5,6

-40°C≤TA≤+120°C,

-55°C≤TD ≤+150°C, 3V≤VDD≤3.6V ±3 °C

Remote Sensor Resolution 0.25 °C

Temperature Conversion Time7

From Stop Bit to Conversion

Complete, One-Shot Mode, 2

Sensors, Averaging On

115 ms

Temperature Conversion Time7 One-Shot Mode, Averaging Off 30 ms

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aSC7511

Logic Electrical Characteristics

(TA = 25 °C, VDD = 3.3V unless otherwise noted)

Parameter Symbol Conditions Min Typ Max Units

Input Voltage Logic High VIH 3V≤VDD≤3.6V 2.1 V

Input Voltage Logic Low VIL 3V≤VDD≤3.6V 0.8 V

Output Voltage Logic Low

( ALERT and THERM ) VOL VDD=3.6V, IOL= -6mA 0.4 V

Output Low Sink Current

( ALERT and THERM ) IOL ALERT or THERM

forced to 0.4V 1 mA

Input Leakage Current IIN

VIN = 0V or 5.5V,

-40°C≤TA≤+125°C ±1.0 µA

SMBus Output Sink Current IOL TA = 25 °C, VOL = 0.6V 6 mA

SMBus Logic Input Current IIH, IIL -1 +1 µA

Output Leakage Current IOH VOH = VDD = 3.6V 0.1 1 µA

Output Transition Time tFCL= 400pF, IOL = -3mA 250 ns

Input Capacitance CIN All Digital Inputs 5 pF

Serial Port Timing

(TA = 25 °C, VDD = 3.3V unless otherwise noted, Guaranteed by design, not production tested)

Parameter Symbol Min Typ Max Units

SCL Operating Frequency fSCL 400 kHz

SCL Clock Transition Time tT:LH , tT:HL 300 ns

SCL Clock Low Period tLOW 1.3

μs

SCL Clock High Period tHIGH 0.6 50

μs

Bus free time between a Stop and a new Start Condition tBUF 1.3

μs

Data in Set-Up to SCL High tSU:DAT 100 ns

Data Out Stable after SCL Low tHD:DAT 300 ns

SCL Low Set-up to SDA Low (Repeated Start Condition) tSU:STA 600 ns

SCL High Hold after SDA Low (Start Condition) tHD:STA 600 ns

SDA High after SCL High (Stop Condition) tSU:STO 600 ns

Time in which aSC7511 must be operational after a power-on reset tPOR 500 ms

tHD:STA tSU:STO

tSU:DAT

SCL

tBUF

tSU:STA

tT:HL

tT:LH

tLOW tHIGH

tHD:DAT

SCL

SDA

Data Out

- 4 -

aSC7511

Pin Descriptions

Pin # Name Direction Description

1 VDD Supply Supply Voltage

2 D+ Current

Source Remote Diode Anode or Positive Lead

3 D- Current Sink Remote Diode Cathode or Negative Lead

4 THERM Output Open-drain logic output that may be used to control a fan or throttle CPU

when programmed temperature limit is exceeded.

5 GND Supply Ground

6 ALERT / THERM2 Output Open-drain logic output used as a mask-able interrupt or SMBus alert.

Configurable as second THERM output.

7 SDA Input/Output Serial Data—Open drain I/0-data pin for two-wire serial interface.

8 SCL Input Serial Clock—Clock for two-wire serial interface.

Note: Open-drain pins require a pull-up resistor.

Conversion Rate

Figure 1. Block Diagram

Remote Offset

Com-

parator

Status

Remote THERM Limit

Local THERM Limit

Remote High Limit

Remote Low Limit

Local High Limit

Local Low Limit

Address Pointer

Local Temp.

Remote Temp.

ADC

Remote Diode Open

Busy

SCL

D +

D -

DD VSS

Mask

Local

Senso

Configuration

SMBus Interface

7 8

8 6

THERM

LERT /

THERM2

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aSC7511

Basic Operation Overview

The aSC7511 temperature sensing circuitry continuously

monitors two thermal diode base-emitter voltages, one on-

chip, called “local” and one remotely located, connected to

the D+ and D- pins. At regular intervals the aSC7511

converts both analog voltages to digital values, which are

placed into the temperature registers.

The aSC7511 has an SMBus-compatible serial interface

that allows the user to access the data in the temperature

registers at any time. In addition, the serial interface gives

the user easy access to all other aSC7511 registers to

customize operation of the device.

The aSC7511 temperature-to-digital converter has two

temperature formats, 0°C to +127°C binary and extended-

range, -55°C to +150°C, offset-binary. The local sensor

resolution is 8-bits, with an LSB of 1°C. The remote or

remote diode sensor resolution is 10-bits with an LSB of

0.25°C. The temperature range of the local and remote

sensors are controlled by bit 2 of the configuration register,

default value is 0, 0°C to 127°C.

Table 1 gives examples of the relationship between the

output digital data and the measured temperature for the

default range. Table 2 gives examples for the extended

range. All output values are offset by +64°C when in this

mode.

The aSC7511 has a Shutdown Mode that reduces the

operating current to < 20µA. This mode is controlled by

RUN / STOP, bit 6 in the configuration register.

Comparisons to limits and diode open test are suspended

until the next measurement has taken place.

Digital Output (Binary)

High Byte Low Byte

Temperature

Always Zero

Local Sensor 8-Bit Resolution 00 00 0000

Remote Sensor 10-Bit Resolution 00 0000

>127°C 0111 1111 00 00 0000

+127°C 0111 1111 00 00 0000

+125°C 0111 1101 00

00 0000

+100°C 0110 0100 00

00 0000

+50°C 0011 0010 00

00 0000

+25°C 0001 1001 00 00 0000

+10°C 0000 1010 00 00 0000

+1.75°C 0000 0001 11

00 0000

+0.25°C 0000 0000 01 00 0000

0°C 0000 0000 00

00 0000

< 0°C 0000 0000 00

00 0000

Table 1. Relationship Between Temperature and Digital

Output, Default Range, 0°C to +127°C

Digital Output (Offset Binary)

High Byte Low Byte

Temperature

Always Zero

Local Sensor 8-Bit Resolution 00 00 0000

Remote Sensor 10-Bit Resolution 00 0000

+150°C 1101 0110 00 00 0000

+127°C 1011 1111 00 00 0000

+125°C 1011 1101 00 00 0000

+100°C 1010 0100 00

00 0000

+50°C 0111 0010 00 00 0000

+25°C 0101 1001 00 00 0000

+10°C 0100 1010 00 00 0000

+1.75°C 0100 0001 11 00 0000

+0.25°C 0100 0000 01 00 0000

0°C 0100 0000 00 00 0000

-55°C 0000 1001 00 00 0000

Table 2. Relationship Between Temperature and Digital

Output, Extended Range, -55°C to +150°C

Power-Up Default Conditions

The aSC7511 always powers-up in the following default

state:

• Configuration Register: 00h (i.e., ALERT enabled, Run

Mode, ALERT pin selected, normal range)

• Conversion Rate: 16 per second, 08h

• All Temperature and Offset Registers: 00h

• Consecutive

ALERT : 1 fault (i.e., 01h in the register)

• Local and Remote Low Limit: 0°C

• Local and Remote THERM Limit: 85°C

• THERM Hysteresis: 10°C

• Register Address Pointer: Undefined, must be set by

first write sequence.

• Normal / Extended Range: Normal

After power-up, these conditions can be reprogrammed via

the serial interface. Refer to the Serial Data Bus Operation

section to for aSC7511 programming instructions.

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aSC7511

Temperature Measurement

The aSC7511 measures temperature by calculating the

change in sensing a diode-connected transistor’s base-

emitter voltage (VBE) when two different currents are

applied sequentially. This difference has a linear positive

slope with temperature, unlike the non-linear VBE under a

constant current.

The VBE is amplified and scaled depending on the type of

transistor being measured. The typical case for the remote

measurement is to connect to the substrate thermal diode

of a CPU or ASIC. This will provide the die temperature of

that device to a high level of accuracy for the purpose of

controlling system cooling or reporting routine or over-

temperature conditions.

For each measurement cycle, an internal 2:1 multiplexer

alternates between the local and remote sensor diodes and

provides the input to a filter and amplifier. An analog-to-

digital converter takes this signal, converts it to a digital

value and stores the alternating values in the appropriate

temperature register of the aSC7511. These stored values

are continuously compared to several user-selected limit

values for sending alarm conditions or turning on an

external fan driver.

Conversions for both sensors will proceed automatically at

the default rate of 16 conversions per second until a

different rate is selected or one-shot or stand-by mode are

selected. The conversion rate is user-selected by writing to

the conversion rate register. Table 3 provides a list of

conversion rates ranging from 0.0625 to 64 conversions

per second. Sensor power consumption is directly

proportional to the conversion rate and should be taken into

account in power-limited applications as well as the impact

that power dissipation has in self-heating of the local

sensor. More details are provided in the Operation section.

Thermal Alarm and Alert Functions

The aSC7511 thermal alarm function, THERM , provides

user programmable thermostat capability and allows the

aSC7511 to function as a standalone thermostat without

constant attention over the serial interface. This signal is an

open drain output. When either the remote or local

temperature reading exceeds the selected limits it goes low

and will remain low until the measured temperature falls

below the alarm limit by the amount set into the THERM

hysteresis register (default value is 10°C).

The aSC7511 thermal alert function, ALERT , provides

another open-drain pin that is driven low when either the

internal or remote temperature is greater than the high limit

or less than or equal to the low limit selected by the user. In

addition, an SMBus Alert is generated, requiring the bus

master to inquire on the SMBus which client has

interrupted in order to re-set the alert. The ALERT pin may

be masked by the user with bit 7 of the configuration

Note that limit comparisons are triggered only by a

measurement action, not by a change in limits. An actual

alarm condition may exist but will not be reported until a

measurement takes place. This should be taken into

account when using slow conversion rates.

The ALERT pin may also be configured as a second

THERM pin, THERM2 . This will behave in the same way

as the THERM pin, but will be controlled by the high limit

used for the ALERT pin, although it will not need to be

reset by the master and does not use the hysteresis value.

A more detailed discussion and examples is provided in the

Operation section.

Fault Tolerance

The number of out of limit readings required before the

ALERT is asserted may be set by writing to the

Consecutive ALERT register. The default value is 1 and

the user may select requiring 2, 3, or 4 consecutive out of

limit readings before is ALERT asserted.

Registers

The ASC7511 contains 22 8-bit registers. All of these

registers may be accessed by the user via the digital serial

interface at any time. A detailed description of these

registers and their functions is provided in the following

paragraphs. Reading and writing to registers is covered in

the SMBus Operation section. Use of the register set to

control and interrogate the aSC7511 is covered in the

Operation section. A table of the registers is provided in

Table 4.

Address Pointer Register

The Address Pointer Register is a write-only register that is

automatically written by the first byte that follows the R/ W

bit of a write transaction. If R/ Wis low, It will then contain

the address to which the following byte is written, when

R/ W bit is high it will be the read address. Details of the

reading and writing sequence are covered in the Serial

Interface Operation section.

Measured Temperature Value Registers

The aSC7511 has two sensors whose measured values

are stored in registers. Remote temperature is two bytes, at

00h. The power-on default values are zero and the

aSC7511 will automatically begin filling these registers with

values after the power on reset sequence is complete.

These are read-only registers.

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aSC7511

Status Register

The status register is a read-only register for reporting the

state of the aSC7511’s alarms. It is a read-only register

located at 02h.

Bit Name Function

0 LTHERM Local sensor > THERM limit

1 RTHERM Remote sensor > THERM limit

2 ROPEN Remote sensor open-circuit

3 RLOW Remote sensor  low limit

4 RHIGH Remote sensor > high limit

5 LLOW Local sensor  low limit

6 LHIGH Local sensor > high limit

7 BUSY Converter in process of conversion

When any high or low local limits or high or low remote

limits are exceeded, bits 3 through 6 are set accordingly

and the ALERT pin 6 will be driven low. If the remote

sensor is open-circuit, bit 2 will be set and the ALERT will

be asserted. Reading the status register will re-set these

flags if the alerted condition has been removed, however,

the ALERT pin will remain asserted until the master has

serviced the SMBus alert.

The local and remote THERM limit trip are reported in bits 0

and 1 respectively. These two bits are reset only by the

temperature falling below the THERM limit by the amount

set into the hysteresis register. Table 3. Status Register Bit Assignments

Bit 7 will be high when the converter is busy. The list of

status register bit assignments is in Table 3. Each condition

is asserted when the bit is high. Default is 0.

Read

Address Write

Address Description Default

Value Read

Address Write

Address Description Default

Value

n/a n/a Address Pointer n/a

00h n/a Local Temperature (high-byte)200h / 0°C

01h n/a Remote Temperature (high-byte)200h 10h n/a Remote Temperature (low-byte)200h / 0°C

02h n/a Status n/a

03h 09h Configuration 00h

04h 0Ah Conversion rate 08h

05h 0Bh Local High Limit 55h / 85°C

06h 0Ch Local Low Limit 00h / 0°C

07h 0Dh Remote High Limit (high-byte)255h / 85°C

13h 13h Remote High Limit (low-byte)200h / 0°C

08h 0Eh Remote Low Limit (high-byte)200h / 0°C

14h 14h Remote Low Limit (low-byte)200h / 0°C

n/a 0Fh One-Shot Measurement n/a

11h 11h Remote Temp. Offset (high-byte) 2 00h / 0°C

12h 12h Remote Temp. Offset (low-byte)200h / 0°C

19h 19h Remote THERM Limit 55h / 85°C

20h 20h Local THERM Limit 55h / 85°C

21h 21h THERM Hysteresis 0Ah /

10°C

22h 22h Consecutive

LERT 01h

FEh n/a Manufacturer ID 61h

FFh n/a Die Revision Code 00h

Notes:

1. Low-byte values are fractional degrees, MSB of lower byte is 0.5°C

2. Changing to extended range adds 64°C to values reported, but limit settings are not changed and must be corrected by the user.

Table 4. aSC7511 Registers

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aSC7511

Configuration Register

The configuration register is a read-write register that

stores the controls for masking the ALERT signal, RUN /

STOP control, extended temperature range select and the

pin 6 function select for ALERT or THERM2 . It is located at

address 03h for read and 09h for writing.

Power on default is for all bits reset: no ALERT mask, RUN,

pin 6 is ALERT and normal range, 0°C to 127°C. Table 5

lists the bits of the configuration register.

The mask bit is only functional when pin 6 is configured as

the ALERT pin. When selecting extended range, note that

the values reported will be offset by 64°C and any limits will

have to be adjusted accordingly to match this offset-binary

coding. It is recommended that this configuration not be

changed again, once selected, to avoid confusion.

Bit Name Function

0, 1 Reserved

0 = 0°C to +127°C

2 Range Select 1 = -55°C to +150°C

3, 4 Reserved

0 = pin 6 is ALERT

5 ALERT / THERM2

1 = pin 6 is THERM2

0 = RUN

6 RUN / STOP 1 = STOP

0 = ALERT Enabled

7 MASK

1 = ALERT Masked

Table 5. Configuration Register Bi t Assignments

Conversion Rate Register

The sensor conversion rate register sets the rate of

conversions. Both local and remote sensors are measured

during a measurement cycle.

Conversions per

Second Seconds per

Conversion Code

0.0625 16 00h

0.125 8 01h

0.25 4 02h

0.5 2 03h

1 1 04h

2 0.5 05h

4 0.25 06h

8 0.125 07h

16 0.0625 08h

32 0.03125 09h

64 0.015625 0Ah

Reserved Reserved 0Bh to FFh

Table 6. Conversion Rate Register Bit

Assignments

The conversion rate register may be written-to at address

04h. The value stored may be read back at any time from

address 0Ah. The lower four bits define the rate from

0.0625 to 64 conversions per second. The default rate is 16

conversions per second designated by a code of 08h. The

rates are described in Table 6.

A single measurement is controlled separately by the one-

shot register, 0Fh, that is described below.

ALERT Limit Reg isters

There are four limit registers for the ALERT function using

six register locations:

• ALERT Remote High Limit (high and low bytes)

• ALERT Remote Low Limit (high and low bytes)

• ALERT Local High Limit

• ALERT Local Low Limit

These registers may be written or read-back at any time at

the addresses in shown in Table 2. Each limit has a default

value at power-up of 85°C for the high limit and 0°C for the

low limit. The ALERT high limits have a dual purpose in that

they may be used to control the alternate function of pin 6,

the ALERT /THERM2 output when that mode is selected.

Note that the values in the alarm registers must match the

data format selected by bit 2, the normal / extended range

selector in the configuration register. The user should

choose either normal or extended range on power-up and

not change this setting otherwise all limits will be invalid

and have to be adjusted accordingly.

Operation of these registers in thermal management

applications is described in the Operation Section.

One-Shot Register

While the aSC7511 is in standby mode with configuration

initiated by a write to the one-shot register at address 0Fh.

Any data written is ignored. After the conversion is

completed a set of readings is written to the temperature

registers, comparisons made and alerts generated. The

aSC7511 will then return to standby mode, awaiting the

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aSC7511

next one-shot reading or full activation. Standby mode is

discussed further in the Operation section.

THERM Limit Registers

There are two limit registers for the THERM function:

• THERM Remote High Limit

• THERM Local High Limit

These registers may be written or read-back at any time at

the addresses in shown in Table 2. Both limits has a default

value at power-up of 85°C.

The THERM alarm will be set when this limit is exceeded

and will reset when the temperature falls below that limit.

However, there is also a THERM hysteresis register that

may be used to set the temperature difference below

the THERM limit setting where the THERM alarm will be

reset once it has been triggered. This value is defaulted to

10°C and may be set to any value after power-on.

Operation of these registers in thermal management

applications is described in the Applications Section.

Remote Sensor Offset Register

Offset errors may be encountered on the remote sensor

readings caused by factors such as system clock noise

induced into the sensor interconnect or by a difference

between the measured temperature and the actual

temperature of interest in the system. A correction offset

value may be provided by the user to add or subtract from

the measured value resulting in a corrected value being

stored in the remote temperature registers. The limit values

will then be compared to these corrected values.

The offset register coding is two’s complement and it is

allocated two bytes at addresses 11h and 12h. Table 7

describes some examples of values in the range from -

128°C to +127.75°C that may be applied.

Offset Value Offset Register

High Byte (11h) Offset Register

Low Byte (11h)

+127.75°C 0111 1111 11 00 0000

+4°C 0000 0100 00 00 0000

+1°C 0000 0001 00 00 0000

+0.5°C 0000 0000 10 00 0000

0°C 0000 0000 00 00 0000

-0.5°C 1111 1111 10 00 0000

-1°C 1111 1111 00 00 0000

-4°C 1111 1100 00 00 0000

-128°C 1000 0000 00 00 0000

Table 7. Offset Register Sample Codes

Consecutive ALERT Register

This register will set the number of out of limit value

readings it will require before ALERT is asserted. It is

stored at register address 22h. The default value is for a

single out of limit reading to assert ALERT . The register

values for up to 4 out-of-limit readings are found in Table 8.

Number of Out-of-Limit

Measurements Required Register Value

1 yxxx 000x

2 yxxx 001x

3 yxxx 011x

4 yxxx 111x

x = Don’t Care

y = SMBus Timeout Enable

Table 8. Consecutive Alert Register

This register is also used to control activation of the SMBus

timeout feature. It is disabled by default and enabled by

writing a 1 to the MSB, bit 7.

Manufacturer’s Registers

Manufacturer’s identification is stored in the register at

address FEh and set to the value 61h. Register FFh

contains the die revision code.

Serial Data Bus Operation

General Operation

Writing to and reading from the aSC7511 registers is

accomplished via the SMBus-compatible two-wire serial

interface. SMBus protocol requires that one device on the

bus initiate and control all read and write operations. This

device is called the “master” device. The master device

also generates the SCL signal that is the clock signal for all

other devices on the bus. All other devices on the bus are

called “slave” devices. The aSC7511 is a slave device.

Both the master and slave devices can send and receive

data on the bus.

During SMBus operations, one data bit is transmitted per

clock cycle. All SMBus operations follow a repeating nine

clock-cycle pattern that consists of eight bits (one byte) of

transmitted data followed by an acknowledge (ACK) or not

acknowledge (NACK) from the receiving device. Note that

there are no unused clock cycles during any operation—

therefore there must be no breaks in the stream of data

and ACKs / NACKs during data transfers.

For most operations, SMBus protocol requires the SDA line

to remain stable (unmoving) whenever SCL is high — i.e.

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aSC7511

any transitions on the SDA line can only occur when SCL is

low. The exceptions to this rule are when the master device

issues a start or stop condition. Note that the slave device

cannot issue a start or stop condition.

The aSC7511 supports packet error checking (PEC) per

the SMBus protocol. It will interpret the PEC byte when

provide and respond with a PEC byte when expected by

the master. The PEC byte is calculated using CRC-8 and

conforms to the frame check sequence with the polynomial:

C(x) = x8 + x2 + x1 + 1

Refer to SMBus specification 2.0 for more details.

SMBus Definitions

The following are definitions for some general SMBus

terms:

Start Condition: This condition occurs when the SDA line

transitions from high to low while SCL is high. The master

device uses this condition to indicate that a data transfer is

about to begin.

Stop Condition: This condition occurs when the SDA line

transitions from low to high while SCL is high. The master

device uses this condition to signal the end of a data

transfer.

Acknowledge and Not Acknowledge: When data are

transferred to the slave device it sends an “acknowledge”

(ACK) after receiving each byte. The receiving device

sends an ACK by pulling SDA low for one clock. Following

the last byte, a master device sends a "not acknowledge"

(NACK) followed by a stop condition. A NACK is indicated

by forcing SDA high during the clock after the last byte.

Slave Address

Each slave device on the bus has a unique 7-bit SMBus

slave address. The aSC7511’s slave address is 4C hex.

Writing to and Reading from the aSC751 1

All read and write operations must begin with a start

condition generated by the master device. After the start

condition, the master device must immediately send a

slave address (7-bits) followed by a R/ Wbit. If the slave

address matches the address of the aSC7511, it sends an

ACK by pulling the SDA line low for one clock. Read or

write operations may contain one- or two-bytes. See

Figures 2 through 6 for timing diagrams for all aSC7511

operations.

Setting the Register Address Pointer

For all operations, the address pointer stored in the

address pointer register must be pointing to the register

address that is going to be written to or read from. This

first byte following the R/ Wbit being set to 0.

After the aSC7511 sends an ACK in response to receiving

the address and R/ Wbit, the master device must transmit

an appropriate 8-bit address pointer value as explained in

the Registers section of this data sheet. The aSC7511 will

send an ACK after receiving the new pointer data.

The register address pointer set operation is illustrated in

Figure 2. If the address pointer is not a valid address the

aSC7511 will internally terminate the operation. Also recall

that the address register retains the current address pointer

value between operations. Therefore, once a register is

being pointed to, subsequent read operations do not

require another Address Pointer set cycle.

Writing to Registers

All writes must start with a pointer set as described

previously, even if the pointer is already pointing to the

desired register. The sequence is described in Figure 3.

Immediately following the pointer set, the master must

begin transmitting the data to be written. After transmitting

each byte of data, the master must release the SDA line for

one clock to allow the aSC7511 to acknowledge receiving

the byte. The write operation should be terminated by a

stop condition from the master.

Reading from Register s

To read from a register other than the one currently being

pointed to by the address pointer register, a pointer set

sequence to the desired register must be done as

described previously. Immediately following the pointer

set, the master must perform a repeat start condition that

indicates to the aSC7511 that a read is about to occur. It is

important to note that if the repeat start condition does not

occur, the aSC7511 will assume that a write is taking place,

and the selected register will be overwritten by the

upcoming data on the data bus. The read sequence is

described in Figure 4. After the start condition, the master

must again send the device address and read/write bit.

This time the R/ Wbit must be set to 1 to indicate a read.

The rest of the read cycle is the same as described in the

previous paragraph for reading from a preset pointer

location.

If the pointer is already pointing to the desired register, the

master can read from that register by setting the R/ Wbit

(following the slave address) to a 1. After sending an ACK,

the aSC7511 will begin transmitting data during the

following clock cycle. After receiving the 8 data bits, the

master device should respond with a NACK followed by a

stop condition.

If the master is reset while the aSC7511 is in the process of

being read, the master should perform an SMBus reset.

This is done by holding the data or clock low for more than

- 11 -

aSC7511

35ms, allowing all SMBus devices to be reset. This follows

the SMBus 2.0 specification of 25-35ms.

When the aSC7511 detects an SMBus reset, it will prepare

to accept a new start sequence and resume

communication from a known state

S 0

Figure 2. Register Address Po inter Set

A7 A6 A5 A4 A3 A2 A1 A0

Start

SMBus Device Address Byte (4Ch) Register Address Byte

1 1 1 0 0 S A A

ACK

from

aSC7511

ACK

from

aSC7511

1 9 1

SCL

SDA 0

Figure 3. Register Write

A7 A6 A5 A4 A3 A2 A1 A0

Start

SMBus Device Address Byte (4Ch) Register Address Byte

1 1 1 0 0 R/W

S A A

ACK

from

aSC7511

ACK

from

aSC7511

SCL

SDA 0

1 9 1 9

Stop

Master

1 9

D7 D6 D5 D4 D3 D2 D1 D0

ACK

from

aSC7511

Stop

Master

SMBus Device Address Byte (4Ch)

ACK

from

aSC7511

NACK

from

Master

SCL

SDA

1 9 1 9

Stop

Master

Figure 5. Register Read When Read Address Already Set

D7 D6 D5 D4 D3 D2 D1 D0

Start

1 1 1 0 0 S A

0 R/W

R/W

Figure 4. Register Read

1 0 0 1 1 0 0 1

Start

SMBus Alert Response Address Byte (0Ch) aSC7511 SMBus Address

1 1 0 0 A N

ACK

from

aSC7511

NACK

from

Master

SCL

SDA 0

1 9 1 9

Stop

Master

espo

R/W

D7 D6 D5 D4 D3 D2 D1 D0

Re-start

1 1 1 0 0 S A

0 R/W

SMBus Device Address Byte (4Ch) aSC7511

ACK

from

NACK

from

Master

Stop

Master

Pointer Set

(Figure 2.)

without stop by Master

1 9 1 9

- 12 -

aSC7511

Operation

Alarm Outputs

The aSC7511 has two alarm functions, ALERT and

THERM . THERM has a high temperature limit and

ALERT has both high and low limits and will also respond

to a remote diode open circuit failure. These limits are

settable separately for the local and remote sensors. Any

alarm condition is reported individually in the status

Alarm conditions are logically combined and used to drive

two open-drain outputs, the ALERT output, (pin 6) and

THERM output, (pin 4).

Output pins may be used as an interrupt signal the CPU

or to turn on remote drivers for fans or indicators. The

ALERT pin will remain asserted until it has been reset by

the host via the SMBus. The THERM pin will remain

asserted until the temperature falls below the alarm level

by the amount set into the THERM hysteresis register.

ALERT Limits

Figure 7 shows use of the ALERT high and low limits.

The user sets up the alarm by writing the upper and lower

limit temperatures into the limit registers over the SMBus.

After each measurement, the comparator tests the

readings against the programmed limits and if the

measurement exceeds the high limit is or is equal to or

less-than the low limit, it will assert the particular alarm

bits in the status register and cause the ALERT pin to go

low.

Figure 7. ALERT Limits and Responses

The status bits will remain high until the status register is

read and then, if the condition is no longer present those

bits will be reset, otherwise they will remain high until the

conditions are no longer met and the register is read

again. The same sequence applies to the local readings

and limits.

The ALERT pin will remain low until the status bits have

been reset and an Alert Response has been issued by

the master and responded by the aSC7511. This flow is

described below.

The user may mask-out or disable the ALERT signal pin

should it be necessary to prevent a processor interrupt.

This is controlled by setting bit 7 of the configuration

SMBus Alert Output

The ALERT pin may be used to signal an SMBus Alert to

the host processor. This is a special mode of the SMBus

interface that requires the SMBus host to send an Alert

Response Address (ARA) to all slaves sharing the

ALERT pin in order to isolate clear and service the

alerting device. This sequence is described below and in

Figure 6.

The sequence of servicing this interrupt is as follows:

1. SMBALERT is asserted by the aSC7511 driving

pin 6 low.

2. The SMBus master begins a read operation with

a start followed by the ARA response address,

0001 100. This is an SMBus General Call

Address to be used only for requesting an alert

response. The

3. The device providing the SMBALERT signal

responds to this by providing an ACK followed

by its own bus address, an aSC7511 will

provide, 100 1100, with the LSB of the data byte

set to 1. A NACK response is expected from all

devices not giving an SMBALERT .

Conversion

4. If more than one device responds, the device

with the lowest device address will have priority

and will be serviced first by the master.

5. When the aSC7511 has responded with its own

address, it will de-assert the ALERT pin and the

status register bit that caused it, if that condition

and no other ALERT condition no longer exist.

THERMLimits

The THERM alarms operate differently from the alert

alarms. THERM alarm status bits for remote and local

Ext. Low ALERT Limit

Temperature

Ext. High ALERT Limit

Status Bit-4, EXHIGH

Status Bit-3, EXLOW

Status Register Read

ARA Response

ALERT Pin 6

- 13 -

aSC7511

limits, RTHERM and LTHERM, will change as soon as a

reading is greater than the limit and will reset as soon as

a reading goes below the limit minus the programmable

hysteresis value.

This hysteresis value applies to both remote and local

sensors. The scenario is described in Figure 8.

Figure 8. THERM Limits and Responses

The THERM limits default to 85ºC with 10ºC hysteresis.

The hysteresis value may be set from 0ºC to any positive

value up to 127ºC.

All limit values must take into account whether

measurements are being made in normal or extended

range. In extended range, there is a 64ºC offset in

reported values and limits must be adjusted accordingly.

THERM2 Option

The ALERT pin and associated alarm bits may be re-

assigned as a second THERM alarm. This alarm will

work exactly like THERM . The ALERT mask will have no

effect and there is only a high limit. The THERM

hysteresis value is applied to this alarm.

Sensor Open Detect

A protective circuit monitors the D+ pin for a voltage level

that would indicate the path to the remote diode is open.

If the voltage exceeds a typical value of VDD-1V, bit 2 of

the status register and the ALERT flag are set and

the ALERT pin is driven low.

This will require the master to service the ALERT in order

to reset the condition. If the remote diode is not being

used, it is recommended that D+ and D- be shorted to

prevent setting the open alarm.

In the event that a remote diode open-circuit has caused

an ALERT condition to occur and that condition is

restored to normal, when the host sends an Alert

Response and reads the Status Register the alert pin

may not clear. To ensure that the ALERT pin clears,

perform a read to internal register 42h.

Standby Mode

The aSC7511 may be placed in a minimum-power

standby mode by writing a 1 to bit 6 of the configuration

interface will respond when addressed.

Any measurement in progress when standby is selected

will be terminated and no new values will be written into

the temperature registers.

While in this mode, a one-shot measurement of both

channels may be commanded by the user by writing any

data value to the one-shot register, 0Fh. All alarm

comparisons will continue to be made and reported. The

alarm values may be changed while in standby and

current measured temperatures will be compared and

alarms generated if an out-of-limit condition exists.

Operating current will be 10 A or less when there is no

activity on the SMBus and 100 A or less when clock and

data are active.

Applications Information

Remote Diodes

The aSC7511 is designed to work with a variety of

remote sensors in the form of the substrate thermal diode

of a CPU or graphics controller or a diode-connected

transistor. Actual diodes are not suited for these

measurements.

There is some variation in the performance of these

diodes, described in terms of its departure from the ideal

diode equation. This factor is called diode non-

ideality,

.nf

The equation relating diode temperature to a change in

thermal diode voltage with two driving currents is:

VBE = (nf )KT

qln(N)

where:

nf = diode non-ideality factor, (nominal 1.008).

= Boltzman’s constant, (1.38 x 10-23).

= diode junction temperature in Kelvins.

q= electron charge (1.6 x 10-19 Coulombs).

N= ratio of the two driving currents (16).

The aSC7511 is designed and trimmed for an expected

value of 1.008, based on the typical value for the Intel

Pentium™ III and AMD Athlon™. There is also a

tolerance on the value provided. The values for other

CPUs and the 2N3904 may have different nominal values

and tolerances. Consult the CPU or GPU manufacturer’s

data sheet for the factor. Table 8 gives a

representative sample of what one may expect in the

Temperature

Conversion

Ext. THERM Limit

THERM Hysteresis

Status Bit-1, EXTHERM

THERM Pin 4

- 14 -

aSC7511

range of non-ideality. The trend with CPUs is for a lower

value with a larger spread.

When thermal diode has a non-ideality factor other than

1.008 the difference in temperature reading at a particular

temperature may be interpreted with the following

equation:

⎟

⎠

⎞

⎜

⎝

⎛

=actual

reportedactual n

T T 008.1

where:

reported

T= reported temperature in temperature register.

actual

T= actual remote diode temperature.

actual

n= selected diode’s non-ideality factor, .

Temperatures are in Kelvins or °C + 273.15.

The temperature error caused by non-ideality difference

is directly proportional to the difference from 1.008, but a

small difference in non-ideality results in a relatively large

difference in temperature reading. For example, if there

were a ±1% tolerance in the non-Ideality of a diode it

would result in a ±2.7 degree difference (at 0°C) in the

result (0.01 x 273.15).

This difference varies with temperature such that a fixed

offset value may only be used over a very narrow range.

Typical correction method required when measuring a

wide range of temperature values is to scale the

temperature reading in the host firmware.

Part nf Min nf Nom nf Max

Pentium™ III (CPUID 68h) 1.0057 1.008 1.0125

Pentium 4, 130nM 1.001 1.002 1.003

Pentium 4, 90nM 1.011

Intel Pentium M 1.0015 1.0022 1.0029

AMD Athlon™

Model 6 1.002 1.008 1.016

AMD Duron™

Models 7 and 8 1.002 1.008 1.016

AMD Athlon

Models 8 and 10 1.0000 1.0037 1.0090

2N3904 1.003 1.0043 1.005

Table 8. Representativ e CPU Therm al Diode

and Transistor Non-Ideality Factors

CPU or ASIC Substrate Remote Diodes

A substrate diode is a parasitic PNP transistor that has its

collector tied to ground through the substrate and the

base (D-) and emitter (D+) brought out to pins.

Connection to these pins is shown in Figure 13. The non-

ideality figures in Table 8 include the effects of any

package resistance and represent the value seen from

the CPU socket. The temperature indicated will need to

be compensated for the departure from a non-ideality of

1.008.

Figure 9. CPU Remote Diode Connection

Series Resistance

Any resistance in the connections from the aSC7511 to

the CPU pins should be accounted for in interpreting the

results of a measurement.

The impact of series resistance on the measured

temperature is a result of measurement currents

developing offset voltages that add to the diode voltage.

This is relatively constant with temperature and may be

corrected with a fixed value in the offset register. To

determine the temperature impact of resistance is as

follows:

ΔTR = RS×TV×ΔID

or,

ΔTR = RS×90

230

V/°C=RS×0.391°C/Ω

where:

TR= difference in the temperature reading from actual.

R= total series resistance of interconnect (both leads).

ID= difference in the two diode current levels (90µA).

T= scale of temperature vs. VBE (230µV/°C).

For example, a total series resistance of 10 would give

an offset of +3.9°C.

Discrete Remote Diod es

When sensing temperatures other than the CPU or GPU

substrate, an NPN or PNP transistor may be used. Most

commonly used are the 2N3904 and 2N3906. These

have characteristics similar to the CPU substrate diode

with non-ideality around 1.003. They are connected with

base to collector shorted as shown in Figure 14.

While it is important to minimize the distance to the

remote diode to reduce high-frequency noise pickup, they

may be located many feet away with proper shielding.

Shielded, twisted-pair cable is recommended, with the

shield connected only at the aSC7511 end as close as

possible to the ground pin of the device.

As with the CPU substrate diode, the temperature

reported will be subject to the same errors due to non-

D+

D-

CPU aSC7511

Substrate

- 15 -

aSC7511

ideality variation and series resistance. However, the

transistor’s die temperature is usually not the temperature

of interest and care must be taken to minimize the

thermal resistance and physical distance between that

temperature and the remote diode. The offset and

response time will need to be characterized by the user.

Figure 10. Discrete Remote Diode Connection

Board Layout Considerations

The distance between the remote sensor and the

aSC7511 should be minimized. All wiring should be

defended from high frequency noise sources and a

balanced differential layout maintained on D+ and D-.

Any noise, both common-mode and differential, induced

in the remote diode interconnect may result in an offset in

the temperature reported. Circuit board layout should

follow the recommendation of Figure 15. Basically, use

10-mil lines and spaces with grounds on each side of the

differential pair. Choose the ground plane closest to the

CPU when using the CPU’s remote diode.

Figure 11. Recommended Remote Diode Circuit

Board Interconnect

Noise filtering is accomplished by using a bypass

capacitor placed as close as possible to the aSC7511 D+

and D- pins. A 2.2nF ceramic capacitor is recommended,

but up to 3.3nF may be used. Additional filtering takes

place within the aSC7511.

It is recommended that the following guidelines be used

to minimize noise and achieve highest accuracy:

1. Place a 0.1µF bypass capacitor to digital ground

as close as possible to the power pin of the

aSC7511.

2. Match the trace routing of the D+ and D- leads and

use a 2.2nF filter capacitor close to the aSC7511.

Use ground runs along side the pair to minimize

differential coupling as in Figure 14.

3. Place the aSC7511 as close to the CPU or GPU

remote diode leads as possible to minimize noise

and series resistance.

4. Avoid running diode connections close to or in

parallel with high-speed busses, staying at least

2cm away.

5. Avoid running diode connections close to on-board

switching power supply inductors.

6. PC board leakage should be minimized by

maintaining minimum trace spacing and covering

traces over their full length with solder mask.

Thermal Considerations

The temperature of the aSC7511 will be close to that of

the PC board on which it is mounted. Conduction through

the leads is the primary path for heat flow. The reported

local sensor is very close to the circuit board temperature

and typically between the board and ambient.

In order to measure ambient air temperature, a remote

diode-connected transistor should be used. A surface-

mount SOT-23 or SOT-223 is recommended. The small

size is advantageous in minimizing response time

because of its low thermal mass, but at the same time it

has low surface area and a high thermal resistance to

ambient air. A compromise must be achieved between

minimizing thermal mass and increasing the surface area

to lower the junction-to-ambient thermal resistance.

The power consumption of the aSC7511 is relatively low

and should have little self-heating effect on the local

sensor reading. At the highest measurement rate the

dissipation is less than 2mW, resulting in only a few

tenths of a degree rise.

Application Circuit

The aSC7511 may be used to turn a fan on and off in

response to the internal or remote sensor. The active-low

THERM pin offers a programmable turn-on temperature

and the THERM hysteresis setting will turn the fan off.

An SMBus host is used to provide the settings

for THERM and THERM hysteresis. The fan will come on

when the THERM limit is reached and will turn off when it

falls below THERM temperature by the amount set into

the THERM hysteresis register. Figure 16 provides a

circuit diagram.

10 mils

D +

10 mils D -

GND

D -

2N3906

D +

aSC7511

D -

2N3904

D +

aSC7511

- 16 -

aSC7511

Figure 12. Simple Fan Control

Evaluation Board

The aSC7511EVB provides a platform for evaluation of

the operational characteristics of the aSC7511. The

board features a graphical user interface (GUI) to control

and monitor all activities and readings of the aSC7511.

The provided software will run on a Windows™-based

desktop or laptop PC with a DB-25 parallel printer port.

Features:

• Interactive GUI for setting limits and operational

configuration

• Powered and operated from PC parallel port

• LEDs for THERM and ALERT signals

• Graphical readout of temperature and alarms

• Selectable NPN or PNP sensor transistors

• Selectable remote diode connector

• Log file of readings

• Saving of setting configurations

• Optional use of external power and SMBus

SCL

CPU

3.3V

aSC7511

SMBus

Host

Interface

SDA

ALERT

THERM

5 V or 12V

Fan Drive

Circuit

10k

2.2nF

0.1

Preliminary Specification – Subject to change without notice

- 17 -

aSC7511

D8 Package – 8-Lead SOP Package Dimensions

Pb-Free Package

4.80mm (min)

4.98mm (max)

0.36mm (min)

0.46mm (max)

3.81mm (min)

3.99mm (max)

5.80mm (min)

6.20mm (max)

1.27mm BSC

1.52mm (min)

1.72mm (max)

0.53mm

0° (min)

8° (max)

0.25mm (min)

0.50mm (max)

x 45°

0.10mm (min)

0.25mm (max)

1.37mm (min)

1.57mm

(max)

7°

0.41mm (min)

1.27mm (max)

Detail A

Detail

A 0.19mm (min)

0.25mm (max)

Preliminary Specification – Subject to change without notice

- 18 -

aSC7511

M8 Package – 8-Lead MSOP Package Dimensions

Pb-Free Package

2.85mm (min)

3.05mm (max)

4.75mm (min)

5.05mm (max)

0.95mm BSC

2.90mm (min)

3.10mm (max)

0.25mm (min)

0.40mm (max)

2.90mm (min)

3.10mm (max)

4.75mm (min)

5.05mm (max)

0.65mm BSC

1.10mm (max)

0.525mm

BSC

α 0° (min)

6° (max)

2.85mm (min)

3.05mm (max)

0.10m

0.78mm (min)

0.94mm (max)

0.05mm (min)

0.15mm (max)

2.90mm (min)

3.10mm (max)

0.25mm (min)

0.40mm (max)

0.25mm (min)

0.35mm (max)

0.13mm (min)

0.23mm (max)

0.13mm (min)

0.18mm (max)

0° (min)

6° (max)

9° (min)

15°

(max)

0.40mm (min)

0.70mm (max)

Detail

Section A

Detail

Andigilog, Inc.

8380 S. Kyrene Rd., Suite 101

Tempe, Arizona 85284

Tel: (480) 940-6200

Fax: (480) 940-4255

- 19 -

aSC7511

Data Sheet Classifications

Preliminary Specification

This classification is shown on the heading of each page of a specification for products that are either under

development (design and qualification), or in the formative planning stages. Andigilog reserves the right to

change or discontinue these products without notice.

New Release Specification

This classification is shown on the heading of the first page only of a specification for products that are either

under the later stages of development (characterization and qualification), or in the early weeks of release to

production. Andigilog reserves the right to change the specification and information for these products without

notice.

Fully Released Specification

Fully released datasheets do not contain any classification in the first page header. These documents contain

specification on products that are in full production. Andigilog will not change any guaranteed limits without

written notice to the customers. Obsolete datasheets that were written prior to January 1, 2001 without any

header classification information should be considered as obsolete and non-active specifications, or in the best

case as Preliminary Specifications.

Andigilog® is a Registered Trademark of Andigilog, Inc.

Pentium™ is a trademark of Intel Corporation

Athlon™ and Duron™ are trademarks of AMD Corporation

LIFE SUPPORT POLICY

ANDIGILOG'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES

OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF

ANDIGILOG, INC. As used herein:

1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b)

support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in

the labeling, can be reasonably expected to result in a significant injury to the user.

2. A critical component is any component of a life support device or system whose failure to perform can be reasonably

expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.