Rainbow-electronics MAX5971B Bedienungsanleitung PDF herunterladen (Seite 38)

38 _____________________________________________________________________________________

MAX5971B

Single-Port, 40W, IEEE 802.3af/at,

PSE Controller with I

mode. When DET_BY is set to 1 however, the MAX5971B

can power the port without doing the detection routine.

AC_TH[2:0] (R23h[2:0]) allows direct programming of

the AC disconnect threshold. The threshold is defined

as a current since the comparator verifies that the peak

current pulses sensed at the DET input exceeds a preset

threshold. The current threshold is defined as follows:

AC_TH

= 85.28FA + 10.64FA x N

AC_TH

where N

AC_TH

is the decimal value of AC_TH[2:0]. The

default N

AC_TH

is 4 (AC_TH[2:0] = 100) which corre-

sponds to a default I

AC_TH

of ~128FA.

PWM Register (R24h)

The PWM register (R24h, Table 33) is used to program

the PWM duty cycle. On a power-up or after a reset

condition, this register is set to a default value of 0x00h.

PWM_TH[1:0] (R24h[5:4]) is used to set the PWM duty

cycle. The default PWM_TH[1:0] value of 00 corresponds

to a 6.25% duty cycle, while the maximum PWM_TH[1:0]

value of 11 corresponds to a 25% duty cycle (see Table 34).

Table 33. PWM Register

Table 34. PWM Duty-Cycle Settings

PWM_TH[1:0] DUTY CYCLE (%)

00 6.25

01 12.5

10 18.75

11 25.0

ADDRESS = 24h

DESCRIPTION

SYMBOL BIT NO. R/W

Reserved 7 — Reserved

Reserved 6 — Reserved

PWM_TH

5 R/W PWM_TH[1]

4 R/W PWM_TH[0]

Reserved

3 R/W

Internally connected. For a write command, always write a zero to this bit.

2 R/W

1 R/W

0 R/W

1 2 ... 33 34 35 36 37 38 39 40 41 42 43 44 45 46

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