LM64 datasheet(18/29 Pages) NSC

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2.0 LM64 Registers (Continued)

2.4 LM64 REGISTER DESCRIPTIONS IN FUNCTIONAL ORDER

Fan Control Registers

Address

Hex

Read/

Write

Bits

POR

Value

Name

Description

HEX PWM AND RPM REGISTER

R/W

7:6

PWM

Program

These bits are unused and always set to 0.

0: the PWM Value (register 4C) and the Lookup Table (50–5F) are

read-only. The PWM value (0 to 100%) is determined by the current

remote diode temperature and the Lookup Table, and can be read from

the PWM value register.

1: the PWM value (register 4C) and the Lookup Table (Register 50–5F)

are read/write enabled. Writing the PWM Value register will set the

PWM output. This is also the state during which the Lookup Table can

be written.

PWM

Output

Polarity

0: the PWM output pin will be 0 V for fan OFF and open for fan ON.

1: the PWM output pin will be open for fan OFF and 0 V for fan ON.

PWM Clock

Select

if 0, the master PWM clock is 360 kHz

if 1, the master PWM clock is 1.4 kHz.

[Reserved]

Always write 0 to this bit.

1:0

Tachometer

Mode

00: Traditional tach input monitor, false readings when under minimum

detectable RPM.

01: Traditional tach input monitor, FFFF reading when under minimum

detectable RPM.

10: Most accurate readings, FFFF reading when under minimum

detectable RPM.

11: Least effort on programmed PWM of fan, FFFF reading when under

minimum detectable RPM.

Note: If the PWM Clock is 360 kHz, mode 00 is used regardless of the

setting of these two bits.

HEX FAN SPIN-UP CONFIGURATION REGISTER

R/W

7:6

Fast

Tachometer

Spin-Up

These bits are unused and always set to 0

If 0, the fan spin-up uses the duty cycle and spin-up time, bits 0–4.

If 1, the LM64 sets the PWM output to 100% until the spin-up times out

(per bits 0–2) or the minimum desired RPM has been reached (per the

Tachometer Setpoint setting) using the tachometer input, whichever

happens first. This bit overrides the PWM Spin-Up Duty Cycle register

(bits 4:3) — PWM output is always 100%.

If PWM Spin-Up Time (bits 2:0) = 000, the Spin-Up cycle is bypassed,

regardless of the state of this bit.

4:3

PWM

Spin-Up

Duty Cycle

00: Spin-Up cycle bypassed (no Spin-Up), unless Fast Tachometer

Terminated Spin-Up (bit 5) is set.

01: 50%

10: 75%–81% Depends on PWM Frequency. See Applications Notes.

11: 100%

2:0

111

PWM

Spin-Up

Time

000: Spin-Up cycle bypassed (No Spin-Up)

001: 0.05 seconds

010: 0.1 s

011: 0.2 s

100: 0.4 s

101: 0.8 s

110: 1.6 s

111: 3.2 s

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