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参数资料
| 型号： | NCT1008DMT3R2G |
| 厂商： | ON SEMICONDUCTOR |
| 元件分类： | 模拟信号调理 |
| 英文描述： | %2B-1℃ temperature monitor with series resistance cancellation |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, DSO8 |
| 封装： | 2 X 2 MM, 0.50 MM PITCH, LEAD FREE, DFN-8 |
| 文件页数： | 6/20页 |
| 文件大小： | 251K |
| 代理商： | NCT1008DMT3R2G |
NCT1008
http://onsemi.com
14
When reading data from a register there are two
possibilities.
If the address pointer register value of the NCT1008 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 writing to the
NCT1008 as before, but only the data byte containing
the register read address is sent, because data is not to
be written to the register see Figure 16.
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 see Figure 17.
If the address pointer register is known to be at the
desired address, data can be read from the corresponding
data register without first writing to the address pointer
register and the bus transaction shown in Figure 16 can
be omitted.
Notes:
It is possible to read a data byte from a data register
without first writing to the address pointer register.
However, 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.
Some of the registers have different addresses for read
and write operations. The write address of a register
must be written to the address pointer if data is to be
written to that register, but it may not be possible to
read data from that address. The read address of a
register must be written to the address pointer before
data can be read from that register.
ALERT Output
This is applicable when Pin 6 is configured as an ALERT
output. The ALERT output goes low whenever an
outoflimit measurement is detected, or if the remote
temperature sensor is open circuit. It is an opendrain output
and requires a pullup resistor to VDD. Several ALERT outputs
can be wireOR’ed together, so that the common line goes
low if one or more of the ALERT outputs goes low.
The ALERT output can be used as an interrupt signal to a
processor, or as an SMBALERT. Slave devices on the SMBus
cannot normally signal to the bus master that they want to
talk, but the SMBALERT function allows them to do so.
One or more ALERT outputs can be connected to a
common SMBALERT line that is connected to the master.
When the SMBALERT line is pulled low by one of the
devices, the following procedure occurs (see Figure 18):
Figure 18. Use of SMBALERT
ALERT RESPONSE
ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
DEVICE SENDS
ITS ADDRESS
RD
START
ACK
DEVICE
ADDRESS
NO
ACK STOP
MASTER
RECEIVES
SMBALERT
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the
alert response address (ARA = 0001 100). This is
a general call address that must not be used as a
specific device address.
3. The device whose ALERT output is low responds
to the alert response address and the master reads
its device address. As the device address is seven
bits, an LSB of 1 is added. The address of the
device is now known and it can be interrogated in
the usual way.
4. If more than one device’s ALERT output is low,
the one with the lowest device address takes
priority, in accordance with normal SMBus
arbitration.
Once the NCT1008 has responded to the alert response
address, it resets its ALERT output, provided that the error
condition that caused the ALERT no longer exists. If the
SMBALERT line remains low, the master sends the ARA
again, and so on until all devices whose ALERT outputs
were low have responded.
Low Power Standby Mode
The NCT1008 can be put into low power standby mode by
setting Bit 6 of the configuration register. When Bit 6 is low,
the NCT1008 operates normally. When Bit 6 is high, the
ADC is inhibited, and any conversion in progress is
terminated without writing the result to the corresponding
value register. However, the SMBus is still enabled. Power
consumption in the standby mode is reduced to 5
mA if there
is no SMBus activity, or 30
mA if there are clock and data
signals on the bus.
When the device is in standby mode, it is possible to
initiate a oneshot conversion of both channels by writing to
the oneshot register (Address 0x0F), after which the device
returns to standby. It does not matter what is written to the
oneshot register, all data written to it is ignored. It is also
possible to write new values to the limit register while in
standby mode. If the values stored in the temperature value
registers are outside the new limits, an ALERT is generated,
even though the NCT1008 is still in standby.
1.8 V Logic Operation
The NCT1008 is 1.8 V logic compatible; this means that
the communication lines (SDA and SCL) and THERM can
be pulled up to a 1.8 V supply while still remaining within
spec.
The ALERT/THERM2 pin is also 1.8 V logic compatible,
however, in order to keep the quiescent current to it’s
minimum, it is recommended that this pin is pulled to VDD.
Sensor Fault Detection
At its D+ input, the NCT1008 contains internal sensor
fault detection circuitry. This circuit can detect situations
where an external remote diode is either not connected or
incorrectly connected to the NCT1008. A simple voltage
comparator trips if the voltage at D+ exceeds VDD 1.0 V
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