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MAX6640 Datasheet(PDF) 13 Page - Maxim Integrated Products |
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MAX6640 Datasheet(HTML) 13 Page - Maxim Integrated Products |
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13 / 21 page 
• D5: SMBus Timeout Disable. Writing a zero enables SMBus timeout for prevention of bus lockup. When the timeout function is enabled, the SMBus interface is reset if SDA or SCL remains low for more than 74ms (typ). • D4: Temperature Channel 2 Source. Selects either local or remote 2 as the source for temperature chan- nel 2 register data. Writing a zero to this bit selects remote 2 for temperature channel 2. Extended Temperature Registers (05h and 06h) These registers contain the extended temperature data from channels 1 and 2. Bits D[7:5] contain the 3 LSBs of the temperature data. The bit values are 0.5°C, 0.25°C, and 0.125°C. When bit 0 is set to 1, a diode fault has been detected. Channel 1 and Channel 2 ALERT, OT, and THERM Limits (08h Through 0Dh) These registers contain the temperatures above which the ALERT, THERM, and OT status bits set and outputs assert (for the temperature channels that are not masked). The data format is the same as that of the channel 1 and channel 2 temperature registers: the LSB weight is +1°C and the MSB is +128°C. Fan 1 and 2 Configuration 1 (10h and 14h) The following registers control the modes of operation of the MAX6640: • D7: PWM Mode. D7 = 1 sets the fan into manual PWM duty-cycle control mode. Write the target duty cycle in the fan duty-cycle register. D7 = 0 puts the fan into RPM control mode. To set RPM manually, set both fan-control temperature channels (bits D2 and D3) to zero and write the desired tachometer count into the TACH count register. • D[6:4]: Fan Duty-Cycle Rate-of-Change. D[6:4] sets the time between increments of the duty cycle. Each increment is 1/120 of the duty cycle. By adjust- ing the rate of change, audibility of fan-speed changes can be traded for response time. Table 4 shows the effect of D[6:4] and, for reference, the time required for the fan speed to change from 33% to 100% duty cycle as a function of the rate-of-change bits. 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller ______________________________________________________________________________________ 13 READ/ WRITE REGISTER NO. ADDRESS POR STATE FUNCTION D7 D6 D5 D4 D3 D2 D1 D0 W 26h 0011 1100 Fan 1 target duty cycle MSB —— ———— LSB R 27h 0000 0000 Fan 2 current duty cycle MSB —— ———— LSB W 27h 0011 1100 Fan 2 target duty cycle MSB —— ———— LSB R/W 28h 0100 000 Channel 1 minimum fan-start temperature MSB —— ———— LSB R/W 29h 0100 0000 Channel 2 minimum fan-start temperature MSB —— ———— LSB R 3Dh 0101 1000 Read device ID 010 11000 R 3Eh 0100 1101 Read manufacturer ID 010 01101 R 3Fh 0000 0000 Read device revision 000 00000 Table 3. Register Map (continued) |
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