EVALUATION KIT AVAILABLE MAX6620 Quad Linear Fan-Speed Controller General Description The MAX6620 controls the speeds of up to four fans using four independent linear voltage outputs. The drive voltages for the fans are controlled directly over the I2C interface. Each output drives the base of an external bipolar transistor or the gate of a FET in highside drive configuration. Voltage feedback at the fan’s power-supply terminal is used to force the correct output voltage.
MAX6620 Quad Linear Fan-Speed Controller ABSOLUTE MAXIMUM RATINGS VCC to GND ..........................................................-0.3V to +6.0V FAN_FAIL, SDA, SCL to GND ...............................-0.3V to +6.0V ADDR, SPINUP_START, DAC_START, WD_START, X1, X2 to GND ........................................-0.3V to (VCC + 0.3V) All Other Pins to GND..........................................-0.3V to +13.5V Input Current at DACOUT_ Pins (Note 1) ...............
MAX6620 Quad Linear Fan-Speed Controller ELECTRICAL CHARACTERISTICS (continued) (TA = -40°C to +125°C, VCC = 3.0V to 5.5V, unless otherwise noted. Typical values are at TA = +25°C, VCC = 3.3V.) (Note 3) PARAMETER SYMBOL Fan Control Accuracy (Note 4) CONDITION MIN MAX Using 32.768kHz crystal, test at 850RPM -1 +1 Using on-chip oscillator -3 +3 XTAL Oscillator Startup Time X1 Input Threshold POR Threshold TYP UNITS % 2 s 0.7 V VCC 2 VFAN 3.
MAX6620 Quad Linear Fan-Speed Controller ELECTRICAL CHARACTERISTICS (continued) (TA = -40°C to +125°C, VCC = 3.0V to 5.5V, unless otherwise noted. Typical values are at TA = +25°C, VCC = 3.3V.) (Note 3) PARAMETER SYMBOL CONDITION MIN Maximum Receive SCL/SDA Fall Time tF Minimum Receive SCL/SDA Fall Time tF (Note 7) Transmit SDA Fall Time tF (Note 7) 20 + 0.
MAX6620 Quad Linear Fan-Speed Controller Typical Operating Characteristics (VCC = 3.3V, VFAN = 12V, TA = +25°C, unless otherwise noted.) 1.0 0.5 TA = 0°C TA = +25°C 0 -0.5 -1.0 TA = +70°C TA = +125°C -1.5 -2.0 4.0 4.5 5.0 TA = 0°C, +70°C, +125°C 0.5 0 -0.5 TA = +25°C -1.0 -1.5 MAX6620 toc03 2.0 VFAN = 12V 1.5 1.0 0.5 VCC = 5.0V 0 -0.5 -1.0 VCC = 3.3V -1.5 -2.0 3.0 3.5 4.0 4.5 5.0 5.5 -55 -10 35 80 TEMPERATURE (°C) TACH COUNT ACCURACY WITH EXT CLK vs.
MAX6620 Quad Linear Fan-Speed Controller Typical Operating Characteristics (continued) (VCC = 3.3V, VFAN = 12V, TA = +25°C, unless otherwise noted.) TA = 0°C TA = +25°C 1.0 0.5 0 TA = +70°C TA = +125°C -0.5 -1.0 -1.5 -2.0 4.0 4.5 5.0 TA = 0°C, +70°C, +125°C 0.5 0 -0.5 TA = +25°C -1.0 -1.5 5.5 VCC = 5.0V -1.0 -1.5 -2.0 3.0 3.5 4.0 4.5 5.0 -55 5.5 -10 35 80 -0.5 -1.0 1.5 0.5 -0.5 -2.5 -3.5 -2.0 -4.5 35 80 VCC = 5.5V VCC = 3.3V -1.5 -1.5 -10 VCC = 3.0V 2.5 125 4.5 3.
MAX6620 Quad Linear Fan-Speed Controller Pin Description PIN 1 2 NAME FUNCTION 2 SCL I C Serial-Clock Input. Can be pulled up to 5.5V regardless of VCC. Open circuit when VCC = 0V. SDA Open-Drain, I2C Serial-Data Input/Output. Can be pulled up to 5.5V regardless of VCC. Open circuit when VCC = 0V. Startup Watchdog Set Input. This input is sampled when power is first applied and sets the initial I2C watchdog behavior. When connected to GND, the watchdog function is disabled.
MAX6620 Quad Linear Fan-Speed Controller whether lack of I2C activity will force the fans to full speed. When the watchdog function is enabled, the fans will be driven to full speed if there is no I2C activity for a period of 2s, 6s, or 10s. Detailed Description The MAX6620 controls the speeds of up to four fans using four independent linear voltage outputs. The drive voltages for the fans are controlled directly over the I 2 C interface.
MAX6620 Quad Linear Fan-Speed Controller A tLOW B tHIGH C E D F G H I J K M L SCL SDA tSU:STA tHD:STA tSU:DAT A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE tHD:DAT tSU:STO tBUF E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = MASTER PULLS DATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK
MAX6620 Quad Linear Fan-Speed Controller Slave Address A master initiates communication with a slave device by issuing a START condition followed by a slave address byte. As shown in Figure 5, the slave address byte consists of 7 address bits and a read/write bit (R/W). When idle, the MAX6620 continuously waits for a START condition followed by its slave address. The first four bits (MSBs) of the slave address have been factory programmed and are always 0101 and the seventh bit is 0.
Maxim Integrated S 0 AS ACK BIT 0 AS 7-BIT SLAVE ID 0 AS BIT 7…………….………… BIT 0 ACK BIT BURST READ 7-BIT SLAVE ID S: 2-WIRE BUS START CONDITION BY MASTER P: 2-WIRE BUS STOP CONDITION BY MASTER AS: ACKNOWLEDGE BY SLAVE AM: ACKNOWLEDGE BY MASTER AM: NO ACKNOWLEDGE BY MASTER S BURST WRITE 7-BIT SLAVE ID BIT 7…………….…………BIT 0 S ACK BIT 7-BIT SLAVE ID AS ACK BIT AS ACK BIT AS 8-BIT REGISTER ADDRESS AS BIT 7…………….…………… BIT 0 ACK BIT 8-BIT REGISTER ADDRESS BIT 7…………….
MAX6620 Quad Linear Fan-Speed Controller nominally 12V or 5V. The drive to the fans is proportional to VFAN. See the Fan_ Target Drive Voltage Registers and the Applications Information sections for more details. Fan-Speed Control DAC (Voltage) Mode. In DAC mode, the MAX6620 simply sets the voltage that powers the fan. The fan’s speed is related, but not precisely proportional to, the drive voltage.
MAX6620 Quad Linear Fan-Speed Controller ter’s bit D4 can be used to cause a fan failure to force the remaining fan speeds to 100%. Watchdog The MAX6620 includes an optional I2C watchdog function that monitors the I2C bus for transactions. When the watchdog function is enabled, all fans will be forced to full speed if no I2C transactions occur within a selected period (2s, 6s, or 10s).
REGISTER NO./ADDRESS 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W 0100 1100 0100 1100 0100 1100 0100 1100 0XX0 0000 0XX0 0000 0XX0 0000 0XX0 0000 0000 1111 0000 0XXX POR STATE D4 D3 Same as Fan 1 Dynamics Same as Fan 1 Dynamics Same as Fan 1 Dynamics Fan 2 Dynamics Fan 3 Dynamics Fan 4 Dynamics Fan 1 Dynamics TACH/ Locked Rotor: 0 = TACH 1 = locked rotor DAC Rate-of-Change: 000 = 0s per LSB (DAC mode) 0.
Maxim Integrated 0000 0000 0000 0000 0011 1100 0000 0000 0011 1100 0000 0000 0011 1100 0000 0000 0011 1100 0000 0000 XXXX XXXX X000 0000 XXXX XXXX X000 0000 XXXX XXXX X000 0000 XXXX XXXX X000 0000 20h 21h 22h 23h 24h 25h 26h 27h 28h 29h 2Ah 2Bh 2Ch 2Dh 2Eh 2Fh 0000 0000 19h 1Fh 0000 0000 18h 1Eh 1110 0000 17h 0000 0000 1111 1111 16h 1Dh 1110 0000 15h 0000 0000 1111 1111 14h 1Ch 1110 0000 13h 0000 0000 1111 1111 12h 0000 0000 1110 0000 11h 1Ah 1111 1111 10h 1Bh
MAX6620 Quad Linear Fan-Speed Controller Register Descriptions Global Configuration Register (00h)—POR = 0000 0XXX BIT R/W 7 R/W Run: 0 = run 1 = standby R/W POR: 0 = normal operation 1 = reset all registers to POR values This bit automatically resets itself and will always return a 0 when read. R/W I2C Bus Timeout: 0 = enabled 1 = disabled The I2C interface will reset if SDA is low for more than 35ms.
MAX6620 Quad Linear Fan-Speed Controller Global Configuration Register (00h)—POR = 0000 0XXX (continued) BIT R/W FUNCTION I2C Watchdog: When active, the watchdog monitors SDA and SCL for valid I2C transactions. If there are no valid transactions between the master and the MAX6620 within the watchdog period, all fan output voltages will go to full-scale drive voltage. 2 If the watchdog times out and valid I2C transactions begin to occur again, operation will resume with the previous DAC value.
MAX6620 Quad Linear Fan-Speed Controller Fan Fault Register (01h)—POR = 0000 1111 BIT R/W FUNCTION Fan 4 Fault Status: Indicates which fans have had faults detected. When a fan fault is detected, the drive to the fan is disabled and the corresponding fault bit is set. The fault bits latch until they are cleared by reading, thus allowing short-term faults to be identified.
MAX6620 Quad Linear Fan-Speed Controller Fan_ Configuration Registers (02h, 03h, 04h, 05h)—POR = 0XX0 0000 BIT 7 R/W R/W FUNCTION RPM/DAC: 0 = DAC mode. The fan drive voltage is set by the value in the Fan_ Target Drive Voltage register. 1 = RPM mode. The fan drive voltage is adjusted to produce the TACH count value in the Fan_ Target TACH Count register.
MAX6620 Quad Linear Fan-Speed Controller Fan_ Dynamics Registers (06h, 07h, 08h, 09h)—POR = 0100 1100 BIT R/W 7 R/W FUNCTION Fan_ Speed Range: The MAX6620 determines fan speed by counting the number of internal 8192Hz clock cycles (using an 11-bit counter) during one or more fan tachometer periods. Three bits set the nominal RPM range for the fan, as shown in the table below.
MAX6620 Quad Linear Fan-Speed Controller Fan_ Dynamics Registers (06h, 07h, 08h, 09h)—POR = 0100 1100 (continued) BIT R/W FUNCTION Fan_ DAC Rate-of-Change: The fan drive voltage (at the DACFB_ inputs) varies from 0 to full scale in 512 increments. The rate-ofchange bits determine the time interval between output voltage increments/decrements. In RPM mode, a setting of 0 would result in an unstable feedback loop, so a default value of 0.0625 is in effect when 0 is selected.
MAX6620 Quad Linear Fan-Speed Controller Fan_ TACH Count Registers (10h, 12h, 14h, 16h)—POR = 1111 1111 BIT R/W FUNCTION 7 6 5 4 3 R 2 Fan_ TACH Count D10:D3: Indicates the number of 8192Hz clock pulses counted during the counting period. The Fan_ TACH Count consists of 11 bits contained in two bytes. To minimize noise from spurious tachometer transitions, pulses less than 25µs are ignored.
MAX6620 Quad Linear Fan-Speed Controller Fan_ Target TACH Count Registers (20h, 22h, 24h, 26h)—POR = 0011 1100 The Fan_ Target TACH Count consists of 11 bits contained in two bytes. The two bytes must be written in order in one or two I2C transactions, with no other I2C BIT writes in between. These target registers are updated internally at the same time when a second byte (LSB) is written. R/W FUNCTION Fan_ Target TACH Count D10:D3: In RPM mode, write the desired tachometer count to this register.
MAX6620 Quad Linear Fan-Speed Controller Fan_ Target Drive Voltage Registers (28h, 2Ah, 2Ch, 2Eh)—POR = XXXX XXXX The Fan_ Target Drive Voltage consists of 9 bits contained in two bytes. The two bytes must be written in order in one or two I2C transactions with no other I2C BIT R/W writes in between. These target registers are updated internally at the same time when a second byte (LSB) is written.
MAX6620 Quad Linear Fan-Speed Controller Applications Information External Pass Transistors Match external pass transistors to the fans being used. Ensure that the pass transistor is capable of handling the maximum fan current. For best results, the pass transistor’s maximum current rating should be at least 50% greater than the fan’s nominal supply current.
MAX6620 Quad Linear Fan-Speed Controller VFAN +12V 0.33µF VC VIN PQ20RX VO VADJ DACOUT1 470Ω 47µF 2.4kΩ 27kΩ DACFB1 VFAN VCC 3.0V TO 5.5V VFAN +12V TACH1 0.1µF FAN1 0.1µF VFAN 0.33µF FAN_FAIL VC VIN PQ20RX VO VADJ DACOUT2 470Ω SDA 47µF 2.4kΩ 27kΩ TO I2C MASTER DACFB2 SCL VFAN TACH2 FAN2 VCC VFAN ADDR DAC_START I2C INTERFACE, REGISTERS, AND CONTROL LOGIC DAC OUTPUT DRIVER 0.33µF TACH MONITOR VC VIN PQ20RX VO VADJ SPINUP_START DACOUT3 470Ω 47µF 2.
MAX6620 Quad Linear Fan-Speed Controller Initial Settings: • Begin with the POR settings. The POR value of the fan_ DAC rate-of-change bits (4:2 of the Fan_ Dynamics register) can yield slower fan speed changes than desired. If this is the case, choose a faster value, such as 001. • Write the desired number of tachometer periods to be counted in the speed range bits (7:5 of the Fan_ Dynamics register). • Write the maximum allowable tachometer count to the Fan_ Target TACH Count registers.
MAX6620 Quad Linear Fan-Speed Controller Typical Application Circuit 0.1µF 4.7kΩ DACOUT1 VFAN DACFB1 0.1µF VCC VFAN 4.7kΩ TACH1 0.1µF FAN1 0.1µF FAN_FAIL 0.1µF 4.7kΩ DACOUT2 VFAN DACFB2 0.1µF 4.7kΩ SDA TACH2 FAN2 TO I2C MASTER SCL 0.1µF 4.7kΩ DACOUT3 ADDR VCC DAC OUTPUT DRIVER I2C INTERFACE, REGISTERS, AND CONTROL LOGIC DACFB3 0.1µF TACH MONITOR DAC_START VFAN 4.7kΩ TACH3 FAN3 SPINUP_START 0.1µF WD_START 4.7kΩ DACOUT4 X1 VFAN DACFB4 0.1µF (OPTIONAL CRYSTAL) 4.
MAX6620 Quad Linear Fan-Speed Controller Package Information Chip Information PROCESS: CMOS Maxim Integrated For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
MAX6620 Quad Linear Fan-Speed Controller Revision History REVISION NUMBER REVISION DATE 0 3/08 Initial release 1 1/13 Corrected Fan_ Dynamics register typos and hex values; added soldering temp; updated package info DESCRIPTION PAGES CHANGED — 12, 18, 20, 21, 24, 29 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied.