ADM1029ARQZ-R7(2012) データシートの表示（PDF） - ON Semiconductor

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ADM1029ARQZ-R7
(Rev.:2012)

Dual PWM Fan Controller and Temperature Monitor for High Availability Systems

ON Semiconductor 

ADM1029

In the case of the ADM1029, write operations contain

either one or two bytes, and read operations contain one

byte, and perform the following functions:

To write data to one of the device data registers or read

data from it, the Address Pointer Register must be set so that

the correct data register is addressed, data can be written into

that register or read from it. The first byte of a write

operation always contains an address that is stored in the

Address Pointer Register. If data is to be written to the

device, the write operation contains a second data byte that

is written to the register selected by the address pointer

register.

This is illustrated in Figure 18. The device address is sent

over the bus followed by R/W set to 0. This is followed by

two data bytes. The first data byte is the address of the

internal data register to be written to, which is stored in the

Address Pointer Register. The second data byte is the data to

be written to the internal data register.

When reading data from a register there are two

possibilities:

1. If the ADM1029’s Address Pointer Register value

is unknown or not the desired value, it is first

necessary to set it to the correct value before data

can be read from the desired data register. This is

done by performing a write to the ADM1029 as

before, but only the data byte containing the

register address is sent, as data is not to be written

to the register. This is shown in Figure 19.

A read operation is then performed consisting of

the serial bus address, R/W bit set to 1, followed

by the data byte read from the data register. This is

shown in Figure 20.

2. If the Address Pointer Register is known to be

already at the desired address, data can be read

from the corresponding data register without first

writing to the Address Pointer Register, so

Figure 19 can be omitted.

NOTE: although it is possible to read a data byte from a data

register without first writing to the Address Pointer Register,

if the Address Pointer Register is already at the correct

value, it is not possible to write data to a register without

writing to the Address Pointer Register, because the first

data byte of a write is always written to the Address Pointer

Register.

Alert Response Address

The ADM1029 has an interrupt (INT) output that is

asserted low when a fault condition occurs. Several INT

outputs can be wire OR’d to a common interrupt line. When

the host processor receives an interrupt request, it would

normally need to read the interrupt status register of each

device to identify which device had made the interrupt

request. However, the ADM1029 supports the optional

Alert Response Address function of the SMBus protocol.

When the host processor receives an interrupt request it can

send a general call address (0001100) over the bus. The

device asserting INT will then send its own slave address

back to the host processor, so the device asserting INT can

be identified immediately.

If more than one device is asserting INT, all devices will

try to respond with their slave address, but an arbitration

process ensures that only the lowest address will be received

by the host.

After sending its slave address, the first device will then

clear its INT output. The host can then check if the INT is

still low and send the general call again if necessary until all

devices asserting INT have responded.

The ARA function can be disabled by setting Bit 2 of the

Configuration Register (address 01h).

Temperature Measurement System

Local Temperature Measurement

The ADM1029 contains an on-chip bandgap temperature

sensor, whose output is digitized by the on-chip ADC. The

temperature data is stored in the Local Temp Value Register

(address A0h). As both positive and negative temperatures

can be measured, the temperature data is stored in two’s

complement format, as shown in Table 6. Theoretically, the

temperature sensor and ADC can measure temperatures

from –128C to +127C with a resolution of 1C, but

temperatures outside the operating temperature range of the

device cannot be measured by the internal sensor.

Remote Temperature Measurement

The ADM1029 can measure the temperature of one or two

remote diode-connected transistors, connected to Pins 13

and 14 and/or 16 and 17. The data from the temperature

measurements is stored in the Remote 1 and Remote 2 Temp

Value Registers (addresses A1h and A2h).

If two remote temperature measurements are not required,

Pins 16 and 17 can be reconfigured as general-purpose logic

I/O pins, as explained later.

The forward voltage of a diode or diode-connected

transistor, operated at a constant current, exhibits a negative

temperature coefficient of about –2 mV/C. The absolute

value of VBE varies from device to device and individual

calibration is required to null this out so, unfortunately, the

technique is unsuitable for mass production.

The technique used in the ADM1029 is to measure the

change in VBE when the device is operated at two different

currents.

This is given by:

DVBE + KTńq ln(N)

where:

K is Boltzmann’s constant

q is charge on the carrier

T is absolute temperature in Kelvins

N is ratio of the two currents

(eq. 1)

Figure 21 shows the input signal conditioning used to

measure the output of a remote temperature sensor. This

figure shows the external sensor as a substrate transistor,

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