f75384s Feature Integration Technology Inc., f75384s Datasheet - Page 11

• Manufacturer Part Number: f75384s
• Description: ?1o C Accuracy Temperature Sensor Ic Datasheet
• Manufacturer: Feature Integration Technology Inc.

F75383/F75384
6.6 THERM#
6.7 ADC Conversion Sequence
6.8 Thermal Mass and Self Heating
6.9 ADC Noise Filtering
(2). Reading the Status register to clear the status
When ALERT# acts as a SMBALERT, the ALERT# will be de-asserted until the following 3 conditions are matched:
(1). The abnormal condition is gone
(2). Reading the Status register to clear the status
(3). The ALERT# has been serviced by the SMBus master reading the device address.
For more information about SMBALERT, please see SMBus 1.1 specification.
Either VT1(Local) or VT2(Remote) temperature exceeds the corresponding THERM limit, the THERM# output will assert low. The
asserted output will be de-asserted until the temperature goes below (THERM Limit – Hysteresis). The hysteresis default value is
10°C and it can be programmed. Both VT1 and VT2 have their own THERM limits and Hysteresis values.
If a START command is written, both channels are converted and the results of both measurements are available after the end of
conversion. A BUSY status bit in the status byte shows that the device is actually performing a new conversion; however, even if the
ADC is busy, the results of the previous conversion are always available.
Thermal mass effect can seriously degrade the F75383’s effective accuracy. The thermal time constant of the SOP package is about
140 in still air. For the F75383/S junction temperature to settle to within +1°C after a sudden +100°C change requires about five time
constants or 12 minutes. The use of smaller packages for remote sensors such as SOT23, improves the situation. Take care to
account for thermal gradients between the heat source and the sensor package do not interfere with measurement accuracy.
Sel-heating does not significantly affect measurement accuracy. Remote sensor self-heating due to the diode current source is
negligible. For the local diode, the worst case error occurs when auto-converting at the fastest rate and simultaneously sinking
maximum current at the ALERT# output. For instance, at an 64Hz rate and ALERT# sink around 0.7mA when pull up resistor 4.7K
ohm to 3.3VCC, the typical power dissipation is VCC x 220 uA plus 0.4V x 0.7mA. Package θ
3.3V and no copper PC board heat-sinking, the resulting temperature rise is:
Even with these contrived circumstances, it is difficult to introduce significant self-heating errors.
The ADC is integrating type with inherently good noise rejection. Micro-power operation places constraints on high-frequency noise
rejection; therefore, careful PCB board layout and suitable external filtering are required for high-accuracy remote measurement in
dT = 1.01mW x 120 °C/W = 0.12 °C
-7-
F75383/F75384
JA
is about 120 °C/W, so with VCC =
July, 2007
V0.32P