Rainbow Electronics MAX6512 - Manual (Page 5)

Hysteresis Input
The HYST pin is a CMOS-compatible input that selects
hysteresis at either a high level (10°C for HYST = V
DD )
or a low level (5°C for HYST = GND). Hysteresis pre-
vents the output from chattering when the temperature
is near the trip point. The HYST pin must not float.
The output asserts when the temperature exceeds the
trip point and deasserts when the temperature falls
back below the trip point minus the hysteresis. For
example, if the trip point is 105°C, the output will assert
at 105°C and will not deassert until temperature falls
below 105°C minus the hysteresis (e.g., 95°C if 10°C
hysteresis is chosen) (Figure 2).
Applications Information
Remote-Diode Selection
To ensure best accuracy, use a good-quality diode-
connected transistor. Suggested devices are listed in
Table 1. Large power transistors are not recommend-
ed. Tight specifications for forward current gain indi-
cate the manufacturer has good process controls and
that the devices have consistent V
be
characteristics.
The MAX6511/MAX6512/MAX6513 can also measure
the die temperature of CPUs and other integrated cir-
cuits having on-board temperature-sensing diodes.
Use the monitor’s output to reset the µP, assert an inter-
rupt, activate a cooling fan, or trigger an external alarm.
Noise Filtering Capacitors
A quality ceramic capacitor must be connected across
the DXP/DXN inputs to maintain temperature threshold
accuracy by filtering out noise. The capacitor should be
located physically close to the DXP/DXN pins and
should typically have a value of 2200pF. Larger capaci-
tor values can cause temperature measurement errors.
A 50% variation from the recommended capacitor
value can cause up to ±1°C error.
MAX6511/MAX6512/MAX6513
Low-Cost, Remote SOT Temperature Switches
_______________________________________________________________________________________ 5
Figure 2. Temperature Trip Threshold Hysteresis
TRIP TEMPERATURE
TRIP TEMPERATURE HYSTERESIS
TOVER (MAX6511)
TIME
MANUFACTURER MODEL NUMBER
Central Semiconductor (USA) CMPT3904
ON (USA) MMBT3904
Rohm Semiconductor (Japan) SST3904
Samsung (Korea) KST3904-TF
Siemens (Germany) SMBT3904
Zetex (England) FMMT3904CT-ND
Table 1. Sensor Transistor Manufacturers
Note: Transistors must be diode connected (base shorted to
collector).