SA56004X Datasheet, PDF (17/23 Pages) NXP Semiconductors – 1 Degrees Celcious accurate, SMBus-compatible, 8-pin, remote/local digital temperature sensor with over temperature alarms

Philips Semiconductors
±1 °C accurate, SMBus-compatible, 8-pin, remote/local
digital temperature sensor with over temperature alarms
Product data sheet
SA56004X
Remote diode selection
To measure the remote temperature or the temperature of an
externally attached diode, the device automatically forces two
successive currents of about 160 µA and 10 µA at D+ pin. It
measures the voltage (VBE) between D+ and D–, detects the
difference between the two VBEs or the ∆VBE and then converts the
∆VBE into a temperature data using the basic PTAT voltage formula
as shown below. The device typically takes about 38 ms to perform
a measurement during each conversion period or cycle, which is
selectable by programming the conversion rate register.
ǒ Ǔ DVBE + n
kT
q
ln
I2
I1
where:
n: Diode ideality factor
k: Boltzmann’s constant
T: Absolute temperature (° K) = 273 °C + T (°C)
q: Electron charge
ln: Natural logarithm
I2, I1: Two source currents
Because the device does not directly convert the sensed VBE as in
the old method of temperature measurement systems, the VBE
calibration is not required. Furthermore, the device remote
temperature error is adjusted at the manufacturer to meet the
specifications with the use of the reference diode-connected
transistors such as the 2N3904/2N3906. The diode type to be used
in customer applications must have the characteristics as close to
the 2N3904/2N3906 as possible in order to obtain optimal results.
Finally, to prevent the effects of system noise on the measured VBE
signals, an external capacitor of about 2200 pF connected between
the D+ and D– pins as well as the grounded-shield cable for the
diode connection wires are recommended.
Diode fault detection
The SA56004X is designed with circuitry to detect the fault
conditions of the remote diode. When the D+ pin is shorted to V_DD
or floating, the Remote Temperature High Byte (RTHB) register is
loaded with +127 °C, the Remote Temperature Low Byte (RTLB)
register is loaded with 0 °C, and the OPEN bit (bit 2 of the Status
register) is set. Under the above conditions of D+ shorted to V_DD or
floating, if the Remote T_CRIT setpoint is set less than +127 °C, and
T_CRIT Mask are disabled, then, the T_CRIT output pins will be
pulled LOW. Furthermore, if the Remote HIGH Setpoint High Byte
(RHSHB) register is set to a value less than +127 °C and the Alert
Mask is disabled, then the ALERT output will be pulled LOW.
Note: the OPEN bit itself will not trigger an ALERT.
When the D+ pin is shorted to ground or to D–, the Remote
Temperature High Byte (RTHB) register is loaded with –128 °C
(1000 0000) and the OPEN (bit 2 in the Status register) will not be
set. Since operating the SA56004X is beyond its normal limits, this
temperature reading represents this shorted fault condition. If the
value in the Remote Low Setpoint High Byte (RLSHB) register is
more than –128 °C and the Alert Mask is disabled, the ALERT
output will be pulled LOW.
SMBus INTERFACE
The device can communicate over a standard two-wire serial
interface System Management Bus (SMBus) or compatible I²C-bus
using SCLK and SDATA. The device employs four standard SMBus
protocols: Write Byte, Read Byte, Receive Byte, and Send Byte.
Data formats of four protocols are shown in Figure 17. The following
key points of protocol are important:
1. The SMBus master initiates data transfer by establishing a
START condition (S) and terminates data transfer by generating
a STOP condition (P).
2. Data is sent over the serial bus in sequences of 9 clock pulses
according to each 8-bit data byte followed by 1-bit status of
device acknowledgement (A).
3. The 7-bit slave address is equivalent to factory-programmed
address of the device.
4. The command byte is equivalent to the address of the selected
device register.
5. The receive byte format is used for quicker transfer data from a
device reading register which was previously selected.
Serial interface reset
If the SMBus master attempts to reset the SA56004X while the
SA56004X is controlling the data line and transmitting on the data
line, the SA56004X must be returned to a known state in the
communication protocol. This may be accomplished in two ways:
1. When the SDATA is LOW, the SA56004X SMBus state machine
resets to the SMBus idle state if SCLK is held LOW for more
than 35 ms (maximum TIMEOUT period). According to SMBus
specification 2.0, all devices are required to time-out when the
SCLK line is held LOW for 25 to 35 ms. Therefore, to insure a
time-out of all devices on the bus, the SCLK line must be held
LOW for at least 35 ms.
2. When the SDATA is HIGH, the master initiates an SMBus start.
The SA56004X will respond properly to a SMBus start condition
only during the data retrieving cycle. After the start, the
SA56004X will expect a SMBus Address byte.
2004 Oct 06
17