Rainbow Electronics MAX6692 - Manual (Page 14)

MAX6648/MAX6692
Precision SMBus-Compatible Remote/Local
Temperature Sensors with Overtemperature Alarms
14 ______________________________________________________________________________________
When measuring temperature with discrete remote sen-
sors, smaller packages, such as SOT23s, yield the best
thermal response times. Take care to account for ther-
mal gradients between the heat source and the sensor,
and ensure that stray air currents across the sensor
package do not interfere with measurement accuracy.
Self-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 autoconverting at the
fastest rate and simultaneously sinking maximum current
at the ALERT output. For example, with V
CC
= 5.0V, at a
4Hz conversion rate and with ALERT sinking 1mA, the
typical power dissipation is:
5.0V x 500µA + 0.4V x 1mA = 2.9mW
ø
J-A
for the 8-pin µMAX package is about +221°C/W,
so assuming no copper PC board heat sinking, the
resulting temperature rise is:
∆T = 2.9mW x (+221°C/W) = +0.6409°C
Even under nearly worst-case conditions, it is difficult to
introduce a significant self-heating error.
MUX
REMOTE
LOCAL
ADC
2
CONTROL
LOGIC
SMBus
READ
WRITE
8
8
ADDRESS
DECODER
7
S
R
Q
DIODE
FAULT
DXP
DXN
SMBCLK
SMBDATA
REGISTER BANK
COMMAND BYTE
REMOTE TEMPERATURE
LOCAL TEMPERATURE
ALERT THRESHOLD
ALERT RESPONSE ADDRESS
V CC
S
R
Q
OVERT
ALERT
MAX6648
MAX6692
OVERT THRESHOLD
Functional Diagram