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MAX6650EUB+ Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX6650EUB+ Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 25 page Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible Interface 8 Maxim Integrated MAX6650/MAX6651 SMBCLK AB C D E FG H I J K SMBDATA tSU:STA tHD:STA tLOW tHIGH tSU:DAT tHD:DAT tSU:STO tBUF A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW L M F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = SLAVE PULLS SMBDATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION, DATA EXECUTED BY SLAVE M = NEW START CONDITION SMBCLK A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE AB C D E FG H I J SMBDATA tSU:STA tHD:STA tLOW tHIGH tSU:DAT tSU:STO tBUF K E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION Figure 3. SMBus Write Timing Diagram Figure 4. SMBus Read Timing Diagram Command-Byte Functions The 8-bit Command-Byte Register (Table 2) is the mas- ter index that points to the various other registers within MAX6650/MAX6651. The register’s power-on reset (POR) state is 0000 0000, so that a receive-byte trans- mission (a protocol that lacks the command byte) occurring immediately after POR returns the current speed setting. Fan-Speed Register In closed-loop mode, the MAX6650/MAX6651 use the Fan-Speed Register to set the period of the tachometer signal that controls the fan speed. The Fan-Speed Register is ignored in all other modes of operation. The MAX6650/MAX6651 regulate the fan speed by forcing the tachometer period (tTACH) equal to the scaled reg- ister value. One revolution of the fan generates two tachometer pulses, so the required Fan-Speed Register value (KTACH) may be calculated as: tTACH = 1 / (2 x Fan Speed) KTACH = [tTACH x KSCALE x (fCLK / 128)] - 1 where the fan speed is in rotations per second (RPS), tTACH is the period of the tachometer signal, fCLK is the internal oscillator frequency (254kHz ±10%), and KSCALE is the prescaler value (see Configuration-Byte Register). Since the fan speed is inversely proportional to the tachometer period, the Fan-Speed Register value (KTACH) does not linearly control the fan speed (Table 3). Select the prescaler value so the fan’s full speed is achieved with a register value of approximately 64 (0100 0000) to optimize speed range and resolution. The MAX6651 may be controlled by an external oscilla- |
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