Datasheet

LM96000

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SNAS234C –APRIL 2004–REVISED MARCH 2013

If the temperature is above Fan Temp Limit, then drops below Fan Temp Limit, the following will occur:

• – The fan will remain on, at Fan PWM Minimum, until the temperature goes a certain amount below Fan

Temp Limit.

• – The Hysteresis registers control this amount. See below table for details.

These registers become Read Only when the Ready/Lock/Start/Override register Lock bit is set. Any further

attempts to write to thses registers shall have no effect. After power up the default value is used whenever the

Ready/Lock/Start/Override register Start bit is cleared even though modifications to this register are possible.

Table 12. Hysteresis Settings

Setting HYSTERESIS

0h 0°C

. .

5h 5°C

. .

Fh 15°C

4.21 Register 6Fh: Test Register

Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1

Address Write Name (MSB) (LSB) Value

6Fh R/W Test RES RES RES RES RES RES RES XEN 00h

If the XEN bit is set high, the part will be placed into XOR tree test mode. Clearing the bit (writing a 0 to the XEN

bit) brings the part out of XOR tree test mode.

This register becomes Read Only when the Ready/Lock/Start/Override register Lock bit is set. Any further

attempts to write to this registers shall have no effect. After power up the default value is used whenever the

Ready/Lock/Start/Override register Start bit is cleared even though modifications to this register are possible.

4.22 Registers 70-7Fh: Vendor Specific Registers

These registers are for vendor specific features, including test registers. They will not default to a specific value

on power up.

4.22.1 Register 74h: Tachometer Monitor Mode

Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Lock?

Address Write Name (MSb) (LSb) Value

74h R/W Tach RES RES T3/4-1 T3/4-0 T2-1 T2-0 T1-1 T1-0 00h

Monitor

Mode

Each fan TACH input has 4 possible modes of operation when using the low frequency range for the PWM

outputs. Mode 0 is the only mode that is available when using the high frequecy range for the PWM outputs. The

modes for TACH3 and TACH4 share control bits T3/4-[1:0]; TACH2 is controlled by T2-[1:0]; TACH1 is controlled

by T1-[1:0]. The result reported in all modes is based on 2 pulses per revolution. In order for modes 2 and 3 to

function properly it is required that the:

• PWM1 output must control the fan that has it's tachometer output connected to the TACH1 LM96000 input.

• PWM2 output must control the fan that has it's tachometer output connected to the TACH2 LM96000 input.

• PWM3 output must control the fans that have their tachometer outputs connected to the TACH3 or TACH4

LM96000 inputs.

Product Folder Links: LM96000