Datasheet MAX6511, MAX6512, MAX6513 (Maxim) - 5

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