LM63 datasheet(17/28 Pages) NSC

17 / 28 page

2.0 LM63 Registers (Continued)

Fan Control Registers (Continued)

Address

Hex

Read/

Write

Bits

POR

Value

Name

Description

HEX FAN PWM AND TACHOMETER 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 LM63 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%. Register x03, bit 2 = 1 for

Tachometer mode.

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

HEX FAN PWM FREQUENCY REGISTER

R/W

7:5

000

PWM

Frequency

These bits are unused and always set to 0

4:0

10111

The PWM Frequency = PWM_Clock / 2n, where PWM_Clock = 360

kHz or 1.4 kHz (per the PWM Clock Select bit in Register 4A), and n =

value of the register. Note: n = 0 is mapped to n = 1. See the

Application Note at the end of this datasheet.

HEX PWM VALUE REGISTER

Read

(Write

only if

reg

4A bit

5 = 1.)

7:6

PWM

Value

These bits are unused and always set to 0

5:0

000000

If PWM Program (register 4A, bit 5) = 0 this register is read only and

reflects the LM63’s current PWM value from the Lookup Table.

If PWM Program (register 4A, bit 5) = 1, this register is read/write and

the desired PWM value is written directly to this register, instead of

from the Lookup Table, for direct fan speed control.

This register will read 0 during the Spin-Up cycle.

See Application Notes section at the end of this datasheet for more

information regarding the PWM Value and Duty Cycle in %.

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