Datasheet

MAX6694
5-Channel Precision Temperature Monitor
with Beta Compensation
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For a real temperature of +85°C (358.15K), the mea-
sured temperature is +84.41°C (357.56K), an error of
-0.590°C.
Series Resistance Cancellation
Some thermal diodes on high-power ICs can have
excessive series resistance, which can cause tempera-
ture measurement errors with conventional remote tem-
perature sensors. Channel 1 of the MAX6694 has a
series resistance cancellation feature (enabled by bit 3
of the configuration 1 register) that eliminates the effect
of diode series resistance. Set bit 3 to 1 if the series
resistance is large enough to affect the accuracy of
channel 1. The series resistance cancellation function
increases the conversion time for channel 1 by 125ms.
This feature cancels the bulk resistance of the sensor
and any other resistance in series (wire, contact resis-
tance, etc.). The cancellation range is from 0Ω to 100Ω.
Beta Compensation
The MAX6694 is optimized for use with a substrate pnp
remote-sensing transistor on the die of the target IC.
DXP1 connects to the emitter of the sensing transistor
and DXN1 connects to the base. The collector is
grounded. Such transistors can have very low beta
(less than 1) when built in processes with 65nm and
smaller geometries. Because of the very low beta, stan-
dard “remote diode” temperature sensors may exhibit
large errors when used with these transistors. Channel
1 of the MAX6694 incorporates a beta compensation
function that, when enabled, eliminates the effect of low
beta values. This function is enabled at power-up and
can be disabled using bit 2 of the configuration 1 regis-
ter. Whenever low beta compensation is enabled,
series-resistance cancellation must be enabled. When
a sense transistor’s base and collector are shorted
together (as with a discrete sensing “diode”), disable
beta compensation.
Discrete Remote Diodes
When the remote-sensing diode is a discrete transistor,
its collector and base must be connected together.
Table 10 lists examples of discrete transistors that are
appropriate for use with the MAX6694. The transistor
must be a small-signal type with a relatively high for-
ward voltage; otherwise, the A/D input voltage range
BIT NAME
POR
STATE
FUNCTION
7 (MSB) Reserved 0 —
6 Reserved 0 Not Used. 0 at POR, then 1.
5 Reserved 0 Not Used. 0 at POR, then 1.
4 Diode fault 4 0
Channel 4 Remote-Diode Fault Bit. This bit is set to 1 when DXP4 and DXN4
are open circuit or when DXP4 is connected to V
CC
.
3 Diode fault 3 0
Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3
are open circuit or when DXP3 is connected to V
CC
.
2 Diode fault 2 0
Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2
are open circuit or when DXP2 is connected to V
CC
.
1 Diode fault 1 0
Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1
are open circuit or when DXP1 is connected to V
CC
.
0 Reserved 0 —
Table 9. Status 3 Register
MANUFACTURER MODEL NO.
Central Semiconductor (USA) CMPT3904
Rohm Semiconductor (USA) SST3904
Samsung (Korea) KST3904-TF
Siemens (Germany) SMBT3904
Zetex (England) FMMT3904CT-ND
Table 10. Remote-Sensors Transistor
Manufacturers (for Channels 2, 3, and 4)
Note: Discrete transistors must be diode connected (base
shorted to collector).