Datasheet

LM96000
SNAS234C –APRIL 2004–REVISED MARCH 2013 www.ti.com
Setting (Tn[1:0]) Mode Function
00 0 Traditional tach input monitor, false readings
when under minimum detctable RPM
01 1 Traditional tach input monitor, FFFFh reading
when under minimum detectable RPM
10 2 Most accurate readings, FFFFh reading
when under minimum detectable RPM
11 3 Least effect on programmed PWM of Fan,
FFFFh reading when under minimum
detectable RPM
• Mode 0: This mode uses the conventional method for fan tachometer pulse detection and does not include any circuitry to
compensate for PWM Fan drive. This mode should be used when PWM drive is not used to power the fan. This mode may
report a false RPM reading when under minimum detectable RPM as shown in the following table.
• Mode 1: This mode uses the conventional method for fan tach detection. The reading will be FFFFh if it is below minimum detectable
RPM.
• Mode 2: This mode is optimized for accurate RPM readings and activates circuitry that extends the lower side of the RPM reading as
shown in the following table.
• Mode 3: This mode minimizes the effect on the RPM setting and activates circuitry that extends the lower side of the RPM reading as
shown in the following table.
PWM Frequency Mode 0 and 1 Minimum RPM Mode 2 and 3 Minimum RPM
10.01 841 210
15.02 1262 315
23.14 1944 420
30.04 2523 420
38.16 3205 420
47.06 3953 420
61.38 5156 420
94.12 7906 420
This register is not effected when the Ready/Lock/Start/Override register Lock bit is set. 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.
4.22.2 Register 75h: Fan Spin-up Mode
Register Read/ Register Bit 7 Bit 0 Default
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Lock?
Address Write Name (MSB) (LSB) Value
75h R/W Fan RES RES RES RES RES PWM3 PWM2 PWM1 7h ✓
Spin-up SU SU SU
Mode
The PWM SU bit configures the PWM spin-up mode. If PWM SU is cleared the spin-up time will terminate after
time programmed by the Fan Configuration register has elapsed. When set to a 1, the spin-up time will terminate
early if the TACH reading exceeds the Tach Minimum value or after the time programmed by the Fan
Configuration register has elapsed, whichever occurs first.
This register becomes Read Only when the Ready/Lock/Start/Override register Lock bit is set. Any further
attempts to write to this register 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.
4.23 Undefined Registers
Any reads to undefined registers will always return 00h. Writes to undefined registers will have no effect and will
not return an error.
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